Monday, October 9, 2017

Humid weather and storm chances - then what?

I don't think many of us were pleased to see the return of summer over the weekend. We can thank the atmosphere surrounding Hurricane Nate for that, as it dragged humid Gulf air into the southern (and in fact, eastern) U.S. That airmass featured dewpoints in the lower 70s and high temperatures in the upper 80s. Which is just miserable for early October if you ask me, especially when most of us (except some lucky folks in Tipton and Fayette Counties) only got enough rain to make a mess of our vehicles.

So what's on deck for the rest of the week? First, maybe some better rain chances. A high pressure airmass that promises some relief will draw closer to start the week, but first an upper level disturbance will trigger scattered showers and thunderstorms in the daytime heat today (and it will be hot - 90° this afternoon with that humidity baked on top). Chances of showers and a few thunderstorms continue overnight.

The morning run of the high-resolution NAM model indicates scattered storms should ignite after 2-3pm in the daytime heat, triggered by an upper-level disturbance. Loop runs from 1pm-10pm. (WxBell via NOAA - click here if it doesn't loop)

By Tuesday, the leading edge of the high pressure system will push a cold front through during the evening hours. Another chance of showers and thunderstorms accompanies the front Tuesday afternoon/evening in continued heat and humidity, as highs again reach near 90°. While severe thunderstorms are not expected today, there is a small chance of a few strong wind gusts on Tuesday. The Storm Prediction Center currently believes the highest risk (which is still fairly low, at "Marginal") is just north of the city. It's worth watching. Overall storm coverage will probably be in the 30-40% range.

The Storm Prediction Center outlook for Tuesday indicates a Marginal (category 1 of 5) Risk of a few severe storms, mainly capable of producing gusty wind, north of Memphis. This outlook could change, stay tuned.

Between today and tomorrow, I'm hoping most of us get some rain, because after that... there's no rain in sight. The cold front will do a good job of pushing the humid air out of the region as dewpoints fall from near 70° tomorrow afternoon to the mid 50s on Wednesday and look to remain there for the rest of the week. It will also be cooler on Wednesday as highs return to "normal" levels in the mid 70s. However, a return of warm temperatures occurs heading towards the weekend as sunny skies and increasingly anomalous pressure levels aloft result in afternoon highs back in the mid 80s after about two days reprieve.

The upper level (500 mb or 18,000') pressure pattern on Friday evening looks more like mid-summer than autumn as anomalously high pressure dominates the eastern 2/3 of the nation. The 594 "circle" over MS is where the high is centered, at a strength that in mid-summer would be capable of producing temperatures in the mid 90s to near 100. Fortunately, it's October... but still will be much warmer than average. (Pivotal Weather)
Looking out a bit further, another cooler airmass looks to arrive in about a week, preceded by a slight chance of rain on Sunday, which should again keep humidity at autumnal levels. However, the signals from the upper atmosphere indicate above normal pressure levels could put a damper on what otherwise would be cool fall weather. We'll have to see how that one plays out, but the last two times I've seen major cool-downs on the horizon (including the one that arrives tomorrow night), they've turned out to be short-lived... The Climate Prediction Center agrees, indicating that week 2 temperatures have a high probability of averaging above normal.

NOAA's Climate Prediction Center outlook for next week indicates a high probability of above normal temperatures. (NOAA/CPC)

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Erik Proseus
MWN Meteorologist

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