458
FXUS63 KDTX 290730
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
330 AM EDT Fri Aug 29 2025

.KEY MESSAGES...

- Below average temperatures today and for most of the weekend,
  although a gradual warming trend will commence Saturday.

- Aside from a few sprinkles over The Thumb today, mainly dry
  conditions expected through Labor Day and into the middle of next
  week.

&&

.DISCUSSION...

Thermal troughing is now fully entrenched throughout Southeast
Michigan this morning, marked by a cool start with pre-dawn lows in
the 50s, and even upper 40s for some outlying areas further north.
This post-frontal airmass will ensure mainly dry conditions for most
of the region through the weekend. The one exception is over
portions of The Thumb where cyclonic low-level NNE cold advection
over the mild waters of Lake Huron could induce a few afternoon
sprinkles or light lake-effect rain showers later today. Otherwise,
highs are only expected to peak in the mid to upper 60s as surface
high pressure centered over The UP funnels in continental Canadian
air southward. If realized accordingly, such readings would mark a
10-15 degree (F) departure from climatological daily normals.
Diurnal cumulus field wanes quickly this evening yielding a chilly
night as winds trend toward calm, aiding in efficient nocturnal
cooling. Most locations will dip into the 40s late tonight into
Saturday. Did add in a patchy fog mention given expected crossover
dewpoints.

Broad governing upper low drifts slightly further east over southern
Quebec Saturday, which leads to column expansion of anticyclonic
trajectories over Lower Michigan. This causes sub-700 mb winds to
back toward the northwest, cutting off lake-effect shower potential.
Thermodynamic profiles are set to begin moderating Saturday as an
upper level ridge spills southeast from the Canadian Prairies. It
will take the rest of the weekend and into early next week for the
ridge axis to make more meaningful inroads through Great Lakes
region. A sharply tilted low amplitude shortwave trough riding the
tail of the departing upper low becomes cut-off over Appalachia
Sunday night, which leads to a quasi-Rex Block over the Great Lakes.
This keeps the warmest 850 mb temperatures over northern Ontario and
Hudson Bay (upper teens Celsius) while local values will be closer
to 10C. Ultimately, this should still translate to more seasonable
readings for Lower Michigan early next week (upper 70s to near 80F).
No precipitation expected Friday through Labor Day with more sun
than clouds.

Gradient flow organizes out of the south midweek, maybe as early as
Tuesday, which ushers in an opportunity for dewpoints to make a run
at 60F. This lends potential for destabilization should mid-level
lapse rates cooperate, but the better chance for widespread QPF
comes with the approach of another cold front dropping out of the
Upper Midwest. This should produce a swath of rainfall, a distinct
wind shift, and perhaps the coldest airmass of this astronomical
summer. Operational GFS and CMC bring the 0C 850 mb isotherm into
northern Lower Michigan behind the boundary. Additional, strong LLJ
dynamics in the vicinity could generate a period of enhanced gusts
toward the end of the workweek.

&&

.MARINE...

Northerly flow in the wake of a cold front will continue to maintain
elevated wave heights in the outer Saginaw Bay and across the Lake
Huron shorelines, where Small Craft Advisories remain in effect.
High pressure will build through the day, alleviating wind speeds
and wave heights which will allow the Small Craft Advisory to expire
late this morning. Otherwise, some scattered lake effect rain
showers remain possible across the southern Lake Huron basin. This
area of high pressure will sustain over the region through the
weekend.

&&

.PREV DISCUSSION...
Issued at 1158 PM EDT Thu Aug 28 2025

AVIATION...

Strong static stability is developing between 1.5 and 9.5 kft agl
this evening. Despite aggressive dry air advection, satellite
observational trends support ceilings below the inversion as
moisture remains trapped. Went decidedly more pessimistic with VFR
ceilings overnight. Lake effect cloud is anticipated downwind of
Lake Huron particularly after 10Z. Did go with MVFR cloud at the
northern taf sites. VFR overcast is anticipated midday at DTW.

For DTW/D21 Convection...No thunderstorms during the period.

THRESHOLD PROBABILITIES...

* High for ceilings less than 5000 ft Friday.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 10 AM EDT this morning for MIZ049-055-
     063.

Lake Huron...Small Craft Advisory until 10 AM EDT this morning for LHZ421-
     441>443.

Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

DISCUSSION...KGK
MARINE.......AM
AVIATION.....CB


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