textproduct: Marquette

KEY MESSAGES

- Rain showers and a few isolated thunderstorms along the lake breeze today.

- Tonight through Tuesday morning will be dry and cool, and temperatures should remain below normal this week.

UPDATE

Issued at 238 AM EDT Sun Jun 21 2026

The going forecast remains mostly on track this morning as the last of the Saturday showers has dissipated and GOES-East Nighttime Microphysics just shows scattered upper level clouds and a few patches of low level fog (verified by isolated METARs such as at IWD, IMT, and EGV showing reduced vis). Fog will be the main story of the morning as RAP analysis shows a very slack pressure gradient across the Upper Midwest. At 500mb, a shortwave over the Central Plains is projected to miss the Great Lakes to the south, though high pressure is struggling to form as the UP remains downstream of a closed low over far northwestern Ontario. The lack of a strong pressure gradient is leading to mostly light winds and with only scattered cloud cover and a moistened boundary layer from the earlier rain showers, the ingredients are in place for some dense fog, though models are widely spread on the coverage and intensity of such fog. LAMP guidance has trended downwards from this time yesterday about the fog potential, though the HREF still carries up to 40% probabilities of visibility falling below half a mile especially over the eastern two thirds of the UP. Will keep the "patchy" wording from the previous forecast, but will monitor satellite and METAR trends if an advisory becomes necessary for the Sunday AM commute.

For this afternoon, the HREF continues to show rain shower formation along the lake breeze this afternoon, so will continue to carry the lake breeze PoPs from the previous forecast. Mean SBCAPE looks to be around 250-300 J/kg, though with flow being generally sub-15kt in the lowest ~300mb of the atmosphere, if that instability is fully realized into a thunderstorm, its strength will be sub-severe. Expect highs to be lower than normal (around 70) as being in the neighborhood of the closed low aloft is keeping 500mb heights around the 20th percentile of normal and flow at that level still carries some cool northerly component (even though over time it becomes more zonal).

Dry weather is then forecast tonight through Tuesday morning as the closed low aloft shifts east of the UP and ridging over the Plains causes high pressure to build. The next chances for widespread precip look to be late Tuesday into Wednesday as the GEFS shows a cluster of 1010-1015mb low pressures cutting from North Dakota to Wisconsin, but confidence is too low to deviate from the NBM much at this time.

DISCUSSION

Issued at 321 PM EDT Sat Jun 20 2026 Amended at 238 AM EDT Sun Jun 21 2026

With the robust Hudson Bay/Canadian low finally moving toward the North Atlantic, weak surface ridging begins to build in today as mid-level flow trends zonal. Heights over the region remain anomalously low as another mid-level, closed low drops down toward the CWA from western Ontario. This low is shunted to the north as the remnants of Saturday's jet streak move from meridional flow toward zonal and propagate eastward. During this time, PWATs also remain anomalously low for this time of year, between 0.5" and 0.8", according to the EPS. Thus, today and Monday look to be drier, with little to no accumulations, and still cool. Both days can expect highs in the mid 60s to low 70s, and lows down to 40 in the interior, and high 40s closer to the Great Lake shorelines.

By Tuesday morning, ensembles show a swath of high pressure extending from Ontario to the Midwest firmly in place. This is followed quickly by a weak surface low traveling from Saskatchewan and reaching MN/WI by Tuesday night. Along with this system, the UP could see rain and thunderstorm chances late Tuesday into Wednesday, though no serious impacts are expected. The cool trend is expected to continue through the week, as the ECWMF's EFI shows anomalously cold maximum and minimum temperatures through Friday.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 734 AM EDT Sun Jun 21 2026

FG that has impacted SAW and IWD this morning is currently in the process of dissipating and should not be a factor for the rest of the morning. Winds will be light and variable today, especially in the vicinity of the Lake Superior lake breeze, which is up to 50% likely to cause -SHRA at SAW between 18Z and 00Z. Otherwise, the only other aviation impact for this TAF period is the potential for redevelopment of FG overnight tonight, which is only 10-15% likely at IWD and CMX, and around 25% likely at SAW, so have left mention of FG out of the TAFs at this time, but future TAFs may include TEMPO groups for FG if forecast confidence improves.

MARINE

Issued at 321 PM EDT Sat Jun 20 2026 Amended at 238 AM EDT Sun Jun 21 2026

Light, generally northerly flow with winds and gusts <10kt prevail on Lake Superior and Bay of Green Bay through Thursday. Monday afternoon and night, the eastern part of Lake Superior may experience NW'ly gusts to 15 kt, and western Lake Superior may see NE'ly gusts on Wednesday during the day. Significant wave heights are expected to be mostly <1ft on Lake Superior, occasionally reaching 2ft through Thursday, and well below 1ft on the northern part of the Bay of Green Bay except for a brief period during the second half of Monday when they may reach 1.5ft.

MQT WATCHES/WARNINGS/ADVISORIES

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