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KEY MESSAGES

- Frost Advisory for eastern upper Michigan tonight

- Slightly warmer overnight temperatures in northern lower Michigan, with isolated pockets of mid 30F or lower in typical cold spots

- Dry conditions and slow warming trend continue into the weekend

DISCUSSION

Issued at 104 PM EDT Tue Sep 22 2026

Earlier this morning, some lake effect clouds formed off Lake Huron and resulted in partly cloudy skies over northern MI. This morning's 12z KAPX RAOB depicts nice lapse rates around 3 kft and below, with some breezy east winds right off the surface in this layer (above the shallow morning surface inversion). These ideal lapse rates are halted around 3 to 4 kft as a fairly thick warm and dry layer exists up to the mid levels. Earlier satellite revealed the prominence of this inversion with cumulus becoming spread out and eventually dissipating as the clouds track east to west over northern MI. This cloud cover kept overnight temperatures in the high 30s to mid 40s in northern lower. A few cold pockets of low to high 30s were seen in typical cold spots. Widespread 30 to 35 degree temperatures were seen over the eastern U.P. where less cloud cover and even light drainage winds off the CAN shield were seen last night. This afternoon, the boundary layer is slightly rising and mixing into that dry inversion layer resulting in a gradual dissipation of cloud cover over northern lower.

Above our heads, an upper ridge is taking shape on the northern side of a weakening closed upper low over the northern plains. This rex block will become established over MI as it creeps east tonight and into Wednesday. This feature will help anchor the surface high pressure to the northeast, keeping northern MI influenced by this drier airmass through the weekend. Although the airmass remains dry, warmer temperatures will slowly work there way in each day as this airmass modifies and warmer air aloft sinks closer to the surface. Northeast winds will veer southeast this evening, remaining breezy near the Lake huron coast. High swim risk exists through late this evening for the sunrise side beaches due to gusty winds and waves of 4 ft.

As the core of the surface high shift to the east tonight before anchoring for the next several days, temperatures aloft will slightly warm with winds remaining breezy near the coast. Near freezing temperatures continue to be forecasted for eastern upper due to ideal flow off the CAN shield, however slightly warmer conditions (high 30s to high 40s) are expected over northern lower tonight. Isolated pockets of low to mid 30s remain likely tonight for cold spots, however the surface inversion should continue to remain shallow and only allow for a few hours of temperatures at their coolest near sunrise.

Besides gradual warming each day, occasionally breezy southeast winds and dry conditions will continue into the weekend. Slight chances for rain return near the end of the forecast period (mid to late next week), however we have been teased on day 7 in fall before.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 725 PM EDT Tue Sep 22 2026

Only concern is potential for a period of mist a KAPN early this overnight, as well as some low level wind shear tonight at KPLN, KTVC, and KMBL. Otherwise, VFR conditions will continue under mostly clear/sunny skies. East to southeast surface winds, becoming a bit gusty at times on Wednesday.

APX WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement until 8 PM EDT this evening for MIZ018- 024-030-036-042. Frost Advisory until 8 AM EDT Wednesday for MIZ086-087-095-096. MARINE...Small Craft Advisory until 8 PM EDT this evening for LHZ345. Small Craft Advisory until 8 PM EDT Wednesday for LHZ347. Small Craft Advisory until midnight EDT tonight for LHZ348-349. Small Craft Advisory until 11 PM EDT this evening for LMZ342- 344.