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KEY MESSAGES

-- Rain/storms today.

-- Breezy, cool, and showery Sunday with high swim risks.

DISCUSSION

Issued at 310 AM EDT Sat Aug 22 2026

PATTERN SYNOPSIS/FORECAST:

Ridge axis stretches from British Columbia down to the Four Corners region, where the 598/599dm upper level heat dome remains in place...with an upper low just off the West Coast poised to try to eject northward. Meanwhile, downstream, NW flow overtaking the Central US, with sharp trough axis focused from KY northward through MI into central Ontario...and another shortwave trough dropping out of Manitoba as of 3z. Shortwave ridge axis over eastern Canada as upper troughing exits the Canadian coast. Bulk of the moisture across the continent is focused along the SE US coast along a boundary stretching loosely down the Atlantic coast and through the Gulf Coast states...and secondly, across the Upper Great Lakes up into Hudson Bay near/beneath the incoming troughing. Anticyclonic flow in the low/mid-levels over central Canada helping to reinforce cold northwesterly flow across Manitoba and western Ontario, where 850mb temps are in the 4-8C range attm...and a surface cold front stretching from MN to Hudson Bay reflects this cold advection idea. A cold front does stretch from the central UP down into the Mid MS Valley and Central Plains, though for our neck of the woods, the thermal change is less impressive than the wind shift attm, with winds distinctly turning around to the NW behind it (as opposed to the southerly surface flow ahead of it).

Expect this latter feature will be exiting NE MI this morning as that energy digs nearly straight south from northwestern Ontario. This should keep the threat for showers and perhaps storms going through the day as multiple waves dig through the region. Strengthening pressure gradient between departing pressure falls and approaching surface high will result in strengthening northwest winds later today into tonight...and hanging on into Sunday as an somewhat unseasonable wad of PV drops in and results in a strengthening of aforementioned pressure falls to our E/NE. Falling temps aloft should generate overlake instability and lake effect rain showers to wrap up the weekend. Not impossible this idea hangs on into the start of the workweek, but attm, appears ridging should build eastward into the Upper Midwest later Monday...ahead of the next feature plowing its way across southern Canada...which should reach us by midweek, though its warm advective influences may reach us a tad sooner. It is still somewhat unclear attm how the end of next week will evolve, though signals the last few nights suggest the flow may try to flatten out across the northern CONUS as bits of energy continue to track across Canada.

FORECAST DETAILS...

Rain/storm chances today through Sunday (Monday?)...

Think there is a reasonable shot at a PV max lifting through around midday/afternoon today, and another, more potent bit of PV digging in from the northwest toward late afternoon/evening...perhaps not all that dissimilar to yesterday's setup, but translated eastward a bit...though certainly possible there will be other, smaller-scale perturbations to contend with. We will continue to hang onto several hundred to around 1000 joules of elevated instability this morning, and think this could have a shot at becoming surface based with time today, especially toward NE Lower which should remain in the warm sector longest...though if we are able to warm enough to mix out any weak nocturnal inversion this morning, we could become surface based right away with low-LCLs, and do wonder (with my very worst-case- scenario brain) if a rogue spin-up is possible?...though shear generally remains weak till perhaps the afternoon (and even at that, is likely marginal, around 20-30kts at best)...though I am perhaps a bit aggressively biased toward the idea of lifting/negatively tilted shortwaves tending to be spicy. Some upscale growth is possible with shear vectors largely parallel to the boundary, and cooling/weak stability aloft suggests some marginal hail could be possible...but some localized heavy rains could also be a concern, especially if storms move slowly or hang out in an area for an extended time.

925mb temps falling below 14C as early as 3z tonight suggest we will begin to transition to more of a lake effect regime, and this should remain firmly in place Sunday as temps fall even further -- 850mb temps could fall below 4C, which would be sufficient to generate overlake instability over even the colder waters of central Lake Superior. Prevailing flow should generally be NW to NNW but may fluctuate back and forth a bit with the encroaching perturbations, with more northerly flow likely by later Sunday into Sunday night. Deepest moisture should remain over NE Lower MI Sunday, and this is where best coverage should be...though will expect most of the usual lake effect areas to see a little activity off and on this weekend. Fly in the ointment for the lake effect idea is that inversion heights should take a tumble later Sunday into early Monday, which could limit the extent of actual shower activity into the start of the work week. Would not be surprised to see some kind of drizzle hang on where upsloping is maximized...though attm, some (typically drier) guidance soundings hint at the idea of aggressive drying on Monday, which could help clear things out quicker. With potential for steep (15+C) delta-Ts Sunday, and 850mb winds most likely remaining at or below 30kts (at least till perhaps late), think we could have a shot at seeing some waterspouts on the northern Great Lakes, though not a sure bet.

Winds this weekend...Pressure gradient will begin to strengthen this afternoon...and will only further expand/strengthen through the night into Sunday as that next wad of PV drops in, kicking cyclogenesis into high gear toward Georgian Bay/western Quebec. This should put the strongest synoptic winds generally from the EUP down into northeast Lower MI...with potential for sustained winds 10- 20kts through Sunday night. The low-level jet should strengthen as well, from 20-25kts even as early as this afternoon, upwards of 30+kts overnight. Think there could be some isolated gale-force gusts on the nearshores, but do not have much confidence in this idea attm, given that winds aloft aren't necessarily supportive.

As mentioned above, prevailing winds should flit back and forth between NW and NNW with time as various perturbations pass through...but this will lead to building waves and dangerous swim conditions especially along our west/northwest facing beaches of northwest Lower, and across north(ish) facing shores of northeast Lower. While we do not specifically issue a beach forecast for Whitefish Bay, would anticipate much of that north-facing coastline from Bay Mills/Point Iroquois toward the mouth of the Tahquamenon River will also see high wave action and dangerous swimming conditions (not to mention high waves out on the Bay itself). ...Not that the cool, showery, blustery weather is overly inviting for beachgoing in the first place.

Cool temps Sunday...Seasonably cool air mass supports highs in the 60s for most, though possibly closer to 70 near Saginaw Bay, particularly where downsloping and some clearing could come into play. Given anticipated showers/cloud cover (though it could end up less bullish than current expectations), have suspicions some of the interior areas could struggle to get out of the lower 60s, and would not be surprised if parts of the EUP stayed in the upper 50s. Combined with showers and breezy winds... it will definitely feel more like fall than late August. Temps should begin to warm Monday, about 5-10 degrees compared to Sunday, and if more aggressive drying occurs, perhaps bounce back up much closer to normal than current expectations...with potential for lows in the 40s again Monday night, especially if high pressure settles in overhead, though do have to wonder if we will end up with fog after the expected showers this weekend.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 634 AM EDT Sat Aug 22 2026

Areas of lower cigs out there this morning, most widespread in northern lower MI (mainly MVFR, in spots IFR). These cigs will tend to gradually improve thru early afternoon. These are also some showers out there, especially north of TVC. The best chance for heavier SHRA and TSRA will be this afternoon/early evening at APN. Precip coverage will decrease somewhat tonight. Winds become nw and somewhat breezy this afternoon.

APX WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...Small Craft Advisory from 5 PM this afternoon to 5 PM EDT Monday for LHZ345. Small Craft Advisory from 5 PM this afternoon to 8 PM EDT Monday for LHZ346. Small Craft Advisory from 5 PM this afternoon to 9 PM EDT Monday for LHZ347-348. Small Craft Advisory from 11 PM this evening to 5 PM EDT Monday for LHZ349. Small Craft Advisory from 5 PM this afternoon to 5 PM EDT Monday for LMZ323-341-342-344. Small Craft Advisory from 10 PM this evening to midnight EDT Sunday night for LMZ345-346. Small Craft Advisory from 5 PM this afternoon to 5 PM EDT Monday for LSZ321-322.