Stormy lead-in to a fabulous holiday weekend

The heat and humidity has built this week with spotty precipitation over the past couple of days. High temperatures have generally been near 90 degrees, though as of early Thursday afternoon we had yet to actually reach 90 degrees yet this year. Looking ahead to the Memorial Day holiday weekend, fabulous weather is on tap - low humidity, cool mornings, pleasant afternoons and sunshine! However, we'll first need to deal with a late spring cold front...

Storm chances the next 24 hours

With unstable and humid air in place ahead of a cold front that arrives on Friday, the ingredients are in place for thunderstorms, and those will affect us over the next 24 hours. There are multiple small-scale (or "mesoscale") atmospheric features that are affecting thunderstorm development well to our northwest today - chiefly over the central plains. The development and propagation of those storms will determine when we see storms in the Mid-South, which makes pinpointing the timing somewhat complex. In addition, the timing of the arrival of those storms will also factor into the risk of severe weather. 

Our best educated guess at what to expect is that an initial wave of thunderstorms will move into the area late this evening, most likely after 8-9pm. Models hint at these mainly affecting northern AR and western TN. The Memphis area may be on the tail end of this cluster or line. After what should be a lull of perhaps a few hours, a more substantial threat of storms arrives in the wee hours of Friday morning. The exact timing is again in some doubt, but most model sets suggest that they will roll through at some point between 2-3am and morning rush hour. These storms, due to their timing in the "coolest" part of the day (though it will still be relatively warm and muggy) will likely be weaker when they arrive than when they are moving across AR during the overnight hours and should mostly fall apart as they shift east of the metro. Below is the HRRR model's opinion of how the scenario unfolds, with caveats that it's timing and/or intensity could vary, perhaps quite a bit.

The mid-day Thursday HRRR model showing forecast radar through noon Friday. Model output does not equal gospel. (WeatherBell)

Storm threats and preparation

Our main threats with any severe weather would be strong wind gusts due to the expected linear nature of the storms - in other words a squall line, though weakening. Minor flash flooding or small hail are also possible. The tornado threat appears minimal. Below is our latest impact graphic. Best ways to prepare include tying down anything that might blow away in strong wind and garaging vehicles if able. After a fairly long dry spell, the ground should readily accept most water than falls with little issue as rainfall will average under an inch.

A Memorial Day weekend to remember!

Speaking of the weekend ahead, we'll have quite a nice few days to spend outdoors without too much sweat! Overnight lows behind the cold front are expected to dip into the mid 50s with highs Saturday and Sunday in the 70s! We'll warm up some Monday, but still should feel very pleasant for holiday cookouts. Look for more humidity to build into the middle of next week with daily rain chances by Wednesday.

Erik Proseus

MWN Meteorologist

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Farewell spring, it's been fun...

It has been a wonderful spring so far across the Mid-South, and for many in the Southeast. April was a below average month for temperatures, and that trend has continued into May. In fact, we are 5-7 degrees below average so far for the month of May! With average high temperatures now rising into the 80s, this has given us several weeks of beautiful, pleasant spring weather overall. However, after today, rain chances and cloud cover will decrease, allowing temperatures to quickly rise through the 80s and approach 90 degrees by Saturday. Farewell spring!

This month-to-date (May) high temperature anomaly map for the U.S. shows much of the eastern two-thirds of the country has experienced well below average temperatures for the first half of May. (WeatherBell)

We knew it couldn’t last forever, and sure enough a major pattern shift is coming for us here in the Memphis area. The cool weather was caused by a persistent trough of low pressure over the Mid-South and eastern U.S., which helped to continually funnel cool air down into the south from the northern US and Canada over the last month and a half. The hot weather has been confined to western portions of the country, as a large ridge of high pressure with sinking, hot air has refused to budge for the month of April and into the first half of the month of May. Now, that pattern is finally changing. A trough will dig into the western US, bringing the West Coast and Rocky Mountain region some much needed rain, cooler air, and wildfire relief. 

Unfortunately for us, a large ridge of high pressure looks to build in over the next few days and intensify, ending our very nice spring weather and setting the stage for the arrival of more summer-like weather. With this high pressure center sitting to our south and east, the clockwise flow around the high will pump Gulf moisture directly into the Mid-South, quickly warming our temperatures. Due to the sinking air of the high pressure, rain chances will also diminish, leaving us with lots of hot sunshine and humidity. 

As we go into the latter part of this week, an upper level pattern known as an ‘omega block,’ because the pressure pattern resembles the Greek letter omega, will set up across the United States. This will keep the ridge of high pressure parked over the central and eastern US for at least the next week, if not longer. This is a classic pattern for hot temperatures under the high - a “heat dome” is not a bad way to describe it.

The upper air pattern setting up for this weekend and early next week features an 'omega block' across the country, with high pressure covering most of the eastern half of the nation. (European model, WeatherBell)

The ridge sitting over us for so long will allow temperatures to quickly climb each day, and our first 90 degree days of 2021 are in the forecast for this weekend. In fact, almost every day next week has the potential to reach the 90 degree mark. Luckily, many area pools are beginning to open for the season, and next week is looking like prime time to inaugurate the neighborhood pool for the summer. The center of the high pressure will be to our east, so we should escape the more extreme heat expected for areas like southern GA and northern FL. Some of those areas could approach 100° next week! 

These kind of patterns are notoriously hard to break, and we could be looking at a couple weeks of hot, dry weather. Dry as in lack of precipitation, not in lack of moisture, as there will be continuous southerly flow off the Gulf, keeping our dewpoints high and making for a pretty unpleasant feel outside. Feels-like temperatures will be several degrees higher than actual temps, so find a way to stay cool. Summer weather lovers, your time is coming! 

Another concern for this pattern is the persistent lack of precipitation. With temperatures well above normal and very little cloud cover, evaporation rates will be high, and the nearly 3 inch rainfall surplus for the year could quickly be erased. Models are showing very little in the way of precipitation for the couple weeks. Looking at the European model through next Thursday, only a quarter inch of rain is forecast to fall, with most of that coming today. The GFS model is a little more optimistic on rain chances returning late next week, but that could change as we get a closer in time - definitely something to watch, especially for those with interests in agriculture. 

The European model forecast precipitation from today through the next 10 days. (WeatherBell)

As the heat of summer approaches, it’s a good time to revisit some heat safety tips. Wear sunscreen, especially during the afternoon hours, as UV indexes will be maxed out across the area next week. Stay hydrated, especially if you are planning on being outside in the peak heating of the day, and take plenty of breaks.

If you are planning on working out outside, it would be best to do it in the morning or evening hours. Heat is not something to mess around with, it kills more people each year than hurricanes, floods, earthquakes and tornadoes combined! Stay cool and stay safe Memphis, and get ready - summer is well on the way! 

Christian Bridges

MWN Social Media 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
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