textproduct: Marquette

KEY MESSAGES

- Scattered showers and a few thunderstorms move west to east this evening into tonight. Rainfall amounts will be light, generally around 0.1" or less, though some higher amounts are possible in storms.

- Showers and storms re-develop along the cold front over the central UP Friday afternoon, then move eastward into the evening. Additional rainfall totals are expected to be 0.1" or less, though higher amounts are possible in storms.

DISCUSSION

Issued at 304 PM EDT Thu Aug 20 2026

Afternoon water vapor imagery shows nicely the midlevel shortwave over North Dakota, with RAP analysis showing surface low pressure over the ND/MN border region. WAA out ahead of this, coincident with a 30-40kt LLJ, has touched off convection over eastern MN and western Lake Superior. Associated midlevel cloud cover continues to work eastward into the UP, and though some weak radar returns have drifted over the western UP at times, dry air is winning out so far (dewpoint depressions on the order of 20 degrees) and preventing anything from reaching the ground. With that, have pulled back the onset timing of convection over the western UP closer to 00Z. By then, a few hundred j/kg of CAPE indicate that some thunder will be possible, and this continues overnight as the initial batch of showers and storms works eastward. Heavy rainfall is not expected, with most spots seeing a tenth of an inch or less. However, higher totals of a quarter-inch would be possible in storms (HREF showing embedded 30-50% probability of such totals per 6-hourly period tonight). Otherwise, expect temperatures, rising comfortably through the 70s this afternoon, to fall back into the 50s to near 60 overnight.

Friday, the surface low off to our west tracks through the UP (perhaps opening up into a surface trough). This brings a cold front through the area, which looks to be draped somewhere across the central UP by mid-morning. Destabilization ahead of the front over the central and eastern UP will allow showers and storms to redevelop into the afternoon, but with very limited shear and MUCAPE below 1000j/kg, strong to severe storms are not expected. This should not be a washout, again with most areas receiving additional rainfall totals of a tenth of an inch or less. However, ensembles show as much as a 50% chance for higher embedded totals in excess of a quarter-inch in heavier downpours. Friday is looking otherwise breezy ahead of the front, with southerly wind gusts to around 20mph over the eastern UP. Temperatures peak in the lower to mid 70s behind the front, and the mid to upper 70s ahead of it.

Additional chances for showers and storms return for Saturday as a midlevel low drops into northern Ontario, sending additional shortwaves and a shot of cold air advection into the Great Lakes. That said, the main story will be marine hazards and gusty northerly winds Saturday/Sunday. Modest pressure rises coupled with cold air advection (850 mb temps between 3-6C Sunday) will create northerly gusts 20-30 kts with a 40-50% chance of gales to 35 kts over the eastern portions of the lake.

Model discrepancies follow into next week, though Sunday and Monday looks mainly dry, followed by on and off rain chances the rest of the forecast period as a series of shortwaves drop through the Great Lakes.

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

Issued at 716 PM EDT Thu Aug 20 2026

Showers and storms continue to push into the area tonight through Friday with the passage of a shortwave low. While generally VFR conditions are expected through the evening hours, low MVFR to IFR cigs are expected to roll-in Friday morning across the west and central U.P. as the low's center moves into the area. While some lake effect/enhanced rain showers could be seen behind the low on Friday, thinking the best chances for showers and storms will be relegated to SAW by the afternoon hours once some diurnal instability comes into play. Generally southerly winds tonight give way to northwesterly winds by Friday afternoon behind the low, with skies clearing out and becoming VFR again by the late afternoon hours.

In addition to the above, some marginal LLWS could be seen over the terminals. However, because chances are too low (<30%), decided to not have mentions of it in the TAFs.

MARINE

Issued at 304 PM EDT Thu Aug 20 2026

Lake Superior - ESE wind gusts pick up to around 20kts over the east- central portions of the lake tonight, then gusts fall back below 20kts Friday afternoon while a passing cold front causes winds to shift over to the NW. The main marine hazards return Saturday and Sunday as a pair of systems bring modest pressure rises and cold air advection over the Lake resulting in gusty N to NW winds upwards of 20-30 kts beginning Saturday morning through Sunday night. At this time, there is a low chance (30-50%) for a few gales to 35 kts mainly between Marquette and Whitefish Point. Winds fall back below 20kts Sunday night, and stay mainly below 20kts through early next week.

Northern Bay of Green Bay and northern Lake Michigan - Southerly wind gusts up to 15-20kts will be possible over the Bay beginning later this evening, but become more common over the Bay and northern Lake Michigan late tonight and linger through Friday as low pressure traverses the area. This results in waves building between 1-3 ft (greatest in the open waters closer to Lake Michigan). A brief reprieve in winds comes Friday night behind a weak cold front, however, two systems then dive into the area Saturday and Sunday, resulting in gusty north to northwest winds 15-25 kts through Sunday night. Wind gusts briefly fall back below 20kts for Monday before potentially increasing again into the midweek period.

MQT WATCHES/WARNINGS/ADVISORIES

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