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KEY MESSAGES

- Rain chances return Saturday, esp north; cooler Sunday

- Heavy rain possible early next week

DISCUSSION

Issued at 356 AM EDT Fri Sep 11 2026

PATTERN SYNOPSIS/FORECAST:

Rather quick flow across the northern tier of the country attm...with 100-120kt upper jet axes from WA to Manitoba ahead of a positively tilted trough axis over western Canada...and from the Lower Great Lakes northeastward into ME ahead of another elongated positively tilted trough axis stretching from the Central Plains to the OH Valley. Deepest absolute moisture (pwats greater than 1.5- 2in) ahead of the latter feature across the SE US and Gulf Coast, and its attendant surface front draped from TX to OH up toward Boston though some Pacific moisture (pwats 1-1.5in) is located along and ahead of the former, from the Northern Plains to Manitoba/Ontario, and down into the Upper Midwest. Mid-level warming and upper-level cooling resulting in steepening lapse rates across the northern Plains, with cooling aloft steepening lapse rates beneath the trough axis itself over western Canada. Cold baroclinic zone/surface boundary stretches from central Canada to the PacNW (where a nice baroclinic leaf is evident on satellite imagery over WA, attendant to a PV max digging in from the Pacific), and warm baroclinic zone, from Manitoba down into the Upper Midwest/Central Plains...with 850mb temps in the teens and 20s across the Plains. Return flow developing across the Plains/southern Canada around surface ridge in the Upper Great Lakes...resulting in a maximum of warm advection across Ontario/Manitoba, shunting the pool of 0C 850mb air eastward across James Bay. In the meantime, beneath said surface ridge and abundant subsidence...we are calm, dry, and cool...with temperatures dropping back into the upper 40s and lower 50s as of 3z under clear skies.

Upper ridge axis builds overhead today, with generally quiet conditions expected, though return flow will be strengthening ahead of upstream perturbations. This should also lead to some warm advection cloud cover drifting through today. The upstream trough axis will approach late tonight into Saturday, dragging a SW-NE oriented surface trough eastward across the Upper Midwest, resulting in even stronger return flow on Saturday, and think some convective activity will be around the Midwest into Ontario during this timeframe, most likely impacting our area later Saturday into Saturday night as the trough axis sweeps by to our north, while OH Valley activity likely remains to our south. Hot on its heels, however, is another perturbation over the Canadian Prairies, which currently looks to dig a little deeper into the Great Lakes than the first system, keeping things active early Sunday...and bringing some cooler air into play. We could see a brief break in the action Monday, unless warm advection convection rears its head...and warm advection will certainly be a concern ahead of a sharper PV maxima digging across the US/Canadian border upstream Monday. This currently looks to pass by the area Monday night into Tuesday, and a notable concern with this is that signals currently point toward a wide-open Gulf and subsequently, potential for deep moisture and heavy rainfall in the Upper Midwest. Southwesterly flow aloft generally looks to persist across the eastern US/Great Lakes into the latter half of the week, with additional perturbations in the northern stream trying to affect us toward Wednesday/Thursday, though quite a bit of uncertainty attm in the details/timing of these. Overall, expect active weather off and on through the course of the next week.

FORECAST DETAILS...

Rain/storm chances tonight into Saturday... Non zero chance some activity could sneak in toward Saginaw Bay Saturday morning on the very northern edge of the OH Valley system's influence, noting signals for an increase in low-level moisture...and there are some signals for a subtle positively tilted PV maxima to slip through around 12-15z...though not sure if this will be enough to generate precip or not. Primary concern tonight/Saturday morning will be how quickly the upstream warm advection precip moves in from the W/NW...and given that we are likely to stay quite dry in the low- levels today, think onset of rain will be a tad slower. Most likely chance of anything getting in during the early morning would be for the EUP and perhaps Straits. Better chance for rain/storms would be in the afternoon and evening from west to east along/ahead of the front, particularly toward the EUP and NE Lower where there is potential for somewhat deeper moisture and better influence of synoptic forcing from the PV max...and where there are signals for an increase in low-level fgen toward 18-0z.

Rain/storm chances Saturday night into Sunday... Current expectation is for temps to fall rather dramatically behind the front Saturday night, with 850mb temps approaching 4-5C or colder by 12z Sunday. This should result in at least some daytime instability, if not overlake instability...and think we have a reasonable shot at NW flow lake enhanced showers through Sunday, especially with a sharper PV max looking to dig across the area Sunday afternoon. This latter feature could set off some better shower activity across parts of northern Lower (M-72/M-55 corridors) during the afternoon into the evening hours, before things quiet down again...but not impossible the lake-induced clouds (and/or showers?) hang on into the overnight.

Chilly Sunday/Sunday night... Sunday will be quite cool otherwise (highs in the lower to middle 60s likely), with warmest temps in the morning hours and especially across the Saginaw Bay region. With high pressure likely moving in Sunday night...not impossible we could be looking at more widespread lows in the lower 40s, and perhaps a few more of the typical interior cold-spots make a run at the middle to upper 30s by Monday morning, noting signals for the air mass to dry right out behind that PV max Sunday afternoon.

Rain/storm chances Monday night into Tuesday (Heavy Rain potential?)...Return flow Monday into Monday night should result in a slug of Gulf moisture (pwats in excess of 1.5in) and a maximum in theta-e advection over the Upper Midwest and Great Lakes region Monday night into Tuesday with a strong S/SW low-level jet through the MS Valley. Combined with a PV maxima slipping by to our north during this timeframe, will need to monitor for heavy rain potential. There are signals for weak stability aloft which could support better rainfall production, and freezing levels should be well above 3km again (noting 700mb temps around +8C Monday/Monday night); current mean wind vs low-level flow suggests potential for slower moving (perhaps training?) cells, which could also boost rainfall amounts across some lucky (sarcasm) portion of the region. Not impossible better convective activity could develop to our southwest and track by to our southwest (the usual idea)...though the low-level jet looks to remain strong enough far enough north into the Upper Midwest that we may well end up in the path of better convection. Probabilistic guidance (currently based more on global than hi-res guidance given this is still 96-120hrs out) suggests a 40-50 percent chance of 24-hr totals of at least an inch across WI into parts of northern MI, with decreasing certainty in 24-hr totals in excess of 2in, though worth noting that the potential for rainfall in excess of 3in is not zero attm. The current area of interest seems to be the EUP and perhaps the Straits/Tip of the Mitt...stretching back into WI where ensemble guidance hints at a climatologically high maximum in moisture transport late Monday.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 621 AM EDT Fri Sep 11 2026

VFR conditions are expected to persist through the issuance period with sout-southhwest winds increasing through this afternoon with gusts around 15 kts. Winds will turn more southerly tonight and slightly decrease before increasing and turning southwest through Saturday afternoon. Light scattered showers will also be possible Saturday.

APX WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...Small Craft Advisory from 1 PM this afternoon to 6 PM EDT Saturday for LMZ341.