DISCUSSION
Issued at 304 PM CDT Wed Sep 11 2024

Through Thursday night...

Our stretch of summer-like warmth will continue through Thursday as a broad area of high pressure continues to reside over the eastern CONUS and Great Lakes. High temperatures on Thursday will once again top out in the mid to upper 80s areawide, however; the combination of onshore winds and a lake breeze will result in slightly cooler readings along the lakeshore. These temperatures in combination with the antecedent dry conditions will maintain a heightened threat for grass and brush fire starts through the day on Thursday. Thus anyone conducting outdoor burns should exercise caution.

Otherwise, expect skies to remain generally cloud free for tonight through Thursday before cloud cover increase Thursday night as the cirrus from now Hurricane Francine drifts overhead. Some low concentrations of wildfire smoke aloft will maintain a slight haze to the sky tonight into Thursday morning.
Regardless, temperatures tonight should still be able to cool into the low to mid-50s (lower 60s in Chicago), but more modest lows are expected Thursday night (readings in the upper 50s to mid-60s) due to increasing clouds.

Friday through Wednesday...

The main forecast concern for the upcoming weekend continues to be the chances for showers associated with the remnants of now Hurricane Francine. Francine is still expected to make landfall along the LA Gulf Coast tonight and then track into the Mid- Mississippi Valley on Friday as a decaying tropical depression.
At the same time, the broad ridge (high pressure) over the eastern CONUS is expected to develop into a closed high and pivot over the eastern Great Lakes over the weekend. In doing so, the upper high should cutoff the remnants of Francine from the upper trough forecast to pivot through the Mountain west and northern Plains over the weekend.

What this means for us is that the bulk of Francine's moisture should become trapped along the Ohio and Tennessee River vallies and struggle to make much progress into northern IL and northwest IN. While this solution is conveyed nearly identically amongst all ensemble and deterministic guidance, there continues to be some indications that a subtle ribbons of moisture may be able to creep into the western half to third of our forecast area (roughly areas along and west of a Rockford to Paxton line) during the late Friday through Monday timeframe.
Since the better dynamics and resultant forcing should remain closer to Francine's remains to our south, coverage of showers associated with the moisture plumes continues to be a point of uncertainty. Therefore, have decided to maintain a slight chance (20-30%) mention for showers areawide during this period for now but suspect that many locations (especially those east of the aforementioned line) will remain dry. Nevertheless, any rainfall that occurs does not look to be sufficient enough to provide much, if any, relief to the prevailing dry conditions.

Heading into the early part of next week, what is left of Francine is progged to shift east into the mid-Atlantic region as another upper-ridge builds across the central CONUS. While it does look like we may hang on to some residual moisture with this ridge, dry conditions are still forecast through at least the middle part of next week. Though, temperatures do look to moderate some with readings more into the lower to mid-80s this weekend through midweek.

Yack

AVIATION /06Z TAFS THROUGH 12Z FRIDAY/
Issued at 1241 AM CDT Thu Sep 12 2024

VFR with no concerns.

Light/calm winds overnight will become easterly this morning and then increase to around 10 kt toward mid day. Easterly speeds will diminish a bit tonight,

Castro

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM...None.