textproduct: Detroit/Pontiac

KEY MESSAGES

- There is a chance for another round of showers and thunderstorms as a cold front moves through the region tonight.

- Dry and a little cooler weather will dominate the mid week period.

UPDATE

Atmospheric conditions are recovering from the substantial period of wake subsidence that trailed the afternoon MCS across the southern Great Lakes. Increasing coverage of convection to the north and west is centered around the northern Great Lakes cold front and its connection to WI surface low pressure. The parent mid level short wave also provides a broader environment of at least weak vertical motion. These larger scale features combine with moisture laden MLCAPE lingering in the 1500-2000 J/kg range to favor increasing coverage of showers and thunderstorms as the surface low and front sweep across Lower Mi. There is lingering support for organized storms with about 40 knots of NW flow at 500 mb, but perhaps limited by how much updrafts can remain surface based along and ahead of the surface low track. The scenario may favor an increase in coverage while intensity holds below severe thresholds. Assuming sufficient coverage, then there is also a heavy rainfall component to consider along and north of the surface low track given how the front settles southward while the low moves eastward along it effectively producing a slower moving pattern. Best estimate on the surface low track is along the I-69 corridor into southern Ontario by about 3 am followed by a diminishing trend in showers/storms through sunrise.

PREV DISCUSSION

Issued at 705 PM EDT Mon Jul 27 2026

AVIATION...

The storm complex to the SW tracking south places southern Lower Mi between it and the cold front across the northern Great Lakes this evening. Surface wind across SE Mi was enhanced in the wake of the storms during late afternoon as stratiform rain ended, which has now settled into a steadier SW wind ahead of the WI surface low. This low moves into Lower Mi and pulls the northern Great Lakes cold front southward this evening and into Ohio by sunrise. Thunderstorm trends will be monitored as these pressure features move through the region while surface based instability recovers and/or remains elevated. The low and cold front also become the focus of borderline IFR/MVFR ceiling that shows expansion during the night through early morning, especially as cooler air surges in on increasing northerly wind after the frontal passage. The cooler air also becomes less humid by Tuesday afternoon, and this helps lift ceiling into scattered VFR coverage from mid afternoon into Tuesday evening.

D21/DTW Convection... Attention has shifted to the northern Great Lakes cold front in evaluation of thunderstorm potential tonight. This front enters the northern fringe of D21 shortly after midnight and thunderstorm trends will be monitored for southward persistence as the front enters the area.

DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 feet or less tonight. High by Tuesday morning.

* Low for thunderstorms overnight.

PREV DISCUSSION... Issued at 405 PM EDT Mon Jul 27 2026

DISCUSSION...

Convection was targeting Southeast Michigan from several angles this afternoon. The complex originating from the western UP/Wisconsin spilled into southwest Lower, merging with a line of storms that formed rapidly/linearly near the western shores of Lake Michigan. Near-term confidence is rising that all these storm interactions will miss the local area, based on current trajectories. Regional radar trends alone continue to support avoidance of the most impactful convection, with the strongest activity holding just west of the CWA. This keeps the most robust updrafts over the GRR and IWX domains, reflecting an overall diminishing pattern for thunder as advertised in the latest Hi-Res runs given a tendency for upstream convection to steer southerly.

From an environmental perspective, the synoptic drivers are absent the locations of ongoing convection. The cold front(s) remain displaced well off to the north and west while weak capping persists locally. 27.18Z KDTX RAOB indicates significant cap erosion compared to the prior measurement, but still not a state of free-convection which explains the lack of convection. Surface dewpoints are quite a bit lower than those upstream where storms fed off values in the upper 70s to mid 80s. Add to that ample cold air aloft and an uncapped environment. Note that 27.12Z ML products have aggressively backed off severe threats, taking into account some basis of muted resolved diurnal convection. Some CAMs try again to get another round of organized storms through tonight (see 18Z HRRR), therefore cannot rule out potential through the early overnight hours. Conditional severe threat remains, should storms finally materialize, but would favor elevated storms given the distribution of instability aloft. Based on the abysmal performance of NWP handling local convection during the last 30 hours, latest PoP adjustments are a low confidence 35 percent Chance between now and 06Z. Baseline blended guidance of 90 percent were too unreasonable. Satellite trends currently show a subsidence wake/dry slot moving in from northern Michigan, limiting potential during the evening time- frame.

A mostly dry start is expected Tuesday morning as the jet streak aloft crosses Lower Michigan. Geopotential heights initially hold steady before gradually rising during the afternoon hours. Embedded weak vorticity signature should be inconsequential given the dryness of the column and warming mid-level profiles. 850 mb temperatures will trend inversely, cooling into the low teens. High temperatures should be capped in the upper 70s to lower 80s as flow turns northerly during the day, modified by Lake Huron water temperatures in the 60s. Lower column anticyclone emerges over the Upper Midwest Tuesday night with subsidence building overhead. This should make for clearer skies and a seasonably cool night as dewpoints fall into the 50s.

High pressure tendency becomes established over portions of the Great Lakes through midweek favoring a mainly dry forecast and breezy afternoon periods. Temperatures gradually rise toward climo by the end of the week as surface flow flips southerly. Next opportunity for organized precipitation comes during the weekend.

MARINE...

A low pressure system over Wisconsin progresses across the central Great Lakes this afternoon and evening. Potential for scattered to numerous thunderstorms is maintained across marine areas, especially as the cold front tracks through late this evening and overnight. The main threat with any storms will be wind gusts in excess of 35 kt and large hail. Post-frontal NNW wind will increase early Tuesday morning and peak in the afternoon at 15 to 25 kt, with potential for gusts to 30 kt across the southern basin of Lake Huron. This will result in building wave heights, and Small Craft Advisories have been issued. High pressure builds across the western Great Lakes on Tuesday and Wednesday, maintaining a northerly gradient and potential for continued Small Craft Advisory conditions across southern Lake Huron. The high will slowly advance eastward Thursday and Friday, ensuring dry conditions with lighter wind.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None.

Lake Huron...Small Craft Advisory from 8 AM Tuesday to 4 PM EDT Wednesday for LHZ421.

Small Craft Advisory from 10 AM Tuesday to 4 PM EDT Wednesday for LHZ441>443.

Lake St Clair...None.

Michigan waters of Lake Erie...None.