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KEY MESSAGES

- High Swim Risks in place across many northern Michigan beaches today. Breezy NW winds continue through Wednesday.

- Additional showers and a few storms possible again this afternoon. Outside shot at a severe storm the closer one gets to Saginaw Bay

- Cool temperatures through the middle of the week, warming back close to seasonal averages through the end of the week.

DISCUSSION

Issued at 112 PM EDT Tue Jul 21 2026

Pattern / Forecast Synopsis:

Northwest flow regime to carry through the forecast period, bringing quick moving disturbances, and variable short-term weather patterns across the Great Lakes region. Current upper air analysis showcases a closing surface low approaching James Bay that is currently in the process of dragging a cold frontal boundary across the region. Modest moisture pooling ahead of this front has allowed surface dewpoints to hold in the upper 50s to mid 60s. With ample lift with the onset of cold advection aloft in the wake of the front, coupled with diurnal heating to drum up instability, already festering convective responses are anticipated to increase in coverage across the region. Loss of daytime heating should put the kibosh on convection into the overnight hours, coupled with drier, cooler air streaming in from the northwest. Shortwave ridge intrudes by Wednesday, with large area of surface high pressure currently over the western Canadian Prairies moving in by Thursday. This will be quick to traverse the region, with backside return flow building by Friday. Resulting increase in moisture and heat will allow for instability to build back into the region by the weekend, carrying to early next week. In addition, additional subtle shortwave height disturbances will provide enough synoptic support to generate additional episodes of convection across the region Friday and beyond.

Details:

Today - Tomorrow: Cold front already advancing through the region, and has already commenced convective shower development across northern Michigan. Most of this activity set to produce minimal to no thunder... the lone exception being northeast lower south of M- 32. Axis of better instability progged to nose into this area, peaking around Saginaw Bay. While not exclusively outlooked, this area should be monitored for stronger discrete mode storms producing gusty winds and hail, owing to modest streamwise vorticity along with progged SBCAPE values ballooning up to 1500 J/kg. Limiting (not eliminating) the ceiling on convective potential is sub 30kt bulk shear, which may lead to a pulse-dominant mode to these storms... so if anything robust were to occur at the surface, it would be during the collapse of any updrafts. Anticipating diurnal instability to wane, and storm coverage to follow into the evening / overnight as drier air surges in at the surface.

Other story the next couple days will be the breezy WNW to NW winds. Sustained 10-20mph flow, gusting 35mph+ (strongest lakeshores) at times this afternoon... slackening a touch overnight before ramping back up sustained 10-15mph, gusts 30mph+ (again strongest lakeshores). Drier air at the surface and an intruding subsidence inversion should put a pretty big cap on shower activity into Wednesday... likely resulting in not much more than some autumnal feeling, poofy diurnal cumulus dominant day. Temps today today stonewall in the upper 60s to mid 70s for most, perhaps low 80s near Saginaw Bay. Overnight lows will respond well to the drier air moving in, despite winds limiting radiational cooling responses. Lows tonight in the upper 40s / low 50s inland, mid-upper 50s coasts. Highs Wednesday low-to-mid 60s eastern upper / west of I-75 in northern lower, 70s elsewhere. Temps Wednesday night may make a run at 40 degrees flat in most cold spots, with mid 40s to near 50 most other places... around 55 on the coasts. For those wondering if this is "windows open" sleeping weather regarding Canadian wildfire smoke... the answer should be yes. Latest modeled smoke trends are not robust over our area as recent rains across northwest Ontario and the Boundary Waters region of Minnesota have led to significant improvements in fire hot spots. Continued cooler weather in that region should keep things relatively under control the next few days, and conceptually should limit additional robust smoke plumes.

Rest of the Period: Seasonable air with temps in the upper 70s to lower 80s anticipated Thursday and beyond. High pressure keeps things dry and pleasant Thursday and Friday. Aforementioned return flow will bring more humid air into the region for the weekend, and with it, more chances for showers and thunderstorms. By no means does this pattern scream "washout", but certainly looks like chances for storms in the afternoon and evening hours Saturday through Monday. Overnight lows to creep a touch higher, possible settling into the upper 50s to mid 60s for a night or two. Not much of a signal for severe potential in this pattern, but it is important to note that NW flow dominant waves tend to have a high ceiling if everything can come together... but the chances of that actually happening are low for the time being.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 112 PM EDT Tue Jul 21 2026

Trending MVFR at most sites, and holding IFR at CIU through this evening. Will have to contend with some -SHRA and -TSRA at PLN and especially APN, and to a lesser extent, -SHRA potential at CIU and TVC. This should trend down after 20-21z, leaving the rest of the night dry but socked in with mid to low level cloud. MVFR across the board to improve later tonight, with all sites progged to be VFR by daybreak, carrying through Wednesday. Gusty NW winds expected through the period, with potential for 30kt gusts this afternoon... tapering to 20kts tonight, and perhaps 25kts Wednesday.

APX WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement through Wednesday evening for MIZ016- 018-020-021-025-031-098-099. MARINE...Small Craft Advisory until 11 PM EDT Wednesday for LHZ345>349. Small Craft Advisory until 11 PM EDT Wednesday for LMZ323-341- 342-344>346. Small Craft Advisory until 11 PM EDT Wednesday for LSZ321-322.