Fall weather returns as a warm and humid airmass moves out

Fall arrived a couple of weeks ago with the type of weather we all hope for in autumn, but this past week, that was replaced by much warmer temperatures and above-normal humidity for the end of September. That gave way to a wetter pattern the past few days, but a cold front tomorrow promises to usher in a new airmass as we head into the first week of October. Let’s look ahead to what we expect in the coming week. 

Rest of this weekend

A cold front will arrive Sunday evening, but the rains of the past couple of days will start to relent a bit before then. Fortunately heavy rain has been spotty and localized and no flooding concerns have popped up. As we head into Saturday night, the day’s rain (the result of an upper level wave of energy) has moved out and we’re left with just a few light rain showers and humid conditions. Later tonight, a pre-frontal trough of low pressure will move in ahead of the cold front. Additional showers, some of which could be heavy, and an isolated thunderstorm will accompany that front in the wee hours of Sunday morning as temperatures hang near 70 degrees. However, by the time many of us are up and around Sunday morning, that round of precip should be just about gone. 
The HRRR model from late Saturday afternoon shows the only decent chance of precipitation through Sunday morning arriving between about 4-7am tonight. (WxBell) 

The rest of Sunday will be fairly tranquil with very little precipitation expected and maybe even some sunshine peeking through the clouds Sunday afternoon. An isolated shower is possible, but don’t change any outdoor plans. Temperatures will likely rise into the lower 80s with semi-uncomfortable air in place due to dewpoints in the upper 60s. The front arrives Sunday evening with little fanfare other than a subtle wind shift. Dry weather is expected overnight as temperatures fall into the mid 60s.

Monday-Wednesday

Monday should turn out to be a very pleasant day. In the wake of the front, dewpoints fall to near 60 degrees with partly cloudy skies, light north wind, and highs near 80. 
By Tuesday, an upper level low pressure center drifts into the Mid-South. In fact, we call it a “cut-off low” due to the pressure center detaching from the prevailing flow aloft and basically losing much of its forward motion.
(A GIF for all you band nerds out there…?)

That low will result in more cloud cover and additional shower chances as long as it sticks around. Thus, mainly daytime rain shower chances will be a part of the forecast Tuesday and Wednesday. The clouds will keep afternoon temperatures at bay with highs in the mid to upper 70s, while morning lows drop as low as 60 degrees. 
The European model shows a cut-off low at the mid-levels of the atmosphere develop and move slowly across the region this week. It’s effects will be most noticeable Tuesday and Wednesday before it weakens and lifts back north. (WxBell)

End of the week into next weekend

Fortunately, the cut-off low doesn’t linger too long and by Thursday we’ll see improving conditions from a sky and rain perspective. Looks for clear nights, partly cloudy days, and highs near 80. Cool mornings will feel great as temps dip to near 60. As high pressure ridging aloft takes over leading into next weekend, temperatures will warm just a bit with highs in the low 80s but abundant sunshine and low humidity. Next weekend looks to have near ideal fall weather! 

Erik Proseus
MWN Meteorologist

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