Area Forecast Discussion

KEY MESSAGES

- A chance of showers and thunderstorms returns Tuesday. The best chance of storms and heavy rainfall is late afternoon and evening south of I-69.

- A chance of showers lingers Wednesday before becoming more numerous again Wednesday night and Thursday.

- Dry weather with temperatures around normal Friday into next weekend.

AVIATION

Thickening high based cloud overnight, as elevated moisture transport increases along the southern flank of a strengthening low level jet positioned north of the region. This process brings potential for scattered shower activity late night and early Tuesday, particularly from PTK northward, with overall coverage and intensity likely limited too some degree by ample dry air held within the lowest layers. This will support predominant VFR conditions through this time. Prevailing wind from the southeast tonight, veering to southerly with some modest gustiness for the afternoon. Secondary window for convective development may emerge along the cold frontal boundary Tuesday evening with a focus across the Detroit corridor.

D21/DTW Convection...No thunderstorms are forecast through Tuesday afternoon. A lower probability exists for thunderstorm development Tuesday evening /21z-01z/.

DTW THRESHOLD PROBABILITIES

* Low for ceiling 5000 ft or less Tuesday afternoon and evening.

* Low for thunderstorms Tuesday evening.

PREV DISCUSSION

Issued at 327 PM EDT Mon Sep 14 2026

DISCUSSION...

High pressure has led to a dry but cool day across SE Michigan. Many locations have seen temperature readings hold in the upper 60s, even under plenty of sunshine. Anticyclonic surface wind pattern over western Michigan identifies the center of the surface high, which will drift overhead this evening and cause winds to back to the southeast. Flow backs further to the southwest overnight, drawing a theta-e ridge into the Great Lakes region Tuesday. This brings warmer temperatures, increased rain chances, and breezy southwest flow to SE Michigan.

The theta-e surge will be aided initially by a belt of ~50 to 60 knot h8 winds late tonight, driven on the larger scale by SE CONUS high pressure. The nose of the jet reaches northern Michigan early Tuesday morning, focusing a broad area of precipitation toward the Saginaw Valley for the first half of the day. A deep closed low across Ontario will simultaneously drag a cold front across northern CONUS, which will push rain chances eastward and thus into the rest of the CWA through the day Tuesday. One questionable aspect of this system is how well the stratiform rain can hold up against the dry airmass sampled overhead today (PWAT of 0.44" per 12z KDTX sounding for reference). Soundings are showing a good amount of dry air surviving at the low levels, which could eat into QPF amounts and even rain chances altogether, especially as the low level jet forcing departs mid-day Tuesday. The waning LLJ presence will still be enough to produce breezy conditions with gusts of 25 to 30 mph possible.

As the cold front and associated moisture convergence arrive Tuesday afternoon-evening, event character becomes more convective with showers and thunderstorms redeveloping along the boundary. Instability is not expected to be overly impressive, but several models bring 70 degree dewpoints across the state line Tuesday evening which is enough for about 1000 J/kg MLCAPE. This occurs in a fairly tight time window between about 21z-01z (5pm-9pm) south of I- 94. SWODY2 continues to designate a Marginal Risk for severe weather across Lenawee/Monroe Counties, mainly for isolated precipitation loaded downbursts in a marginal shear environment. The broader threat looks to be heavy rainfall, especially given the high moisture environment and proximity of the frontal zone. More details are in the Hydrology section.

SE Michigan through the rest of the work week will be in the hands of the frontal zone. The baroclinic zone certainly stays within reach of us, but models generally shove it into the Ohio Valley for Wednesday before lifting back north Thursday-Friday. Broad brushed PoPs reflect the uncertainty in coverage/timing of this pattern rather than a full wash out over the next several days. Wavering nature of the frontal zone will also cause temperatures to waffle between 70s and 80s through the rest of the work week with unsettled conditions possibly extending into the weekend.

MARINE...

Strong high pressure over the Great Lakes tracks eastward this evening, giving way to a mature low pressure system over the upper Midwest. This system advances across northern Ontario on Tuesday and directs a strong southerly low-level jet across the region. The strongest winds are still on track for northern Lake Huron where gales to 35 to 40 kt are forecast. A Gale Warning remains in effect north of Alabaster from 4 AM to 4 PM. Farther south, gusts of 20 to 30 kt will be more common and Small Craft Advisories remain in effect for the Lake Huron nearshore waters. A band of showers with a few embedded thunderstorms accompanies the gale event with highest coverage across Lake Huron during the morning. Additional scattered showers and thunderstorms are forecast across Lake St. Clair and western Lake Erie during the late afternoon and evening ahead of a cold front. This front eases across the area Tuesday night, bringing the end to showers and causing wind to shift from south/southwest to north/northeast by Wednesday morning.

HYDROLOGY...

A moisture rich airmass surges into the region Tuesday ahead of a cold front which tracks through in the afternoon and evening. The front then stalls out across the northern Ohio Valley before lifting back north later this week. This will result in multiple opportunities for widespread rainfall throughout the week. In the near-term, the best opportunity for heavy rain will be south of I-69 Tuesday afternoon and evening where thunderstorm development may enhance rainfall rates to over an inch per hour. Depending on where the front stalls, rain may linger overnight to produce storm totals over one inch by Wednesday morning with training storms not out of the question. Localized ponding or minor flooding of low-lying or urban areas will be possible.

DTX WATCHES / WARNINGS / ADVISORIES

MI...None. Lake Huron...Gale Warning from 4 AM to 4 PM EDT Tuesday for LHZ361>363.

Small Craft Advisory until 4 PM EDT Tuesday for LHZ421-422-441.

Small Craft Advisory until 4 PM EDT Tuesday for LHZ442-443.

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