textproduct: Detroit/Pontiac

KEY MESSAGES

- Warm and humid conditions exist today and Tuesday which support the risk of severe thunderstorms each day, mainly during the afternoon and evening hours. The strongest storms are capable of damaging wind, large hail, and isolated tornadoes.

- A cold front Tuesday night ushers in dry and cooler weather for Wednesday and Thursday.

- The next chance of rain arrives Friday and Friday night.

DISCUSSION

Severe Thunderstorm Watch 221 is in effect until 800 pm for the mature MCS inbound into SE Mi. Damaging wind gusts of 70 mph or greater have been reported and remain the primary hazard as the line tracks across SE Mi. Instability trends remain on track as full morning to early afternoon sun lifted temperatures to near 90 all areas. Model MLCAPE up around 2000 J/kg in HREF mean and RAP projections of hourly mesoanalysis add confidence to persistence. The system is already demonstrating benefits of the locally enhanced wind shear profile supplied by the parent MCV resulting in a mature linear convective mode now expected to maintain organization while crossing SE Mi. Storms exit eastward into Ontario by 00Z at or before watch expiration.

Another round of severe thunderstorm potential for Tuesday is set up by Midwest low pressure as it moves into upper Michigan while pulling a cold front through the central Great Lakes. SE Mi remains firmly in the warm sector of this system throughout the day with early to mid evening cold front timing offering time for instability to become sufficient. Morning clouds and a stray shower likely slow the pace of surface heating compared to today, however model projections of MLCAPE place 2000 J/kg in reach by 21Z Tuesday afternoon, especially toward the Ohio border. This occurs in a very similar wind profile compared to today in terms of moderate unidirectional shear except with a deeper 40-45 knot layer through 500 mb. Storm initiation timing is the primary uncertainty as shown in the wide range of hi-res model solutions that collectively suggest a later afternoon consensus. Later timing equates to less impact to SE Mi in terms of coverage area and also a more isolated severe threat before storms can better organize while the cold front moves through the area.

Frontal passage Tuesday night, before midnight, sweeps storms out of SE Mi and sweeps in cooler air for the mid week period. A broad area of surface high pressure and short wave ridging ensures below normal temperatures but dry weather during this time period as well. Central Plains to Ohio valley low pressure then brings the next round of showers into Lower Mi later Friday and Friday night.

MARINE

Attention to the near-term forecast will focus on the ongoing line of thunderstorms that extend across central Michigan. This line will pass across the eastern Great Lakes this evening and will bring heavy downpours, frequent lightning, and strong to severe weather. Strong to severe thunderstorms will be capable of producing wind gusts aoa 50 knots for all of the open water locations. Hail to an inch and/or a waterspout cannot be ruled out but are secondary hazards for severe weather. Prior to this line of thunderstorm arriving, isolated to scattered thunderstorm activity will be possible. A Severe Thunderstorm Watch is in effect until 8 PM EDT.

Outside of any thunderstorm activity, breezy southwest to south flow will persist, bringing non-thunderstorm gusts on the order of 20 to 25 knots. The main line of storms will exit late tonight but isolated to scattered showers and thunderstorms will be possible overnight. Renewed strong to severe thunderstorm chances will again be possible tomorrow afternoon and evening which will bring additional chances to see all storm hazards included wind gusts aoa 50 knots. These stronger storms will be most favorable from central Lake Huron and locations south. Outside of thunderstorms, gusts to 25 knots will again be possible during daylight hours. Re-issuance of Small Craft Advisories will be likely.

PREV DISCUSSION

Issued at 158 PM EDT Mon May 18 2026

AVIATION...

Conditions deteriorate this afternoon and evening as a line of strong to severe thunderstorms moves through the airspace. VFR ceilings and visibilities drop sharply along the interface of the convective line with temporary IFR conditions likely. Upstream observations and local storm reports indicate gusts in excess of 70 mph are possible with this organized line. Current trajectories reveal storm motion of approximately 45 mph, forecast to move through the terminals between 20Z and 23Z. A conditionally unstable airmass is allowing for a few pre-trough storms to develop ahead of the line with low confidence that these storms survive across the airfields. However, did move up the TEMPO period for the Metro terminals to account for the possibility of slightly earlier discrete activity. Limited model signal for widespread redevelopment late this evening behind the line, although better chances exist at MBS. Winds decrease slightly overnight, holding from the southwest into Tuesday with a mainly dry start and

D21/DTW Convection...Most likely time-frame for thunder will be from 20-22Z. A period of IFR visibility will accompany the line of storms. Potential for additional thunderstorms has decreased for Tuesday afternoon/evening, but a chance remains.

DTW THRESHOLD PROBABILITIES...

* High for thunderstorms this afternoon and early evening, then low- medium for thunderstorms Tuesday afternoon/evening.

* Medium for ceilings at or below 5000 ft with thunderstorms this afternoon and evening.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None.

Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422- 441>443.

Lake St Clair...Small Craft Advisory until 10 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...None.