Tuesday, July 17, 2018

Brief "cool-downs" expected over the next several days

A couple of frontal passages today and in the coming days have allowed our forecast to have a little bit more variability than a typical summertime pattern. Overall, while temperatures look to stay in the 90s throughout the foreseeable future, we will have periods of both slightly above and slightly below average temperatures, and also reduced humidity, which should really lift our spirits!

GEFS temperature forecast through the beginning of August. *MODEL DATA - SUBJECT TO CHANGE* (WeatherBell)

Even if you look at the next couple weeks, you can see this small roller coaster type feature of some above average temps and some below average temps. It will be nice to have this variability in the coming weeks.


Today

We're still highlighting above average warmth today though as temperatures are expected to reach the mid 90s by this afternoon with dewpoints in the very muggy mid 70s. With temps and dewpoints so high, portions of the Mid-South are currently under a Heat Advisory as heat index values will top off between 105 and 110 this afternoon.

Counties highlighted in orange are under a Heat Advisory until 8 PM this evening. 
The good news is that a "cold" front is expected to pass through the area today. While this won't knock down our temps a whole lot, we will feel some relief in the coming days, particularly a reduction in the dewpoint. 

Current surface analysis shows a surface low pressure system located near the Missouri Bootheel with a frontal boundary draped across Arkansas and northern Tennessee. (NOAA/WPC)
I don't know about you , but I am really looking forward to the somewhat drier airmass!


This front could initiate some shower and thunderstorm activity into this afternoon. Like most summertime thunderstorms, coverage will likely begin to decrease after sunset.  Overnight temps will fall back into the mid 70s.

HRRR model loop shows scattered thunderstorms developing in the afternoon hours and continuing into the early evening.  (WeatherBell)

Wednesday & Thursday

Into tomorrow, we will begin to feel this somewhat cooler and drier weather pattern. An upper-level trough will continue to dig into our area over the next few days. What does this mean for us? Well, it will help to keep our winds out of the north, bringing cooler and drier air into the Mid-South. 

300mb analysis shows a trough digging into the eastern half of the U.S. through the middle and second half of the week. (Pivotal Weather)

Looking at temperatures just above the surface across the U.S., the western half of the U.S. is experiencing some pretty warm temperatures. Luckily for us, our winds will stay out of the north, northeast over the next few days, ushering in the cooler and drier air.

850mb (5000 feet) temperatures and winds show cooler air being brought into the Mid-South, keeping the much warmer temperatures to our west. (Pivotal Weather)

Overall, temps look to hang around near 90 over the next couple days with dewpoints backing off into the upper 60s. These lower dewpoints will keep the extreme mugginess away. However, with the upper levels of the atmosphere exhibiting northwest wind (what we call "northwest flow"), storm complexes moving out of the Plains could affect the Mid-South. This possibility means we'll keep shower and thunderstorm chances in the forecast Wednesday, and a lower chance Thursday.

Friday

Good things can only last so long as warmer and muggy air attempts to make a comeback on Friday. 



The predominately northerly winds discussed above will begin to shift to more westerly, allowing all those hot temperatures from the western U.S. to slowly migrate over to our area.


850mb (5000 feet) temperature and winds show westerly winds by Friday afternoon across the Mid-South, allowing warmer temperature to push eastward. (Pivotal Weather)
Highs on Friday will reach back into the mid 90s with dewpoints creeping back into the humid 70s. As for rain chances, we will have to keep an eye on another front that poses to sweep through the Mid-South late Friday into Saturday. Depending the timing of this front, we could see some shower and thunderstorm activity later in the day.

Surface analysis for early Saturday morning shows a closed low pressure located in Michigan with a cold front sweeping across the Ohio River Valley into portions of the Mid-South. (NOAA/WPC)


Weekend and beyond

Our muggy and hot weather pattern will begin to move out following the frontal passage. Temps look to stay in the mid 90s on Saturday before backing off into the low 90s on Sunday.

GFS shows a chance of thunderstorms moving through late Friday into early Saturday, with rain chances clearing through the weekend. (Tropical Tidbits)

Luckily, rain chances will be minimal through the weekend. So if you have any outdoor weekend plans, it looks like you picked a fantastic weekend to have them!

Caroline MacDonald
MWN Meteorologist Intern

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Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app
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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Thursday, July 12, 2018

Extreme heat & high pressure continue to dominate the Mid-South

It's summer. It's hot. We know it's coming every year, but somehow it always feels worse when it does arrive. The big weather maker to highlight for the next week is in fact the heat. Heat index values are expected to climb well over 100 degrees for the rest of the week and even into the beginning of next week. For the past couple of days, several of our counties have been included in a Heat Advisory for these dangerous heat indices. A Heat Advisory is issued when heat index values are expect to rise above 105 degrees. While the current Heat Advisory will expire this evening, given the forecast, it will be back before long!

Late afternoon warning map shows the Heat Advisory in orange. A Special Weather Statement, also highlighting heat potential, is shown in tan and also includes the Heat Advisory counties.

As we head into the weekend, be sure to remember some heat safety tips. I would also suggest finding a pool to cool off in!


Tomorrow and this weekend

Hot, muggy, afternoon showers. With any summertime pattern, like we are in right now, those three phrases are the ones to live by. Expect temps to stay a few degrees above average the next few days with dew points hanging in the 70s. This will provide that sticky feeling we all love during the summertime.


I'm sure many are wondering about our precipitation chances. Well, it looks like our afternoon pop-up showers and thunderstorms will hold on for now. Scattered showers and thunderstorms will likely develop each afternoon with coverage decreasing once the sun sets. This translates to a 20 to 30% chance each day. Whether you have plans to head to Levitt Shell or the Memphis Botanic Gardens for concerts or have other outdoor plans this weekend, things will likely stay muggy, but any afternoon showers should be on the downward slope by evening. 

Saturday and Sunday look to have the same old song and dance on the surface, but not necessarily in the middle and upper atmosphere. While temps will stay in the mid 90s during the daytime and "cool" into the upper 70s at night, the high pressure system that has been dominating our weather pattern will begin to lose strength. 

GFS shows a ridge pattern initially that begins to lose strength into Sunday. By Monday and next week, a mid-level trough begins to take its place. (Pivotal Weather)
With any meteorological phenomena, it usually takes some time for things that start aloft to reach the surface. So while the ridge appears like it will break down aloft, it will take some time for the extreme heat to go away. 


Beginning of next week

While we may not begin to feel the implications of the ridge weakening and the trough taking over, we will notice some increased thunderstorm coverage for the first half of the week. Temps will stay mild, muggy, and in the mid 90s Monday and Tuesday with overnight temps coasting in the upper 70s, proving little nighttime relief.

As for our rain chances, each day will likely have a few more showers and thunderstorms than we have seen in recent times. Typically in this pattern, they fizzle out after sunset, so that is good to keep in mind when making evening plans. 

GFS loop from Saturday evening through Tuesday evening shows scattered showers each day. (TropicalTidbits)


Second half of next week

With the mid-level trough digging into the eastern half of the U.S for the second portion of the week, expect things to finally cool off just a tiny bit compared to the above average temperatures and extreme heat we've been having recently. 


The Climate Prediction Center releases daily graphics highlighting the 6 to 10 day temperature and precipitation outlooks for the U.S. They currently span from next Wednesday through the following Sunday. On average over the period, temps will likely stay right around average here in Memphis with precipitation being a little higher than average for summertime. I don't know about you, but I could use some more showers and a little less heat. Stay cool until then!

The Climate Prediction Center's 6 to 10 day outlook shows a near normal temperature outlook over the Mid-South. (NOAA/CPC)

The Climate Prediction Center's 6 to 10 day outlook shows a slightly above average (33%) precipitation outlook over the Mid-South. (NOAA/CPC)

Caroline MacDonald
MWN Meteorologist Intern

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Follow MWN on Facebook and Twitter for routine updates and the latest info!
Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app
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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Monday, July 9, 2018

June 2018 Climate Data for Memphis, TN

June Climate Recap

Continuing the trend from May (but not quite the anomaly that May was), June temperatures averaged well above normal, to the tune of over 2 degrees, placing the month twelfth warmest on record. Twenty-four of the thirty days in June were above normal (although four of those six that were below normal were within a degree of the normal temperature). No daily records were set during the month. Also as in May, precipitation for the month of June was below average by over one and a half inches at the official observing site at Memphis International Airport, however scattered thunderstorms with heavy downpours on several days resulted in a wide range of precipitation. For example, MWN in Bartlett recorded 6" more rain than the airport in June.

Severe weather reports received during the month were primarily from downed trees due to high wind associated with powerful scattered storms. These include in Marshall County overnight on the 2nd/3rd, in the immediate metro on the afternoons of the 13th and 21st and the morning of the 23rd (when a 65 mph wind gust was measured at a secondary sensor at Memphis International Airport). Hail was recorded in DeSoto County on the 12th and flash flooding occurred in north Bartlett near MWN HQ on the morning of the 24th.  There were multiple Severe Thunderstorm and Flash Flood Warnings during the month in the metro, but no Tornado Warnings. Most Flash Flood Warnings were in Shelby County for urban flooding from localized heavy downpours.

Memphis International Airport, Memphis, TN


Temperature
Average temperature: 81.9 degrees (2.3 degrees above average)
Average high temperature: 91.6 degrees (2.7 degrees above  average)
Average low temperature: 72.1 degrees (1.8 degrees above average)
Warmest temperature: 96 degrees (15th, 16th)
Coolest temperature: 64 degrees (4th)
Heating Degrees Days: 0 (0 below average)
Cooling Degree Days: 513 (75 above average)
Records set or tied: The month ranked 12th warmest on record.
Comments: Twenty days recorded high temperatures at or above 90 degrees, which is 6 days above average. Only six daily temperatures were below average.

Precipitation
Monthly total: 2.06" (1.57" below average)
Days with measurable precipitation: 9
Wettest 24-hour period: 0.66" (23rd)
Snowfall: 0.0"
Records set or tied: None
Comments: Only a single day recorded more than 0.5".

Miscellaneous
Peak wind: Southwest/50 mph (23rd)
Average wind: 7.3 mph
Average relative humidity: 69%
Average sky cover: 40%

Click here for a daily statistical recap for Memphis International Airport.

Cirrus Weather Solutions / MemphisWeather.net, Bartlett, TN


Temperature
Average temperature: 80.9 degrees
Average high temperature: 91.2 degrees
Average low temperature: 70.0 degrees
Warmest temperature: 97.2 degrees (28th)
Coolest temperature: 60.0 degrees (4th)
Comments: None

Precipitation
Monthly total: 8.08" (automated rain gauge), 8.62" (manual CoCoRaHS rain gauge)
Days with measurable precipitation: 12
Wettest date: 2.56" (21st) (via automated gauge)
Snowfall: None
Comments: In stark contrast to Memphis International Airport, four days recorded precipitation of 0.99" or higher (zero at the airport).

Miscellaneous
Peak wind: South/33 mph (1st)
Average relative humidity: 76%
Average barometric pressure: 29.94 in. Hg

Click here for a daily statistical recap for Bartlett, TN.

MWN Forecast Accuracy

MWN average temperature error: 1.48 degrees
MWN forecast temperatures within 2 degrees of actual: 84%
MWN average dewpoint error: 1.88 degrees
MWN forecast dewpoints within 2 degrees of actual: 74%

MWN's forecasts extend out five periods (2.5 days, or roughly 60 hours). Historical accuracy statistics can be found here.

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Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app
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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Why has the rain been moving backwards?

I've been asked several times over the past week why our showers and thunderstorms have been moving "the wrong way." Isn't it more typical in the summer for us to be watching skies to the south or southwest than to the east? While sometimes we just call them "Crazy Ivans" (you remember this scene from "The Hunt for Red October," right?), there is a real explanation for this phenomena.


A Typical Summertime Weather Pattern

To answer the second question first - yes. Our weather usually originates from the southwest or south in the summer. To understand the answer to the first question, we need to know that the wind at the surface does not determine the direction clouds or storms move. The wind at the mid-levels of the atmosphere direct most weather patterns. Specifically, the wind between about 5,000-10,000 feet up (or 850-700 mb if you are a meteorologist using pressure values rather than feet).

Typically, much of the summer in the southeast U.S. is controlled by the "Bermuda High," a high pressure system that takes hold in the western Atlantic centered near Bermuda. Remember that wind flows clockwise around high pressure. That means that the air around the western side of that high, which is where we are located relative to it, flows from the south tor southwest. Thus our weather  usually follows that same pattern.

Bermuda High pressure extending into the southeast U.S. Clockwise air flow means south to southwest wind for Memphis when the Bermuda High controls our weather. (Original graphic credit: NASA Goddard Space Flight Center)

But sometimes we get Crazy Ivans...

In the past week or so, the Bermuda High has not had control over our weather. More influential highs have been located to our north or northeast. You undoubtedly heard about the record heat from the Midwest to the Northeast last week? That was because of a massive, hot high pressure center over that region. Even this weekend, despite it weakening some, high pressure at that crucial 5,000-10,000 -foot level has been centered over the Ohio Valley.

Satellite imagery from July 4 show the clockwise motion of clouds around high pressure over Kentucky. That results in weather moving from east to west across the Memphis area.

Let's look a little closer at Sunday afternoon, when our scattered afternoon showers were moving from southeast to northwest...The national picture at 10,000 feet shows high pressure over southwest OH and a strong low off the Carolina coast (that is Tropical Storm Chris). The green arrows show the flow of the wind around those features, while the colors show the wind speed (less than about 25 mph is white). Note that over our area the wind is light from the southeast.


Zoomed in a bit, you can see how the high over southwest OH results in clockwise wind flow around it, or from the southeast in the Memphis area.


Finally, if we look just at the metro area, the wind barbs are angled from southeast to northwest. The little flags at the tail of the wind barbs tell us how fast the wind is blowing. The longer flags are 10 knots (mph) and the short flags are 5 knots (mph). So the wind over the metro yesterday afternoon was blowing from the southeast at roughly 15 knots (mph).


And guess which way yesterday's showers were moving? To the northwest at 15-20 mph! Now you know why sometimes a radar loop shows rain moving in a different direction than you would expect! It's all in the (movement of the) air up there! Or maybe, we need to watch out for those Crazy Ivans!

Erik Proseus
MWN Meteorologist

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Follow MWN on Facebook and Twitter for routine updates and the latest info!
Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app
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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Wednesday, July 4, 2018

On the Fourth of July, keep an eye to the sky!

Happy Independence Day!


Image credit: BigRiverCrossing.com
The Fourth of July will likely feature a few strokes of bright light and loud booms that are not man-made today. An upper level disturbance moving through the region from east to west (yes, sneaking up from behind, "Crazy Ivan"-style) today that will likely result in widely scattered storms forming this afternoon into the evening.

With a very hot and humid airmass in place (heat indices will reach 105° this afternoon), and some moderate wind aloft to boot, a few of these storms could become strong to possibly severe. The primary threats with any storm that forms will be dangerous lightning, strong wind, and localized downpours. With the impulse continuing through the region into the evening, it's quite possible that the threat continues later into the evening than it usually does in the summer, which means we'll all need to keep one eye on the sky for this evening's fireworks displays around town. (Note that despite the possibility of strong storms, not everyone will see rain today.)



The latest high-resolution models seem to point to a potential threat during the afternoon hours, then a lull early this evening, followed by another threat after 9-10pm. We won't get that fancy with timing - just be prepared the rest of the day and be ready to seek shelter if you hear thunder. We also recommend you take our MemphisWeather.net mobile app with you and have StormWatch+ activated in-app to warn you if severe weather threatens while you are out and about.

Besides the severe weather threat that some of us might face, we'll all be affected by the heat. Temperatures in the mid 90s and heat indices of 105°+ means you'll need the sunscreen, water, and some occasional shade. A Heat Advisory is in effect for the entire metro, which is triggered as heat indices are expected to be 105+.


Thursday brings another summery day with similar temperature and humidity levels as today. The storm threat appears to be slightly lower with no clear instigator in the atmosphere to trigger development, but a 20% chance of rain is in the forecast because... summer.

Friday into the weekend

By Friday, the pattern starts to change a bit. A cold front (don't get too excited just yet) will seep into the northern reaches of the Mid-South, resulting in enhanced rain and storm chances, particularly in the afternoon. Heat indices will still climb above 100 as humidity tends to "pool" ahead of these fronts, making it even stickier despite ever-so-slightly cooler temperatures. The scattered storm chances continue into Friday night as the front drops closer to I-40.

By Saturday morning, there's a decent chance that the cold front slips just to our south. If it does, humidity levels will drop a bit and storm chances should push to the south as well. Saturday has the potential to be the best looking day of the forecast with highs only in the upper 80s, a north breeze, and dewpoints dropping into the tolerable range. Still can't rule out a thunderstorm, mainly over north MS. We'll be keeping a close eye on the front's progress, as sometimes the models over-promise and under-deliver when it comes to summertime fronts this far south. Here's hoping...


The front, wherever it ends up, will weaken and wash out Sunday into Monday. That means the return of summertime scattered storms and less acceptable humidity levels. Fortunately, at least for now, it appears that high temperatures early next week will be closer to seasonal levels (90-93° for highs), or a bit cooler than we have had most days over the past week. For our complete forecast, check the app or click here.

Erik Proseus
MWN Meteorologist

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Follow MWN on Facebook and Twitter for routine updates and the latest info!
Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!
MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder