Thursday, October 31, 2013

Quick trick-or-treat update - get those costumes ready!

The forecast for tonight is looking decent, as long as you don't mind a brief shower with your Kit Kat(TM) and sour gummy worms.

The bulk of today's rain will be moving out of the metro early this afternoon. I expect Memphis/Shelby County to be on the backside of the large rain shield that has covered the Mid-South this morning by 2pm.  Counties to our east and south may take another hour or two to clear.

The Slight Risk for severe weather is still technically in place, though the atmosphere is very stable right now thanks to all the rain this morning. A break in the precipitation this afternoon will allow a little instability to creep in, but cloud cover keeps it marginal.  Latest computer model data agrees with me.  Therefore, I would be very surprised if we see any watches or warnings, or even more than a rumble of thunder, the rest of the day.

This evening, the advertised cold front will move through between 7-10pm.  Until it moves through, we will still see a chance of a shower (or a lonely thundershower). In fact, there's a decent chance that are few fast-moving showers will escort the front through Mid-South neighborhoods this evening.  That is what this morning's high-res NAM model depicts (image below, valid at 7pm).  The good thing about anything that does fall tonight is it won't last long - showers will be moving at up to 50-60 mph overhead thanks to a mid-level jet stream on a Halloween sugar high.

Hi-res model "future radar" valid at 7pm tonight. MODEL means one possibility. It does not accurately predict each and every shower and it's location. Expect a chance of a shower around this time. Graphic courtesy WeatherBell.

So would I plan on trick-or-treating tonight? Well, *I* won't... but my kids will, and I see no reason to get between them and a sack of chocolate based on the forecast.  I'll go along and carry the umbrella, just in case, then expect at least a 10% candy commission for moving the weather out in time to hit up the neighbors for their sweet confections.

Folks, be SAFE tonight, take the MWN mobile app with you so you can keep an eye on local radar (link below), be a good chaperone and carry the ponchos or umbrella just in case, and if you see lightning or hear thunder, it'll be time to call it a night. Here's to full bags of sugary American goodness for all of you!

--Erik Proseus, MWN Meteorologist

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Wednesday, October 30, 2013

Halloween Eve forecast update: Tricks... or treats?

Seems there is a holiday or great importance tomorrow... everyone with children want to know if they will be able to trick or treat! This is our 3rd blog in 3 days on the Halloween storm system that seems to be bringing a bag of tricks with it.  I'll try and provide more specific impacts and timing in this edition.  Pictures tell the story well, so I've included several.

Severe Weather Outlook

Since this past weekend, the Storm Prediction Center, who monitors severe weather across the nation, has been warning that this storm was coming and had the potential to bring strong to severe storms to the Mid-South.  As it turns out, it's not only the Mid-South under the gun, but a very large area from the central Gulf Coast to the southern Great Lakes region.  However, the highest probability of severe storms (30%, which is not insignificant) lies over the Mid-South and up into the Ohio Valley.  See graphic below.

Probability of severe weather within 25 miles of a point (such as your house), courtesy NWS/SPC.

The main threat with any strong storms will be straight-line wind of 60 mph or higher. However, the wind speeds over the Mid-South from the lowest couple thousand feet all the way up to the jet stream level will be strong and wind shear will be high. This means that there is also a CHANCE of a few tornadoes.  While not the greatest threat, we can't leave it out of the conversation. Hail does not seem to be a major threat.  The most likely time for severe weather will be in the afternoon, or roughly from 1-5pm, though thunderstorms will be likely throughout the day.

The other point worth mentioning is that it will be windy all day long, even outside of thunderstorms. South winds will peak in the 15-25 mph range with gusts above 30 mph likely.  Any items you do not want to have blown around outside should be secured tonight.

Rainfall Amounts

The amount of moisture in the air is high and is loading up as we head into the day Thursday.  Rainfall amounts could be heavy from individual showers and storms and collectively throughout the day.  We will likely see rain start in the metro overnight tonight, likely after midnight, and continue off and on throughout the day.  Models are hinting at a lull in the mid-late morning hours with rain and maybe a few claps of thunder early in the morning, then rain and storms in the afternoon.  Overall, rainfall amounts will likely be 1-2"+ area-wide with some locations possibly seeing 3-4".  Most steady rain will end by 5-6 pm, though a few showers could linger into the prime trick-or-treat hours, as the cold front will move through between ~7-9pm.  Plan accordingly. While widespread flash flooding is not expected due to a lack of recent rainfall, areas that tend to fill up first will likely do so, including streams and small rivers, drainage ditches, and low-lying areas in the concrete jungle.  Monitor these areas, especially if they are near your trick-or-treat route.

Forecast rainfall amounts from NWS from 7pm tonight to 7pm Thursday. The Mid-South is generally in line for 1.5-2"

The images below show one model's representation of what radar COULD look like at a few specific times tomorrow.  These are not official forecasts, but represent one possibility which looks fairly reasonable to the trained eye.  The images are of the high-resolution NAM model courtesy of  As you can see, if this model is fairly close to accurate, rain will be over the metro by morning rush hour, then some storms and heavy rain would be possible by lunch, and most precipitation would be east of us by 6pm with a few lingering showers hanging back to our west.

Hi-Res NAM model "future radar" at 7am Thursday

Hi-Res NAM model "future radar" at noon Thursday

Hi-Res NAM model at 6pm Thursday

Bottom line: how to prepare

Secondary (fall) severe weather season is real and this event likely marks the beginning of it.  While severe weather is not guaranteed by any means, everyone in the area should prepare for the possibility, particularly during the afternoon hours Thursday.  Severe Thunderstorm or Tornado Watches are possible.  If a Tornado Warning is issued and sirens sound, what will you do?

One suggestion: go to the Android or iPhone app store now and download the app if you haven't already. Thousands of people rely on it for the latest weather info specifically for our area.  You'll find the latest radar loop, our updates throughout the day sent to our Twitter nowcast stream (without subscribing to Twitter), plus you can relay any severe reports back to us via the app as well.  Also in the app, you should go ahead and make the one-time purchase of StormWatch+, which will notify you if severe warnings or watches are issued for your specific location. It's easy to set up and it's the cheapest way to get peace of mind we are aware of.  Links to the apps & more info on them are below.  If you don't have or want to get a smartphone app, stay in touch with the weather conditions in some way tomorrow.  Our social media feeds are another good way to do that.

Definitely plan on heavy rain, perhaps during both rush hours and school drop-off and pick-up.  Take your time when driving in heavy rain. And by all means, keep children away from high or swiftly-moving water and don't drive across areas where water covers the road!

Regarding trick-or-treating, at this point I would suggest just monitoring the weather as the afternoon goes on tomorrow.  My educated guess is that, armed with an umbrella or poncho for the stray showers, trick-or-treat bags will get filled tomorrow evening after 6pm.  If I'm wrong, you won't find me.  I'll be in the custody of federal marshals entering the Witness Protection Program.

"You don't know me" - photo courtesy Wikipedia, public domain

Be safe and stay weather aware!  Hit us up on Facebook, Twitter, or the blog comments below if you have specific questions.

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Tuesday, October 29, 2013

Update on Mother Nature's Halloween tricks

A brief update on our Halloween forecast, as I know many of you have kids that are REEALLLY wanting to get some cavities trick-or-treat on Thursday.  (Do you know how difficult it is to be a meteorologist with a crummy forecast on Halloween?? :-) )

Precipitation outlook

Overall, the bulk of the day looks wet and nasty. Rain will likely begin overnight Wednesday night (though it should hold off until after the University of Memphis football game at the Liberty Bowl), leading to a wet start to Halloween. Rain will continue, perhaps most of the day, and will be occasionally heavy. In fact, the GFS computer model (which is not out of line with other models and is shown below) predicts 2-4" of rain with this system.  [The NWS is currently forecasting about 2".]  Rainfall totals will have to be monitored as downpours could produce flash flooding in localized low-lying areas or areal flooding of urban areas or near streams and rivers.

Tuesday morning GFS computer model showing 24-hour rainfall amounts from 1am Thursday to 1am Friday. Brown colors are 2-3" with whiter areas indicating 3-4".

Severe weather probability

As far as severe weather potential, as discussed yesterday, this system will be moving through a "high shear, low instability" environment, which means there will be plenty of wind at all levels to support severe storms, but marginal instability to get them going.  Instability is the potential for air to rise when forced upward by a lifting mechanism like a front.  The higher the instability, the more likely storms are to form.  In other words, if storms can get started, the atmosphere will allow them to become strong to severe based on the shear.

High-shear environments, particularly when abundant shear is present in the lowest layers of the atmosphere, are also supportive of tornadoes. This will be the case on Thursday; therefore storms that form could produce a few tornadoes.  The more likely form of severe weather though will be damaging wind due to the very high wind speeds in the storm environment, which will also contribute to fast-moving storms.

There is a 30% chance of severe weather within 25 miles of the Memphis metro on Thursday, according to the Storm Prediction Center. Damaging wind and a few tornadoes are the main threats.

The good news (if there is some)

Models continue to indicate that the bulk of the rainfall will be during the day and may move out by 6-7pm.  However, a couple models still point to the chance of light rain Thursday night during prime trick-or-treating hours. Timing of the front will ultimately determine when rain comes to an end and we can't get it down to the hour this far in advance. Cross your fingers that it all moves out by the time the kids are ready to hit the streets!

One additional note of caution, even if things do clear up by evening, is some areas could see excessive standing water and the ground will be saturated. Plan accordingly (footwear for the kids).  Temperatures should still be mild Thursday evening (60s) so fortunately it won't be a heavy coat Halloween!

Lastly, not only should you plan ahead for your "fun" activities, but this is the first storm system of our secondary severe weather season with the real potential for producing severe weather. Know your plan ahead of time in case warnings are issued, including the possibility of Tornado Warnings and outdoor sirens sounding, in the afternoon hours in particular. Re-read the addendum to yesterday's blog for more details and make sure your StormWatch+ alerts are setup on your mobile app so that you will receive location-specific warnings if they are issued (link below).

We'll follow up again tomorrow with more on timing and specific threats.

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Monday, October 28, 2013

Halloween Week Forecast: Warmer through Wednesday, then a stormy Halloween

To start your week off, we're going to focus on weather through Halloween. The big picture is increasing moisture with warmer temps each day, then a frontal passage and precipitation for Halloween. Get the details below.

Visible Satellite Imagery at 1402 UTC (9:02 AM CDT)
We started this morning off with a large area of fog across the Mid-South. As a result temps will sit near 60 for much of the morning but as fog starts to clear, expect peaks of sun this afternoon which will help bring temps into the low 70's. Southerly wind will slowly increase moisture tonight, this combined with mostly cloudy conditions will limit temperatures from falling much below 60 in the metro.

Weather Prediction Center's 60 hour surface forecast. This map shows the Mid-South well into the warm sector with a warm front far to our north and a cold front still well to the west at 12Z Wednesday (7 AM CDT)
Tuesday looks quite similar to today, with the main difference being less fog in the morning. This will allow for periods of sunshine much earlier and as a result higher temperatures (near 80). As for overnight conditions, expect low temperatures to be warmer as a result of clouds, higher moisture content at the surface, as well as light to moderate winds. Wednesday is nearly a carbon copy of Tuesday with both days seeing an isolated to slight chance of a shower.

Storm Prediction Center Day 4 Outlook, highlighting the Mid-South in an area with a 30%+ chance for severe weather on Halloween.

Thursday is when things start to get tricky (pun intended!). An approaching cold front will provide the lift mechanism necessary for thunderstorms, while plenty of moisture (dewpoints in the 60s), modest instability, and strong wind shear should be present to fuel them. Details including intensity and timing will still need to be refined, but as of now plan on a wet and stormy Halloween with both heavy rain and severe storms a possibility. Currently, the majority of activity looks to occur during daylight hours, but we cannot quite rule out a lingering shower or thunderstorm Halloween evening. We'll have more details by Wednesday.

--William Churchill (Social Media Intern)

Addendum by MWN meteorologist Erik Proseus:

This time of year is not off-season for severe weather. In fact, November into early December is considered "secondary severe weather season" in the south. As seasons transition, it's not unusual to have strong fronts move through. In these transitions seasons of spring and fall, typically the jetstream is stronger and low and mid-level wind is also stronger, providing more fuel for the storms in the form of wind shear. The key ingredient that (sometimes) is not as plentiful is instability. Showers ahead of the main storms, timing offset from peak heating, and other factors can play a negative role in instability.  With the upcoming system, instability seems to be the biggest question mark, though we expect there will be enough to fuel storm activity. The more instability, the higher the potential for strong to severe storms.

Now is a great time to review your severe weather safety plans as we enter a season that can bring hazardous weather.  It's been some time since we've had to exercise those plans, so review ahead of time. Here is a good place to start.  School administrative personnel should also review how they get their severe weather information and what their plans are in case action needs to be taken during the school day.

You should also know where you will get your severe weather information. If you have the mobile app, now is the time to go ahead and spend the few extra dollars to add StormWatch+ to your app in the Alerts tab, then program in the specific locations you want alerts for. Links to our apps are available below if you do not yet have the app.

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Friday, October 25, 2013

Why does the forecast on my weather app always seem to be wrong?

I've been asked this, or a variation of it, many times so I figured I would unravel the mystery behind the forecast data on most weather-related mobile apps/websites (from here on I'll just refer to them as apps).

Two categories of forecasts

Forecasts that you see in weather apps basically fall into one of two categories: those that are manually produced (typically by a meteorologist who works in the area the forecast is for) and those that are automated.  Most national apps, such as those produced by huge news and weather companies like Yahoo! and The Weather Channel among others, fall into the latter category.  In fact, there are now also companies that mass-produce "local" weather apps that are nothing more than a template with automated forecasts.

A range of blended forecasts

There are also a few "in-between-ers" that have local forecasts that are slightly-tailored versions of an automated forecast.  In the forecasting world, we have terms for these 'tweeners depending on how much tailoring is done.  A "human over the loop" forecast is one in which a meteorologist (or many times just a data quality checker) monitors the forecasts produced but only edits them if they are grossly in error, usually due to a computer error of some sort, not because the automated forecast is wrong. A "human in the loop" forecast is one in which the meteorologist (typically) monitors the automated forecast but modifies or edits it based on meteorological reasoning. In other words, in these 'tweener forecasts, automation produces the forecasts, but the output is quality checked for obvious computer errors or meteorological reasoning.  We consider "human in the loop" forecasts of generally acceptable quality, while "human over the loop" and strictly automated forecasts to be of unacceptable quality.

Automation and forecast models

In all but those manually generated, automation plays a significant role in the mass production of local forecasts.  The automated forecasts are produced by weather computer models - often the same models that meteorologists use to prepare their forecasts. So why is that bad?  It's not always. But the forecasts typically get worse the farther into the future you're looking.  This is mainly because there are so many variables that can change even a little bit that could set off a completely different set of outcomes.  (Think of the pebble that is dropped in a tranquil lake in which the ripples expand out from the center, or the butterfly effect in which a tiny wind current is disturbed, triggering a series of events downstream).

First a short background: there are MANY computer models available that could be used to produce a forecast. The ones that go farthest out (past 3-5 days) are generally global models (they produce data for the whole world) and are run 2-4 times a day and typically produce data at 3-6 hours intervals. In the short-term (0-3 days), there are many more options, they  can be run anywhere from hourly to every 6 hours, and many times produce forecast data at 1-3 hour intervals.  When a meteorologist talks about a "run" of a particular model, he/she is referring to the time that the model initialized, which for most models, except the high-resolution short-term models, is 00Z, 06Z 12Z, or 18Z (or 6am, noon, 6pm, or midnight CST).  So for each computer model of this type there are 4 "forecast runs" produced each day and each can vary (sometimes widely) from the previous run - even for the same model!

Model output example

Let's take the example of Halloween night (6 1/2 days out from this writing).  A fairly significant storm system is expected to be in the area mid-week, so it's a good example (and pertinent since many people's plans will depend on the forecast).  The model output below was produced by two different computer models (the U.S.-based GFS and U.K.-based European model) and three different runs (2 from the European and 1 from the GFS).  They all show precipitation accumulation over the preceding 6 hours leading up to the valid times shown.  Commentary on each is below the graphic.  (All graphics courtesy of WeatherBell - click any image to enlarge it.)

The European (Euro) model is only run twice a day so we start with yesterday morning's run.  It shows rain, not heavy but an organized area, moving through Memphis Halloween afternoon/evening.  Enough to mess up some costumes!  If your weather app is based on this model, it tells you your trick-or-treaters will get wet.

The next run of the Euro, from last night, shows the weather system a little wetter, but also slower.  The chances of getting wet in Memphis Halloween night are pretty good (remember this precip accumulation ends at 7pm, so we would presume - correctly - that the heavier rain would be directly over Memphis after 7pm). Your Euro-based weather app though might indicate only a "chance of rain" Wednesday, because most of it falls after 7pm that night. 

Shifting to last night's overnight run of the GFS model (which is produced 4 times a day), the above graphic is the precip expected Thursday afternoon and early evening.  Obviously it shows the weather system well east of Memphis.  A dry evening for trick-or-treating!  (We could also assume it would be cooler than the Euro model shows since the front pushing the precip has moved through versus the Euro which would have the cold front still to our west.)  Your weather app says rain chances are zero!

Finally, we look at the same GFS run as above, but the scenario on Wednesday evening (24 hours earlier and the night the Tigers take on Cincinnati on national TV at the Liberty Bowl). Compare that image to the Euro images above. It looks like almost the same solution, only 24 hours earlier!  The two models are handling the same system in a similar manner, only the Euro is about a day later than the GFS!

[Caveat: European data is rarely used for weather apps, but the point is the same.  Different models can and often do have vastly different results.]

Crap apps -- garbage in, garbage out

Automated forecast apps are captive to one particular forecast model and will change every time the model runs and produces new output (up to 4 times a day).  If the computer model has a good handle on the forecast, they can be very accurate.  If the model is wrong ("garbage in"), the output is "garbage out."  The farther into the future you look, the more likely you are to see wildly-varying forecast and forecasts that are just plain wrong.  These automated forecasts come from what a noted Birmingham broadcast meteorologist calls "crap apps" and I completely agree.  No skill, no human intervention, just a pile of manure!

Automated forecasts can do a decent job, especially in the first day or two of a forecast, but also rarely provide any level of detail.  "40% chance of t'storms" with a cloud/lightning icon doesn't tell you whether your morning soccer game, or afternoon outdoor chores, or evening outing will get wet!

Take the example below for one.  If you have both apps, which do you use?

So is my weekend a washout or sunny?

In the same category, you get stuff like this (even "local" sources can sometimes be misleading):

Which is it - sunny or mostly cloudy?  And what is a 17% chance of rain? 

How Cirrus-produced forecasts differ

The most accurate forecasts tend to be those that are locally-produced and manually-generated by a degreed meteorologist that knows the area he/she is forecasting for like the back of their hand.  It is also preferable that he/she has forecasted for the region (as well as verified forecasts against actual conditions) for a number of years.

The forecast you will find in mobile apps produced by Cirrus Weather Solutions ( and StormWatch+) are of two varieties, and neither are automated.  First,'s "MWN Forecast" meets the above criteria - hand-written by a degreed meteorologist (ME) that has been in the same area for a number of years (27) and verified years of forecasts against actual conditions.  The forecasts that appear on StormWatch+ are all produced by National Weather Service meteorologists in the local area that the forecasts are generated for.  No haphazard computer models that change run to run or are way off base.

The benefit of a forecast generated by a qualified meteorologist is that that person can look at ALL of the model data (not just one as in an automated crap app), use their training and skills, and produce a forecast that is a blend of data that is more realistic than any one model.  When searching for just the right weather app from a forecast standpoint, know the source, and more importantly TRUST the source.  If it costs a small amount to get the opinion of a trusted source over a free, mass-produced automated forecast, you're probably much better off in the long run!

Do you have experience with "crap apps" or forecasts from sources that seem to always be changing or wrong? We'd love your comments.

--Erik Proseus, Meteorologist, Cirrus Weather Solutions, LLC

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Thursday, October 24, 2013

Frost/freezing conditions expected the next couple of nights

With the issuance of our first Freeze Warning of the fall (for Fayette and Tipton Counties) and Frost Advisory for the rest of the metro except Tunica County, it's a good time to provide some meteorological insight on why these freezes are able to occur and remind you to protect any tender vegetation.

It's not too hard to reach sub-freezing temperatures in the winter, but at this time of year the atmosphere needs a few specific conditions to get there:
  1. Clear night
  2. Relatively dry air
  3. Close to calm winds
So it's no surprise that these are the conditions we're experiencing over the Mid-South as rural areas will begin to see these freeze effects.

A clear night is required because heat radiates off the surface of the Earth and into space most efficiently when there are no clouds to re-emit radiation back to Earth. [EP: Clouds act like a "blanket" at night trapping heat near the Earth's surface.  Areas outside the city, where concrete, buildings, etc. tend to hold heat more efficiently than grass, dirt, and vegetation, tend to be the coldest on clear nights.  This is why outlying areas are colder on cool nights than areas within a city.]

Relatively dry air is required because the amount of moisture in the air places a limit on how far the temperature can fall. The less moisture presence, the lower the temperature can get before reaching saturation. Once this happens condensation can occur which will further damage vegetation if the temperature is at or below freezing. [EP: Dewpoints are the measure of humidity we use to determine how far the temperature can fall at night. Tonight dewpoints will be in the mid to upper 20s.]

Last but not least, light winds are required because winds act to mix warmer air to the surface. Usually the coldest temperatures right at dawn are very close to the surface. This is a typical time for temperatures to be increasing with height in the lowest parts of the atmosphere rather than decreasing with height which is more typical during the day. This is because of radiational cooling which can only cool the air at the surface. [EP: Tonight's saving grace, keeping temperatures from dropping to freezing in the city, will be a wind of about 5 mph. A calm wind would mean even colder temps!]
NAM meteogram showing two nights of potential freezing in the Mid-South (This graphic is for the airport. Outlying areas will be cooler than shown above at night.)
Modeled temperatures and wind show favorable conditions for frost and freeze tonight and Friday night. The dotted green line represents the dew point which is the bound on how low the temperature can fall and also when condensation starts. Each night the temperature should reach this bound that will be near freezing. Winds are shown below that which are light throughout the period, even becoming calm during the overnight hours.
Weather Prediction Center's forecast of fronts and pressure systems for Friday morning
Light to calm winds are mostly due to the Mid-South being positioned under a high pressure. This is typical for a high pressure system because the pressure gradient is lowest near the center of the high.

As far as protecting vegetation, since sub-freezing temperatures are expected to be brief (a couple of hours or less), a hard freeze is not expected, and they will affect mostly rural areas, you can protect any vegetation that cannot be brought inside by putting a light cloth sheet over any plants. This acts to reduce radiational cooling, with the sheet playing the role of clouds in the atmosphere by keeping heat in. Just remember to remove this sheet in the early morning after temperatures begin to rise so that it can warm up quickly as well.

--William Churchill (Social Media Intern)

[Editor's comments are marked by EP and italicized.]

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Friday, October 18, 2013

The struggle between warm and cold in the atmosphere - which will prevail?

Cool air has settled in the past couple days resulting in below average temperatures in the Mid-South. How that cool air will change is the topic of discussion this weekend and heading into next week. Simply put, the atmosphere is having trouble deciding on whether it wants to get warmer or colder. Or perhaps more accurately, the atmosphere is trying to reconcile the cold/dry air from the north and the warm/humid air from the south. This is of course very typical of fall, but for the foreseeable future the cold/dry air will be winning the battle in the Mid-South.

NAM modeled meteogram, displaying temperatures/dew points (top) and wind direction/speed (bottom)
Today we can expect slightly warmer temperatures than previous days with a highs in the lower 70's. Our highest chance of rain in the period comes tonight with the passage of a cold front. I say "our highest chance" but this is quite relative, with most areas in the metro receiving sprinkles at best. Colder air returns tomorrow, resulting in high temperatures in the 60's and low temperatures in the 40's for Sunday morning. This cold spell looks to be brief, with south winds returning promptly Sunday, resulting in temperatures near 70.

GFS modeled meteogram, displaying temperatures/dew points (bottom) and wind direction/speed (top)
While Monday could be our warmest day, this process looks to repeat itself again Monday night, with another mostly dry frontal passage resulting in temperatures back in the 60's for your Tuesday.

This summarizes the difficulty the atmosphere is having with reconciling the different air masses in our region. Fast and frequent cold fronts will not allow warm, moist air to return with much force to our region. With that said, we won't be hearing many complaints at MWN with beautiful days, chilly nights and mostly dry frontal passages in the forecast.

--William Churchill (Social Media Intern)

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Monday, October 14, 2013

Rain is almost a certainty tomorrow, but why?

As always we'll begin the blog with a synopsis of current weather. Lets start with a visible satellite image of Tropical Storm Octave in the eastern Pacific Ocean:

Visible Satellite Image of Tropical Storm Octave at 14Z (7AM Pacific)
But wait, isn't this a blog for Memphis weather?! Why in the world do we care about what is going on in the eastern Pacific Ocean. Well, often times meteorologists have to look at the bigger picture to understand what is going on with the weather locally.

GOES-Composite Rainbow Infrared Image at 1345Z (8:45AM Central)
This infrared satellite image gives you a much better idea of why Tropical Storm Octave matters. The moisture, shown in the green and yellow colors, is streaming northeast from the eastern Pacific into the southern US. Increasing clouds can be expected into tonight with a slight chance of a shower by morning. Better chances of rain arrive tomorrow.

Weather Prediction Center's 48-hour forecast valid at 00Z Wednesday (7PM Tuesday)
Best chances of rain, including the heaviest activity, should arrive by Tuesday evening as a cold front slowly pushes this stream of tropical moisture directly over the Mid-South. Rain will continue well into tomorrow night with some lingering precipitation Wednesday morning.

24-hour forecast rainfall from 7am Tuesday through 7am Wednesday, indicating over 1.5 inches over Memphis

The reason Tropical Storm Octave is so important is because of how much it increases overall precipitation amounts. Of course we would probably still get rain if Octave was not a factor, but that tropical moisture enhances our precipitation totals by quite a bit. The Weather Prediction Center has a 2 inch bulls-eye just southwest of Memphis. Precipitation totals of 1-2 inches are certainly expected across the Mid-South. [EP: Severe weather chances are minimal despite some thunder possible Tuesday afternoon/evening.]

Mostly cloudy conditions are expected for most of the day Wednesday as the front passes through the Mid-South. Once the cold front and rain has finally cleared our area, expect clearing skies and much cooler air to push into the region. We may even get a glimpse of a sunset Wednesday night!

William's Memphis Forecast

Increasing clouds with a high of 80, low of 66.

Cloudy with a chance of rain, becoming rainy by the evening. High of 77, low of 56.

Mostly cloudy becoming partly cloudy overnight with a high of 70, low of 51.

 --William Churchill (MWN Social Media Intern)

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Friday, October 11, 2013

More on how the government shutdown is affecting the NWS

Additional information is becoming available regarding the scope of the shutdown impacts to the public-sector weather community. None of the info in this update comes from the Memphis NWS office and none of it runs counter to the statements made in our previous post on impacts to the NWS (which I encourage you to read if you haven't), just some additional details.

According to blogs posted by the Capital Weather Gang, who I have followed for some time and who do a great job providing insight to the weather enterprise, and Dr. J. Marshall Shepherd, President of the American Meteorological Society, there are numerous effects being felt at weather offices across the nation.

The primary effect, which we have confirmed from multiple sources, is that NWS employees are working for the "promise of pay." In other words, their paychecks for October are delayed until a new appropriations bill is signed or a continuing resolution is passed. In fact, NWS employees will receive a partial paycheck in the coming days for time worked through September 30, but after that they must wait until their funding is voted on to get their next paycheck. On top of working for the "promise of pay," these dedicated employees are doing things like hiking to work through snow drifts measured in feet (or not leaving the office altogether) in South Dakota in order to make sure their job duties are carried out.

NWS office in Rapid City after a mega-dumping of snow and blizzard conditions over the weekend. Image courtesy NWS-Rapid City.
In addition, public outreach has ceased, preventative maintenance has slowed or stopped (only emergency repairs are made), the main public source of historical weather and climate data is not accessible due to the shutdown of web servers at the National Climatic Data Center, and damage surveys are disallowed other than by special exception (the Wayne, NE EF-4 late last week is an example). We won't go into detail here, but Dr. Shepherd digs deeper into the possible long-term effects of the shutdown, especially if it drags on, in his blog linked above.

The typical stereotype of the government worker is not necessarily a good one.  But given the anecdotes above, and knowing many NWS meteorologists and staff personally, I dare anyone to find a more dedicated, hard-working, and under-appreciated group of public servants. Their overall budget is minuscule compared to many behemoth agencies. Yet most of them work in a field they truly love, with service to the community on the forefront of their minds. Their job is to protect life and property from elements that are beyond anyone's control and they are the best in the world at it!


Unpaid Rapid City NWS staff slept at the office as blizzard totals hit 58 inches, MPR News15 ways the Federal shutdown is hampering the National Weather Service, Capital Weather Gang blog
Implications of the "Shutdown" on the Weather Community and Beyond, Dr. J. Marshall Shepherd
"No clocking out during storms – and no pay for weather forecasters," Omaha World-Herald

--Erik Proseus, Meteorologist,

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A warm weekend forecast and a shot at scattered showers


Low level clouds have been in the picture for several days now and we'll be dealing with a few again this morning. In fact cloud cover (and even a few showers) can be expected for much of Saturday as well due to an approaching weak cold front. However, highs in the mid 80's with lows in the mid 60's can be expected for basically the entire weekend. Check out the analysis and forecast below.


NAM sounding valid for 12Z (7AM) Friday.

This vertical profile of the atmosphere shows the low level moisture present around 1500 feet this morning, indicating some low clouds. Above that level there is much drier, and even slightly warmer air that is trapping the moisture below it.

NAM 850 mb (5,000') relative humidity and wind vectors at 18Z (1PM) Saturday.
Looking toward Saturday afternoon, modeled mid-level moisture indicates the arrival of more clouds from the west. These clouds are associated with the approach of a weak cold front which could also stir up some scattered showers.

NAM 6 hour accumulated precipitation valid between 15-21Z (3-9PM) Saturday.
This particular weather model shows small amounts of accumulated precipitation in the afternoon hours of Saturday. Any rain showers would likely be scattered in nature.

By Sunday we can expect to see some significant clearing in cloud cover, as well as very slightly cooler, drier air. While not a major change it will be good enough until our next major system comes through next week.

William's Memphis Forecast

Mostly cloudy in the morning with some clearing in the afternoon. High of 83, low of 66.

Mostly cloudy with a high of 84, low of 65. 30% chance of showers.

Partly cloudy with a high of 81, low of 62.

--William Churchill (MWN Social Media Intern)

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Thursday, October 10, 2013

Germantown residents to hear outdoor sirens less often

Residents of Germantown, TN will be hearing outdoor warning sirens less often, but it's not necessarily a bad thing.  A couple of weeks ago, Germantown flipped the switch on new software and an updated siren policy that allows the city to make their own decisions about warning their residents and visitors during severe weather episodes. [Media release from the city of Germantown]

Background and warning policy

Using a $77,000 grant from the Department of Homeland Security, Germantown installed a complete weather system from Earth Networks (the company that owns WeatherBug) that includes a professional weather station, an HD camera, and Streamer RT software.  The weather station, located on top of fire station #3 adjacent to the Germantown Municipal Center, and HD camera, mounted on top of the city's tallest water tower, provide realtime local conditions and a great view of the sky to Germantown officials and anyone else who visits the WeatherBug website or mobile app. However it is Streamer RT that allowed Germantown to modify their tornado warning policy.

The city of Germantown and it's 17.6 square miles and 38,000+ residents are well-covered by 15 outdoor warning sirens with overlapping coverage. (On average, each siren has an audible range of just over a 1 mile radius, or 3.5 square miles.)  Until recently, Germantown followed the siren policy used by the rest of Shelby County and it's municipalities, which required that all sirens county-wide be sounded when any part of the county was affected by a Tornado Warning.

Now, using the graphical overlays available in the software, city dispatchers (whose duties include activating the city's sirens) will look at the display that depicts the Germantown city limits and the warning polygon issued by the National Weather Service (example below) and determine whether to activate the sirens. If the warning polygon does NOT include a portion of the city, sirens will not be sounded.  If any part of the city IS in the warning, sirens will be sounded. And once the warning is lifted for all of Germantown (even if it still encompasses other parts of Shelby County), sirens can be shut off.

Streamer RT software by Earth Networks provides Germantown dispatch and fire with current weather info, as well as warning polygons and the city limits, making the decision to warn the city, or not, an easy one.  In this case, sirens would not be activated. Image courtesy Germantown FD.

Fewer sirens = more trust in the system

In 2007, the National Weather Service ceased warning entire counties for tornadoes, severe thunderstorms, and flash floods.  Instead, these warnings are now issued on a storm basis.  As we've described before, a polygon is drawn around the area expected to be impacted by these events, irrespective of political boundaries (such as the red polygon in the image above).  However, many warning systems, including the NWS' own NOAA Weather Radio, still send alerts on a county-wide basis, resulting in larger areas being warned than the NWS intended via their polygon system.

County-wide alerting result in "perceived overwarning" because people using those warning systems perceive a threat, when oftentimes they are not in the warned area.  Besides weather radio, some commercial radio and TV stations still warn based on counties (though most are moving away from county-based warning), and in most places sirens still warn entire counties, including in Shelby County.  Because the cities of Germantown, Bartlett, and Collierville (as well as Memphis) activate their own sirens, they are able to break away from county-based siren activation simply by changing their internal policies.  Germantown is the first to do so.  Bottom line: going forward, when sirens sound in Germantown, residents can be certain that all or some part of their city is under a direct threat.

The process to transition to this policy actually began two years ago with a search by Germantown Fire officials for companies that would provide the tools to allow them to sound their own sirens.  When asked why Germantown decided to change their siren policy, Chief John Selberg summed it up this way: "I believe in being prepared without over-sensationalizing the emergency."  Ultimately, he expects the change in philosophy to "reduce complacency" since the sirens will only sound for actual threats to the city.


Of course, we can't have a discussion of outdoor warning sirens without discussing the caveats.

First and foremost, never rely on sirens when indoors! It's very important to remember that outdoor warning sirens are called that for a reason - they are intended to alert people who are OUTDOORS to go inside and seek additional information on the threat.  Though Germantown's sirens have excellent coverage, if you are asleep with the air conditioner running and it is raining outside, it is doubtful that you will hear the sirens and you place yourself at risk.

Have a programmed NOAA Weather Radio with good batteries and, if you have a smartphone, install a severe weather app that will alert you (and wake you) in case of severe weather.  It should have a feature that will wake you for the most intense storms, allow you to program multiple locations, and preferably have a "follow me" feature for when you are traveling. We highly recommend our MWN app with StormWatch+, which fits the bill perfectly.

One of these methods in and of itself is not sufficient.  Always have multiple ways of receiving severe weather information.  Any one of them can fail at any time and you need a backup or two.

NOTE: Germantown sirens are tested on Saturdays at noon (unless the weather is threatening) and the sirens are all equipped with two-way communication which means the Germantown Fire Department knows, without activating the sirens or being on-site during a test, when a siren is not working properly.

Additional links/info:
Outdoor Warning Sirens page on
Germantown Fire Department page on City of Germantown website
Germantown Fire Department on Facebook
"Weather system to limit siren sounds in Germantown" - Commercial Appeal

Outdoor warning sirens series on the MWN Blog:
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Wednesday, October 9, 2013

How the government "slimdown" is affecting your local NWS office

If you have visited any of several NOAA-related websites since the partial government shutdown (or "slimdown") took effect on October 1, you probably recognize the image above.  Reports indicate that approximately half of the employees of the National Oceanographic and Atmospheric Administration (NOAA) have been furloughed, though about 6,600 remain on the job, most of those in, and in support of, more than 120 local National Weather Service (NWS) forecast offices across the country. According to the article above, the NWS "is required to continue functioning because its work can identify 'imminent threats to protect life and property.'"  In fact, the shutdown of many NOAA-based websites has not affected weather forecast office sites or any other page in the domain.

Knowing this, and given that the Memphis NWS office promptly and accurately warned of a tornadic storm on Saturday evening in northwest Tennessee, I contacted Jim Belles, Meteorologist-in-Charge at NWS-Memphis, to find out how the shutdown is affecting the local forecast offices. Belles indicated that their office remains fully staffed, providing their usual suite of products - from critical Tornado Warnings to useful daily forecasts to the more mundane, but no less important, daily climate data.

Belles iterated more than once that their mission to "protect life and property" has not been compromised and that that remains their core focus.  Asked about a few specific duties and responsibilities, he dutifully went back to the mission statement and, in a nutshell, said it is "business as usual" for job functions that are directly related to the mission.  The public should not be concerned about a lack of essential services from their local NWS office.  The one supplemental service that has had to be postponed, according to Belles, is SKYWARN storm spotter training sessions that are scheduled during the shutdown. Those classes will have to be re-scheduled when the NWS has a budget with which to operate.

I can also report that the forecast models that are run on NWS supercomputers continue to churn out terabytes of forecast data daily, Doppler radars continue to scan the skies, Hurricane Hunter aircraft flew into Tropical Storm Karen, and weather balloons are still launched twice daily around the nation, even during the shutdown. In other words, the public and private sectors are getting the necessary information to continue disseminating weather information and forecasts to the nation.

So, Mid-Southerners, rest assured that no matter how long the budget battle drags on, the NWS will continue to provide services that will keep us safe and informed, in good weather and bad.

UPDATE #1 - Oct 10, 2013 - A source at the National Weather Service (not Belles) has confirmed that all NWS employee travel to the annual National Weather Association (NWA) meeting in Charleston, SC has been cancelled.  The NWA meeting, in particular, is a excellent time of education and renewal for the operational meteorologists and others that attend.  For many others who attend, such as broadcasters, private sector meteorologists, etc., NWS meteorologists' presentations often provide exceptional post-event research on weather events that result in better forecasts from the entire sector. I only hope that many of their presentations are able to be given via webinar so that others may still benefit.

--Erik Proseus, Meteorologist,

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Monday, October 7, 2013

Beautiful work week temps ahead with one mainly cloudy day mid-week


After an absolutely gorgeous Monday I'm pleased to inform you fall will continue across the Mid-South for at least the next few days. The drier air streaming in from the north is most welcome and I find that to be a bigger relief than the cooler temperatures themselves. Not too much to talk about weather-wise this week, but we do have a little upper-level disturbance that could bring some clouds Wednesday. Lets take a look.


NAM 500 mb (10,000') relative vorticity and heights at 12Z (7AM) Wednesday.
Above is a modeled image of mid-level atmospheric vorticity. It shows a dip in the heights at this pressure level over the Mid-South (the kink in the black line over the area) as well as a small amount of spin, or vorticity, over us. This indicates a shortwave trough, or upper-level disturbance, which can provide some uplift in the atmosphere. This feature gives me the clue to look for associated moisture as a result of this lifting process.
NAM 850 mb (5,000') relative humidity and wind vectors at 12Z (7AM) Wednesday.
After scouring the many levels of the atmosphere, I found the most pronounced area of moisture to be in the lower-levels. The map above indicates overcast skies in the region through Wednesday morning, however peaks of sun will be possible in the afternoon and evening. Closer to the surface, moisture values will remain fairly low, inhibiting any chances of precipitation.

[EP: This minor "fly in the ointment" will be transient and have little effect on the forecast beyond Wednesday. We'll be back to partly cloudy skies on Thursday as some left-over moisture produces some clouds, with highs back near or slightly above normal.]

William's Memphis Forecast

Sunny with a high of 75, low of 60.

Overcast with possible peaks of sun in the afternoon, high of 75, low of 60.

Partly cloudy with a high of 83, low of 62.

--William Churchill, MWN Social Media Intern

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Friday, October 4, 2013

September 2013 Climate Data and MWN Forecast Accuracy

Climatological fall starts in September but it didn't feel like autumn with temperatures well above normal and precipitation highly variable. At the official observing site at Memphis International, rainfall was below normal, but on the north side of the county, at MWN headquarters in Bartlett, rainfall totaled nearly 2" more than at the airport. Climate details for September can be found below.

Memphis International Airport, Memphis, TN

The average temperature for the month of September was 78.2 degrees, or 3.0 degrees above normal. The average high temperature was 87.4 degrees (2.3 degrees above normal) and the average low was 68.9 degrees (3.7 degrees above normal). The coolest temperature of the month was 59 degrees, reached on the 15th, 22nd, and 23rd, while the highest temperature was 98 degrees on the 8th. This also was the hottest temperature recorded all summer in Memphis. There were 14 days which saw high temperatures at or above 90, which is 6.3 more than normal.

Precipitation for the month totaled 2.69", which was 0.40" below the average monthly rainfall for Memphis International. There were nine calendar days with measurable rainfall, but only two which recorded at least 0.1" and one which saw 1" or more.  Through September 30, annual precipitation at Memphis is 48.64", which is 10.17" above the 30-year average.  The maximum 24-hour rainfall was 1.87" on the 20th.

The peak wind was 30 mph from the east on the 1st with an average wind speed for the month of 6.7 mph. The average relative humidity was 62 percent and average sky cover was 40 percent. Click here for a daily statistical recap for Memphis International Airport.

Cirrus Weather Solutions, Bartlett, TN

The average September temperature at Cirrus Weather Solutions was 74.1 degrees with a maximum of 97.7 degrees on the 8th and a minimum of 49.4 degrees on the 15th (which was also the only morning low below 50 for the month). September precipitation was much higher than at the airport and measured 4.59" via the Cirrus automated gauge and 4.79" in a manual gauge used for the CoCoRaHS program. Much of this was recorded on 3 days which each saw 0.85" of rain or more. For the year, the CoCoRaHS gauge at MWN has recorded 46.11" of precipitation. The measured peak wind gust was 21mph on the 9th and again on the 10th. Average relative humidity was a muggy 79%. Click here for a daily recap on

MWN Forecast Accuracy

For the month of September, the average temperature error in all MWN temperature forecasts was 1.64 degrees, lower than all available computer data models and the National Weather Service forecasts with the exception of the LAMP short-range model, which only extends 25 hours into the future. MWN's forecasts extend out five periods (2.5 days, or roughly 60 hours). Over 81% of the MWN temperature forecasts for the month were within 2 degrees of the actual temperature. For dewpoint accuracy, the MWN forecast averaged 2.17 degrees error and fell within 2 degrees of the actual dewpoint 63% of the time. Historical accuracy statistics can be found here.

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Autumn air awaits behind a big cold front; Karen's effects on the Mid-South

As we discussed a couple of days ago, confidence in the weekend forecast has been lower than we like to see it, mainly due to Tropical Storm Karen moving into the Gulf Coast region as a cold front pushes through the Mid-South. The overall scenario is starting to come into focus however, and it appears that the cold front will have the most influence on our weather this weekend, with Karen contributing indirectly.

Daytime Saturday - Unsettled

With a warm and humid airmass in place, and the front approaching, the Mid-South is positioned to start seeing scattered showers and possibly a thunderstorm as early as Saturday morning. A few models are trending towards a chance of rain in the morning, then possibly a break in the afternoon, before the main rainmaker - the cold front - arrives late Saturday evening. Even given those trends though, I'm hesitant to remove all rain chances during the PM hours on Saturday given the warm, humid airmass in place and model solutions like the one below.

While most storms that form Saturday will be sub-severe, the Storm Prediction Center has placed the Mid-Mississippi Valley south to Memphis in a Slight Risk for severe storms.  The main threat will be a few strong wind gusts embedded in storm cells.  So, for those of you with Saturday plans in the Memphis/Tunica areas, it would be a good idea to have your umbrellas or rain ponchos handy. Any storms that pop-up could have some brief heavy downpours and lightning, as well as an isolated high wind threat.

SPC places the Mid-Mississippi Valley south to Memphis in a Slight Risk of severe weather for Saturday.

High-res NAM model forecast radar between 3-7pm Saturday, indicating possibility of scattered thunderstorms.
Click for larger image. Graphic courtesy WeatherBell.

Saturday night - Wet

As for the bug kahuna - the fall cold front and it's associated low pressure system are responsible for a heavy dumping of snow over the northwest and north-central U.S., as well as severe storms in the Midwest, proving it's potency. It will get hung up just a bit as it sweeps towards the Mississippi Valley on Saturday thanks in part to Tropical Storm Karen's approach in the northern Gulf of Mexico.  Karen will be pushed from coastal Louisiana across the central Gulf by the upper-level trough trailing the front before being absorbed by the front as it moves into the Deep South and Mid-Atlantic. Click here for more information on Karen from the MWN Tropical page.

Scattered thunderstorms will be likely along and just ahead of the front as it moves through the Memphis metro in the 7pm-midnight timeframe Saturday night. Trailing the front, periods of rain (possibly heavy) will last much of the night Saturday night. The excess rain will be due in part to Gulf moisture riding up over the front from Karen. Depending on the speed of the front and Karen's exact track, showers may linger into Sunday morning in the Memphis area.

Precip totals projected by the NWS through Sunday 7am. Click for larger image. Courtesy WeatherBell.

Next week - Autumn!

The best news with this cold front is the cool Canadian high pressure behind it. Much of next week will see sunny skies and temperatures that fall into the 70s for highs and 50s for lows.  In fact, some cooler spots may see 40s on Monday and Tuesday mornings! Temperatures will moderate slowly through the week but after above normal temps and humidity this week, it will be a welcome change, just in time for Shelby County Schools fall break! You can find the complete MWN Forecast for the weekend and next week here.

Tuesday AM projected low temps (GFS model) - near 50 in Shelby County! Click for larger image. Courtesy WeatherBell.

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