textproduct: Detroit/Pontiac

KEY MESSAGES

- Periods of scattered to numerous rain showers with embedded thunderstorms this afternoon into tonight.

- Additional showers and storms possible early Saturday afternoon. Isolated storms may be strong to severe, capable of producing damaging wind gusts and large hail.

- A hot and stormy pattern is becoming increasingly likely during the middle of next week.

DISCUSSION

Quiet start to early June comes to an end today as a series of shortwaves begin to break down the existing ridge. A more active pattern is already observed upstream where clusters of convection are ongoing: one cluster from southern Iowa to northeast Kansas and another over South Dakota. The leading wave is associated with a low level trough and strong low level jet that will draw moisture initially into the Saginaw Valley early this afternoon and the rest of SE Michigan this evening. Daytime impact will be an increase in cloud cover with highs near 80 degrees for the Saginaw Valley versus mid-upper 80s in the Detroit Metro area where sunshine is expected for most of the day.

Moisture transport peaks between approximately 21z-06z tonight (5pm- 2am), tied to the passage of a convective vort max and a lagging trough axis. Remnants of the Midwest convection reach the Saginaw Valley mid to late afternoon, but ultimately outpace the theta-e axis and lose convective vigor given only a few hundred J/kg of MUCAPE available. Coverage then increases this evening, especially north of I-69, as the trough approaches. Poor lapse rates limit updraft strength, while models pull the two waves out of phase to limit organized convective potential this evening and overnight. That said, mechanical mixing of the strong low level jet winds could result in gusty showers/thunderstorms (40+ mph). Other factor to consider is heavy rainfall potential, which will be focused again over the Saginaw Valley/Thumb as the trough passes overhead. Consistent hi-res signal for over an inch of rain north of I-69 before expanding across the rest of SE Michigan late in the evening. A Marginal Risk for excessive rainfall exists across the north.

Much lower predictability exists heading into the overnight hours and Saturday, mainly in terms of thunderstorm initiation and coverage. First feature in question is the South Dakota convective wave, and how that may interfere with otherwise expected subsidence/drying aloft. There is also plenty of nocturnal convective activity being triggered in the hi-res guidance, which is often not handled well by models. Uncertainty compounds Saturday morning with the arrival of a deep synoptic wave, which quickly steepens lapse rates to 6.5-7.0 C/km and spreads a broad region of ascent over SE Michigan. Most solutions project the wave to reach the Detroit Metro region around peak heating (early-mid afternoon), which will be the favored time/location for any convective redevelopment. The wave also supplies plenty of deep layer shear, supporting organized convection potential if enough instability stays in tact to sustain strong updrafts. Latest trends have pushed the greatest thunderstorm coverage south of the Ohio Border, although the conditionality of this setup keeps SE Michigan within a Marginal Risk for severe weather Saturday. Large hail and damaging winds are the primary threats.

Heights then begin to rise rapidly Saturday night as longwave ridging re-establishes itself. Dry weather thus returns for Sunday- Monday while the ridge axis builds overhead. H5 heights push into the climatological 90th percentile and remain there throughout the week, leading to well above normal temperatures. Ensemble interquartile max T values range from upper 80s to low 90s by late next week alongside unobstructed gulf return flow. Thunderstorm chances thus accompany increasingly warm and muggy conditions for much of the work week, with heavy rainfall potential already highlighted in the Day 5 Excessive Rainfall Outlook.

MARINE

Warm southerly flow will keep wind speeds in check (mainly up around 20 knots) today due to the increased low level stability. A surface low tracking through the central Great Lakes this evening will bring numerous showers and a few thunderstorms to the region. Expected light, mostly westerly winds on Saturday. A weak cold front will sink southward late in the day, serving as the focal point for scattered, potentially marginally severe thunderstorms, with the highest probability over Lake St. Clair and Lake Erie. Very light northeast flow and dry conditions will follow for Saturday night and Sunday. Warm weather returns early next week, bringing a chance of showers and thunderstorms on Tuesday.

HYDROLOGY

Clusters of showers and thunderstorms are forecast to track west to east across Southeast MI this afternoon through tonight. Another round of showers and storms is possible early Saturday afternoon. Most areas will receive a quarter inch of rainfall or less, but there will be the potential for localized areas (mainly north of I- 69) to see up to 1.50 inches. The extended period of dry conditions recently suggests the potential for flooding is low, but isolated flooding will be possible if any of the higher amounts affect the typical flood prone locations in urban areas.

PREV DISCUSSION

Issued at 1148 PM EDT Thu Jun 4 2026

AVIATION...

SE Mi is between mid Atlantic high pressure and Plains low pressure that sets up increasing low to mid level moisture transport into the area late tonight and Friday. VFR under scattered to broken cirrus and light south wind persist until clouds thicken and lower after sunrise as the first sign of the inbound moisture. This is followed by showers initially toward MBS which spread slowly southward and eastward during the afternoon into Friday evening. The best time window for thunderstorms is mid afternoon from MBS to FNT while the strongest activity takes until closer to 00Z Friday evening to reach DTW. MVFR ceiling is likely Friday night in the rain-cooled but humid air trailing the shower/storm pattern. D21/DTW Convection... Showers are likely with a chance of embedded thunderstorms Friday evening.

DTW THRESHOLD PROBABILITIES...

* Moderate for thunderstorms Friday evening.

* Moderate for ceiling 5000 ft or less Friday afternoon and night.

DTX WATCHES/WARNINGS/ADVISORIES

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