textproduct: Detroit/Pontiac

KEY MESSAGES

- There is a Marginal to Slight Risk of severe intensity thunderstorms as coverage becomes numerous this afternoon.

- An Air Quality Alert remains in effect north of I-69 today due to wildfire smoke returning from the north this afternoon. A statewide Air Quality Alert has been issued for Sunday.

- Dry weather with cooler temperatures and lower humidity moves in by Sunday.

DTW THRESHOLD PROBABILITIES

* Moderate in ceilings aob 5000 feet today.

* Moderate in thunderstorms between 18z and 22z today.

PREV DISCUSSION

Issued at 1006 AM EDT Sat Jul 18 2026

UPDATE...

Mid-morning surface analysis shows a west-east oriented cold front easing southeastward across mid MI. Thunderstorms ahead of the front have thus far been sub-severe but outflow may provide a trigger for additional convection in the Thumb as CIN decreases the rest of the morning. Radar and satellite imagery also indicate fresh convective growth beginning to percolate along the front in Clare and Osceola Counties. These will be the areas to watch for development over the next couple hours.

The 12z DTX raob showed modest lapse rates through the column but with high near-surface moisture that will provide fuel for deep convection - observed MUCAPE is already over 2000 J/kg. Of note is a very dry layer between 750mb and 350mb that should initially inhibit stronger convection. RH will increase through this layer as moisture pools ahead of the cold front, and dry air entrainment should be less of a limiting factor for updraft strength past noon. DCAPE over 1000 J/kg and steepening low-level lapse rates continue to point to a damaging wind threat as the primary hazard today. Scattered coverage of strong to severe storms remains favored south and east of a line from Sandusky to Owosso mainly between 12p and 4p. Will note several 12z CAMs (with support from 00z and 06z runs) tend to target areas east of I-75 with the highest coverage of thunderstorms today - this appears to be tied to a corridor of higher moisture and elevated instability tracking through this area. Adjusted PoPs slightly to account for this trend, otherwise the going forecast remains in good shape.

PREV DISCUSSION... Issued at 341 AM EDT Sat Jul 18 2026

DISCUSSION...

A low pressure system tracking across Ontario, just north of Lake Superior will bring a chance of strong to severe thunderstorms today locally as the cold front drops through SE MI. Much of the guidance has remained fairly consistent the last couple runs in terms of the parameter space and storm potential, though the CAMs continue to offer the typical variety of scenarios ranging from a dry afternoon to multiple lines of storms. SPC Day 1 has remained unchanged as it transitioned from the previous Day 2 outlook. Even the Wind, Hail and Tornado risks remain unchanged at 15-30%, 5%, and 2% respectively. This is all reasonable taking account the instability and dynamics present with the setup today. The front will be over Mid MI around sun up, fighting capping and lack of instability so low risk of strong to severe early. Southwesterly flow will advect instability ahead of the front which the front will then compact as it pushes SE. Strong low level lapse rates (but weaker in the mid levels) along with daytime heating should help a few storms break the cap out ahead of the front. CAPE builds as the front sinks toward the Metro Detroit area peaking around 2500-3000 J/kg with bulk shear increasing to around 35-40 knots later in the afternoon. Hodographs initially have some turning before low level jet perks up later making longer, straighter hodographs. This would lead to any isolated cells merging and becoming linear through most of the event. Damaging wind will be the main threat with hail and isolated tornadoes possible as well. Very moisture rich environment with PWATs around 2 inches and surface dewpoints in the low to mid 70s will lead to efficient rain makers, but a fast storm motion around 40-50 mph should help offset any flooding risk with progressive storms. Timing still looks to be mainly in the noon to 4pm window with an hour or so buffer on either side.

High pressure builds back into the region tonight through Sunday with northerly winds tonight bringing cooler and drier air into the area. There is a chance some smoke could get pulled back over the region, but unsure as to how much would be surface based verse elevated so will be something to watch. Models show the plume of smoke setting up more to our west by the end of the weekend.

The ridge breaks down locally and rebuilds over the western conus through the first half of the week. This put the jet and northwesterly flow over the region presenting a couple opportunities for storms mid week. Troughing over the region will help keep temps down, with highs in the 70s and lower 80s.

MARINE...

Still monitoring upstream convection associated with weak low pressure systems approaching northern Lower Michigan and the lower Ohio Valley. Some of this activity should reach Lake Huron late this evening and early tonight. Latest Hi-Res models indicate a weakening trend for these showers and thunderstorms, once they reach the waterways. A warm front lifts into the central Great Lakes this evening and overnight marking a south-southwesterly wind shift which pushes the wildfire smoke plume back into Canada, improving visibilities. A secondary, and more robust, low pressure system passes through The Straits and across northern Lake Huron Saturday morning. This drags an attendant cold front through the region with time, causing winds to veer northwesterly. Pre-frontal (southwesterly) gusts over Saginaw Bay are now expected to exceed 25 knots, therefore a Small Craft Advisory is in effect. Extensions are possible for the rest of the Lake Huron nearshores with later updates to account for stronger post-frontal gusts during the afternoon hours. Additionally, isolated brief gusts to gales cannot be ruled out over central Huron later on Saturday, but confidence is too low for a Gale Warning. High pressure then builds back into the region late Saturday and Sunday supporting drier conditions and prevailing winds below headline criteria for rest of the weekend.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement until 10 PM EDT this evening for MIZ049.

Lake Huron...Small Craft Advisory until midnight EDT tonight for LHZ421-422.

Small Craft Advisory until 4 AM EDT Sunday for LHZ441>443.

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