Special Weather Statement, NWS Detroit, MI

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
253 PM EDT Thu Aug 7 2025

.KEY MESSAGES...

- Hot and muggy weather builds in this weekend with heat index well
into the 90s Saturday through Monday.

- Low chance of showers and thunderstorms tomorrow.

- Mainly dry over the weekend, with a better chance of showers and
thunderstorms returning early next week.

&&

.DISCUSSION...

Moderate instability (MLcapes 1500+ J/kg) has built up over
southeast Michigan as temperatures have risen well into the 80s with
mid to upper 60 dew pts. The near surface flow remains weak, which
has allowed some backing off the winds over far eastern areas near
the Lakes, which is allowing for some modest convergence areas,
which should be sufficient to touch off isolated-scattered activity.
Particularly across northern two thirds of the CWA as a significant
shortwave tracks through the northern Great Lakes. There is 25-30
knot effective shear tracking into southeast Michigan from the west,
and with borderline downdraft capes, could see a stray cell become
strong and approach severe limits with a downburst, as suggested by
machine learning. Slow movement will bring localized heavy rain
threat, especially if storms re-fire near the same location like
they did yesterday.

Another shortwave/MCV tracking in from the western Great Lakes
tomorrow looks to bring another low chance of showers and
thunderstorms. Once again, best chance over the northern half of the
CWA. Considerable uncertainty with the potential upstream activity
late tonight around the Milwaukee/Chicago areas however.

Strong upper level wave/500 MB low tracking through the Pacific
Northwest this afternoon into the northern Rockies tonight before
heading off into south central Canada over the weekend.  This will
allow upper level ridge axis and associated heat from the ridge
center established over New Mexico/Four Corners region to fold over
into Lower Michigan Friday night into Saturday, with 591+ DAM
heights at 500 MB over southeast Michigan. Main instability
axis/steep mid level lapse rates look to remain back across the
western Great Lakes during this time, but instability gradient does
push into the CWA, offering up a very low chance of a
shower/thunderstorm as low level southwest flow ramps up. Mid level
flow will be very weak however, and no clear trigger at this time,
along with the mid levels being very warm and dry. Assuming
convection holds off on Saturday, 850 MB temps of 19 C supportive of
highs reaching into the lower 90s. Bulk of the guidance suggests dew
pts mainly in the upper 60s to around 70 degrees, thus heat index
holding in the 90s, short of heat advisory criteria. Further low
level warming supports highs in the low to mid 90s on Sunday, but
convection could short circuit highs. However, it appears the subtle
height falls will not arrive until Sunday evening/night. Cumulative
heat effects could potentially support a heat advisory in urban
settings. Indications (Euro) are then the front and moisture axis
will get hung over over far southern Lower Michigan Monday through
Wednesday, supporting a diurnal chance of showers and thunderstorms
each day with above normal temperatures.

&&

.MARINE...

South-southeast flow continues this afternoon following the
departure of high pressure. Peak winds expected over the northern
half of Lake Huron, given the fetch, with gusts up around 15-20kts.
The rest of the region sees slightly weaker wind gusts closer to 10-
15kts. Shower/storm chances this afternoon are generally confined
towards the nearshore waters with the bulk of activity occuring
overland. Better chances to see scattered thunderstorms over the
open waters of Lake Huron comes late this evening into Friday as a
weak warm front lifts into the upper Great Lakes. Region remains on
the northern edge of a central CONUS ridge Friday through the
weekend which brings continued lighter southerly winds and periodic
scattered storm chances.

&&

.PREV DISCUSSION...
Issued at 128 PM EDT Thu Aug 7 2025

AVIATION...

Healthy 3.5-5kft cu field has rapidly developed across the region
early this afternoon. While the greatest chance to see scattered
showers or storms remains over the Thumb area, satellite does show a
convergence axis in the cloud field from Lapeer down through Oakland
county so have added Prob30 mention for PTK this afternoon. No
changes to the inherited mentions for FNT/MBS as confidence in
coverage is not high enough to switch up to a Tempo group. Will
still need to monitor the Detroit terminals as lake breezes from St
Clair/Erie could support pop-up activity towards the city, however
for now will continue to run with dry forecast today.

For DTW/D21 Convection... At this time, thunderstorm potential is
too low to include in the forecast.

THRESHOLD PROBABILITIES...

* Low for thunderstorms this afternoon.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

DISCUSSION...SF
MARINE.......KDK/SS
AVIATION.....KDK

You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.

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