Tuesday, May 31, 2011

Severe weather season over for the Mid-South?

Looks like the Mid-South severe weather season, which typically encompasses April and May may have gone out with a bang following last Wednesday's High Risk event.  After a couple of cool days, Memorial Day weekend hit and the heat is ON!  The official high on Saturday was nearly 20 degrees warmer than Friday and it hasn't relented since - and won't anytime soon according to the MWN Forecast.

We can thank strong high pressure at the surface and aloft, a rising sun angle, and climatology for the hot weather.  Though it typically warms up nicely around Memorial Day, this year's late May/early June pattern has left us with temperatures that are about 10 degrees above normal and will be approaching record category by week's end.  In fact, the dreaded "heat index" is back over a several-month hiatus, as the air "feels like" 100+ beginning tomorrow.  Even a weak cold front over us tonight will do almost nothing to help stifle the heat.  High temps in the 90s will last into early next week!  The strong ridge of high pressure likely means the beginning of summer and fewer chances of severe weather. Remember though that summer doesn't mean there won't be severe weather, just as temps in the 90s now doesn't guarantee that all summer will be like this week!

Upper-level high pressure ridge directly over the Mid-South late Wednesday
Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!

Thursday, May 26, 2011

2011 Atlantic Hurricane Season Outlook

Hurricane Isabel, 2003
With all of the severe weather, tornadoes, and flooding getting the press lately, the Atlantic Ocean is probably thinking "what about me?" The official forecasts have been issued and it's Hurricane Preparedness Week this week as coastal areas gear up for another round of tropical peek-a-boo.  Last year at this time, we were talking about a series of events that contributed to a general feeling of angst as hurricane season approached, among them the Deepwater Horizon oil spill, a recently-earthquake-ravished Haiti, and forecasts of doom and gloom.

As it turned out, 2010 produced a very active season that was unusual in the lack of U.S. landfalls given the number of storms.  There were 19 named storms, 12 hurricanes, and 5 major hurricances (Category 3 or higher). Amazingly, with 12 hurricanes, there were no U.S. hurricance landfalls and only one Tropical Storm - Bonnie, which grazed south FL and fell apart as soon as it hit southeast LA. Another storm, T.S. Hermine, made landfall just south of the U.S.-Mexico border, technically in Mexico.  Though the U.S. was spared, there were two landfalling hurricanes in Canada - Earl in southeast Nova Scotia and Igor, near St. John's, Newfoundland.  Both reached Major Hurricane status over the Gulf Stream.

Tracks of all named 2010 Atlantic tropical systems (click for larger image)
The number of storms in 2010 was pretty close to (actually slightly over) predictions from Dr.'s Klotzbach and Gray from Colorado State University and Dr. Joe Bastardi, then of Accuweather.  However, both expected multiple U.S. landfalls, as would be expected in this type of active year.  The number of storms was also in the range provided at this time last year by NOAA.

So, onto this year!  NOAA indicates that the climate factors that will affect this year's Atlantic hurricane season include the fact that we are in a continuing high activity era, which has been ongoing since 1995 and is multi-decadal, warm sea surface temperatures about 2° F above the long-term average in favored storm development regions (a phenomena referred to as the Atlantic Multidecadal Oscillation, or AMO), and, though La Nina is dissipating, it's impacts such as reduced wind shear over the Atlantic will continue into the hurricane season.  Wind shear is a hurricane killer - less wind shear allows storms to develop and maintain strength. Tropical Atlantic forecasts issued for 2011 are listed below.

Named storms: 12-18
Hurricanes: 6-10
Major hurricanes: 3-6

Colorado State University
Named storms: 16
Hurricanes: 9
Major hurricanes: 5
72% chance of a U.S. landfall

Named storms: 15

Hurricanes: 8
Major hurricanes: 3

Last year, I closed my hurricane forecast blog with this statement, and it is appropriate again this year:

"As hurricane season begins, it is wise for those that could potentially be in the path of one of these storms to make all necessary preparations and pay close attention to forecasts and watches/warnings as they are issued by the National Hurricane Center. For those living in the Mid-South, MemphisWeather.net's tropical page will have the latest storm tracks and bulletins. Be mindful that, while the threat is not nearly as great here [in the Mid-South], remnants of tropical systems can bring widespread flooding rains, tropical storm force wind, and/or severe weather to this region of the country."

Stay tuned... Hurricane season begins on Wednesday!

Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!

Wednesday, May 25, 2011

A word on Tornado Warnings and outdoor warning sirens

There is always a lot of confusion regarding the sounding of "tornado sirens" during severe weather.  Here is some information that might help:

1. Tornado Warnings are not issued by county, they are issued by polygon, meaning that the track of the storm is identified and a box is placed around the track.  Whatever counties that box intersects (no matter how much or what part of the county), the county is considered "warned."
2. In most areas, including Shelby County, outdoor warning sirens are activated by Emergency Management Agency officials or other designated agencies, such as area fire departments.  The sirens are almost always sounded COUNTY-WIDE when a polygon/warning touches that county, even if the entire county is not in the path of the storm.
3. The sirens will continue until the warning expires or is cancelled (sometimes even continuing until the original expiration time, even if the warning is cancelled early).  They do not stop when the threat has passed the immediate area if the warning is still in effect.
4. The sirens are OUTDOOR warning sirens.  They are meant to alert people outdoors to go inside and find out where the threat is then take cover.  Please don't complain that "I didn't hear the sirens" when you are inside with the TV or entertainment system on, etc.  If you are inside and there is a threat, be tuned in to local media or other information trusted sources, especially if you know you can't hear sirens well inside your home.

There has been a great deal of confusion on the subject and a sense by the public of "overwarning," however this is the way it works (for now). If a warning is in effect for Collierville and you are in Millington, your sirens will sound.  Do NOT become siren-weary or start ignoring the sirens because "the storms are never in my area" or "those things always go off for nothing."  The next one could be for a storm approaching your home!

In the meantime, hopefully city and county officials will understand the issues that county-wide warnings pose and come up with a reasonable solution.  They are out there, but some are very costly to implement.  For more information on the warning sirens in Shelby County, check out MWN's new Outdoor Warning Sirens page.

Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!

Brief update on severe weather outbreak expected later today

Severe weather is still expected later today across the Mid-South.  I refer you to yesterday's blog post for the nitty-gritty... very little has actually changed from then.  The biggest change is that all of west TN and northeast AR is now in a HIGH RISK for severe weather, as issued by the Storm Prediction Center.  All of north MS is in a MODERATE RISK. (see map below)

Briefly: Scattered storms will fire in AR and MO by early afternoon and begin moving towards the Mississippi River. I expect these storms to begin affecting the metro area (Shelby County and all counties that border Shelby) after 4pm. Any of these storms will be capable of producing large hail, high wind, and tornadoes, some of which could be violent and long-track. The strongest weather is expected between roughly 6pm-10pm, during which time some areas will see multiple storms or rounds of storms. A semi-solid squall line will likely move through the metro between 9-11pm, bringing an end to the strongest storms.

Please make preparations now for the possibility of severe weather. A previous blog post on severe weather preparations will help.  HEED ALL WARNINGS as they are issued. It's possible that "siren-weariness" will set in if multiple tornado warnings are issued. Take cover if the warning affects your area.

We will provide continuous coverage throughout the event.  We ask for your patience, especially if you are monitoring our social media channels, during the event. We are not able to answer everyone's questions individually during severe weather.

MemphisWeather.net provides many resources to keep you safe during storms.  Download the MWN App for iPhone or Android (search "Memphis weather" in the App Store or Market), sign up to receive severe weather alerts via e-mail, and follow @shelbyalerts and @memphisweather1 on Twitter and MemphisWeather.net on Facebook.  On MemphisWeather.net, the MWN Storm Center has the latest watches and warnings, as well as severe weather safety tips.  StormView Radar is interactive and will show you warnings and hail and storm rotation signatures detected by the radar. Finally, the MWN Forecast will help you plan ahead for possible severe weather as well.

Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!

Tuesday, May 24, 2011

Severe weather outbreak possible in the Mid-South Wednesday evening

A strong low pressure system will move very slowly through Missouri Wednesday night and will push an equally strong cold front through the region by early Thursday morning. This low has already been responsible for the deadly tornado in Joplin, MO on Sunday night (which was just the highest profile of several tornadoes that day).

Today, a widespread severe weather outbreak will take place in the Plains in an area the Storm Prediction Center has tagged with a "High Risk" - indicating that destructive tornadoes and large-scale severe weather is likely.  Hopefully the strongest storms avoid highly populated areas, but there are major cities under the gun today as well. By tomorrow, the threat shifts east and the lower Mississippi River Valley and Mid-South will get their turn to deal with this powerful system.

SPC risk areas for Wednesday/Wednesday night
The map above shows the area most at risk from this "potentially volatile situation," as the Storm Prediction Center has stated.  The Moderate Risk area includes the Memphis metro.  The map below shows the probability of severe weather within 25 miles of any point, while the hatched area is the area most likely to experience "significant" severe weather.

Probabilities of severe weather within 25 miles of any point - Wednesday
Several things to cover.  First, the threats... This weather system has already shown (and will do so again tonight) the potential to produce strong tornadoes.  Little will change by the time it reaches the Mid-South.  The subtleties with a system like this are what make the difference though, and these are hard to predict even just 24 hours in advance (they're very subtle), so we prepare for their possibilities.  Bottom line: with this system, tornadoes are possible.  In addition, very large hail and damaging thunderstorm wind (straight-line wind) is also very possible.  The system will be somewhat of a slow mover and thunderstorms could affect the same areas repeatedly, so flash flooding will be another threat.

Next, timing, which is based on the arrival of severe weather ingredients... the map below was issued by the Memphis office of the NWS today and indicates the potential timing for severe weather.  I generally agree with this map and will further refine it for the Memphis metro area specifically. An ongoing round of severe weather will move across Arkansas overnight tonight. I expect this area to be weakening after midnight as it moves east of Little Rock, but we could still see some storms, possibly with strong wind gusts, very early Wednesday morning (perhaps sometime between 2-6am).

Then, clouds will thin and perhaps clear out in the morning and sunshine will help temperatures rise into the upper 80s, possibly to near 90 by mid-afternoon. If you know anything about severe weather, you know that this is not good ahead of an approaching system, as it contributes to high instability in the atmosphere. In addition, sufficient moisture will be in place as dewpoints will be in the upper 60s to near 70.  Plenty of juice. As the afternoon goes on, upper-level winds will pick up and wind at the surface will also be gusty from the south at 25-35 mph. This brings about another required ingredient - wind shear.

Finally, the trigger.  Tomorrow it will be an upper-level disturbance that makes it's appearance over Arkansas during peak heating, or mid-afternoon. Storms will fire in response to the disturbance and quickly become severe, likely supercellular with the threat of tornadoes, by late afternoon.  These storms could affect the Memphis metro area by rush hour Wednesday and will be in the form of scattered supercells or clusters of storms.  By mid-evening, say 7-10pm, the storms will likely begin to form into a large-scale squall line that will move through the metro area around midnight, give or take an hour or two.  The passage of the squall line should end the severe weather threat for the remainder of the night.

Timing of potential severe weather, as indicated by NWS-Memphis
So, in sum, the probability of severe weather is moderate, which means preparations and action plans need to be polished off.  All modes of severe weather are possible, including the risk of tornadoes. Timing appears to be between 4pm and midnight, with the greatest chance of tornadoes ahead of the main line and the greatest risk of damaging straight line wind along the line.

None of this is meant to hype the situation or scare anyone.  We don't hype at MWN - we tell it straight, but also don't sugar-coat it.  Plan ahead and know what to do should severe weather strike where you will be.  Be prepared, not scared, and rest assured that we will keep you informed.  The best way to do that is to follow our social media channels, listed below, stay in touch with MemphisWeather.net on the web, download our apps for weather on your smartphones, or hit our mobile website at http://pda.memphisweather.net/. Also, familiarize yourself with the MWN Storm Center, including the Safety Tips at the bottom of the page.  Finally, HEED ALL WARNINGS as they are issued and don't be afraid to exercise your plan.  More resources and ways to prepare are listed in this blog we posted before the April 26-27 severe weather event.

Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!

Sunday, May 22, 2011

Severe weather, NAFTA-style, and threats in the Mid-South

You don't see this often... as of 4:40pm this afternoon, there are TWELVE (count 'em, 12!) Severe Thunderstorm and Tornado Watches in effect, stretching from northern Michigan (basically the Canadian border) all the way to south Texas, at the border with Mexico.  (I'm not sure this is what the government had in mind when they put together NAFTA, but you could travel from Canada to Mexico and not leave a watch box!) When the watches were originally issued, 53.5 MILLION people were affected, or over 1/6 of the U.S. population (also greater than the populations of Spain, South Africa, and South Korea).

Twelve watch boxes are in effect at 4:40pm, affecting 53.5 million people from Canada to Mexico
For the upcoming week, the Mid-South is going to be under a threat of severe weather (though likely not a high threat of tornadoes) until a cold front finally passes through on Thursday.  A Slight Risk of severe weather exists the rest of today, Monday, and Tuesday, and the Storm Prediction Center has highlighted the threat of severe weather across the Mid-South Wednesday and Wednesday night as well. The MWN Storm Center shows all of these maps in detail.  The main threats will be large hail (1" or larger) and damaging thunderstorm wind of 60 mph or greater each day.

Though rain chances aren't particularly high any day through mid-week, the combination of very warm temperatures, abundant moisture, and marginal wind shear, will mean that any storms that pop up could produce some severe weather. By Wednesday night and Thursday, a cold front will move through and clear everything out, however it too will bring a likely round of severe storms. The timing for this event is not certain just yet, but stay with MWN for the latest as the situation develops.

Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!

Thursday, May 19, 2011

Mid-South transitions from late-March to mid-June in a week

The weather pattern last weekend and early this week that resulted in morning lows in the 40s and highs only in the 60s (and one record low at Memphis International Airport) was more typical of late March than mid-May. Now, as we head into the weekend, a quick transition is taking place as southerly wind increases and the Gulf of Mexico "opens up," allowing more moisture to stream into the region. The result will be weather more typical of a month from now with highs well into the 80s, lows near 70, increased humidity, a south wind, and scattered showers and thunderstorms.

Though rain chances are not particularly high, we will see some scattered echoes on StormView Radar over the Mid-South, particularly Friday night into Saturday as a trough of low pressure over the central portion of the country inches closer.  It won't make it all the way to the Mid-South however, so we'll be stuck in the "warm sector" of the storm with southerly wind pumping moist Gulf air into the region. The pattern looks to remain that way for several days before the trough finally moves through on the heels of a cold front sometime around the middle of next week.  In the meantime, plan for muggy conditions this weekend and early next week, and keep the umbrella handy!  The MWN Forecast has the specifics for the next 7 days.

Surface map forecast valid 7pm Saturday evening
Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!

Monday, May 16, 2011

How metro rivers respond to local rainfall and why the flooding was so severe in 2011

The recent flooding has brought more attention to river gauges than perhaps any time in recent history. One of the questions I have heard multiple times over the past few weeks, phrased in different ways, is why one river rises much more quickly than another after local rainfall.  Many folks don't understand why the Mississippi River doesn't fluctuate much on the Memphis gauge when it rains locally (or assume it does), while others question the rise and fall of it's tributaries, especially the rate of change.

Below are a couple of examples of the readings of local rivers following a fairly heavy rain event in the metro area (primarily over Tipton County). All three of the graphs below start at the same time and are labelled with the location of the gauge.

The first, the Loosahatchie River at Arlington, rose significantly (mainly after the rain ended) from about 2' to 7.5' in a matter of a few hours, then fell back to below 2' within 24 hours.  The Loosahatchie in northeast Shelby County, takes runoff from the local area after recent rains and drains it to the Mississippi River.  It fluctuates quickly based on local rainfall and is delayed from the period of heaviest rain as it takes some time for runoff to all collect in the river.  Note that when the Mississippi River is very high, as recent weeks have shown, the Loosahatchie floods over western Shelby County as it cannot discharge into the Mississippi.  This backwater does not make it as far east as Arlington, however, so the high waters are not recorded on this gauge.

The Wolf River reacts similarly to the Loosahatchie, as it too captures runoff, this time from south and east Shelby County and Fayette County. However in this case, the rain was much lighter over these areas and the Germantown Parkway gauge (south of the Agricenter) barely registered a blip at the same time that the Loosahatchie was rising by feet.

Finally, the Mississippi River fluctuates very little based on local rainfall and instead responds to large amounts of water running downstream from the middle Mississippi River Valley, the Ohio River, and to a lesser extent, the Missouri River.  The middle Mississippi Valley and the Ohio River each contribute approximately 50% to the water in the lower Mississippi Valley, where Memphis is.  So, in the case of our recent severe flooding event, extremely heavy rain in the Ohio Valley, which caused record floods along that river, and excessive snowmelt in the Upper Mississippi River Basin, combined to produce a deluge of water in the Lower Mississippi.

As you can see below, the local rainfall reflected in the Loosahatchie River readings did nothing to the Memphis gauge, as the volume of water contributed by the Loosahatchie was literally a drop in the bucket compared to the 2,000,000 cubic feet per second of water that were flowing down the Big Muddy.  (In fact, due to backwater flooding downstream on the Loosahatchie, the local runoff probably didn't even reach the Mississippi and just contributed to more backwater.)

Now that the Mississippi River is falling below 45', the backwaters will begin draining from the western ends of the tributaries that run through the metro area and flooding from the Wolf, Loosahatchie, and Nonconnah Creek will subside, allowing the evaluation and clean-up process to begin.

Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!

Sunday, May 15, 2011

Upper-level low bringing unseasonably cool weather

In the wake of a cold front that moved through late last week, a pair of upper level low pressure centers have brought overcast and unseasonably cool conditions to the Mid-South this weekend.  The second of the upper level lows will move into the region tonight, bringing a chance of rain showers and also reinforcing the cooler air.  From my perspective, a few days in the 60s is welcome during mid-May, especially after near record high temperatures earlier this week. We'll be wishing for days like these again in June!  The highs this weekend are only a few degrees above record minimum high temps.

Below, a hi-res computer model shows the upper-level low on our doorstep by 10pm.  The image depicts energy at about 18,000 feet in bright colors.  The energy will be diving south from the Midwest, then heading towards Alabama in "northwest flow" aloft, meaning the wind at these levels is from northwest to southeast.  The only significant moisture in place is at the low levels, so I'm not expected more than a chance of light showers as a result of this low.

Upper-level energy moves into the Mid-South late this evening (valid 10pm Sunday)
By Monday, the low will be well to the east and a clearing trend will commence.  We'll then see abundant sunshine Tuesday through Thursday as high pressure dominates the southeastern U.S.  Late in the week, wind turns back to the south and a warm front moves through, allowing humidity and temperatures to increase.  In addition, showers and thunderstorms will become more common again Friday through Sunday.  The complete forecast can be found on MemphisWeather.net.

Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!

Thursday, May 12, 2011

Pork-cast: what to expect weather-wise for this weekend's Memphis in May barbecue contest

Memphis in May's annual World Championship Barbecue Cooking Contest is this weekend and the smell of pork and "everything else" will be wafting across the Fairgrounds very soon thanks to Mississippi River flooding causing a change of venue to newly-completed Tiger Lane.  I love the Memphis in May marketing teams BBQ contest poster this year - check it out to the left.

While the recent heavy rains here and to our north have forced a location change, unfortunately that doesn't guarantee a dry event! The MWN Forecast has all the details, but it looks like BBQ teams will be dealing with a few scattered thunderstorms this afternoon (hopefully not over the Fairgrounds, because these could have some heavy rain associated with them). Then, after midnight, a round of showers and thunderstorms will move into the area, perhaps lasting until Friday morning.

For Friday, a cold front inches closer to the region with thunderstorms re-developing during the afternoon and lasting into the evening. The Mid-South is under a Slight Risk for severe storms during this time period, so a few storms could pulse with hail or a brief high wind gust. Most will remain below severe limits, but will produce some areas of heavy rain and lightning. If you plan to be at the BBQ Contest Friday afternoon/evening, bring an umbrella and plan to take cover if skies turn threatening.  One great way to stay on top of the latest weather information is via the MWN iPhone and Android apps - links are provided at the bottom of this post.

Post-front, we'll be under the influence of an upper level low throughout the weekend.  This will result in much cooler temperatures, mostly cloudy skies, and low chances of showers Saturday and Sunday, with highs only in the 60s!

Monday will transition from cloudy/cool to a little more sun.  Then, the middle of next week looks fabulous with springtime temperatures in the 70s and abundant sunshine!

Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!

Monday, May 9, 2011

Early summer-like heat wave this week, and a peek at the Memphis in May Barbecue Fest forecast

The Mid-South, and in fact much of the central U.S., is experiencing the effects of an unusually strong ridge of high pressure at the upper levels that will build through tomorrow, then begin to weaken later in the week.  The ridge is bounded on the west and east by troughs of low pressure aloft (see graphic below).  Typically this means dry and warm weather under the ridge and cooler and possibly wetter weather under the troughs.  This time will be no exception.  The jet stream flows around the ridge at the level shown (about 35,000 feet up), so the storm track will also be well to the north while we are under the influence of the ridge.
A large ridge of high pressure aloft builds directly over the Mid-South on Tuesday
In addition, high temperatures will be well above normal with 90s common in many places, as shown by Weather Channel graphics for Tuesday and Wednesday below.  In fact, the ridge and trough over the U.S. (above) are easy to pick out based on the temperature trends for tomorrow and Wednesday in the maps below. Surface high pressure is off to our east, which means southerly wind and higher humidity values for the Mid-South. So not only do we have heat from high pressure aloft, but we are also getting a touch of early summer humidity from surface high pressure to the east!

Heading into late in the week, the computer models are having a difficult time determining how quickly the ridge of high pressure breaks down, which will affect the timing of our next cold front.  Currently, the best guess is that sometime between Thursday night and Friday night, that front will move through, accompanied by thunderstorm chances ahead of and along it.  With several days of moisture and strong heating ahead of it, depending on the timing of the front, some storms may be severe.  The MWN Storm Center will have the details on possible severe weather.

Behind the front, the upper-level low pressure system builds to our north and the pattern remains unsettled.  It appears that small chances of rain are possible through the weekend, depending on where exactly the low pressure system sets up.  This could have an effect on the weather for the Memphis in May Barbecue Festival at Tiger Lane.  At least participants won't have to contend with the mighty Mississippi lapping at their grills! As the slogan adopted by MIM goes, "Memphis is Cookin' Come Hell or High Water!" As the week goes on, the forecast will be come clearer.  Check with the MWN Forecast frequently for the details.

Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!

Pictures of the Mississippi River at Memphis, May 9, 2011

The following pics were all taken by Cirrus Weather Solutions / MemphisWeather.net on May 9, 2011 as the Mississippi River reached a stage of 47.8 feet on the Memphis gauge.  This is the second highest all-time reading in Memphis and the first time it has been above 41 feet since the Great Flood of 1937, which set the record at 48.7 feet.

There were a large number of onlookers/"local tourists" and national media types present at the river's edge.  I tried to also include some pictures of "collateral damage" from the tributaries (particularly the Wolf and Loosahatchie Rivers), although I did not break any laws by driving or walking past barricades.  A high law enforcement presence is keeping sightseers away from the most impacted regions. This event will be one for the history books and likely (hopefully) never seen again in any of our lifetimes.

After starting the slideshow, hover over a picture and click the 4 arrows button in the lower right to go full-screen.  Feel free to click "Share" as long as you provide credit to MemphisWeather.net or Cirrus Weather Solutions for the photos.

Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!

Friday, May 6, 2011

The Great Memphis Flood of 2011 - how it happened and where to get info

The "Big Story" in Memphis, as anyone who has not been living under a rock or in a million dollar fortified ch√Ęteau in Abbottabad, Pakistan would know, is the Great Flood of 2011.  MWN has been updating you on Facebook and Twitter as the water levels continue to increase the past couple of weeks.  We also have deployed the MWN Flood Center to provide meteorological information behind the flooding, as well as a set of resources we use.  Below are a list of some of those fantastic resources.  There's no way to cover the now-historic flooding from every angle, so we'll provide some links and let your fingers do the clicking.

First the facts: the Mississippi River is at 46.3 feet on the Memphis gauge at 3pm, which is above the Major Flood stage level of 46 feet and 12 feet above "normal" flood stage.  It is now at the second highest level ever attained in Memphis (surpassing the flood of 1927 earlier today).  Only the 1937 flood saw higher water, at a record stage of 48.7 feet.  The forecast calls for a crest at 48 feet on May 11, less than a foot shy of that all-time record.  I am not totally convinced that the river will stop at 48 feet. It's currently rising slightly faster than the forecast calls for.

Since this is a "weather blog," the angle that is appropriate to be addressed from our perspective is the chain of events that caused the flooding in the first place.  It is important to point out that it is not just the Mid-South dealing with major flooding.  The map below is a snapshot of locations throughout the Mississippi and Ohio River Valleys that are in flood (as well as a number of locations along the Red River in the Northern Plains).  All of the locations north of the Mid-South feed south eventually, so it's not a problem that will go away quickly.

River gauges in flood as of 5/6/11 are shown in orange, red, and purple
It all starts back in the winter of 2010-2011... you'll recall that it was an especially long winter in many areas of the country - cold and snowy.  The map below shows national snow cover on a mid-winter day (February 10).  Notice that the Northern Plains is under deep snow of 20"+ while even southern portions of the U.S., including the Mid-South, had snow on the ground.  When snow melts, it heads for the oceans, via large rivers and their tributaries.  Those large rivers in the eastern U.S. are the Missouri, Ohio, and Mississippi.  Snowmelt is one cause for the large amounts of water coming downstream.

U.S. Snow Depth on February 10, 2011
The second cause for flooding that is taking place all along the Mid and Lower Mississippi River Valley is excessive spring rainfall.  The next map shows total precipitation that has occurred in the past 30 days. Amounts of 10-20" are common from the Ohio Valley into the Mid-South.  This excessive recent rainfall created vast amounts of runoff, which in turn filled up local creeks, streams, and rivers, which feed the larger rivers.  The combination of these events (excessive local rainfall and large amounts of snowmelt) have created a sort of "perfect storm" of water.  Last week, tributary flooding was a serious issue, especially in eastern Shelby County, due to the excessive runoff from heavy rain.  Now that the runoff is gone, the focus shifts to the west and the rising Mississippi, which in turn is backing up water into the tributaries and causing water in the Wolf, Nonconnah, and Loosahatchie Rivers to rise from west to east.

30 day total precipitation leading up to May 6, 2011
Here are some resources I use to bring you the latest information:
  • MWN Flood Center - radar, precipitation forecast maps, and many other resources (including some of those listed below) in a one-stop flood shop
  • Flooding tips from MWN - published previously on this blog
  • water.weather.gov - the National Weather Service's AHPS system, which produces river readings and forecasts for the entire U.S.
  • LMRFC - The NWS Lower MS River Forecast Center, which has jurisdiction over Mid-South waterways
  • StaySafeShelby.us - The Shelby County Office of Preparedness website that is likely the most comprehensive source of information available for those in Shelby County. Includes excellent flood maps by zip code.
  • Zip code-based flood maps - a direct link to the page on StaySafeShelby.us with the all-important maps
  • Memphis/Shelby County EMA - overseeing the entire flood preparation and relief operation
  • Memphis District of the Corps of Engineers - the great guys/gals trying to keep floodwaters at bay
  • Memphis office of the National Weather Service - doing a great job of forecasting the river stages
  • ReadyShelby.org - Emergency Preparedness website - great info for any emergency
  • MemphisFlood.com - the river has it's own website! Good up-to-date resource for everything Memphis Flood.
  • #memflood - a results-based list of all Twitter posts tagged with #memflood

Those in neighboring counties should check with local authorities for flood risks, maps, etc. for their area.  A couple links for suburban counties are posted in the MWN Flood Center.

Do you have additional links you want to share?  Or perhaps comments on living through the Great Flood?  Post them below!

Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!

Wednesday, May 4, 2011

JacksonWeather.net to receive new location for local weather conditions

As of Thursday evening, May 5th, Cirrus Weather Solutions, which operates JacksonWeather.net (JWN) and MemphisWeather.net (MWN), will transition the local conditions shown on the front page of JWN from North Jackson, TN to Humboldt, TN.

The provider of the North Jackson weather station will be dismantling his equipment in the coming days in preparation for a relocation.  JWN began including conditions from Humboldt several months ago; this station will now become the primary provider of local, real-time conditions for the site.  Conditions from McKellar-Sipes Regional Airport in Jackson will also continue to be provided.  Climate data will also originate from Humboldt (in addition to McKellar-Sipes) beginning on May 5th, however JWN will provide climate records for North Jackson up through the date the station goes offline and maintain those records for your perusal for the foreseeable future.

Cirrus Weather Solutions appreciates the trust you have placed in us as we seek to provide a comprehensive source of weather information for the Jackson, TN area and all of west TN.  In addition, we are extremely grateful for the dedication of the operator of the North Jackson weather station, who for many years has provided an exceptionally reliable service to Jackson and the west TN community. We know you will be pleased with the exceptional service provided by the operator of the Humboldt weather station as well. If you have any comments or questions, you may direct them to us at this page.

Thank you for your patronage and support!

Erik Proseus
Owner, Cirrus Weather Solutions
Meteorologist, JacksonWeather.net

April 2011 Climate Data and MWN Forecast Accuracy

Memphis International Airport, Memphis, TN
Overall, April was warmer and much wetter than average in Memphis and was marked by multiple severe weather events in the region. This included lines of storms on the 4th and 19th that caused widespread power outages, followed by an extended period of severe weather April 25-27, during which the Mid-South was under a High Risk of severe weather for two days.  April 27th will go down in weather lore for the massive outbreak of tornadoes that swept across portions of at least 5 southeastern states, including a violent tornado that struck both Tuscaloosa and Birmingham, AL.

The average April temperature was 65.8 degrees, which was 3.7 degrees above normal. The average high temperature was 76.3 degrees and the average low was 55.3. The coolest temperature of the month was 40 degrees on the 5th and the highest temperature was 88 degrees, recorded on the 9th and 19th.

Precipitation for the month of April totaled 11.76", which was 5.97" above (or more than double) the normal of 5.79". There were 8 days with measurable rainfall (on 4 of those days more than an inch fell) and the maximum 24-hour total was 4.98" on the 26-27th. The peak wind gust was 64 mph on the 4th during a severe thunderstorm with an average wind speed for the month being a brisk 11.3 mph. Click here for a daily statistical recap for Memphis International for April.

Bartlett, TN
The average temperature for April at the WXLIVE! station in north Bartlett was 66.2 degrees with a maximum of 91.4 degrees on the 9th and a minimum of 34.9 degrees on the 5th.

April precipitation ended well above normal with a total of 10.95". A co-located manual gauge used for the CoCoRaHS program measured 11.65". The peak wind gust was 51 mph on the 4th. Average relative humidity was 64%. Click here for a daily recap on MemphisWeather.net.

MWN Forecast Accuracy
For the month of April, the average temperature error in all MWN temperature forecasts was 2.55 degrees, lower than all compared computer models, including the National Weather Service. Over 60% of the MWN temperature forecasts for the month were within 2 degrees of the actual temperature. MWN's forecasts extend out five periods (or 2.5 days). For dewpoint accuracy, the MWN forecast beat all data sources, averaging 3.12 degrees error and falling within 2 degrees of the actual dewpoint nearly 50% of the time. Detailed accuracy statistics can be found here.

Stay up to date on the latest weather conditions and forecast by checking out MemphisWeather.net on Facebook and Twitter and our new iPhone and Android apps!