textproduct: Detroit/Pontiac

KEY MESSAGES

- Scattered thunderstorms are likely this afternoon and early evening. Isolated storms may be strong to severe.

- Widespread rain and thunderstorms are expected Wednesday evening and Wednesday night. Heavy rainfall is likely which may lead to localized flooding, especially in urban areas. The potential also exists for severe weather, mainly south of I-94.

- Slightly below normal temperatures are expected through the week and next weekend.

DISCUSSION

Dry and cool conditions this morning give way to a slight increase in humidity and warmth compared to yesterday as an upstream low pressure system advects higher theta-e air in on a breezy southwest wind. An uncapped profile allows for convection to ensue early this afternoon as forcing for ascent increases in advance of the mid- level shortwave arriving from the west. A prefrontal trough appears to be a focus for convection to organize into a broken line in the 19 to 23z window, then the cold front offers a second round of convection between 23 and 04z tonight. Wind shear through the lowest 6 km is initially weak at around 20 kt but increases to around 30 kt, and MLCAPE is not particularly noteworthy around 1000 J/kg or less. Isolated strong to severe storms will be possible with inverted-V soundings and mid-level dry air supportive of wind gusts of 40 to 60 mph as the most probable threat.

A vigorous wave diving out of the mean troughing centered over Manitoba will drive a powerful low across the Great Lakes Wednesday night. Several solutions show a 500mb low closing off over Wisconsin, producing a sub-990mb surface low that is analyzed 4 to 5 standard deviations below normal for this time of year. Tremendous mass adjustment and lift will occur ahead of this wave with widespread rainfall spreading in late Wednesday afternoon into Wednesday night, followed by gusty winds Thursday. The main threats with this system appear to be heavy rainfall and flooding as well as damaging wind gusts. Deep moisture transport on the nose of the 60+ kt LLJ and through the column will quickly send PWAT to the 1.50 to 2.00" range and warm cloud layer depth to 12 kft, making for efficient rainfall production in any convection. Fast storm motion will be a limiting factor, but intense fgen along the W-E oriented elevated warm front will still support a corridor of heavy rainfall across the area. The most likely outcome will be rainfall totals ranging between 1 and 2 inches for much of SE MI, but upper tails of ensemble QPF guidance and even 16.00z REFS LPMM output hint at potential for localized totals in excess of 3 inches. Most of this is expected to fall between 8pm and 2am.

Will need to monitor the mesoscale environment late Wednesday night closely, as very strong forcing and wind shear will be in place. The limiting factor for severe weather will be instability given moist adiabatic lapse rates and static stability introduced by the feed of warm air at 850mb. Backed flow, high 0-1km SRH, and low LCL heights in the vicinity does bring concern for tornadoes if the warm front lifts northward into the southern counties. Damaging wind gusts would also be likely given the low-level kinematics. Still plenty of finer detail to gather from additional hi-res runs today and tonight, but initial runs this morning look to support heavy convection south of the state line that may suppress the surface front south. Available ML guidance, with confirmation from the day 2 SPC outlook, supports the conditional threat for severe weather mainly south of I-94, but possibly up to the I-69 corridor.

The longwave trough axis slowly passes overhead from Thursday into Friday night, maintaining cool weather for mid June standards. Chances for scattered afternoon showers and storms exist both days as daytime heating capitalizes on steep lapse rates and continued cyclonic flow. Saturday may be an opportunity for drier conditions as the jet stream lifts north and upper confluence gains traction, but additional PVA within the NW flow does still present a low-end chance for another diurnal flare-up of isolated, weak convection. Forecast confidence decreases considerably by Sunday and Monday as there will be multiple wave interactions in the vicinity. Overall, it does look favorable for a more active pattern to continue into next week.

MARINE

A Small Craft Advisory is in effect for Saginaw Bay and The Thumb nearshore for gusty winds and elevated waves. Drier conditions wane this afternoon with the arrival of a low pressure system and it's attendant cold front, leading to showers and thunderstorms for the central waterways later today. Convection should hold-off until after 1 PM and generally conclude before midnight as rainfall works from west to east. A brief break in activity ensues Wednesday as shortwave ridging quickly passes over the region, followed by a secondary stronger system Wednesday night into Thursday. More intense convection is possible with the second system, capable of damaging winds, and to a lesser extent, waterspouts and large hail. Seasonably strong gradient (non-thunderstorm) winds will accompany the low with prevailing speeds climbing above 25 knots as the center of the low approaches Lake Huron late Wednesday night. Gusts to gales are probable for some portion of The Lakes Wednesday night into Thursday, after shallow mixing profiles deepen slightly, and 40- 50 knot flow materializes within the lowest 3 kft. Winds decline a bit and organize out of the west Thursday evening through Saturday, accompanied by additional chances for showers.

HYDROLOGY

Scattered to numerous showers and thunderstorms are forecast this afternoon and evening. Most areas will receive a quarter inch or less of rainfall, and flooding is not likely today.

A seasonably strong low pressure system will then arrive late Wednesday, producing widespread rainfall with numerous heavy thunderstorms through Wednesday night. Rainfall totals ranging between 1 and 2 inches are likely for much of SE MI, and isolated areas may receive over 3 inches. Most of this rainfall is expected to occur in 6 hours or less, currently centered between 8pm and 2am. This rainfall may pose a flash flooding threat, mainly in urban areas, and rises on rivers and streams can be expected.

PREV DISCUSSION

Issued at 1153 PM EDT Mon Jun 15 2026

AVIATION...

Light SW wind maintains a flow milder air into SE Mi between Ohio valley high pressure and a low pressure system in northern Ontario late tonight. Dissipation of earlier cu/ac transitions to a more nocturnally driven but still VFR mid cloud pattern with some signs of virga on radar or a few sprinkles during the late night and early in the morning.

VFR holds during the mid to late morning as secondary low pressure develops on the Midwest cold front and moves toward Lower Mi. Increasing low level wind backs toward the south in response, gusting to around 25 knots, while carrying warmer and more humid air into the region. This sets the stage for scattered strong to isolated severe thunderstorms during the late afternoon and Tuesday evening.

D21/DTW Convection... The chance for thunderstorms is on the increase during the afternoon, beginning after 18Z and lasting into Tuesday evening. The potential for strong to severe intensity is greater after 21Z.

DTW THRESHOLD PROBABILITIES...

* Moderate for ceiling at or below 5000 ft Tuesday afternoon.

* Moderate for thunderstorms after 18Z Tuesday.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory from 10 AM this morning to 10 PM EDT this evening for LHZ421-422-441.

Lake St Clair...None. Michigan waters of Lake Erie...None.