296
FXUS63 KDTX 220342
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1142 PM EDT Thu Aug 21 2025

.KEY MESSAGES...

- Seasonable temperatures and dry weather expected to close out the
work week.

- Chance of showers and thunderstorms Saturday and Saturday night as
a cold front tracks across the area.

- Below normal temperatures Sunday through Wednesday with highs in
the upper 60s to 70s.

&&

.AVIATION...

Current observations indicate fairly low sfc dewpoint depressions at
the terminals aside from the more urban DTW and DET. The latest RAP
soundings show a low level moisture profile conducive for fog
development. Given the clear skies and light winds with sfc high
pressure settling overhead, visibility restrictions due to fog
remain justified in the terminals. LIFR and VLIFR conditions will be
more probable at PTK, FNT and MBS where winds will be nearly calm. A
late August sun angle will efficiently mix out the fog in the 12 to
14Z time frame.

For DTW/D21 Convection... No thunderstorms expected through the TAF
period.

THRESHOLD PROBABILITIES...

* Low in ceilings aob 200 feet and/or visibilities below 1/2 mile
  Friday morning.

&&

.PREV DISCUSSION...
Issued at 324 PM EDT Thu Aug 21 2025

DISCUSSION...

Light northeast flow under an established inversion will continue to
maintain a bkn strato-cu deck, bolstered by diurnal heating.
Degradation of coverage is expected to commence later this evening
with the loss of daytime heating coupled with a boost in low level
subsidence as a ridge folds into the Great Lakes. This will lead to
clear skies overnight under a calm to light wind field that will
extend from the surface through 5kft. This setup will bring
increasing chances to see patchy to areas of fog, possibly dense, as
surface condensation pressure deficits fall to or below 5mb. The
higher probabilities for better fog coverage will reside through the
Irish Hills into the northern Thumb and Tri-Cities. Any observed fog
will burn off after sunrise.

Pending coverage and density of the fog, the late morning to early
afternoon hours could retain low-lying stratus, but the maintenance
of subsidence under a 1018 mb high pressure system should eventually
make way for partly cloudy to mostly sunny skies, allowing for a
warm up into the low 80s. Attention will then turn to the closed
upper level low system which at present resides over Saskatchewan.
This system will progress into western Ontario through the weekend
and will draw a cold front across the Great Lakes on Saturday.
Modeled soundings display a well capped environment around 10kft and
weaker frontogenetic forcing below which will be a limiting factor
for more robust precipitation chances. PoP values will hold around
30% through the Metro region, trending higher towards 50-60% across
the Thumb where the influence of the upper- level trough is more
pertinent.

Following the passage of the front, periodic shortwaves will
continue to drive through the Great Lakes which will establish a
thermal trough. 850 temperatures drop between 6-8C and 500 to -16 -
(-18) which is between the 1th to 2.5th percentile w.r.t
climatology. This will bring extremely high confidence to see below
normal temperatures during the early to middle part of the week with
highs in the upper 60s to low 70s and lows in the 50s. Influence of
the trough and embedded shortwaves brings periodic drizzle and
showers and stratocu development into the middle part of next week.

MARINE...

High pressure over the region is leading to lighter northeasterly
flow today, generally under 15 knots. The high will drift eastward
through Friday which will maintain lighter winds but will be
flipping around to the southwest. A broad low pressure system will
then track across northern Ontario late Friday night-Saturday which
will send a cold front through the Great Lakes on Saturday bringing
the next chances for showers and thunderstorms. An upper trough will
then stall over the region through the rest of the weekend and into
next week resulting in fall like conditions across the Great Lakes.
Gusty west/northwesterly winds will gust to around 25 knots this
weekend building wave heights, but largely over northern and
easterly portions of Lake Huron. Cooler weather brings lake effect
shower and waterspout chances through that timeframe.

&&

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

$$

AVIATION.....SC
DISCUSSION...AM
MARINE.......DRK


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