Tuesday, May 24, 2016

Early summertime weather pattern is here! What about Bonnie?

The atmospheric patterns have shifted, changing from very pleasant and dry weather over the weekend to a more humid and warmer setup with increasing chances of thunderstorms, more akin to early summer.

At the upper levels, which drives how the rest of the atmosphere behaves, a large ridge of high pressure extends from the Southern Plains northeast towards the Great Lakes and is shifting east into the eastern U.S. Meanwhile, a large scale trough over the western U.S. will also push east into the Plains by this weekend.

As of Tuesday evening, a ridge of high pressure at the upper level (30,000') (which looks like a hill in the black contoured lines above) is situated from the western Gulf Coast towards the Great Lakes, causing weather systems in the Plains to move northeast around the ridge and somewhat protecting the Mid-South.
The mid levels respond with a high pressure ridge building briefly over the Mid-South for the middle of the week before moving east, as southerly flow ahead of a mid-level trough of low pressure also moves into the Plains.

By later in the week (Friday night, as shown), the upper level ridge shifts east and the mid-levels (18,000', shown here) respond with southerly air flowing into the region as storm system are allowed to get closer to the Mid-South with the ridge shifting east.
Finally, near the surface, the Bermuda high pressure cell maintains its grip on the southeastern U.S. with the Mid-South positioned on the western periphery of it. Lower pressures dominate the Plains.

Near the surface (5,000'), the Bermuda High (high pressure centered over the southeastern U.S. coastline), keeps weather systems from intruding too far east. Being on the periphery of the high, the Mid-South sees increasing chances of rain from east to west, with areas west of the Mississippi River having higher chances than those of us east of the river. 
Overall, this setup favors a southerly stream of warm, Gulf moisture-laden air into the Mid-South, which is increasing our humidity levels, as well as a stormy pattern (including some severe weather) to our west. As those storm systems encounter higher pressure east of the Mississippi River, they move northeast, up the west side of the ridge. We're left in the middle - with an active pattern to the west and dryness to the east.

Occasionally the systems to the west brush the area and bring us thunderstorm chances, but those are hard to determine more than 24-36 hours out which will fall apart as the encounter the ridge to our east and which will bring elevated chances of thunderstorms. Thus we are left with low chances of thunderstorms each day, some of which may not actually materialize and some which could bring a strong storm or two, as well as localized downpours!

It appears the best chance of more widespread storms in the metro may be in the Thursday night to Friday night time frame as the Plains trough is able to move into western parts of the Mid-South before high pressure re-builds heading into the weekend.

Total rainfall from Friday morning to Saturday morning according to the GFS model is nearly 0.5", so rain chances are expected to be higher to end the week before they fall again heading into the weekend. 
There also are some indications that this afternoon's storms just to our north could build south, or send out an outflow boundary that results in the formation of new storms closer to the metro this evening. Stay tuned to our social media feeds for the latest on this possibility. Most models are firmly opposed to the idea, so we'll see! Get our latest thoughts via the MWN Forecast.

Heading into the weekend, as mentioned, high pressure begins to build once again, reducing rain chances to low end "chance" possibilities, as a possible tropical or subtropical system develops off the southeast U.S. coastline. Atlantic hurricane season begins next Wednesday, but with Alex having developed in January, Mother Nature may not wait until June 1 to throw another named storm our way!

The American GFS model projects an area of low pressure over the Gulf Stream off the SC coastline on Sunday evening. Could this end up being Tropical Storm Bonnie?
Finally, you may know that we rolled out a brand new version of MWN StormView Radar on Sunday night. We've gotten lots of positive feedback on the new interface, features, and mapping! You'll get the full "interactive" experience on the desktop version of MWN, but the interactive version also works on mobile (the previous one did not). We also have a dedicated mobile version with 3 different zoom levels available via MWN Mobile. The new radar map also appears on the MWN mobile apps. For more on how to use the interactive features, check out this video tutorial I put together.

Latest regional view from MWN StormView Radar
I also must offer a big "Thank you!" to our inaugural sponsor of the new and improved StormView Radar, Levitt Shell! If you haven't taken in a free summertime, family-friendly concert at the Levitt Shell at Overton Park, plan to do so this year! And if you have, you're in for a whole new experience as the Shell has been completely renovated to enhance the patron and performer experience! We'll be keeping an eye on the weather for this summer's concerts as MWN is the Official Weather Partner of the Shell. You might even see StormView Radar on their video screens during one of your visits! Thanks Levitt Shell for a great partnership!

Erik Proseus
MWN Meteorologist

Follow MWN on Facebook, Twitter, and Google+
Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone.
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

Sunday, May 15, 2016

Details on below average temperatures and unsettled weather this week

A cool and dry weekend has felt more like early April than mid May after a sharp cold front arrived Saturday morning, bringing very gusty wind and some clouds during the morning hours. That front now sits well to our south but will start to lift north during the day tomorrow. The front, and upper level systems that traverse the area, will set the stage for an unsettled work week ahead in the weather department. Those looking for summer weather will be disappointed this week, though it's a bit early to be expecting mid 80s or warm temps every day.

Cool surface high pressure and an upper level trough centered over the Great Lakes and eastern Canada brought well below normal temperatures to a large portion of the northern and central U.S. this morning.

Cool weather was found throughout the  northern half of the U.S. early this morning  (5am CDT) with over 60% of the U.S. below 50°. An upper level trough over the Great Lakes is responsible for the near freezing temperatures in the Upper Midwest. Graphic courtesy WxBell. 
As the northeastern trough shifts east, a developing trough over the western U.S. moves over the Rockies, replacing upper level ridging (high pressure) over that region. In our section of the U.S., our cool flow from the northwest becomes more westerly, allowing upper level energy over Texas to move across the Mid-South. With dry and relatively cool air in place, that upper level system will bring increased cloud cover but initially only light rain that begins during the day Monday. Eventually, low level dry air will saturate and showers will become likely in the afternoon.

Mid-day Monday's surface map shows a stationary front along the Gulf Coast, but rain chances increasing (greens) in the Mid-South as upper level energy approaches from the west.
Overnight Monday night, as low pressure at the surface moves into the southern Plains, Saturday morning's cold front returns north as a warm front, putting the Mid-South in the warm sector of the approaching low from the Plains on Tuesday. The atmosphere will respond with warmer temperatures but increased chances of thunderstorms on Tuesday after a mainly dry period Monday night. Widespread severe weather is not anticipated as the upper level dynamics and wind energy are fairly weak, but a few storms could contain a strong wind gust or small hail as temperatures aloft become colder. The Storm Predication Center currently has the area under a Marginal Risk (category 1 of 5) severe weather outlook area for Tuesday with a higher risk well to our west.

A Marginal Risk (category 1 of 5) severe weather exists Tuesday with higher chances of strong storms to our southwest, according to the Storm Prediction Center. A few storms could have strong wind gusts or small hail.
The Monday night warm front begins sinking south again Tuesday, prompting some of those thunderstorms, then moves through Tuesday night, once again placing us in the cooler airmass heading into the mid-week period. Scattered showers are possible again Wednesday, though the best chances will be across areas south of I-40 in MS. With the front to our south, high temperatures will be back into to lower end of the 70s. High pressure to the north will push the front a little further south on Thursday, which should mean drier weather. High pressure aloft and more sun also should allow temperatures to warm back up to near 80 on Thursday.

By Thursday morning, the front returns to the Gulf Coast as high pressure builds in to our north once again, leading to what will most likely be the driest day of the week.
Finally, to end the week, low pressure at the surface develops to our west and moves into the region. The track of the low is still uncertain but rain and thunderstorm chances look to increase significantly. The possibility of severe weather is still too uncertain to make a call on, but will need to be monitored, especially if the low tracks by to our west and we can get sufficient wind shear and warm unstable air. Stay tuned.

While still 6 days out, the NWS places a surface low just to our east Saturday morning. As it approaches Friday, rain and thunderstorm chances increase significantly. A few lingering showers or thunderstorms could remain Saturday before a warming period begins heading into the last full week of May.
With an upper level trough remaining to our northwest on Saturday, we could still see some lingering rain chances. It looks like high pressure aloft and at the surface begins building in to end next weekend and start the last full week of May so that those who want to get early use of their pools may get some warmer days in the 80s as we head towards the end of May! Click here for the complete week-ahead look at the MWN Forecast or check it via our mobile apps linked below.

Erik Proseus
MWN Meteorologist

Follow MWN on Facebook, Twitter, and Google+ Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone. 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

Tuesday, May 10, 2016

April 2016 Memphis Climate Data and Forecast Accuracy

April Recap

A record wet March was followed by another month with sufficient precipitation, as April ended about 1/2" above normal. Most precipitation occurred on a few select days. Flash Flood Watches and Warnings were issued on the 14th-15th and last couple days of the month. Temperatures continued the above normal trend as well, about 2° above average, based mainly on warm overnight lows. Overall, there were only 7 days that averaged below normal for the month, but most days were within a few degrees of average.

Very little severe weather occurred in April with the only reports being trees downed by a wake low that produced 50-60 mph wind on the 30th and injuries at the FedEx SuperHub at Memphis International Airport due to lightning on the 6th. No tornadoes occurred in the entire state of TN in April, a fairly rare occurrence for the peak month of the Mid-South severe weather season.

Memphis International Airport, Memphis, TN

Average temperature: 64.8 degrees (1.9 degrees above average)
Average high temperature: 74.2 degrees (1.2 degrees above average)
Average low temperature: 55.5 degrees (2.6 degrees above average)
Warmest temperature: 85 degrees (26th, 28th)
Coolest temperature: 43 degrees (2nd)
Records set or tied: None
Comments: None

Monthly total: 5.97" (0.47" above average)
Days with measurable precipitation: 10 (0.4 days above normal)
Wettest 24-hour period: 2.16" (29th-30th)
Total Snowfall: None
Records set or tied: None
Comments: Six days recorded more than 0.50" of rain and 2 of those received over 1" of rain.

Peak wind: Southwest/54 mph (30th)
Average wind: 8.3 mph
Average relative humidity: 61%
Average sky cover: 50%

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

Cirrus Weather Solutions / MemphisWeather.net, Bartlett, TN

Average temperature: 63.2 degrees
Average high temperature: 74.4 degrees
Average low temperature: 52.1 degrees
Warmest temperature: 84.7 degrees (28th)
Coolest temperature: 39.9 degrees (3rd)
Comments: None.

Monthly total: 5.60" (automated rain gauge), 5.95" (manual CoCoRaHS rain gauge)
Days with measurable precipitation: 12
Wettest date: 1.91" (29th) (via automated gauge)
Total Snowfall: None
Comments: None

Peak wind: 27 mph (10th)
Average relative humidity: 71%

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

MWN Forecast Accuracy

MWN average temperature error: 2.52 degrees
MWN forecast temperatures within 2 degrees of actual: 61%
MWN average dewpoint error: 3.00 degrees
MWN forecast dewpoints within 2 degrees of actual: 57%

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

Follow MWN on Facebook, Twitter, and Google+ Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone. 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

Sunday, May 8, 2016

Facebook Live chat on the upcoming week's weather

This week's weather discussion was presented for the first time on Facebook Live! Check out the discussion below or click here to go straight to the MWN Forecast.

(Here's the link in case the embedded video above doesn't work for you: https://www.facebook.com/memphisweather1/videos/10153994551971140/)

Erik Proseus
MWN Meteorologist

Follow MWN on Facebook, Twitter, and Google+ Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone. 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