textproduct: Detroit/Pontiac

KEY MESSAGES

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

- There is a Marginal Risk for severe thunderstorms this evening and overnight. Isolated damaging winds are the main threat.

- There is a Slight to Enhanced Risk for severe thunderstorms Thursday night. Damaging winds, large hail, and spin-up tornadoes are all possible.

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

DISCUSSION

Departing PV anomaly noted over northern Lake Huron this morning via NT microphysics imagery, with most of the low level moisture concentrated around the low in northern Michigan. Clearer conditions observed over the southern half of the lower peninsula in part due to a slow exit of nocturnal convection/cloud debris. Strong subsidence signature observed upstream, which will move over top a moist boundary layer (dewpoints in the upper 60s-low 70s) and afford a brief window around sunrise for fog and/or low stratus development. This should mix out quickly after day break in favor of clearing skies.

Weak mid level height rises expected to maintain subsident profiles through much of the day. This allows plenty of solar insolation to support high temperatures into the low 90s. Dewpoint gradient from north-south across the cwa thus responsible for the spread in heat indices, ranging from upper 90s for the Saginaw Valley/Thumb to 100 degrees south of M-59. Subsidence also establishes a capping inversion from 5.0-15.0 kft agl through much of the day, preventing convection from disrupting diurnal heating. The Heat Advisory for the Detroit Metro area thus remains unchanged.

Next opportunity for strong-severe thunderstorms arrives this evening-overnight. Subset of solutions break the cap early this evening, although this scenario seems less likely given the absence of moisture advection/organized ascent. Thunderstorm chances then increase after 00z with the arrival of the first of a series of potential decaying MCSs overnight. All of these complexes develop along the surface trough that moves from the Plains into the Upper Midwest today before propagating into the downstream instability pool. First of these MCSs is the most likely to pose a severe threat to SE Michigan, but will struggle to maintain cold pool strength as it encounters subsidence and waning daylight. If the complex holds together, damaging winds are the greatest threat with hail as a secondary threat. While instability struggles, environmental wind fields will actually become more favorable overnight with increasing SW low level jet winds and mid-level flow. Thus cannot entirely rule out low level rotation as hodographs gain curvature.

Low predictability in additional shower/storm chances after the lead MCS overnight, which depends on if instability can rebound over the Upper Midwest this afternoon and generate more convection along the surface trough. Thus have PoPs continuing overnight, although with limited severe potential as the first MCS clears out instability.

Thursday begins in similar fashion to today as post-convective subsidence lingers while mid-level heights build modestly. It will be another day of heat and humidity with highs in the low 90s and heat indices again touching 100 degrees (Heat Advisory threshold) while a capping inversion limits thunderstorm potential during the day. Severe weather threat will be looming however as a squall line develops along the MS River Valley in the afternoon and accelerates toward Lower Michigan Thursday night. SWODY2 has SE Michigan split between an Enhanced Risk west of I-75 and a Slight Risk east. Several factors have to align in order for the line to impact SE Michigan at its full intensity, with a necessary condition being the northward expansion of the instability axis into an otherwise dry/stable column. With plenty of instability, this line has potential to produce damaging winds over 70 mph, spin up tornadoes, and large hail across SE Michigan with a time of arrival after midnight. However, if advection is disrupted this could mean the line falls apart before reaching us or even dives south of Michigan altogether.

The system's cold front sweeps through early Friday morning, bringing a cooler pattern to the Great Lakes Friday through next week, reinforced by another cold frontal passage Saturday night. Highs Friday-Saturday in the 80s will drop into the 70s Sunday into early next week. The next chance of showers/storms occurs with the frontal passage.

MARINE

A weak low pressure system will depart Lake Huron this morning, leaving a frontal boundary stalled across the central Great Lakes. Very humid air in place will maintain pockets of dense fog across the cool open waters of Lake Huron and a Dense Fog Advisory is in effect this morning. A lull in shower and thunderstorm activity is expected much of the day with light westerly winds that back to southerly tonight as the stalled front lifts back northward. A disturbance arrives tonight, bringing the next window for showers and storms, some of which may be severe with wind gusts in excess of 50 kt and large hail. A similar setup will exist for Thursday night ahead of a cold front. 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 and Thursday with multiple opportunities for showers and thunderstorms over the next two days. Progressive nature of expected 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 1203 AM EDT Wed Jun 10 2026

AVIATION...

A stray shower or thunderstorm in the DTW area is exchanged with fog and stratus expansion across the area during the late night. Solid IFR ceiling and fog in northern Lower Mi improves slightly into low end MVFR while downsloping into the MBS area. These clouds attempt to fill in toward the south while loosely confined by the diffuse surface trough settling into the FNT to PTK area, trailing the northern Great Lakes surface low moving into Ontario by sunrise. Observations leading up to midnight indicate open sky south of the trough makes borderline MVFR/IFR fog more likely from PTK to the DTW corridor considering wet ground and saturated boundary layer conditions as rain ends toward 06Z.

The surface trough begins a move back northward to aid improvement of stratus and fog during the morning. The trough responds to new low pressure developing in the upper Midwest that reinforces heat and humidity across southern Lower Mi which leads to broken VFR ceiling for the afternoon. The air mass supports a stray late day thunderstorm however the bulk of new storm activity is projected for later Wednesday evening.

D21/DTW Convection... Thunderstorm clusters move to the south and east of DTW right around the start of the 06Z forecast. No additional activity is expected through afternoon Wednesday.

DTW THRESHOLD PROBABILITIES...

* Moderate for ceiling aob 5000 feet Wednesday.

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...Dense Fog Advisory until 11 AM EDT this morning for LHZ361>363- 462>464.

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