textproduct: Marquette

KEY MESSAGES

- Scattered showers and thunderstorms develop this afternoon and evening along the Great Lakes lake breezes.

- Showers and thunderstorms become more widespread Wednesday morning through Thursday morning. There is a Slight Risk (category 2 of 5) of excessive rainfall and up to a Marginal Risk (category 1 of 5) of severe weather.

- Temperatures will remain above climate normal in the early week, and closer to normal mid-week.

UPDATE

Issued at 257 AM EDT Tues Jul 7 2026

The going forecast remains on track this morning. MRMS reflectivity mosaic shows a rather robust line of thunderstorms draped across MN, but with the northeast end (over western Lake Superior) deteriorating significantly more than the southwest end (towards the MN/SD line), these storms pose little to no threat to Upper Michigan, with the only particular hazard being a stray lightning strike for any boats over the open waters of the western lake.

At 500mb, flow looks quite zonal this week. This leads to a weather pattern close to normal or slightly warmer than normal with mostly weakly forced precipitation. However, weakly forced does not necessarily mean risk-free. With less subsidence thanks to the high pressure and upper ridge weakening, the HREF depicts up to 60 percent chances of rain showers this afternoon forced by the lake breezes off the Great Lakes. HREF mean SBCAPE this afternoon is over 1000 for much of the interior, so the more favored updrafts could become quite buoyant and result in thunderstorms. However, with meager 0-3km SRH (generally sub-100), expecting thunderstorms to be fairly disorganized and thus the severe potential is low. Still, if you have outdoor plans, check the radar first and when thunder roars, go indoors. With the added cloud cover from the morning storms and an increase in the cloud cover forecast from recent hi res guidance, have knocked down the high temperatures today a tad, but still expect slightly above normal temperatures today.

The other area of focus for this forecast period is Wednesday. A subtle 500mb shortwave and height fall will pass over the region through the day. With chances of showers overspreading the UP early in the morning, instability will be pretty weak except in the far south which has up to a 35% chance of over 500 J/kg of SBCAPE, though the shear profiles are looking more favorable as 0-3km SRH is in excess of 150 UP-wide on Wednesday with hodographs showing respectable curvature with height in the lowest 300mb (even if the speed shear is somewhat lacking). Thus, the severe potential is marginal at best, which the SPC outlook agrees with. What may be of greater significance is the rainfall forecast though, as significant PWAT is expected. The HREF shows some parts of the southern UP in excess of 1.75 inches of PWAT (over the 97th percentile of climatology). Of course not the entire PWAT profile will be realized, but still, the HREF is already showing chances of an inch of rainfall by 00Z Thursday at 40-70% along the MI/WI state line. Training showers and thunderstorms may become a threat as the flow aloft looks well- aligned with the surface boundary, so the WPC has the UP in a Slight Risk of excessive rainfall.

A quieter pattern then settles in for the late week and beyond as robust ridging sets up over the central CONUS (500mb heights above the 99th percentile of climatology over the Northern Plains by Sunday). This puts the UP in northwesterly flow aloft, which will initially keep temperatures close to normal, but as the upper ridge gets closer to the UP by early next week, the high heights lead to warmer temperatures, with the NBM deterministic even calling for 90s for the typical warm spots on Monday. Precipitation forecasts are too widely spread to divert from the NBM with this forecast package.

DISCUSSION

Issued at 346 PM EDT Mon Jul 6 2026 Amended at 257 AM EDT Tues Jul 7 2026

Today brings increasing chances of precipitation as the ridge decays eastward and a robust low propagates toward Hudson Bay. Accompanying this system, multiple subtle boundaries could lead to scattered thunderstorms in the west and south-central portions of the CWA in the afternoon and evening. A weak boundary associated with a trailing trough from the Hudson Bay low moves west to east throughout the day. From this boundary alone, CAMs agree that some small totals (<0.15") will reach the ground in the west and central areas. However, given conducive lake breeze conditions - the HRRR shows a Lake Superior breeze penetrating fairly deep inland by afternoon - anomalously high moisture will have multiple opportunities to initiate. HREF shows modest mean CAPE values between 1000-1500 J/kg in afternoon and evening, and soundings show elevated CAPE for locations in the west and south for this same time frame. With PWAT values between 1" and 1.5" per the EPS, some spots could experience isolated stronger thunderstorms and locally higher rain accumulations. However, given only 20-30 knots of bulk shear per the REFS, potential for severe storms remains low and the SPC has the CWA in the General Thunderstorms category.

Periods of rain are expected throughout Wednesday and into early Thursday. As the amplified ridge over Quebec breaks down today and tomorrow and the Hudson Bay low progresses east, gradient flow over CWA becomes strongly zonal. This sends anomalously high PWATs between 1.75" and 2" over the region by early Wednesday morning. At the same time, an upper level jet streak moves over region with a trailing lobe lingering over the area Weds evening, leaving the CWA situated in the jet streak's rear-right entrance region. With synoptic lift present and a moist atmosphere, rain is expected to move west to east beginning early Wednesday morning and continuing through Thursday morning. A moist atmosphere combined with a slow- moving theta-E boundary increases potential for heavy rain; in WPC's Day 2 Excessive Rain Outlook, the CWA is currently outlooked in the Slight (15%) category. NBM plan view 24h probabilities of exceeding 2" exist up to 20%, and the 90th percentile of 6-hour accumulations is over 1" in some locations. Thus, locally higher amounts of heavy rainfall may occur, most likely in the west and south. The northern 2/3 of the CWA is outlooked in SPC's General Thunderstorms category, and the southern 1/3 in Marginal, so potential severe storms on Wednesday is low.

The area dries out by midday Thursday as high pressure moves back in behind the Hudson Bay low, and temperatures should be relatively close to climate normal. Friday marks the beginning of a large ridge building over the Great Plains and extending from the Sierra Mtns to the Appalachians. Anticyclonic mid-level flow sends warm and dry desert air circling toward the Upper Midwest, resulting in very warm temperatures by Sunday.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 720 AM EDT Tue Jul 7 2026

VFR prevails this morning at all sites as weak -SHRA is impacting the vicinity of IWD but precip has yet to be recorded as of 11Z. Lake breeze showers and thunderstorms will be the weather pattern this afternoon, which will remain south of CMX but is up to 20% likely to impact IWD and up to 50% likely to impact SAW. Any precip will end by 03Z tonight, but the break will be brief as more widespread -SHRA and chances of -TSRA will impact all sites by the end of this TAF period. There is some uncertainty in whether the precip will be strong enough to impose a flight category drop, with some guidance suggesting 30-40% chances of MVFR at IWD and SAW and around 25% chance of MVFR at CMX, but confidence is too low to include in this TAF cycle. Expect mainly light winds except for the immediate vicinity of TSRA.

MARINE

Issued at 346 PM EDT Mon Jul 6 2026 Amended at 257 AM EDT Tues Jul 7 2026

Light winds prevail today. Eastern portions of Lake Superior may see higher southerly winds with gusts to 20 knots for a few hours early this morning as flow organizes ahead of a weak frontal boundary. This precedes periods of rain and thunderstorms this afternoon through Thursday morning. Winds may be higher near outflow boundaries, though severe storms are not expected. As high pressure builds back in on Thursday, winds lay down through Saturday afternoon.

MQT WATCHES/WARNINGS/ADVISORIES

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