Monday, July 6, 2015

Holiday weekend rain gives way to building high pressure and summer heat

Before we dive into weather, I have one thing to get off my chest...

OK, so now that that is over with we can move onto less important things!

Holiday weekend rain

First, here's a good picture to recap the holiday weekend we just experienced, courtesy of the National Weather Service in Memphis:

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This doesn't count Saturday's rain, and, because it's interpolated, the 10" reading from New Albany, MS is smoothed over. Honestly, with all the rain (including doubling the previous record precipitation on Friday at Memphis International) and some areas of flash flooding that occurred, the timing wasn't terrible. Major evening holiday events (with the exception of a brief shower at fireworks downtown Saturday evening) stayed dry for the most part. Temperatures also stayed unseasonably cool with highs in the 70s both Friday and Saturday.

Looking ahead

Of course, being July we knew that wouldn't last. Sure enough, we're back in the 80s now and will see 90° readings very soon. One factor that will has kept temperatures at bay a bit Sunday and Monday is the very wet ground. With lower humidity and dry ground, the sun's rays heat the lower atmosphere, resulting in hot temperatures. With all the humidity and wetness, more of the sun's energy has been used by the evaporation process, resulting in less to heat the air. In addition, the abundant low level moisture and evaporation resulted in more cloud cover as the rising air cooled and condensed (remember your water cycle from elementary school?) which turned water molecules from a gas into a liquid and produced clouds, which also reduced the amount of heating that occurred. The result was below normal temperatures the past couple of days.

Now that the ground is drying and fewer clouds will be around, especially by mid-week, our temperatures will respond to the sun's heating power with highs back to near normal levels for early July.

Next 24 hours

There is one more anomaly to deal with in the next 24 hours before the hot July weather can take over though, and that is an approaching front. While it won't make it all the way to the metro (typical of July), it will get close enough, and combine with a mid-level shortwave of energy, to produce a low chance of thunderstorms, mainly in AR, tonight and tomorrow. Rain chances are 20-30%, so don't be surprised if you hear some thunder or get a downpour from one of these widely scattered storms.

HRRR (high-res model output) "future radar" for the overnight hours, showing the possibility of a few t'storms, mainly in AR tonight. The early line of storms and steadier rain is closer to a front that will not move into the metro. Graphic courtesy WeatherBell.

Rest of the week and weekend

Beginning Wednesday, high pressure at the surface and aloft moves overhead, capping off the atmosphere under a heat dome, limiting cloud cover, and warming things up! If you want sunbathing, pool-diving, "Memphis summer" weather, you'll get your wish the latter half of the week into the weekend. Temperatures will reach the lower to mid 90s each day with virtually no rain chances that we see at this point and partly cloudy skies. Heat indices will also likely rise over the 100° mark this weekend.

Upper level (18,000' up) high pressure is noted in red area building from east to west over the next several days. This high will be responsible for capping off any rain chances and causing temps to rise heading into the weekend. Loop is from Tuesday through next Monday , when the high moves to our west, allowing for the possibility of cooler and more unsettled weather early next week. Graphics courtesy WeatherBell.

Here's the "at-a-glance" forecast then for this week...

Erik Proseus
MWN Meteorologist

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