textproduct: Marquette

KEY MESSAGES

- Scattered showers and thunderstorms move eastward with a cold front over central and eastern Upper Michigan through this evening.

- Additional scattered showers and thunderstorms are possible across mainly central Upper Michigan tomorrow with minimal rainfall totals.

- Seasonable temperatures are expected through next week with the exception of slightly below normal temperatures Sunday and Sunday night.

DISCUSSION

Issued at 319 PM EDT Fri Aug 21 2026

Afternoon RAP analysis indicates the weak sfc low has made it over central Lake Superior, opening up into a trough which extends northward into northern Ontario. Sfc obs place the cold front just past the far western UP with temps in the upper 60s to mid 70s ahead of it. Tds in the low to mid 60s support SBCAPE in the 500-1500 J/kg range, but lapse rates are unimpressive. Bulk shear is also below 25 kts, so strong to severe storms are not expected. Latest radar mosaic has showers along this boundary with Day Cloud Phase RGB satellite imagery showing glaciation and GLM/ground networks indicating lightning activity is just starting. These are expected to progress eastward through this evening before diurnal instability decreases and lingering convection falls apart. PWATs of ~1.3 inches indicate some isolated higher amounts up to 0.5 to 1 inch are possible (30-50% chance, highest central UP), but most likely accumulations will be less than 0.25 inches.

In the wake of this front, isolated showers and a few rumbles of thunder are possible (15-30% chance) with a shortwave and limited elevated instability tonight. Lows settle into the upper 40s to low 60s, coldest interior west. Additional scattered showers and weak storms are possible on Saturday as another cold front and shortwave drop southeast overhead. That said, CAMs are even less impressed with this round. Outside the south-central where some spots could reach up to 0.25 inches, accumulations remain below 0.1 inches. Highs will be in the upper 60s to mid 70s.

Temps continue to decrease this weekend, bottoming out Sunday as a mid level trough deepens over the Great Lakes. CAA lowers 850 mb temps to between 3-6C, yielding highs in the 60s to low 70s and lows in the 40s to mid 50s. Some interior spots likely will dip back into the upper 30s Sunday night. Northerly winds are expected to gust up to 20 mph on Saturday and between 20-30 mph on Sunday, highest east...particularly near Lake Superior. High pressure moving in from the west keeps weather dry through Monday, likely through most of Tuesday as well before the next mid level trough moves through the region. This brings back shower and storm chances for Tuesday night and Wednesday, then dry weather is favored the rest of the work week.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 156 PM EDT Fri Aug 21 2026

A weak low pressure system working across Upper Michigan is bringing MVFR/IFR cigs to the area. The main aviation concerns for the 18z TAF cycle are the timing of showers/thunderstorms at SAW, which are presently developing in the western UP. Guidance continues to move them across SAW between 20-00z, so have included prob30s for -tsra at SAW for that time. Otherwise, conditions improve to VFR overnight. As winds fall some patchy fog is possible at SAW, but confidence is not high enough to put into the TAF at this time. Gusty NW winds increase tomorrow morning and afternoon at all sites. Winds 20-30 kts will be common at CMX and SAW.

MARINE

Issued at 348 PM EDT Fri Aug 21 2026

Lake Superior - Northwest winds behind a cold front increase on Saturday to 20-30 kts over the east half of the lake by late afternoon, strongest near the south-central shores. Gusts approach 20 kts over the west. As winds become more northerly Saturday night behind a second cold front, central lake superior winds increase to 15-25 kts; the stronger winds to 30 kts over the east persist. This holds into Sunday morning before winds gradually simmer down from west to east into Sunday night. This builds significant waves of 3-7 ft over the southeastern waters this weekend. Probabilities for gales to 35 kts are only between 15-25%, highest south of Stannard Rock and along the Marquette/Alger County shores. Winds otherwise remain below 20 kts through Tuesday before the next system brings back winds up to 20-25 kts Tuesday night into Wednesday morning.

Northern Bay of Green Bay and northern Lake Michigan - Southerly winds of 15-25 kts ahead of the cold front this afternoon drop off into this evening, becoming northwest for Saturday. Scattered thunderstorms are expected this evening, but severe storms are not expected. Winds increase to 20-30 kts this weekend as a colder airmass descends over the Great Lakes. Winds fall back below 20 kts Sunday night, remaining below 20 kts through much of next week.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... Beach Hazards Statement until 10 PM EDT this evening for MIZ014.

Lake Superior... None. Lake Michigan... None.