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KEY MESSAGES

- Dry and comfortable through Sunday.

- Rain chances increase Sunday night/Monday.

- Several day spell of hot and humid weather starting Tuesday.

DISCUSSION

Issued at 305 PM EDT Sat Jun 27 2026

Pattern Synopsis/Forecast: Large scale pattern to start the weekend features a digging trough into western North America...with gradually amplifying flow downstream in response as higher heights develop over the Plains/Midwest. Main westerlies are across the CONUS with surprisingly little flow aloft across Canada within a broad area of weak ridging. Plenty of deep moisture from the central/southern Plains eastward across the Ohio Valley and points south (precipitable water > 1.50 inches)...small pocket of drier air hanging over the Great Lakes beneath a 700mb short wave ridge. At the surface a broad area of high pressure across eastern Canada/Great Lakes/New England...with a nearly west-east stationary front from the central High Plains to the mid Atlantic with humid air pooling along and south of this boundary.

Upstream trough/closed low will continue to dig into the Intermountain West/Great Basin this weekend...pushing higher heights/short wave ridging into the Great Lakes. 590+dam 500mb heights into northern Michigan by Monday (+1.5 to +2 sigma height anomalies) with the pattern persisting into midweek with 594dam heights flirting with southern Lower Michigan. Ridge amplitude may be blunted a bit by Wednesday with short wave energy coming over the top...some uncertainty as to how much heights over northern Michigan may be "flattened" by this. But this basic pattern likely to hold on until next weekend.

Weak high pressure will hang on across Michigan through the weekend... eventually stationary boundary to the south will have to lift north as a warm front as warm/humid air spreads north. Front likely crosses northern Michigan Monday/Monday night...bringing with it a notable increase in humidity. Anticipating that the warm front will be north of the Great Lakes by Tuesday...with the main surface influence through Friday being broad anticyclonic flow around subtropical ridge.

Primary Forecast Concerns:

Dry and comfortable through Sunday: Not much to argue with this weekend. Decent diurnal Cu/TCu field this afternoon...and a nice westward push of the lake breeze off Grand Traverse bay on the radar. Convergence along colliding lake breezes in eastern Upper may try to squeeze out a few radar returns similar to Friday afternoon. Some mid/high clouds drift in for the overnight and Sunday. Otherwise one last day of dew points in the comfortable 50s and afternoon highs in the 70s...lower 80s along and west of US-131.

Rain chances increase Sunday night/Monday: Surge of warmth and moisture ahead of approaching warm front Sunday evening...with low level jet starting to focus on the upper Lakes. Impressive push of instability into the upper Midwest and into Wisconsin...though capped by an elevated mixed layer with 700mb temperatures at or above +12C. Expect convection to develop along the leading edge of the capping on the other side of Lake Michigan Sunday evening...and eventually develop/propagate east into northern Michigan during the early morning hours of Monday. Threat for convection will continue into the daytime Monday as the initial low level theta-e gradient crosses the state. But with EML on its heels the rain threat may end by afternoon. Monday will be the opening act for what is to come midweek with the first warm/muggy day expected. Temperatures will depend somewhat on cloud cover which may hang around much of the day...but just through warm advection temperatures should warm into the 80s and possibly 90+ across northwest Lower. If that occurs we may need some heat headlines at least along much of the M- 55 and south corridor by Monday afternoon.

Several day spell of hot and humid weather starting Tuesday: Forecast trends lend more confidence in the idea that convective activity will remain north of Lower Michigan and bolster the potential for significant heat starting Tuesday. Expecting widespread highs Tuesday through Thursday in the 90s with mid-upper 90s probable across northeast Lower with downsloping winds. Dew points around 70F (likely 70-75F on Tuesday) will push wet-bulb globe temperatures into the high and extreme heat illness threat level...with heat indices above 100F Tuesday and from 95-105F expected Wednesday and Thursday across northern Lower (90-95F for eastern Upper). Overnight lows in the mid 60s to lower 70s won't provide much relief. No matter how you slice it...it is going to make for a very uncomfortable midweek stretch. Current expectations are that temperatures will trend down a bit for Friday/Saturday but it will still be above normal heading into the Fourth of July holiday weekend.

And just to update this table provided in this space yesterday... forecast versus record highs starting Tuesday (30 June):

KGLR: Tue 92/98 (2018)...Wed 91/96 (1966)...Thu 91/96 (1966). KHTL: Tue 93/99 (1927)...Wed 94/103 (1931)...Thu 93/99 (1921). KTVC: Tue 94/99 (1931)...Wed 93/103 (1931)...Thu 93/100 (1966). KAPN: Tue 95/99 (2018)...Wed 95/100 (1031)...Thu 94/98 (1966). KPLN: Tue 91/94 (2018)...Wed 90/97 (2018)...Thu 90/93 (1966).

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 1136 PM EDT Sat Jun 27 2026

Expect IFR fog late tonight at times at MBL/PLN, and VFR at the other sites. Otherwise VFR thru the forecast, quiet, and warmer Sunday. A se breeze kicks in Sunday afternoon, though it will compete with lake breezes.

APX WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...None.