Wednesday, July 26, 2017

Heat relief is just around the corner!

The heat seems unrelenting...

Heat Warnings and Advisories are in effect today and Heat Advisories continue into tomorrow.

But there is actually great news just around the corner!


The bad news...

We'll start with the bad news first, though. A large ridge of high pressure remains firmly in control of the weather pattern locally and, in fact, for much of the south-central U.S. With few clouds and nary a cooling shower to be found (most likely), temperatures will rocket back into the mid 90s today, reaching a forecast high of 97° in Memphis. Coupled with humidity that we've grown weary of (dewpoints well into the "humid" to "miserable" range on the Muggy Meter), heat indices will reach the mid to upper 100's, perhaps as high as 110°, this afternoon.

A look at watches and warnings across the U.S. as of mid-morning Wednesday. The orange area in the middle of the country represents the Heat Advisories in effect. (weather.gov)
In addition to heat, the "cap" provided by the high pressure ridge and light wind has resulted in a Code Orange Advisory for elevated ozone levels, per the Shelby County Health Department. If you have respiratory issues, stay inside this afternoon until sunset.


On Thursday, conditions will be similar to today with regards to the heat and humidity levels, however by mid-afternoon we could start to see some more clouds and perhaps a few showers or thunderstorms. But there is reason to rejoice... because it'll be the last day with 105°+ heat indices for some time!

Improvement coming!

Thursday night marks the beginning of the end of the recent heat wave as a cold front starts to encroach on the region from the north. Check out afternoon high temperatures just to our north Thursday afternoon for evidence...

Forecast highs from the GFS model for Thursday afternoon. Note the cooler air just to our north, poised to drop south behind Friday's front. (WxBell)

As the front gets closer, thunderstorms that form ahead of it late Thursday will move south into the region. By dawn Friday we will probably be dealing with scattered to widespread (and welcome for those who weren't under the storms that formed Sunday afternoon) showers and thunderstorms that continue into Friday morning and perhaps the afternoon hours. A few storms could be strong to severe ahead of the front.


Clouds and precipitation will likely hold temperatures below 90 degrees, though it will remain humid. The cold front itself moves through by late afternoon Friday (if not earlier), bringing precipitation to an end.

Now the good news... 

In the wake of the front, much cooler and drier air will filter into the Mid-South this weekend on northerly wind. Sunshine will be abundant, dewpoints fall as low as 60° (as compared to the mid to upper 70s we've had the past couple weeks), and temperatures remain in the 80s for highs as morning lows drop into the 60s. And it's all tax-free!!


The general pattern of cooler than average temperatures and dry weather continues into early next week before we start warming back up a bit. But for now, I don't see a need for any Heat Advisories after tomorrow for a while!


(Don't forget, our complete guide to viewing the eclipse in the Mid-South can be found right here on the blog. It's less than a month away!)

Erik Proseus
MWN Meteorologist

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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Friday, July 21, 2017

Excessive heat slowly gives way to increased rain chances

** UPDATED AT 3:00PM FOR EXTENSION OF HEAT WARNING THROUGH SATURDAY **

We'll start this blog with a bit of "hopeful" news as we bake in the Mid-South sauna...

This map by Brian Brettschneider shows the normal midpoint of summer for a given location. Here in Memphis, it's around July 17 according to the data. We're slowly making progress towards fall!
What this means is that the average "peak" of summer heat here in the Memphis area is now in the rearview mirror. We're on the long downhill slide towards autumn. But summer is certainly not over yet!

A sprawling high pressure system at the mid and upper levels of the atmosphere is responsible for bringing the heat the past few days, while surface high pressure just to our east has allowed Gulf moisture to pool over the region, creating a very humid airmass that has exacerbated the hot conditions.

High pressure at the mid-levels of the atmosphere (500mb or 18,000', shown above) sits directly over the region, resulting in very hot air in the Mid-South under this "heat dome." It will slowly weaken as shift east this weekend. (PivotalWx)
UPDATED 3:00PM: An Excessive Heat Warning is in effect for much of the metro through Saturday evening and Heat Advisories remain in effect through Sunday as temperatures rise well into the mid (and for today, perhaps upper) 90s. Heat indices are averaging near 110° at mid-afternoon as the humidity has cranked up as well, evident in dewpoint readings in the upper 70s to near 80.


Like yesterday, there is only a slight chance of a cooling shower today, and it certainly does very little for the high humidity values. The general trend continues Saturday, though the upper level high pressure system that has brought the "heat dome" to the middle part of the country the past few days will start to move east, allowing perhaps a few more clouds and widely scattered showers, which could work to keep the heat index below 110° and temperatures in the mid 90s instead of creeping towards the upper 90s. If you have to be outside the next couple days, please take precautions against the heat and listen to your body for these signs of heat stress:


As high pressure aloft weakens this weekend, the heat will abate just a bit, as well as allowing rain chances to increase a bit, especially during the afternoon hours. Humidity will remain high, but with temperatures still in the mid 90s through Sunday, heat indices will remain above the 105° danger level. A few afternoon t'storms are possible Saturday, then scattered thunderstorms are expected on Sunday into Sunday night.

By early next week, our high shifts further east, a trough of low pressure develops in the Great Lakes region, and another high forms in the western U.S. The overall impact on our weather is that we'll be in a "northwest flow" pattern, meaning the wind aloft will blow from northwest to southeast. This is a pattern that favors upper level disturbances to move across the region from the northwest.

A loop of the mid-level (18,000') pressure and wind pattern, every 12 hours from Friday morning through next Wednesday morning, shows the high pressure ridge over our region breaking down by early next week as a trough forms to our north, then rebuilding from the west by the end of the loop (middle of next week). (PivotalWx)

In addition, a cold front will sink into the Mid-South by Tuesday, but stall out. This combination means the likelihood of scattered showers and thunderstorms to start the week, holding high temperatures down closer to 90°. Humidity remains of course, making for a muggy forecast.

By mid-week, high pressure to the west begins building back into the region, the front lifts back to the north, and temperatures warm back up into the 90s. We will likely still see a few daily thunderstorms typical of summertime but the storm track should shift back a bit north of the metro by Wednesday or Thursday.

But as I said at the top of the post, we're slowly getting closer to autumn than we are moving into the heart of summer! Schools start in a few weeks, which hopefully means the warmest part of the year will soon be behind us!

Erik Proseus
MWN Meteorologist

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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Thursday, July 13, 2017

The dog days have arrived! Rain chances heading into the weekend

Summer has definitely arrived in the Mid-South as temperatures are now consistently rising into the 90s each day. We've also seen dewpoints rise to mid-summer levels, pushing the heat index above 100 degrees each afternoon. Be sure you are taking precautions against the heat - drinking water, checking on the young and old, and avoiding it if possible!

(A side note: today is the 37th anniversary of the hottest day on record in Memphis! July 13, 1980 saw the mercury rise to 108 degrees and was smack in the middle of the longest stretch of 100-degree days the city has ever seen, reaching 15 days!)



With the increased heat and humidity came a few popcorn showers the past couple of days. Unfortunately (if you want dry weather a little longer), rain chances will increase even further heading into the weekend as a front sags south. An upper level trough develops over the eastern U.S. in response to a building ridge of high pressure to the west, placing the region in northwest flow that promotes the passage of upper level disturbances. All of this adds up to: 1) slightly cooler temps due to increased cloud cover, 2) continuing high humidity, 3) higher rain chances, but 4) "marginal" severe weather chances.

The surface map for Friday evening shows high pressure over the Midwest and a front separating that airmass from warm, humid air to the south. The front will move south this weekend then wash out over the area by Sunday. (NOAA/NWS)


The upper level weather pattern this weekend features a strong ridge of high pressure over the western U.S. and a trough over the east, which places the Mid-South in northwest flow (wind following the arrows from northwest to southeast), meaning increased rain chances. (NOAA/NWS)

A Marginal Risk of a few severe storms exists on Friday across west TN and northern AR, according to the Storm Prediction Center. A few storms late in the day could contain strong wind gusts. (NOAA/SPC)

For those trying to plan outdoor events, I believe the best chance of thunderstorms, when a few could contain gusty wind as represented by the level 1 "Marginal Risk" of severe weather donated above, will be late Friday afternoon into the evening, and mainly north of the city. As shown by the afternoon run of the high-resolution NAM model below, an area of storms may fire up to our north and head towards the Memphis area late in the afternoon, but this model believes it could quickly fall apart heading into the evening.

The afternoon run of the NAM3 model from 1pm Friday to 1am Saturday shows a potential line of storms dropping towards the metro but falling apart as it gets close. Have a backup plan for any outdoor activities during the PM hours Friday.
Saturday could also see scattered showers and thunderstorms, but the highest likelihood will be during peak heating roughly south of I-40, or mainly north MS. Don't plan any outdoor activities the next couple of days without a "plan B" however. By Sunday, we should see a more northerly component to the wind as the front washes out just to our south, resulting in a low chance of precipitation and perhaps SLIGHTLY lower dewpoints. Temperatures this weekend will likely peak near 90 degrees each day.


As we head into next week, indications are that the ridge to our west shown in the upper level map above will build east, suppressing precipitation chances and causing temperatures to rise once again, back into the lower to mid 90s. More summertime weather as we work our way through the "dog days!" For the routinely updated, human-generated MWN Forecast, check out our mobile apps linked below or click here.


Erik Proseus
MWN Meteorologist

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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