textproduct: Detroit/Pontiac

KEY MESSAGES

- Scattered showers and a rumble of thunder will be possible north of I 69 this afternoon and into the early evening.

- Dry for much of Sunday. Broader coverage of showers and thunderstorms will develop Sunday night, especially south of I-94. Heavy rainfall is possible if the low pressure system tracks farther north.

- 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

Zonal to pseudo northwest flow will remain in place over Southeast Michigan throughout much of the next 7 days leading to slightly below normal temperatures across the region. A modest southern stream jet impulse is forecasted to eject across the Plains late this weekend phasing with and entrance region to the upper level jet axis over the Upper Midwest and Great Lakes.

Forecast thoughts for this afternoon and early evening were provided in prior discussions including the Update. Shower and thunderstorm chances over the northern forecast area will bring the potential for a heavy downpour and possibly some small hail.

Weak upper level jetlet and potential vorticity anomaly is forecasted to induce leeside cyclogenesis tonight invof Colorado. Strong model consensus then exists that a hybrid baroclinic/MCV low pressure system will then eject eastward through the Mid Mississippi River Valley late Sunday afternoon and evening. Some significant details remain uncertain at this vantage point, including whether or not the MCV will remain attached to any deeper 850-700mb thetae axes. It remains likely that deep column, boundary layer rooted convection will favor a track through central to southern Illinois and southern Indiana based on HREF ensemble mean of CAPE. Great support for large scale ascent is expected to arrive here locally, given the phasing of the northern stream and the configuration/organization to the right entrance region dynamics. Details will needed to be sorted with notable and meaningful north to south differences of most favorable 700mb and 850mb frontogenesis. The NAM and Nam nest solutions are something to monitor given the amount of QPF in the solutions (exceeding 1 inch) for portions of far Southeast Michigan. Additionally, the EPS dataset is very supportive of QPF amounts for Southeast Michigan with the mean at DTW at over 1.00 inch and with the 90th percentile at/above 2.50 inches. The current forecast has categorical/widespread rain chances for areas south of the I 69 corridor Sunday night. Will forgo any Flood Watch this forecast package and will allow for more model data. No severe weather is anticipated with the Sunday night system here in Southeast Michigan.

High confidence exists that shower and rain chances will end by midday Monday. Subsidence and steep downward vertical motion is forecasted after 18z which should lead to a quick clearing trend. Northeast gradient wind is forecasted which could hold on a touch into the evening before laying down. Highs Monday only topping out in the lower 70s, with temperatures lowering into the lower 60s by Midnight.

Strong Canadian ridge of high pressure is expected to build across the state Tuesday and early Wednesday. Deep PV reservoir and troughing is shown to push eastward by Wednesday reestablishign troughing over the Great Lakes for the end of the week. It just looks like a continuation of below normal temperatures at the end of the period.

MARINE

A diffuse area of high pressure will linger over the Great Lakes through Sunday, supporting a continuation of lighter winds. Periodic rain showers will be possible today as an upper-level disturbance slowly moves across the region. A compact low pressure system will through the Ohio Valley and southern Great Lakes region tomorrow night. Rain showers are expected to be concentrated across Lake Erie up to Lake St. Clair. Elevated northeasterly winds will increase tomorrow night and persist through the daylight hours on Monday. The longer onshore fetch on Lake Erie will support higher waves by daybreak Monday.

HYDROLOGY

Unseasonably strong low pressure system is forecasted to eject eastward through the Mid Mississippi River Valley late Sunday and through portions of the Ohio River Valley Sunday night. Widespread shower and thunderstorm activity is expected to develop along the northern periphery of the low pressure system and may bring heavy rainfall. While uncertainty exists to the exact track of the heavy rainfall, the potential exists for rainfall amounts to exceed 1 inch across some portion of southern Southeast Michigan. The current model consensus and forecast supports higher rainfall amounts south of Detroit along the Ohio border. Heavy rainfall and higher amounts will be possible if the low pressure system tracks northward. If heavy rainfall axis trends farther north, some potential for urban flooding will exist.

PREV DISCUSSION

Issued at 122 PM EDT Sat Jun 20 2026

AVIATION...

Weak surface low will continue to move through Lower MI this afternoon and early evening. This in combination with modest instability will keep widespread cumulus developing into showers north of the Detroit TAF sites. There is enough instability that the strongest showers could produce thunder, but should be isolated enough to leave out of the PTK, FNT and MBS TAFs. For those Detroit TAFs, just expect the cumulus to become broken this afternoon. Otherwise, a gusty west wind of 10-15 knots will continue through the afternoon and early evening.

With the surface low moving farther east and the loss of diurnal heating, expect the showers to dissipate quickly just after 00z and the cumulus to follow between 00z and 04z. Upper Midwest high pressure builds into Lower MI late tonight bringing mostly clear skies and light northwest wind. Will delay fog potential until a shallow MVFR restriction develops closer to sunrise, mainly in the FNT to MBS area where wet ground can augment surface based moisture.

The first half of Sunday will feature few-sct diurnal cumulus development as a thickening cirrus deck moves in ahead of the next system for mainly Sunday night.

D21/DTW Convection... Thunderstorm potential holds north of DTW toward the northern fringe of D21 for the remainder of this afternoon and evening.

DTW THRESHOLD PROBABILITIES...

* Low for ceiling at or below 5000 ft this afternoon and evening.

DTX WATCHES/WARNINGS/ADVISORIES

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