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KEY MESSAGES

- Few showers/storms today

- Cool and showery Sunday followed by a chilly night Sunday night

- Increasingly breezy with rain/storm chances Monday night into Tuesday

DISCUSSION

Issued at 306 AM EDT Sat Sep 12 2026

PATTERN SYNOPSIS/FORECAST:

Zonal flow across the western US attm...with ridge axis holding on across the eastern US, including the Great Lakes. Flow remains a bit split attm...with a beautiful swirl in water vapor imagery over the Mid MS Valley associated with a trough axis there...and an elongated positively tilted trough axis stretching from the northern Plains to an upper low over Hudson Bay, with many-a PV maxima in the flow across most of Canada attm. Deepest moisture remains across the SE US and Lower MS Valley nearer that former feature...with a maximum in pwats (around 2in) along the tightening baroclinic zone and deformation axis stretching from central Ontario back into Nebraska...though there is a little bit of moisture hanging back across central Canada along a subtle trough axis, near and north of which 850mb temps drop back to 0-4C. Plume of weak stability also stretches along the aforementioned baroclinic zone, and this is where a line of convective activity fired last evening. Low-level flow is parallel to the upstream boundary and mid-level flow has a little bit more of a westerly component...such that the air mass will overall be moistening here in the Great Lakes (dewpoints as of 3z are in the upper 40s to lower 50s, which is warmer than this time yesterday), but the most notable warm/moist advection should remain to our northwest near and north of Lake Superior tonight. This is reflected by surface warm front well to our north along the southern shore of Hudson Bay to western Quebec. Some moisture is swirling northward through the OH Valley, too, north of the aforementioned PV swirly in the Mid MS Valley; attm, this is slowly attempting to creep northward/northeastward into southern Michigan.

PV maxima swings by to our north today, but will drag some semblance of a boundary across the area through the day...with NW winds picking up as cold advection commences late. Sunday should be seasonably cool with a trough axis pivoting overhead, most likely in the afternoon/evening. Behind this...high pressure builds in Sunday night, and with this cold air mass in place, think Sunday night could be quite cool indeed. Our quiet weather will be short- lived...with an upper low ejecting from the PacNW across the northern Plains Monday...tracking across the Upper Midwest into southern Ontario Monday night into Tuesday. Still have concerns that the Gulf will be open for business with this system, and perhaps some tap of Pacific moisture, too, with southwesterly flow aloft...and thus, have concerns for heavy rain/storm potential across the region for this timeframe (Monday night into Tuesday). Progressive regime will keep this niblet moving, too, as another lobe of energy makes its way eastward across the central continent. Timing of this next feature remains a bit unclear attm, but appears Wednesday night into Thursday will be the broad timeframe for another round of activity. Even more uncertainty in the pattern for the end of the week into next weekend, depending on how strong the southern stream ridge axis will be, and where it will be focused.

FORECAST DETAILS...

Rain/storm chances today...front crosses the region between 15-21z ish today from W-E and think there will be an uptick in low-level forcing and moisture pooling along this boundary to produce at least cloud cover, if not showers, especially toward the EUP and Tip of the Mitt where there is a likelihood of better forcing and deeper moisture...though instability should be lesser here (minus that there should be convective instability present along the edge of the dry slot). There is a better shot at slightly (slightly) deeper instability across northern Lower MI (more likely to be underneath the plume of weakest stability), though this will be further removed from the better moisture and forcing. Not impossible there could be a few showers or even a rumble of thunder this afternoon as the front passes through...but lesser moisture here signals less confidence in shower/storm development here. Deep layer shear picks up this afternoon/evening, generally in the wake of the front, but not impossible it could be a little better right with the front, and if we do end up with more activity along the front than previously expected...not impossible a few cells could get a little better organized and a little spicier. It's possible the boundary may stall over the region tonight, in an east-west fashion, before the next niblet comes rolling in for Sunday, and this idea suggests some shower activity will hang on into at least part of the night.

Cool with showers Sunday; chilly Sunday night...temps will continue to fall Saturday night into Sunday, particularly aloft, with 850mb temps at or below 5C across a good chunk of the area by the afternoon. This will be borderline for overlake instability generation, and combined with an incoming PV max punting Saturday's boundary out of the area, think there is a shot we see lake enhanced shower activity Sunday (particularly with the passage of the PV max around midday/afternoon). With the cooler air and weaker winds Sunday, not impossible there could be a rogue waterspout, though cloud depths and lake-850mb delta-ts are a little on the low side for any great amount of confidence. Assuming skies clear as high pressure moves overhead Sunday night, some locales could drop down into the upper 30s and lower 40s again, similar to last night...though a little unclear attm if the air mass then will be quite as dry as it was last night, when we did drop down into this range. If in fact we are as dry...a 30 degree (give or take) diurnal temperature swing from the lower to middle 60s could drop temps into the mid 30s or colder in some interior locales by Monday morning...so will be something to keep an eye on.

Rain/storm chances Monday night into Tuesday; increasingly breezy... Still looking for an anomalous wad of moisture (pwats pushing the 95- 99th percentile vs climo) to pivot into the area Monday night into Tuesday ahead of a lifting shortwave trough (suggesting potential for better synoptic forcing) and attendant tightly-wound surface cyclone, per deterministic guidance. This sets the stage for a) storm development, and b) heavy rain potential with any storms. Better instability parameters may set up to our southwest as far as storms are concerned...and with stronger winds aloft, think some storms could become organized, especially down in this region, assuming this idea persist, with much less certainty in this idea for northern Michigan. However, we will be near/north of the warm front as it lifts in, which could signal a better position for heavy rainfall for us. Certainly something we will need to monitor...with probabilistic guidance still pointing toward upwards of a 40-50 percent chance of an inch of rain in 24hrs ending Tuesday evening. Worth noting that prob guidance is more confident on the highest rainfall totals to our south and west, which is a reasonable idea based on the setup...but there is still potential for heavier rains to sneak up into our area along the boundary as it drapes in.

Pressure gradient currently looks to strengthen quite dramatically Monday night into Tuesday ahead of the incoming surface low, and think we have a shot at our first gales of the season with this...given sounding-derived wind gust probabilities around 30 percent for gusts of at least 34kts. 850mb winds are on the higher side...+3 standard deviations from the mean...suggesting we could be in for some stronger winds if they can mix down; the caveat being that warm advection typically does not support full mixing, and could keep the stronger winds trapped aloft.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 627 AM EDT Sat Sep 12 2026

Light scattered showers will be possible today, mainly this afternoon/evening, with the best chances across CIU and PLN. VFR conditions are expected to persist through the issuance period, though low end VFR to perhaps MVFR will be possible across the northern most terminals (PLN/CIU). Southwest winds will increase through the day with gusts 15-25 kts possible, turning west through the afternoon/evening, becoming northwest tonight. Winds will also decrease through the evening, becoming light tonight.

APX WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement through this evening for MIZ025-031- 096-098. Beach Hazards Statement through this evening for MIZ095. MARINE...Small Craft Advisory from noon today to 8 PM EDT this evening for LHZ345>347. Small Craft Advisory until 8 PM EDT this evening for LMZ323- 342-344>346. Small Craft Advisory until 8 PM EDT this evening for LMZ341. Small Craft Advisory until 8 PM EDT this evening for LSZ321- 322.