Notes on July heat, plus a look ahead at pleasant August conditions!

Looking back

For those of you who thought July was hot – you’re right! But July is climatologically the hottest month of the year (just barely edging out August). So what made July 2020 different? Was it just our continuing intolerance for more discouraging news, or is there something more to it? It may be a bit of both. Here are some facts.
While July 2020 was indeed hot (averaging about 1.5 degrees above a normal July), the main issue was the persistent heat. Check this out: Memphis hit 90° every day except two in July, and those two days it was 89°! How often does the high temperature reach at least 89° every day in July? Not often! There are only four years out of 146 in Memphis weather records in which every July day reached at least 89°. The last time was 2010. So the heat was persistent
How about the overnight lows? Well, as it turns out, we never dropped into the 60s in July overnight. In fact, all but one morning low was at or above 73° (and the one 71° low we had was on the 1st)! There have only been four years on record in which the low was at or above 73° every day or all but one day. So we also had very little relief from the heat at night.
Temperature anomaly (difference from average) for the U.S. in July. (WeatherBell)
With typical to slightly above average humidity during the month, heat indices eclipsed 100° almost every day as well and touched the danger level of 105° on several days. And while some lucky folks got several days of afternoon thunderstorms, many did not. The airport, and many other places, left the month with less than two inches of total rainfall and in “abnormally dry” condition. I’m OK putting July 2020 in the rearview mirror!

Looking ahead

If you were out last evening, you may have started to notice a change in the air. A pleasant breeze and slightly lower humidity made for a nice evening. This morning, clouds linger over the Mid-South with patchy light rain as low pressure spins over the region. In the wake of a cold front today, and with clouds lingering, we’re set for our coolest day since June 26 with highs only near 80° and a pleasant breeze continuing! 
“Day cloud phase” satellite imagery from GOES-16 on Saturday morning shows a swirl of low clouds (in blues/greens) over the area, representative of low pressure. As long as low clouds stick around, temperatures remain in the 70s. (College of DuPage)
But is this one day of relief or a trend? Fortunately, the latter, though not quite to this extent. A large and persistent trough of low pressure will set up over the northeast U.S. but it’s effects will cover a large portion of the eastern half of the country. With “northwest flow” set up over the Mid-South for the next week, we’re in for less humid days, just spotty rainfall chances, and below average temperatures!
A trough of low pressure at the mid levels (~18,000 feet up) is indicated by the “valley” in the pressure lines over the Midwest and Mississippi Valley. The blue shading shows departure from normal for this time of year. Blue = cool! This map shows the average pressure pattern over the next 5 days from the European ensemble model. (WeatherBell)
This weekend will be a transition to that pattern with warmer weather, but still low humidity and some clouds, on Sunday as highs reach 87° following a morning low in the mid to upper 60s. A reinforcing cold front arrives Monday with a small chance of rain and similar temperatures to Sunday.  Another small rain chance moves in Tuesday with an upper level disturbance rotating around the parent trough. That will knock highs down a couple more degrees, perhaps only the lower 80s north of the city and mid 80s in Memphis and north MS. 
Similar to the map above, the 5-day average temperature anomalies from the European ensemble model shows well below average temperatures the next 5 days over the center of the country. For Memphis, the average temperature departure from normal is 5-6° F, enough to make for pleasant August days! (WeatherBell)
Partly cloudy conditions are expected the rest of the week with highs in the mid 80s, warming back towards 90 by the end of the week, but still pleasant humidity levels. I think you’ll especially like the mid 60s every morning as you drink the first cup of coffee on the patio, as well as 70s in the late evenings for a nice walk!

Further into the future

Starting next weekend, it appears we return to a more average August setup with highs back in the low 90s, lows in the 70s, and rain chances re-emerging occasionally. Overall, though, it does not currently appear that the second week of August will see above average, or excessive, heat.
The temperature outlook from the Climate Prediction Center for the second week of August. Temperatures in the Mid-South should be near to slightly below normal. (via PivotalWx)

Erik Proseus
MWN Meteorologist

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