textproduct: Detroit/Pontiac

KEY MESSAGES

- Several rounds of showers and a few thunderstorms expand in coverage this evening and early tonight; isolated thunderstorm gusts to around 50 mph possible.

- Below normal temperatures return for Wednesday with scattered showers, mainly over The Thumb and Lake Huron coastal communities.

- A warming trend beginning Thursday lifts temperatures into the upper 70s to lower 80s by this weekend with another opportunity for showers and thunderstorms.

DISCUSSION

A progressive shortwave trough digs across the Upper Midwest and into the Great Lakes today, displacing the preceding anticyclonic feature. The first wave of showers, generated via isentropic ascent within the elevated warm front, has struggled to overcome a very dry boundary-layer leading to midday virga signatures per KDTX radar. Some surface obs have now reported -RA, but rates are very minor marked by unrestricted visibilities. 850-700 mb moisture transport is currently increasing with the arrival of a southwesterly low- level jet. This supports a more favorable environment for increasing coverage of showers and thunderstorms late this afternoon and evening. Axis of maximum lower tropospheric ThetaE convergence extends from northern Illinois into northeast Lower Michigan, moving southeastward as the wave carves toward the northern Ohio Valley.

Latest NWP data has trended slightly later with the onset time of meaningful rainfall, pushing back initial measurable QPF along/north of M-46 by another 1-2 hours. Further south, showers and thunderstorms are expected to hold off until closer to 00Z this evening as surface dewpoints lag the northward advance of a warm sector. The development of a secondary surface low (at the upstream triple-point) unfolds slowly, before getting slingshot from northern Wisconsin into northern Lower Michigan late this evening, catalyzing a local precipitation response. The majority of convective activity is likely to occur between 00Z and 06Z tonight, in two phases. The first is a more scattered warm-sector variety, followed by a second more linear round, focused along the system's passing cold frontal boundary. Given a delay in the more favorable dynamics, surface dewpoints exceeding 50F are not scheduled to arrive until after 02Z which reduces the duration/magnitude for SBCAPE. Although 0-6 km shear will exceed 60 knots at times tonight, only a low-end chance of isolated marginally severe gusts exists given thermodynamic profiles, and the hail threat continues to diminish with CAPE largely capped at 250 J/kg or less. Post-frontal conditions characterized by veering WNW flow and decreasing shower activity, but less in the way of a temperature response.

The wave closes off through 300 mb early Wednesday morning as the occluded low stalls over southern Ontario. This maintains a cyclonic flow field overhead for most of the day and into Thursday as mid and upper level moisture is quickly stripped away. Temperatures hold near-steady, in the low-mid 50s throughout the day with ample stratocumulus and cold advection to offset diurnal heating. 850 mb temperatures drop below 0C by 15Z across the CWA with a passing thermal trough. Monitoring the vorticity maxima that should clip The Thumb and possibly Tri-Cities, colocated with the vertically stacked low. Boundary-layer moisture/depth may facilitate afternoon showers. Steep low-level lapse rates ensure efficient mixing of 925 mb level winds, with gusts in excess of 30 mph possible. The central CONUS longwave ridge compresses into the Great Lakes late this evening with clouds dissipating, but NNW surface gradient persists. Note that southern Lake Huron shoreline counties could see clouds and some showers persist into the overnight hours.

Geopotential height rises get underway on Thursday while an expansive corridor of surface high pressure, extending from The Gulf to Hudson Bay, becomes more diffuse. Benign conditions allow for standard warming via insolation, in the absence of more meaningful advective processes. Flow fields flip SSW Friday with ThetaE on the rise. Medium-range deterministic solutions are in agreement with 988 mb surface low pressure tracking along the US/Canada border with a cold front draped along the Mississippi Valley. A period of showers and storms is likely with the frontal passage. Turning much warmer over the weekend with 850 mb temperatures climbing into the mid- teens (Celsius).

MARINE

Southerly flow this evening curves cyclonically from south to north as low pressure slides into northern Lower Michigan. SW gusts increase as a 50 knot low level jet surges overhead tonight. Presence of the elevated warm front keeps near surface conditions stable to prevent the full magnitude of winds from mixing down, but still expecting gusts to average around 25 to 30 knots. An isolated gale force gust cannot be ruled out, especially toward northern portions of Lake Huron where SE flow funnels into the Straits and along the shoreline where land influence exists. Widespread showers and a few thunderstorms will also be possible pre-front, with a few storms capable of gusts in excess of 35 knots. Breezy northwest flow emerges as the front pushes through Wednesday morning, directing elevated waves toward the nearshore waters during the day. Combination of winds and waves keeps Small Craft Advisories in effect through Wednesday evening. High pressure gradually expands into the region Thursday-parts of Friday before the next system arrives this weekend marking the return of showers and storms.

PREV DISCUSSION

Issued at 148 PM EDT Tue May 12 2026

AVIATION...

VFR ceilings mark the beginning of this TAF period as mid-upper level moisture spills into the terminal corridor. The increase in mid-high clouds will come with isolated to scattered light rain showers that will fight a dry surface layer through the afternoon. Will maintain a PROB30 for shower activity from PTK northward as lower levels gradually saturate through the evening. Higher coverage of showers will arrive late this evening as associated low pressure tracks through with a cold front. Enough nocturnal instability looks available for isolated thunderstorms, but confidence in occurrence at any one airport remains low. Front passes through tonight with shower/thunderstorms chances coming to an end around 07Z followed by increasing coverage of MVFR ceilings. Winds turn out of the W and NW and become gusty to around 25 knots tomorrow morning as MVFR ceilings look to persist.

D21/DTW Convection...Very low probability exists for an isolated thunderstorm this evening into tonight.

DTW THRESHOLD PROBABILITIES...

* Very low for thunderstorms mainly between 02Z and 07Z tonight.

* High for cigs aob 5000 feet tonight into tomorrow.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory until 10 PM EDT Wednesday for LHZ421-422- 441>443.

Lake St Clair...Small Craft Advisory from 10 PM this evening to 10 PM EDT Wednesday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 10 PM this evening to 10 PM EDT Wednesday for LEZ444.