SHORT TERM /THROUGH TONIGHT/
Issued at 333 AM EDT Fri Sep 20 2024

Pattern/synopsis: An upstream cold front has pushed into western WI and eastern IA. Decaying pre-frontal convection extends from the WI/IL border up thru central Lk Superior. The front is progged to slow as it crosses eastern WI today, and then moves into northern MI tonight.

Forecast: Cloud cover has increased in nw lower MI, and will become somewhat more extensive as the morning proceeds. However, that cloud cover will also thin with time. Some showers will likely reach the nw lower MI coast, and western Chip/Mack Cos this morning. But otherwise, this initial push of precip will struggle in our initially dry air. Diurnal instability then starts to kick in, and by midday convection will start to regenerate locally. MlCape values of 600-800j/kg can be achieved. Those higher pops will start in western areas at midday, expanding toward and east of I-75 thru the afternoon and into early evening. 0-6km bulk shear reaches of 30-40kt in southern areas, where instability should also be on the higher side. This is into a parameter space where a few strong storms are possible. Maybe even a stray severe? But probably not. (SPC did push the marginal svr risk northward to about GRR, but not this far north.)

500mb trof axis pushes across the area tonight, with mid-level subsidence/drying/warming pushing into western areas. Chance for showers and a few storms will still be present in central and especially eastern areas this evening. By overnight, pops linger only in the far north and east. Without a significant push of cooler/drier air down low, partial clearing will lead us prone to seeing fog late, especially in the west (and perhaps near Lk Huron).

Max temps today mostly in the 70s, perhaps hitting 80f near Saginaw Bay. Lows tonight mid 50s to near 60f.

LONG TERM /SATURDAY THROUGH THURSDAY/
Issued at 333 AM EDT Fri Sep 20 2024

Saturday, skies will clear through the morning hours and lead to a mostly sunny and warm afternoon. Clouds will begin to build back in Saturday evening/night as the next system approaches the state.

An upper level trough over central south Canada will close and start to tilt negatively Sunday. This upper level jet will meet with a SW upper jet over MN/WI, and aid in moisture advection northward towards the Great Lakes Region (PWATs ~1.4 by Sunday afternoon over northern MI). A deeper cold front will move through the state Sunday, as some shallow upper waves move up from the south. All in all, there should be enough larger scale forcing present for scattered to even widespread wetting rain Sunday. At this time, weak instability is present in the mid to lower part of the column, meaning it will be harder for storms to grow. It will likely be widespread light to moderate rains with a handful of embedded low topped cells producing some lightning. Higher uncertainty in actual moisture amounts play into this as well, if there is a little more dry air to work with then gusty winds could be seen with some of that embedded convection. GFS/high res Canadian show saturation through much of the column (after top down moistening), with the NAM hinting at some drier air.

After the ~1015mb air mass moves through, temperatures will start to decrease. Forecasted high temps remain in the mid to high 60s Monday through the end of next week. Winds will be breezy at times, with chances for rain here and there. Low confidence in details for after Sunday rain chances due to chaotic pattern.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
Issued at 1128 PM EDT Thu Sep 19 2024

Looking at some patchy MVFR to even IFR producing fog/mist impacting KAPN early this morning. Otherwise, increasing high clouds expected to give way to a lowering cloud deck today...although trends continue to support cigs remaining VFR. Weak front working into the area will likely kick off some scattered showers and a few embedded thunderstorms...spreading from west to east through the day. Not expecting any widespread significant impacts from these, although suppose any thunderstorms may bring some brief gusty winds and pockets of heavy rain. Conditions will improve from west to east later this afternoon and evening.

APX WATCHES/WARNINGS/ADVISORIES
MI...None.
MARINE...None.