textproduct: Detroit/Pontiac

KEY MESSAGES

- Scattered showers and a rumble of thunder this morning continue this afternoon while shifting with greater coverage toward the Tri Cities and Thumb. There is a better chance for an ordinary thunderstorm this afternoon north of I-69.

- Dry tonight and Sunday.

- Broader coverage of showers and thunderstorms develop Sunday night, especially south of I-94.

- Showers linger Monday morning then dry in the afternoon and evening.

- Cooler than normal temperatures are expected through at least the middle of next week.

DISCUSSION

Modest surface low pressure traversing Lower Mi has pockets of showers ongoing during the late night. The surface system is tied to a compact mid/upper level short wave producing some elevated moisture transport to fuel the observed shower pattern which contains a stray rumble of thunder. This wave quickly shears eastward during the morning and leaves behind larger scale mid/upper level deformation over Lower Mi that is connected to a larger closed low in central Canada. The resulting neutral to slightly upward vertical motion in this zone allows the lingering surface low/trough to be the focus of new shower/storm development during peak afternoon heating, mainly toward the Tri Cities and Thumb. The new 00Z HREF and model soundings advertise low density surface based CAPE hovering around 500 J/kg by mid afternoon, just enough for an isolated ordinary thunderstorm until activity fades with sunset.

A subtle short wave ridge and diffuse surface high pressure maintains dry weather for the rest of tonight and through Sunday. Consensus of 00Z deterministic models then keeps the current central Rockies system on time to reach the Ohio valley Sunday night. The mid/upper level wave initiates textbook lee side surface cyclogenesis during the day which sweeps up readily accessible Gulf moisture to fuel convection. Central Plains MCS development is likely as a result which propagates into the mid MS/lower OH valley during Sunday. The resulting hybrid short wave/MCV keeps the OH valley surface to low level frontal zone active Sunday night while an elevated pattern of moisture transport grazes Lower Mi. The forecast question over the last few cycles has been how far north showers/storms will be able to reach into Lower Mi while the system shears quickly eastward during the night and early Monday. The low level jet is directed more toward the OH/TN valleys keeping the 850- 700 mb flow weaker and quick to flip NW over the Great Lakes later Sunday night. These larger scale trends continue to favor a sharp rainfall gradient with limited northward extent. Deterministic regional model consensus of 1 inch event totals are now near or just south of the Ohio border decreasing to just trace amounts toward the I-69 corridor. This is likely to be reflected in NBM runs over the next few model cycles.

Dry weather holds Monday afternoon and night as slightly cooler north wind develops over Lower Mi on the heels of the Ohio valley system. Surface high pressure influence then lasts through Tuesday followed quickly by the next Midwest low pressure system for Wednesday.

MARINE

A ridge of high pressure will build in this morning which will support light winds through the day. A diffuse area of high pressure will then remain over the Great Lakes through this weekend and will maintain the lighter winds. Periodic rain showers will be possible today as an upper-level disturbance holds over the region. A low pressure system will then arrive over the Ohio Valley and southern Great Lakes tomorrow night. This will bring the next likely chances for rain, embedded thunderstorms and elevated winds centered late tomorrow through Monday morning. Most of this activity is expected to be concentrated across Lake Erie up to Lake St. Clair.

HYDROLOGY

Scattered showers and isolated thunderstorms produce generally less than 0.25 inch of rainfall today. Dry weather tonight and Sunday leads into a more widespread shower and thunderstorm pattern that increases Sunday evening and continues into Monday morning, mainly south of I-69. Stronger low pressure tracking through the Ohio valley pulls Gulf moisture northward into southern Lower Mi resulting in periods of heavier showers and thunderstorms. Rainfall totals from sunset Sunday evening until noon Monday have a chance to reach around 1 inch, mainly from the Ohio border northward but holding south of the I-94 corridor. Totals drop off quickly across metro Detroit to less than 0.25 inch toward the M-59 corridor. This scenario presents a low threat of flooding limited to minor ponding of water on roads and in other prone areas until the rain ends by Monday afternoon.

PREV DISCUSSION

Issued at 116 AM EDT Sat Jun 20 2026

AVIATION...

Weak area of low pressure traversing the region this morning will maintain some pockets of light shower activity within a thicker canopy of VFR cloud featuring bases primarily within the 6 to 10k ft level. A brief reduction of ceiling near MVFR will be plausible as ascent tied to this feature peaks later this morning mainly at MBS. A weakly unstable environment will emerge in the wake augmented by daytime heating. This will maintain potential for isolated to scattered showers and thunderstorms to develop during peak heating, with higher probability from PTK northward based on latest model trends. Brief gustiness up to 20 knots to prevailing westerly wind for the late day period.

D21/DTW Convection... Very low chance of a thunderstorm late tonight and again Saturday afternoon.

DTW THRESHOLD PROBABILITIES...

* Low for ceiling at or below 5 kft late tonight and Saturday.

* Very low for thunderstorm occurrence late tonight and Saturday.

DTX WATCHES/WARNINGS/ADVISORIES

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