YOU CAN FEEL IT IN THE AIR...
Wednesday was by no means a cold day but it did have the look and feel of fall. For me, it was the first time I really sensed that summer was on its last legs (rightfully so considering fall officially arrived at 2:21 PM). On this satellite image, you can observe a cold core upper air low poised just to the east as it spins through the Ohio Valley.
On the backside of the surface low in Ohio, a decent pressure gradient was sending northerly winds and cool air into Iowa and Illinois.
East of the Mississippi it was a rather brisk day where some gusts greater than 25 mph occurred. Around 3:00 PM winds up to 44 were fanning central Illinois.
At that time you can see 60s are prevalent over much of Mississippi River Valley. Further east under a canopy of clouds and rain, late day reading were only in the low to mid 50s in parts of Indiana and Michigan.
With winds relaxing Wednesday night we will reach what appears to be the coldest readings of the season so far by daybreak Thursday. The 3k NAM has widespread low 40s and here and there a sprinkling of upper 30s. That's a sure sign fall is making inroads. Winds will be the key in how cold we actually get. If they hold up a bit longer (which is possible in the east) the mixing will mean lows more in the low to mid 40s. Still fresh.
Thursday under the ridge axis a similar day is anticipated. After a very crisp start, winds will be a little lighter, sunshine more apparent, and temperatures should warm a couple of degrees. That gives us highs around 70 and a spectacular September day. Rich blue skies to be sure!
Friday another fast moving cold front will dive into the mean trough. Ahead of it a return flow of southwesterly winds will give temperatures a nice nudge upwards. Highs should easily reach the mid 70s in most areas with a few upper 70s anticipated in the south. The bigger issue will be whether or not we we have enough moisture and dynamics to whip up a few showers and perhaps an isolate thunderstorm or two when the front comes through in the evening. Initially the air is very dry, these are PWAT's Thursday morning. They are indicative of the amount of water vapor in the atmosphere.
By Friday afternoon they have significantly increased by almost an inch in the pre-frontal environment.
Despite the increase in moisture, the best forcing remains further north. As a result, most areas will have a shot at rain but the greatest chances are over the NE half of my area Friday evening. Despite the likelihood of showers, even in the northeast the amounts are pretty slim with most models indicating amounts 1/10th of an inch or less. At best, a few places north and east of the Quad Cities could see 1/4", especially if we can scare up a couple thunderstorms. Here's what the major models are indicating. The GFS is the odd man out with its dry solution.
The EURO
The 12K NAM
The 3K NAM
The GFS
This fast moving disturbance is long gone by Saturday morning and another burst of cool air drops temperatures back to the upper 60s to low 70s later in the day. The cool down is brief as readings are already on the rebound Sunday. Highs will likely end up in the upper 70s to low 80s for a warm ending to what will be a dry weekend.
Overall, the next 10 days have continue to have dry look to them. The Euro 10 day rainfall departures reflect that idea.
That my friends is all I have for you as we enter the first full day of fall. Hope your day is as good as what mother nature has to offer. Roll weather...TS
