UPDATE
Issued at 1001 PM EDT Sat Sep 7 2024

Large area of strong high pressure remains centered over the Upper Mississippi Valley and the Western Great Lakes region...
and is starting to make a move southward into the Mid Mississippi Valley and Ohio Valley. Some scattered low lake clouds remain across portions of far Northern Lower Michigan...
otherwise skies are mostly clear across our entire CWA Some mid and high clouds have begun to drop into portions of Upper Michigan ahead of a short wave and associated surface low currently moving into Western Ontario. Still expect mainly clear skies and diminishing winds will allow temps to cool into the lower 40s to mid 30s...with coolest temps across inland areas of Northern Lower Michigan. This should result in some areas of frost in these interior sections overnight
Thus
will certainly maintain the Frost Advisory for these areas overnight into early Sunday morning.

SHORT TERM /THROUGH TONIGHT/
Issued at 221 PM EDT Sat Sep 7 2024

Pattern Synopsis and Forecast:

Large, omnipotent upper low ejects east-northeast through the day today and into tonight with northwest flow aloft & sfc. Sfc high pressure will settle in to the west, as sfc low departs northeast.
Gradient should relax a bit tonight, and with the presumed clearing skies, temperatures expected to drop close to frost point in some locations. Sfc winds shift more westerly on Sunday, but subtle energy and cooler air aloft remains on the backside of the departing upper lows northwest flow.

Primary Forecast Concerns:

Main concern through the short term period will be the potential for frost tonight. Will try and brainstorm. An upper low departs to the northeast tonight, with relaxing winds (non-zero west winds though), although weak gradient remains across the region. That being said, there is a little feature on the backside of this upper low which may produce some scattered clouds. Dewpoints drop down into the mid 30s potentially given some guidance. Given clouds and winds remain at bay as the atmosphere decouples, cold temperatures are expected tonight with low to mid 30s across the notoriously cold spots. HRRR & NBM 10-25th percentiles show mid to upper 30s across southern interior norther lower Michigan, and in-house bias corrected guidance hints at the potential for low to mid 30s. This will not be a widespread event, but several locations across the interior south of Otsego county could see frost, or at least near frost, conditions.

Sunday winds shift around more to the west, and thus temperatures increase quite a bit with values in the 60s most places. A bit of breeziness will hang around, but overall not a big deal. Cooler air aloft coupled with the warmer lakes could perhaps fire off a shower or two, but current guidance is not too impressed. Pretty conditional scenario, but overall should not be a big deal.

LONG TERM /SUNDAY THROUGH SATURDAY/
Issued at 221 PM EDT Sat Sep 7 2024

Pattern Forecast: By Sunday evening, closed upper-level low pressure is expected to be situated over Quebec...continuing to propel off to the northeast. Heights will be gradually rebounding locally heading into early next week, only to be amplified through the remainder of the long-term forecast period. Only possible blemish at this juncture comes Sunday night as a trailing shortwave may race through departing troughing. Otherwise, next week looks to be dominated largely by high pressure and little in the way of sensible weather with temperatures rebounding back above normal (potentially well above normal by mid-late week).

Forecast Details: Low chances for showers exist Sunday night as shortwave energy traverses departing larger-scale troughing. Any of these low chances are largely out of the area by Monday morning with little in the way of sensible weather expected through much of next week. Temperatures back into the 70s for Monday, rising into the 80s Tuesday and beyond. Wednesday through Friday feature the highest probabilities for temperatures to hit the mid to even upper 80s in some spots (especially downsloping locales), which if realized would be 10-15+ degrees above normal for the second week of September.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/
Issued at 1145 PM EDT Sat Sep 7 2024

High pressure currently centered over the Upper Mississippi Valley will slowly drop south into the Mid Mississippi Valley and the Ohio Valley overnight thru Sunday night. Aside from some patchy fog causing intermittent IFR vsbys overnight...mainly VFR conditions expected thru Sunday night
Meanwhile
a short wave and associated surface low will swing thru Western Ontario and into Lake Superior Sunday into Sunday night. Small chances of showers and possibly an isold thunderstorm will develop Sunday night as this system approaches Northern Michigan...
impacting mainly Eastern Upper and far Northern Lower Michigan.
NW surface winds around 10 kts will become W/NW on Sunday ahead of that wave.

APX WATCHES/WARNINGS/ADVISORIES
MI...Frost Advisory until 8 AM EDT Sunday for MIZ027>029-033>035.
MARINE...None.