textproduct: Marquette

KEY MESSAGES

- Very hot conditions are expected again today with highs well into the 90s and heat index values near or over 100. Extreme Heat Warnings remain in effect until this evening as high dewpoints and poor overnight recoveries will increase cumulative impacts. Continue to practice heat safety measures.

- Temperatures moderate from Wednesday onward, with precipitation chances returning late in the week.

UPDATE

Issued at 304 AM EDT Tue Jul 14 2026

The going forecast remains on track this morning. An impressive expansive ridge sits directly atop the Midwest with a rare 600 dam 500 mb height contour analyzed over the WI/MN southern border. Closer to home, the UP remains sandwiched between stout high pressure centered over Iowa and a low pressure working into northern Quebec. The resulting pressure gradient is continuing gusty SW winds early this morning and temperatures struggling to fall below the mid 70s or even sub-80F where downsloping is occuring.

Another dangerously hot day is expected with widespread high temps peaking into the 90s to near 100. The Extreme Heat Warning will remain in effect for our entire CWA through this evening. Tonight, a weak cold front may attempt to fire off some showers and thunderstorms, but very dry midlevels and area wide subsidence gives little confidence in development or coverage.

DISCUSSION

Issued at 321 PM EDT Mon Jul 13 2026

Afternoon GOES water vapor imagery and RAP analysis reveal a strong upper level ridge of high pressure encompassing much of the CONUS from the Four Corners region to Lake Superior, supporting the hottest air mass so far this season and indeed one of the hottest on record by some metrics for portions of the Upper Great Lakes. RAP analysis shows 500 mb heights rising to 600 dam this afternoon from the Upper Mississippi River Valley into the UP, nearing or in some cases exceeding the climatological max for several locations around the region. Additionally, this morning's 12z atmospheric sounding from International Falls, MN reported an 850 mb temp of 28.4 C, which is the second highest reading on record dating back to 1948. This upstream air mass has continued to advect eastward into the UP this afternoon, corresponding to widespread temperatures in the 90s and heat index values in the 100s across the UP as of mid afternoon. Will have to keep a close eye on temperature readings through the rest of the day as several temperature records will be in jeopardy, including potentially the all time high temperature reading of 99 degrees at the NWS forecast office in Negaunee Township. In addition to the hot weather, strong low pressure deepening over Hudson Bay is helping to squeeze the surface pressure gradient and produce breezy conditions over the UP and Lake Superior into this evening. Fortunately, dewpoints in the 60s are generally keeping relative humidity values above critical fire weather thresholds, though some locations in the western UP may flirt with 30% RH through this afternoon.

Tonight will offer little relief from the heat as most locations around the UP only cool into the mid and in some cases upper 70s, again nearing the climatological max in terms of warm minimum temperatures. Mid and upper level conditions will begin to retreat some from today's historic values on Tuesday, but 500 mb heights above 590 dam and 850 mb temps of 22-25 C will still easily support highs in the 90s on Tuesday, maintaining a major heat risk across the UP for one more day. Given the cumulative impact of warm overnight lows and multiple days of highs in the 90s coupled with 60s dewpoints again pushing the heat index above 100 degrees, have opted to extend the Extreme Heat Warning through Tuesday evening across the area. Bottom line, people should take precautions to mitigate heat related impacts whenever possible through Tuesday. This includes staying hydrated, limiting outdoor time, and checking on those who are vulnerable to the heat including the elderly, children, and pets.

SPC has notably included the UP in the Day 2 general thunderstorm risk for Tuesday. Currently thinking shower and thunderstorm chances are low enough to keep out of the forecast given capping and subsidence that will still be in place under high pressure, but will keep an eye on this potential as there will be plenty of conditional instability available for an cell that does manage to form.

Temperatures will moderate towards more "normal" summer heat from Wednesday onward as the upper ridge is flattened out by persistent strong troughing over eastern Canada. This will yield highs generally in the low 80s near Lake Superior to around 90 over the south-central UP for Wednesday and Thursday, cooling further into mid 70s to mid 80s by Friday. Overnight lows will also return closer to seasonal norms in the 50s by Wednesday night. The forecast remains mostly dry through Wednesday, but the flattening of the upper level flow will pave the way for the next system bringing a higher chance for widespread rain and thunderstorms back to the area by late Thursday into Friday. Do not see signals for any significantly impactful weather in the long term forecast at this time.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 112 AM EDT Tue Jul 14 2026

VFR conditions are expected to generally prevail through the period as flow slowly becomes W/NW'rly today, with the lake breeze bringing winds out of the N/NE over SAW by the afternoon hours. As we become downwind of the wildfire smoke over far northern MN/northwestern Ontario, we may see some HZ/FU develop over the terminals late in the period, potentially impacting flight categories via vis reductions.

Some LLWS is being seen at SAW early this morning as there is just enough directional shear to qualify. As for IWD and CMX, only low- level turbulence is expected due to winds from the sfc to 2 kft being unidirectional.

MARINE

Issued at 321 PM EDT Mon Jul 13 2026

Southwesterly winds have increased to 20 to 25 kt across the western half of Lake Superior this afternoon as the pressure gradient tightens between surface high pressure to the south and deepening low pressure to the north. Look for winds to increase higher tonight into the 25 to 30 kt range while expanding over the central portions of the lake as well. Both HREF and NBM guidance highlight a 30-50% chance for some gale force gusts between the Keweenaw and Isle Royale this evening, but probabilities and coverage remain low enough to forego any gale headlines at this time. Small craft conditions will impact many of the nearshore zones tonight into early Tuesday as wave build to 4 to 7 feet across western and central portions of the lake. Winds then gradually diminishing through Tuesday and look to remain below 20 kt for most of thew rest of the week.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... Extreme Heat Warning until 10 PM EDT /9 PM CDT/ this evening for MIZ001>007-009>014-084-085.

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