textproduct: Detroit/Pontiac

KEY MESSAGES

- Next round of rain moves through the area between now and 8 AM. There is a slight chance of thunder with this band.

- A Heat Advisory is in effect again today for areas south of M-59. Heat indices peak near 100 degrees this afternoon.

- There is a Slight to Enhanced Risk for severe thunderstorms tonight, mainly between 8 PM and 3 AM. Damaging winds, large hail, and spin-up tornadoes are all possible.

- Not as warm and much less humid Friday through the weekend.

DISCUSSION

Isolated thunderstorm activity over the past hour or so has since exited into Ontario. More cohesive rain potential is on its way as remnants of an MCS move across southern Michigan this morning, with the northern edge of the rain shield right along the I-69 corridor. QPF amounts with this morning rainfall generally hold under a half inch before exiting the area after 12z (8am).

Hot and humid conditions return for the daytime hours, with heat indices in the upper 90s to near 100 degrees in the urban footprint. Mid-level height rises are not as aggressive as yesterday given convective perturbations from this morning, while convection has also cleared out low level moisture and has created quite a bit of cloud debris upstream. These factors create a more uncertain temperature/dewpoint forecast for the afternoon, with most areas likely to see heat indices capped in the mid to upper 90s (temps in the upper 80s-low 90s). The exception is the urban Detroit footprint where there is still an opportunity for the heat index to reach 100 degrees. Opted for a Heat Advisory for these areas despite borderline heat index values given Major risk for heat-related impacts (NWS HeatRisk tool) and wet bulb globe temperatures in the low 90s. Dry conditions expected through most of the day as ongoing convection pushes the instability reservoir further south of the state line.

Attention turns to the severe weather threat late evening and overnight (roughly 8pm-3am). Storms begin well upstream near low pressure that is currently over Kansas. This low will lift northeast throughout the day, in phase with a negatively tilting PV anomaly carving across the northern Plains. The strong synoptic forcing overlaps an area of impressive theta-e advection, initiating convection this morning that quickly grows upscale into a squall line reaching SE Michigan late this evening. Most of the instability currently over the Midwest/Great Lakes is getting cleared out by the MCS moving through Missouri and Illinois. This means instability will need to be restored across the entire region ahead of the line for it to survive this far east. The poleward motion of the surface low helps this process, with most models bringing the warm front/instability axis well into SE Michigan this evening. One thing to watch will be convective initiation along the front, similar to what we saw yesterday where isolated cells were able to break the cap ahead of the main line.

Should see the line accelerate into the instability plume through the evening, with most models placing it on our doorstep between 9pm-midnight. At this point it will have a very mature cold pool, which should be capable of surviving any weak nocturnal surface inversion, especially earlier in the night. If the line is able to maintain its full strength, this could be a high-impact severe weather event with potential for bowing segments of 70+ mph straight- line winds and embedded tornadic circulations. This is supported by a strong low level jet (40-50 knots) and impressive 0-1km SRH/low level hodograph curvature. SE Michigan is on the eastern fringe of the Enhanced Risk, given the tendency for storms to fall apart/become elevated overnight. Most hi-res models show the line decaying as it moves across SE Michigan, similar to what we saw yesterday, but with low predictability as to exactly when/where/if the line begins to weaken.

This line of convection will be driven by a strong cold front that sweeps across the area early Friday morning. Sharp moisture gradient and isentropic downglide behind the frontal passage brings an abrupt end to rain chances with skies quickly clearing around Friday morning. Cooler temperatures prevail with highs Friday around 80 degrees. Slight warming trend Saturday under a brief period of warm advection ahead of another cold front Saturday night. This system brings the next opportunity for showers and thunderstorms, followed by an even milder airmass early next week with temperatures capped in the 70s.

MARINE

Rain and a few thunderstorms this morning will exit the area around 12z (8 am local) in favor of drying conditions for most of the daylight hours. Southwest flow holds in place ahead of a strong cold front that will approach the Great Lakes late tonight into early Friday morning. This is associated with a low pressure system that reaches the Straits around 00z tonight. The cold front brings a line of strong to severe thunderstorms across the Great Lakes, with potential for wind gusts in excess of 50 knots and large hail. This front will pass through early Friday morning, bringing an uptick in westerly winds in its wake as well as a brief period of drier conditions to start the weekend.

HYDROLOGY

A moisture-rich environment remains in place today with additional opportunities for rain this morning and again late this evening and overnight. Progressive nature of expected rain and thunderstorms generally limits widespread flooding concerns, although heavy downpours with rainfall rates over an inch per hour will be possible. Localized flash flooding cannot be ruled out, but is mostly confined to low-lying, urban, or flood prone areas.

PREV DISCUSSION

Issued at 1202 AM EDT Thu Jun 11 2026

AVIATION...

VFR under mid and high convective debris clouds is accompanied by south to SW wind n the 5 to 10 knot range, which keep fog from becoming much of a factor until closer to sunrise. This is when showers that are expanding upstream at forecast issuance spread over SE Mi with scattered to numerous coverage. The extra boundary layer moisture supports MVFR fog and stratus through mid morning.

The terminal corridor is fully in the warm sector of low pressure spanning from northern Ontario into the Midwest during the day. Building daytime instability quickly lifts any lingering fog and stratus by mid morning. Heat and humidity set the stage for the next round of thunderstorms currently projected for later Thursday evening.

D21/DTW Convection... There is a chance for a stray thunderstorm within expanding clusters of showers during the late night. Additional storms then hold off until later Thursday evening.

DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 feet or less late tonight and Thursday morning.

* Moderate for thunderstorms late tonight and Thursday evening.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Heat Advisory from noon today to 8 PM EDT this evening for MIZ069- 070-075-076-082-083.

Lake Huron...Small Craft Advisory from 10 PM this evening to 10 AM EDT Friday for LHZ421-422-441.

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