The first day of Autumn is Thursday officially at 9:21am. But you will not notice a change with our weather. The arrival of autumn cool weather will wait until the back half of the weekend to arrive.
In the meantime, you can plan on enjoying bonus summer weather in the 80s for the next few days. Thursday has a slight rain chance in far northern Missouri especially into Iowa in closer proximity to a frontal boundary. Otherwise partly sunny skies dominate across the area.
Friday brings mostly sunny skies with a south breeze and highs well into the 80s to possibly 90 in spots.
Saturday will be the last day in the 80s of this stretch and a chunk of the day should be fairly dry. However the chance of showers or a thunderstorm will increase deeper into the day as a cold front slowly approaches. The chance of rain spikes up Saturday night through at least half of Sunday before only slowly decreasing late day Sunday.
The big question I have right now is how to handle the speed of the cold front and upper trough driving it through our area. As is typically the case this far out, computer models are having a difficult time handling the details of where the upper trough will ultimately close off and position itself. This is significant in terms of whether we truly get into a dry slot behind the cold front or are stuck with periods of rain into the first half of next week.
I’m keeping a low end 20% rain chance in the forecast next Monday, Tuesday and Wednesday to respect a slower solution. Plus, just the upper low alone can produce instability showers given cold temperatures aloft with breaks of sun. In fact, a random low topper thunderstorm is notorious for developing under just this kind of upper low.
Bottomline, get set for rain ahead and an impressive temperature swing. Here are a few charts captioned with what I see.
Upper trough approaching Saturday night into Sunday morning with cold front
GFS model showing good plume of moisture and vertical rising motion (lift) along cold front for showers or thunderstorms
GFS model showing strongest axis of “lift” with deep red shading in our eastern half of the area. This would likely result in band of moderate to heavy rain with lingering light rain behind it.
GFS model showing best axis of moisture and lift working east of the region for “possible” slot of drier conditions building in. *** Caution on this as other models are not as quick to follow this timeline but it’s worth noting from the GFS
Impressive cool down from the hot 80s and 90s to the 60s to near 70 early next week!!