Monday, June 18, 2018

Increasing rain chances temper temperatures

I think we'd just be happy with average temperatures at this point, right? I mean, in the past 49 days, we have had just TWO days with daily average temperatures that were below normal - and they were each just one degree shy of the daily average! The heat has been persistent, no doubt. Well, if you think like I do, I might have some...

But first we have Tuesday, which will be very similar to Monday. Another day with high temperatures in the lower 90s, heat indices near 100 degrees, and scattered clouds and isolated thunderstorms. Most of us stay dry at least one more day, but then the pattern changes as a ridge of high pressure aloft break down.

The GFS forecast upper level (18,000', or 500mb) pattern from Monday night through Saturday night (each frame is 12 hours apart). See below for explanation and impacts of the "bowling ball" closed low pressure that moves by to our north late this week.(PivotalWeather)

Upper level weather pattern in control

The forecast upper level pattern (at roughly 18,000' above ground level) from Monday night through Saturday night is shown above. Notice the "hill" (or ridge) produced by the black lines over the Mississippi Valley at the beginning of the loop is replaced by a "bowling ball" of concentric circles as the loop progresses, then flattens out at the end of the loop. What happens is that the high pressure ridge is squashed by a fairly strong upper level low pressure system (the bowling ball) that moves by to our north.

The proximity of the low pressure center means a fairly marked uptick in cloud cover and rain chances as it approaches and passes by. With southerly wind at the surface, the energy associated with that low will tap into a good amount of Gulf moisture, triggering the likelihood of showers and thunderstorms from mid to late week. In addition, a semi-tropical system that will bring torrential rain to parts of the Texas coast the next few days will also contribute moisture to this system. We are left with a very different weather pattern for Wednesday-Friday than we have seen in some time - one that features abundant cloud cover and high rain chances, thereby resulting in cooler (though still humid) conditions. I think we'll take some mid/upper 80s and clouds versus the low/mid 90s and sunshine of late (at least for a couple days)!

Severe weather impacts

We'll need to closely monitor the potential for severe weather, as thunderstorms are expected at times during this period. I believe those chances will be fairly minimal though due to the cloud cover which will limit instability a great deal. A few strong wind gusts or hail could be possible at times in stronger storms though. The flash flooding threat will also be monitored, though I expect that also to be fairly low. All of these threats will be refined on a daily basis and communicated through our social media channels, so be sure you are following MWN on Facebook and Twitter and have downloaded our mobile app for the latest details.


  • One more hot day Tuesday with a couple storms possible
  • Increase in clouds and precip chances Wednesday
  • Best chances of showers and thunderstorms Thursday-Friday
  • Cooler temperatures mid- to late-week, but still humid
  • An inch or more of rain for many in the Mid-South
  • Severe weather threats undetermined, but not a major concern

Approximate precipitation expected through Sunday morning across the south-central U.S. (NWS/WPC, WxBell)

Erik Proseus
MWN Meteorologist

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