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KEY MESSAGES

- Showery, cool, and breezy today; chilly tonight

- Rain/storms return Monday night into Tuesday, along with strong winds (possible gales)

DISCUSSION

Issued at 446 AM EDT Sun Sep 13 2026

PATTERN SYNOPSIS/FORECAST:

Generally westerly flow aloft across the CONUS...between a PacNW upper low and ridging over the SW US (amplifying northward into the Intermountain West ahead of said upper low)...with 100-120kt upper jet stretched across the northern tier of the CONUS aiding in some Pacific moisture transport. Broad upper low swirls over the east- central portion of Canada, with energy digging through Manitoba/Saskatchewan and swirling across Ontario. Shortwave troughing even digs as far south as the Upper Great Lakes/OH Valley, picking up cutoff energy over KY. Deepest moisture (pwats 1.5in or greater) over the central Plains into the Lower MS Valley where some convection is ongoing; otherwise, the rest of the deep moisture is being swept eastward ahead of a cold front stretching from OK to Saginaw Bay to northern Quebec. 1022mb surface high oozing into the Plains, with northwest flow aloft over the Great Lakes as a tight thermal gradient slips in...850mb temps falling from the teens over southern MI to 4C near the northern coast of Lake Superior, denoted by a second cold front draped across Ontario at 3z; 0C and colder airmass to our north over northern Manitoba and Ontario, though not sure that current trajectories support this kind of cold for us.

Lobe of PV swings across the Upper Great Lakes today, with some showers, potentially lake effect/enhanced on WNW to NW flow, fading with time going into tonight as energy moves past and winds begin to diminish, though overlake instability will remain as ridging builds in quickly overnight tonight, resulting in a chilly night. The PacNW upper low tracks eastward across the northern Plains tonight into Monday, resulting in an increase in moisture transport through the Upper Midwest Monday night into Tuesday...and potential for heavy rainfall...as a boundary drapes into the area and stalls out to our south somewhere in the OH Valley. This could become problematic for the middle and latter portion of the week...as energy again tries to cut off across the PacNW/Intermountain West while the more progressive northern stream drags some energy across southern Canada, and perhaps the Upper Great Lakes, sometime in the Wednesday night-Thursday timeframe. Quite a bit of uncertainty beyond this for next weekend...but there are signals for the second bit of troughing in the PacNW to eject eastward, which could result in continued active weather across the eastern half of the country.

FORECAST DETAILS...

Lows tonight...With the cold air mass coming in today, and most of the area stuck in the 60s for highs...still have concerns some of the typical cold spots in the interior could drop down into the mid 30s tonight as high pressure builds in...given incoming air mass is dry, perhaps even a smidgen drier than recent cooler air masses. Potential sticky wicket is lingering overlake instability and some potential for a smidgen of low-level moisture to hang on...which could be in the form of some cloud cover that could slow radiational cooling, though not sure how extensive this idea will be. We may also be a bit slower to settle down compared to points west, where the surface high will move in quicker, which could also slow radiational cooling. Have trended lows a little cooler for tonight especially across the interior higher terrain, down into the upper 30s there...where a 25 degree temperature swing would take lows tonight down into the mid thirties.

Heavy rain potential Monday night into Tuesday...Not a ton of change in the overall setup. Strong southwesterly flow ahead of the next system, combined with an increase in absolute moisture, will result in anomalous moisture transport into the Upper Midwest. Attm...signals point toward the most anomalous (beyond climo) moisture transport occurring to our west over WI Monday into Monday night, where there is a greater shot at weaker stability that could produce a better bang for our QPF buck; this area would also be more favored for heavy rain in a Maddox synoptic type setup, to which Monday night is somewhat similar. Expect we will see stronger frontogenetic responses that will enhance QPF in localized swaths...some of which are currently progged to influence the EUP and Tip of the Mitt region late Monday night...and will watch for a potential maximum in QPF up here, as well as elsewhere along the front (including the Saginaw Bay region in the afternoon/evening). Abundant moisture present in this setup is not favorable for typical instability parameters, but think we could still see some convective elements develop along a potential dry slot sweeping through Tuesday. Things appear to become more progressive here late Monday night into Tuesday as the PV max tracks relatively quickly across central Ontario, allowing the cold front to drape down into the region with time going into Tuesday night, and keep the better moisture and forcing from remaining colocated in our region Tuesday (compared to points upstream). That is...not impossible the heaviest rain ends up splitting around us (as usual)...with probabilistic guidance trending a little lower on potential for 1-in in 24hrs here compared to the last couple nights...suggesting heavy rain is not as much of a certainty as it once seemed...though parts of the area should still get some decent rainfall.

Gales possible Monday night into Tuesday...850mb winds will be climatologically anomalous with this system...around 3-4 standard deviations above the mean, lending concerns for strong winds to mix down to the surface. Model guidance suggests potential for a 40+kt low-level jet overhead Monday night into Tuesday morning, though it may be waning a bit in intensity as it arrives in our part of the Midwest, compared to points upstream. Primary question is how much of these winds will mix down, given that this is a warm advection setup. The answer is not crystal clear, as the strong inversion aloft (around 900-800mb) and nocturnal influences could dissuade stronger winds from mixing down; however, do wonder if the lakes will still be warm enough to allow for some downward momentum transport...just not sure if it will be enough to tap the strongest winds or not. Current sounding-derived probs suggest a 30-40 percent (medium confidence) chance of wind gusts in excess of 34kts, particularly at sites near Lake MI (and perhaps up toward DeTour and Drummond Island) where there is better fetch off the effectively frictionless lake surface on S to SW flow...though S/SE flow initially could keep gale potential just to our west on Lake MI Monday night, more over the open waters and areas west of Seul Choix Point. The surface pressure gradient itself will also be quite strong between the incoming surface low over southern Canada and exiting high pressure over New England...supportive of sustained winds upwards of 10-20kts across the region Monday night into the first half of Tuesday.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 618 AM EDT Sun Sep 13 2026

Light scattered showers will be possible today, mainly this afternoon/evening, with the best chances across CIU and perhaps PLN. VFR conditions are expected to persist through the issuance period with gusty west-northwest winds increasing through the day with gusts to 25 kts possible, turning northwest through the afternoon/evening, and becoming light and variable by later tonight.

APX WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement from 2 PM EDT this afternoon through late tonight for MIZ018. Beach Hazards Statement from 2 PM EDT this afternoon through this evening for MIZ099. MARINE...Small Craft Advisory from 2 PM this afternoon to 9 PM EDT this evening for LHZ345. Small Craft Advisory from 2 PM this afternoon to 11 PM EDT this evening for LHZ346. Small Craft Advisory from 2 PM this afternoon to 3 AM EDT Monday for LHZ347-348. Small Craft Advisory from 5 PM this afternoon to 11 PM EDT this evening for LHZ349. Small Craft Advisory from 2 PM this afternoon to 9 PM EDT this evening for LMZ341. Small Craft Advisory from 2 PM this afternoon to 11 PM EDT this evening for LMZ323-342-344. Small Craft Advisory from 2 PM this afternoon to 11 PM EDT this evening for LSZ321. Small Craft Advisory from 4 PM this afternoon to 9 PM EDT this evening for LSZ322.