textproduct: Detroit/Pontiac

KEY MESSAGES

- There is a chance for severe thunderstorms late this afternoon and evening, mainly along and north of I-69. Damaging winds, large hail and isolated tornadoes.

- The risk for severe weather exists again Monday and Tuesday mainly during the afternoon and evening. Warm and windy conditions will also prevail.

- Cooler conditions can be expected Wednesday and Thursday.

DISCUSSION

Ongoing surface analysis and trends show an increasingly more buoyant/unstable airmass advecting northward toward a quasi stationary front extending across the southern Saginaw Valley and thumb. This may provide a focus more more robust convective development later this afternoon/evening. Ascent will be aided by broad mid level height falls associated with an MCV that will track across nrn Lower Mi late this afternoon and evening. The latest RAP indicates surface based Cape nearing 2k J/kg feeding into the frontal boundary this evening. Respectable bulk shear and low level helicity values will favor supercells, with damaging winds, large hail and an isolated tornado remaining the primary severe weather hazards. Convective chances will decrease farther south due to weaker forcing.

Subtle short wave ridging will build across Lower Mi overnight in the wake of the MCS passing across nrn Lower Mi. This will suppress convective development late tonight into Mon morning. Remnant boundary layer moisture convergence along the frontal boundary around the Saginaw Bay and thumb region may support some localized fog. Although strengthening low level wind fields overnight will largely be elevated from the nocturnal boundary layer, model solutions indicate enough boundary layer flow to drive the front north of the forecast area by daybreak Monday, placing the entire forecast area in the warm sector. The light flow combined with elevated sfc dewpoints will warrant relative mild nighttime lows in the 60s.

Diurnal mixing will result in warm and windy conditions on Monday. While temperatures look to make another run into the 80s, the potential for late day convection supports leaning toward the lower end of the model guidance spectrum (low to mid 80s for highs). Convection timing and coverage will depend heavily on the upscale convective growth upstream tonight. There is reasonable agreement among the 12Z hi res suite that convectively induced short wave features will traverse Se Mi Monday afternoon/evening, coinciding with peak diurnal destabilization. The forced ascent would also erode the mid level capping inversion, resulting in scattered to possibly numerous thunderstorms. Weak to moderate instability with good cape density will result in a chance for severe storms, with damaging winds and large hail being the primary severe weather hazards.

Severe chances will be the forecast concern again on Tuesday associated with a cold front forecast to pass across Se Mi late afternoon/evening. This front will be associated with a more amplified mid level wave forecast across the northern Great Lakes region. Deeply sheared profiles within moderate instability will again support strong to severe convection. Warm and windy conditions will also prevail in the prefrontal environment. Model soundings indicate 30 to 35 knots in the mixed layer, which may result in wind gusts approaching 40 MPH outside of any convection. Strong high pressure will expand across the region in the wake of the front by Wednesday, resulting in cooler and dry conditions.

MARINE

Cold front has stalled over southern Lake Huron this afternoon, with southerly winds to its south and northeast winds to its north. Main marine concern this afternoon-evening is potential for strong to severe thunderstorm development along the front and/or lake breezes that have pushed inland from Saginaw Bay, Lake St. Clair, and Lake Erie. All modes of severe weather are in play. Lingering thunderstorms push north across Lake Huron tonight, although the severe threat wanes after sunset. Unsettled conditions continue for the first half of the week as warm and breezy southerly flow supplies plenty of instability to the Great Lakes. Wind gusts for the Lake Huron shoreline/Lake St. Clair approach 30 knots Monday- Tuesday, although an isolated gale force gust over Saginaw Bay Tuesday cannot be entirely ruled out. Small Craft Advisories are in effect for Monday and will be needed again Tuesday. Strong to severe thunderstorm chances exist both afternoons as well. A strong cold front Tuesday night results in a pattern shift for mid-week, bringing a quieter, more seasonable pattern to the Great Lakes.

PREV DISCUSSION

Issued at 108 PM EDT Sun May 17 2026

AVIATION...

A warm front located between KFNT and KMBS will be the focus for convective initiation this afternoon and evening, bringing the chance to see scattered to numerous thunderstorms. Probabilities to see thunderstorm activity will be higher across KMBS given the location of the front, but will retain the TEMPO in KFNT until radar and satellite imagery better define where initiation will take place. Confidence for showers and thunderstorms will be much lower for locations south, but cannot rule out some isolated development within the warm sector. Confidence is too low to retain the PROB30 for thunderstorms at this time. Otherwise a 4-6kft cu field will range from sct-bkn during daylight hours alongside mid to high based cirrus from upstream activity.

D21/DTW Convection...There will be a chance (15-20%) for an isolated thunderstorm between 20Z-24Z

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms this evening.

* Low for ceilings aob 5000ft this afternoon.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory from 10 AM to 10 PM EDT Monday for LHZ421-422- 441>443.

Lake St Clair...Small Craft Advisory from 10 AM to 10 PM EDT Monday for LCZ460.

Michigan waters of Lake Erie...None.