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.

DTW THRESHOLD PROBABILITIES

* High for ceiling aob 5000 feet this morning. Moderate this afternoon.

* Low for thunderstorms late this afternoon into tonight.

PREV DISCUSSION

Issued at 440 AM EDT Wed Jun 10 2026

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.

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.