937
FXUS63 KDTX 211744
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
144 PM EDT Fri Aug 21 2026

.KEY MESSAGES...

- Showers increase coverage tonight with a chance of thunderstorms.

- Showers become numerous to widespread Saturday as a cold front
moves through the region. Scattered thunderstorms present a Marginal
Risk of severe intensity Saturday afternoon.

- Breezy and cooler conditions arrive Sunday with a lingering chance
for showers.

- Dry weather with slightly below normal temperatures start off the
week on Monday.

&&

.AVIATION...

Remaining influence of departing high pressure maintains benign
aviation conditions this afternoon with south to southeast wind
around 10 kt. Increasing coverage of VFR cloud precedes low pressure
tracking through the northern Great Lakes this evening. A narrow
strip of instability is also causing a few showers to develop from
KGRR to KAZO; these will track eastward through this evening and may
hold together long enough to reach the local terminals. Included a
TEMPO for KMBS and KFNT, and a PROB30 for the Metro Detroit sites
this evening. A brief dip to MVFR would be plausible in the heaviest
shower but VFR remains prevalent. Additional intermittent showers
and a few storms will be possible overnight and early Saturday with
relatively low confidence on placement. A cold front midday Saturday
then brings an uptick in convective coverage to numerous/widespread.
Favored window for any MVFR ceilings will be mid to late morning as
the front tracks through.

D21/DTW Convection... A stray thunderstorm will be possible late
this evening and overnight, then increasing coverage of convection
is expected to occur after noon Saturday with the highest
probability between 18 and 23z.

.DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms tonight. Moderate after 18z Saturday.

* Low for ceilings at or below 5000 ft Saturday morning.

&&

.PREV DISCUSSION...
Issued at 407 AM EDT Fri Aug 21 2026

DISCUSSION...

Today starts out with high pressure centered to our east but still
in control of conditions across SE Mi before it departs into the New
England states this afternoon. The very beginning of weak southerly
flow in the lower to mid levels shows signs of moisture transport in
patchy mid level clouds under cirrus streamers during the morning.
Mid and high clouds then increase in the afternoon, mainly toward
the Tri Cities and west of I-75, as moisture transport increases
modestly ahead of Midwest low pressure. Guidance high temperatures
in the lower 80s are reachable given adequate sunshine at least
through early afternoon.

The leading low amplitude 500 mb trough could touch off a stray
shower late in the day, however potential becomes better organized
this evening as the trough combines with deeper and slightly
stronger SW flow within the warm sector moisture axis. Shower
coverage is scattered to briefly numerous during the late night into
Saturday morning as the center of low pressure reaches the Straits
while pulling the cold front into Lower Mi. Frontal timing remains
favorable for passage through SE Mi during Saturday afternoon peak
heating with a boost of forcing from the primary mid level short
wave. However even then, HREF mean surface based CAPE struggles to
exceed 1500 J/kg at least partially due to high temperatures that
also strain to reach 80 across the region. This instability profile
combines with about 25 knots of westerly bulk shear for a standard
multicell convective mode that carries a Marginal Risk of
approaching severe intensity. Numerous to widespread coverage of
showers focusing along the cold front has greater confidence until
the system exits eastward early Saturday evening.

NW wind gusting around 25 mph post front reinforces cooler air
across the region Sunday. A partly sunny/mostly cloudy sky with a
stray shower are expected for much of the day as the low level
thermal trough digs into the central Great Lakes. Cold advection
brings 850 mb temps down into the single digits by Sunday night
which makes low temperatures in the upper 40s reachable outside of
the larger metro areas by sunrise Monday.

MARINE...

Light easterly flow this morning gradually backs to the south-
southwest through the day as high pressure peels off into New
England. Meanwhile, low pressure organizes upstream with shower and
thunderstorm chances beginning as early as this evening near the
Mackinac Straits. Rain chances then spread across the rest of the
marine zones overnight-Saturday. Periods of dry weather mix with
multiple rounds of rain activity throughout the day before clearing
out Saturday night as a cold front sweeps across the region. The
front quickly shifts winds from the south to the northwest, which
will pair with cold advection to produce gusty winds over Lake Huron
Sunday and Monday. Strongest gusts around 30 knots are expected
Sunday afternoon-evening, but will hold around 25 knots through
Monday as well. Elevated waves are also expected, likely to exceed
Small Craft Advisory thresholds from at least Outer Bay to Harbor
Beach. A quieter pattern arrives Tuesday, but is quickly followed by
the next system mid-week.

&&

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

$$

AVIATION.....TF
DISCUSSION...BT
MARINE.......MV


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