textproduct: Detroit/Pontiac

KEY MESSAGES

- Notably warmer and more humid conditions will peak Monday and Tuesday, with afternoon temperatures reaching the mid to upper 80s.

- The potential exists for thunderstorms to become severe this afternoon and evening, capable of producing damaging winds to 60 mph, large hail and isolated tornadoes.

- The risk for severe weather exists again Monday and Tuesday mainly during the afternoon and evening hours, with strong winds, large hail and heavy rainfall possible.

UPDATE

A very well defined meso scale convective vorticity maximum (MCV) now rotating from NE Iowa into SW Wisconsin will track across northern Lower Michigan late this afternoon and evening. Expectation are that the southern edge of the mid level height fall region will move across the Saginaw Valley and thumb region this evening, supporting a broad region of large scale ascent. Meanwhile, warm sector temperatures in the 80s with dewpoints in the 60s will contribute to weak to moderate instability expanding northward today, interacting with a quasi stationary front draped across the Saginaw Valley and thumb. This will contribute to at least scattered convection.

Very steep mid level lapse rates on the order of 7.5 to 8 C/km will contribute to 0-3km MU Cape on the order of 2k J/KG. Various hi res solutions indicate SB Cape values ranging from 1200 to 2k J/kg pooling along the aforementioned surface front. This along with high 0-3km storm relative helicity values and an enhancement to the mid level wind fields along the southern edge of the MCV (producing 0-6km bulk shear values of 45 to 60 knots) will support supercells and all modes of severe weather hazards (large hail, damaging winds and isolated tornadoes). Given the good elevated CAPE density, even locations a bit farther north of the surface front stand a chance for damaging winds and large hail. The chances for thunderstorms and thus the overall severe weather risk will decrease south of the I-69 corridor where forced ascent will be much weaker or non existent. The updated SPC Day 1 convective outlook has increased the severe risk to slight north of the I-69 corridor and has introduced an isolated risk of tornadoes.

PREV DISCUSSION

Issued at 555 AM EDT Sun May 17 2026

AVIATION...

Predominately VFR conditions will prevail through this TAF period as increasing moisture brings higher coverage of mid clouds with some scattered low clouds possible. A warm front lifting through Michigan will present a chance for scattered showers and thunderstorms this afternoon and evening. The greater chance to be impacted by this activity will be across MBS and FNT with a lower probability towards Detroit, though cannot completely rule out an isolated thunderstorm this evening towards the Detroit area. Frontal boundary will make for variable winds at times throughout the day with a more steady south wind developing tonight. Gusty southwest winds expected by mid-late morning tomorrow.

D21/DTW Convection...An isolated thunderstorm is plausible by this evening, but better potential will be across the Saginaw Valley.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms this evening.

* Low for ceilings aob 5000ft through Sunday.

PREV DISCUSSION... Issued at 305 AM EDT Sun May 17 2026

DISCUSSION...

Early morning sfc analysis shows a southward propagating frontal boundary marked by slightly cooler and drier conditions settling into the Saginaw valley and northern thumb regions. To the south, prevailing low level southwest flow sustaining weak low level moisture advection within the backdrop of an already seasonably warm thermal profile. Existing frontal boundary will effectively stall locally today, most likely somewhere within the I-69 to M-46 corridor based on a general consensus of model output. The boundary interface will offer the greatest focus for potential diurnal convective development this afternoon and evening, as supplemental forced ascent augments moderate boundary layer destabilization to overcome lingering capping issues. An additional focus possibly tied to a mid level speed max projected to race northeast from northern IL into northeast lower MI late today. A glancing shot of deeper ascent with this wave could assist in convective initiation and maintenance again targeting areas north of I-69. There remains a smaller subset of model solutions that provide a lower probability for development within the area of greatest instability residing south of the boundary - MLcape 1000-1500 j/kg metro Detroit and points south. Plausible scenario exists for a convective remnant from ongoing activity well upstream tonight to spill into the corridor, but certainly carries much lower confidence and will continue to monitor evolution going forward. Warm sector otherwise lacking in tangible forcing today. Forecast edges the higher rainfall probs toward the north. An isolated severe risk still highlighted within the latest SPC Day 1 outlook, accounting for the possibility for a more organized updraft or two to support larger hail and gusty winds. A noted uptick in 0-6 km bulk shear will emerge north of the frontal boundary as the aforementioned wave tracks by, but with low level winds still generally weak. Svr threat window mid afternoon to early evening.

Higher magnitude warmth by May standards firmly entrenched for the early week period, as deep layer southwest flow governs conditions east of larger scale height falls noted over the west-central conus. Highs projected to reach the mid to upper 80s both Monday and Tuesday. Unclear signal yet on convective potential Monday afternoon and evening, owing to a still ill-defined forcing field carrying some reliance on behavior of upstream convection tonight. A highly unstable late day environment, yet perhaps weakly capped. Conditional setup on realizing meaningful forced ascent, with a plausible scenario for most locations to remains dry. Wind fields overall remain rather lackluster in terms of strength, both at the lower levels and at a greater depth, but could see a localized/brief increase should a stronger mid level/convective wave move through. Local area highlighted within the latest Day 2 SPC outlook with a Slight/Marginal risk designation, with greater probability across the Saginaw valley. The ambient environment virtually unchanged heading into Tuesday. Late day or evening convective organization and expansion plausible along either/both the pre-frontal trough or cold frontal boundary. Improving magnitude of the wind field with time suggests greater potential for storm organization this period.

A stretch of cooler, drier and more stable conditions will emerge Wednesday behind the front. Low to mid level ridging will maintain these conditions through the late week period. Projected temperatures at this stage expected to arrive on the cooler side of average - highs generally in the 60s. Return flow on the backside of the departing high brings a warming trend again next weekend.

MARINE...

A frontal zone stalls over southern Lake Huron today, with northwest flow north of the front and warm southerly flow to the south. This boundary will be the focus for shower and thunderstorm development this afternoon-evening. Isolated strong to severe storms are possible, with winds in excess of 35 knots and large hail to an inch being the main severe concerns. The front then lifts north as a warm front tonight allowing southerly flow to expand across all of Lake Huron. The southerly flow regime holds steady through mid-week and will draw an unstable airmass into the region, supporting several rounds of showers and thunderstorms for the first half of the work week. An enhanced low level jet generates widespread breezy conditions, with gusts peaking aoa 30 knots close to the shoreline. Small Craft Advisories will likely be needed Monday-Tuesday. Gust potential decreases quickly offshore due to cool water temperatures and therefore stable low level conditions. A cold front then tracks through the region mid-week, bringing a bout of quiet and seasonable conditions.

DTX WATCHES/WARNINGS/ADVISORIES

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