240
FXUS63 KDTX 210703
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
303 AM EDT Mon Sep 21 2026

.KEY MESSAGES...

- Extended stretch of seasonably cool conditions will exist into the
  middle of the week.

- Aside from a low chance of rain early this week near the Ohio
  border, dry conditions are expected throughout the week.

&&

.DISCUSSION...

Southeast Michigan will remain positioned between loosely organized
split upper level flow thru the early week period, as a sprawling
1028 mb high pressure system centered to the north maintains a high
degree of influence. This pattern effectively retains east to
northeast low level flow, ensuring a seasonably cool resident
airmass holds firm during this time. 850 mb temperature projected to
dip into the single digits, translating into highs both Monday and
Tuesday of lower 60s most locations. Mainly dry with breezy
conditions as the profile remains dominated by larger scale
subsidence within a generally moisture starved profile. There
remains a lower end rain chance near the Ohio border, as shortwave
energy rippling thru the southern stream into the Ohio valley may
engage the deeper moisture still lingering near the Michigan-Ohio
border. Diurnal mixing will yield afternoon wind gusts generally in
the 20 to 25 knot range - slightly higher downwind of Saginaw Bay.

Weak upper level system will drift across the Ohio valley throughout
the mid-week period. This system will attempt to pull moisture north
and west toward the area Tuesday night into Wednesday. Broader
ascent offered by some degree of deformation may prove sufficient
toward generating some pockets of showers during this time, again
mainly for areas south of the I-94 corridor. Otherwise, stretch of
dry and stable conditions lasting through the end of the work week.
Lack of meaningful thermal advection as low level flow holds out of
the east-northeast maintains this stretch of below average
temperatures. Highs in the 60s with overnight lows dipping into the
mid to upper 40s.

The closed upper level low over the Ohio Valley is forecast to open
up into a progressive trough and fill as it gets absorbed into the
primary northern stream westerlies by Friday. Simultaneously, the
expansive surface anticyclone centered over northern Ontario/Quebec
will slowly shift eastward toward the Canadian Maritimes. Building
upper heights locally will solidify a gradually moderating thermal
profile while maintaining dry and stable background conditions. 850
mb temperatures will ease back toward the 10c range, allowing
readings to work back toward seasonal averages under nearly full
insolation. No rain expected thru the upcoming weekend, as
conditions remains governed by low and mid level ridging.

&&

.MARINE...

The central Great Lakes reside on the southern fringe of broad
northern Ontario high pressure through the first half of this week.
The combination with a lingering stalled frontal boundary over the
Ohio Valley results in a respectable gradient across the region
maintaining moderate northeasterly winds through Tuesday (gusting 20-
25kts with 30kts possible in the Saginaw Bay). Disturbances rippling
along the frontal boundary could offer some sporadic shower chances
over the southern Great Lakes though influence of high pressure is
expected to keep most of the area dry. Westward drift of high
pressure leads to a shift toward more easterly flow Wednesday though
with little to no reduction in wind speeds. Gales remain unlikely
though onshore flow warrants long duration Small Craft Advisories
for all nearshore waters.

&&

.PREV DISCUSSION...
Issued at 1154 PM EDT Sun Sep 20 2026

AVIATION...

Low level moisture associated with the frontal zone has been pushed
south of the airspace, with cloud cover now focused above 10.0 kft.
Localized pockets of low VFR/MVFR have been streaming off of Saginaw
Bay/Lake Huron, but are transient with low confidence in impacts to
the terminals. A similar pattern exists into the daytime hours, and
could see a brief period of broken 3.0-5.0 kft agl ceilings as
diurnal mixing ramps up in the morning. Otherwise, northeast flow
persists with sustained flow around 10-15 knots and gusts up to 25
knots. Wind direction stays locked in through the TAF period.

D21/DTW Convection...Thunderstorms are not anticipated through the
forecast.

DTW THRESHOLD PROBABILITIES...

* Low for ceilings at or below 5000 feet.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 10 PM EDT Wednesday for LHZ421-422-
     441>443.

Lake St Clair...Small Craft Advisory until 10 PM EDT Wednesday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EDT Wednesday for LEZ444.

&&

$$

DISCUSSION...MR
MARINE.......KDK
AVIATION.....MV

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