textproduct: Gaylord

KEY MESSAGES

- Rain, storm chances return late tonight and persist through the weekend (esp Friday and Saturday), though not a washout the whole time.

- Cooler weather to end the weekend.

DISCUSSION

Issued at 227 AM EDT Thu Aug 20 2026

PATTERN SYNOPSIS/FORECAST:

596dm upper ridge over the western US...with a 546dm upper low near James Bay and attendant broad troughing across Eastern Canada oozing influence into the northeastern US, including the Great Lakes...with 4-8C 850mb air just to our north attm. A handful of perturbations in the flow over the PacNW and southern Canadian Prairies, with a notable PV maximum digging through the Mid MS Valley. Deepest moisture is generally focused near and south of the OH Valley along a baroclinic zone stretching from the central Plains to the Lower Great Lakes, where pwats again approach 1.5in or better, generally down to the Gulf Coast, with another BCZ draped from OK to SC. There is, however, a N-S oriented plume of moisture from Saskatchewan down into the Upper Midwest, attendant to aforementioned perturbations and surface reflection stretching from northern Saskatchewan down into the northern Plains...with some warm advection convection north of the US/Canada border and trying to sneak into the tip of MN. For now, the Great Lakes remains generally under the influence of high pressure in the wake of aforementioned OH Valley baroclinic zone...with generally cooler and less humid conditions compared to previous days as prevailing surface flow (albeit light) is broadly northerly.

Subtle ridging briefly takes hold today...but will look for upstream PV max over southern Canada to head our way later today into tonight, which could bring a shot at some activity to the region. This should exit stage right Friday...though upstream niblets of PV look to dig into the OH Valley and reinforce the troughing/unsettled idea to wrap up the work week. Currently expecting energy to dig south into the Great Lakes Saturday and Saturday night as trough axis sharpens over the region; expect this will bring some showers/storms as well, which could linger into Sunday with signals for additional energy to further reinforce the trough idea over the region, and northerly flow should overtake the area as high pressure attempts to build in from the west/northwest. Upper low currently over the eastern Pacific looks to eject early next week and travel overtop the western/central US ridge axis, cresting the ridge early next week and looking to make a beeline for the Upper Midwest going through the first half of the week. Quite a bit of uncertainty yet in the timing of this feature, and how the situation evolves beyond that...but think we could remain unsettled and perhaps a touch cool (depending on how strong troughing ends up in our region) going into the middle of next week.

FORECAST DETAILS...

Rain/storm chances today...While the PV max will approach us later today...do think that it will struggle to produce much given dry air in the lower levels and a mid-level inversion around 600mb (ish) that should keep most, if not all, activity capped. The best shot for anything to develop would be across the EUP where the better moisture and forcing would be located today, though suppose it's not out of the question some showers could pop along the Lake Huron lake breeze in northeast Lower. Additionally, noting a smoke plume aloft drifting in late yesterday, do wonder if this could further limit diurnal heating potential and thus, instability potential as well.

Rain/storm chances tonight/Friday...expect rain/storms should increase from the west/northwest through the night, esp across the Yoop, closer to the better moisture aloft and better forcing, and expect an uptick in activity especially after 6z. Appears there is some marginal deep-layer shear over the region tonight, though unclear attm if this will have any bearing on showers/storms tonight. Otherwise, showers/storms should slowly progress eastward through the day Friday, though some guidance soundings suggest it may take most of the day to saturate the lower levels, which could slow rain chances and diminish QPF to some degree, though not impossible some rain could make it to the ground out of a 7-10kft cloud deck. There are some hints attm for an area of theta-e advection across central Lower MI into northeast Lower MI ahead of the approaching PV max. Do wonder if these are signals for some showers and storms to develop well out ahead of the primary cold front, even as early as 8-10z Friday morning, with signals for some elevated instability to crop up prior to daytime heating. This area of more unstable air across NE Lower seems to persist into the afternoon, which could keep this area at risk for showers/storms for much of the day, especially into the afternoon as lake breezes could take shape. Most likely, QPF totals thru Friday evening should be generally under a half inch, but would not be out of the question if some area sat longer under rain and ended up with a bit more. This idea carries into Saturday as well.

Rain/storm chances through the weekend...depending on how quickly the front moves through...and given that additional niblets of PV are progged to drop into the trough axis, suspect this will ultimately be slowly... think that we will hang onto shower/storm chances through the night, into at least the day on Saturday, though it may not necessarily rain the whole time. Low-level moisture looks to make a return Saturday behind the initial cold front, and given falling temps aloft, some diurnal showers could pop up amid potential strato-cu deck...and cooling temps aloft could also support some . Incoming airmass will be cool...850mb temps in the 4- 8C range by Sunday, perhaps...suggesting lake effect (rain) showers could be in play to wrap up the weekend on somewhat blustery N-NW winds.

Cooler weather this weekend...As mentioned above, the much cooler temps aloft Sunday support highs in the upper 60s to lower 70s, which is about 10 degrees cooler than normal for mid-late August, and this idea seems reasonable given potential for an upper low in the area. Clouds should limit diurnal heating, and some poor souls may even struggle their way into the upper 60s for highs...but potential for cloud cover in the region with this system should limit the radiational cooling some. Do think the cooldown will be somewhat short-lived for our area overall, with ridge building again by Monday...but not impossible we could trend more normal/cooler again by midweek if the trough idea holds.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 646 AM EDT Thu Aug 20 2026

Not much in the way of fog out there at this moment, MBL had vsby restrictions way back at midnight but that was it. VFR expected today and tonight, with any chance for fog overnight limited by increasing cloud cover and a bit of a southerly breeze trying to develop. Not impossible for the sites other than APN to have an isolated shower toward the very end of the TAF period. Better rain chances will wait until after 12Z. Light winds today.

APX WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...None.