647
FXUS63 KDTX 021957
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
357 PM EDT Tue Sep 2 2025

.KEY MESSAGES...

- Breezy and warm Wednesday.

- Showers and a few ordinary thunderstorms move in with a cold front
  late Wednesday afternoon through Wednesday night.

- Cooler temperatures settle in Thursday which last into the weekend
  resulting in afternoon highs about 10 degrees below normal each
  day.

&&

.DISCUSSION...

Surface high pressure that dominated SE Mi over the Labor Day
weekend supplies favorable conditions for a while longer this
afternoon and tonight. Fair weather cumulus and pleasant highs
near 80 lead into a clear and cool evening. The transition toward
influence of the next low pressure system then begins later tonight,
the first sign of which is wind becoming more consistently from the
south. High clouds also begin moving in from the west to combine with
the south wind for support of warmer morning lows compared to recent
days. Readings were frequently in the 40s outside of the metro areas
over the weekend and now are expected to hold in the mid to upper
50s by sunrise Wednesday.

The inbound low pressure system is well presented in satellite
imagery and surface analyses this afternoon compared to model
initializations. The system is set to intensify as advertised across
the range of model solutions as a 120 kt 250 mb jet digs in on the
upstream side of the system during Wednesday into Wednesday night.
SE Mi benefits from peak southerly surface and low level flow in the
warm sector of the system that boosts temperatures into the lower
80s across the region, readings that won`t be seen for at least the
next 5-7 days. There is also a respectable moisture axis with the
system in terms of model 850-700 mb theta-e fields, however surface
Td holds mostly below 60 F and PW rises "only" into the 1-1.5 inch
range. This results in HREF mean MUCAPE below 1000 J/kg as the
bottom line for just a general thunder SPC outlook in this scenario.
The low closes off but the cold front sweeps steadily through
southern Lower Mi to also minimize or eliminate concerns for heavy
rainfall/flooding.

A sharp temperature reversal occurs with the bulk of low level cold
advection during the post front period Wednesday night leading to
upper 40s to lower 50s at most locations by sunrise Thursday. Cold
advection is weaker but still able to push back against daytime
heating and hold temperatures in the 60s across the area Thursday
afternoon. There is also good model consistency regarding the timing
and placement of the larger scale mid level dry slot to hold back
any additional showers across the area, although a hefty diurnal
cloud component is shown in model RH fields into Thursday night.

The next chance of showers and cold air reinforcement arrives with a
potent short wave low pressure system advertised for Friday. This
system continues to gain timing and intensity consensus across
deterministic models as it develops within the lengthy northern
stream upper level jet and into the west flank of the northern
Ontario/Great Lakes closed low. Guidance high temperature recovery
into the 70s Friday is quickly cooled bay down into the 60s to start
next weekend.

&&

.MARINE...

Very light and variable winds around this afternoon over the Central
Great Lakes under mostly clear skies. Weather will deteriorate
tomorrow as a low pressure system and cold front drop south into the
Central Great Lakes, beginning with Small Craft Advisories for gusty
SW wind Wednesday afternoon leading into showers and possible
embedded thunderstorms. The cold front will drive much colder air
across the lakes for Thursday, ushered in by strong northwest winds
(20-30 knots). Another low pressure system diving southeast from
Central Canada will deliver a second shot of cold air, which will
support a chance of waterspouts and isolated showers for the
Weekend. Out ahead of the low on Friday, southwest winds have the
potential to reach gales over Lake Huron, but confidence remains low
as the strength and exact location of the low remains uncertain.
With water temps mostly in the mid 60s over Lake Huron, near lake
stability looks to to be neutral with the warm advection out ahead
of the low. Even so, with the expected strength of the low/pressure
gradient, southwest wind gusts of 30-35 knots appear likely, but the
duration of the gales will probably not be sufficient to justify a
warning, unless a further uptick is noted. Central Lake Huron and
Saginaw Bay look to see the highest winds with the southwest wind
direction. Cold advection on Saturday and increasing mixing depths
lead to further westerly wind gusts around 30 knots and flirt with
low end gales as well, mainly over the northern third of Lake Huron.

&&

.HYDROLOGY...

Showers and a few thunderstorms move across SE Michigan Wednesday
afternoon and night. The more meaningful rainfall occurs over about
a 6 hour time period Wednesday night when 0.25 to 0.5 inch is likely
at most locations. Localized 1 inch totals are possible, however the
associated cold front moves steadily west to east across the region.
This reduces the potential for excessive rainfall and related
flooding hazards until the pattern exits eastward Thursday morning.

&&

.PREV DISCUSSION...
Issued at 153 PM EDT Tue Sep 2 2025

AVIATION...

High pressure will produce another day of VFR conditions today and
tonight before a cold front sweeps across the region Wednesday
afternoon. Diurnal cu field will scour out this evening leaving
mostly clear skies with the exception of some cirrus moving in
tonight. Winds remain light through tonight, under 10 knots, before
increasing Wednesday out of the southwest ahead of the front. Gusts
could reach 20 knots in the afternoon. Frontal clouds and precip
will largely occur after the forecast ends, but some lower clouds
will move into MBS and possibly FNT around 15Z. MBS could also see a
light shower during the 15-18Z window but chances are too low to
include at the moment.

For DTW/D21 Convection...No thunderstorms expected today or tonight.

THRESHOLD PROBABILITIES...

* None


&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...None.

Lake Huron...Small Craft Advisory from 10 AM to 10 PM EDT Wednesday for LHZ421-
     422.

Lake St Clair...None.

Michigan waters of Lake Erie...None.

&&

$$

DISCUSSION...BT
MARINE.......SF
HYDROLOGY....BT
AVIATION.....DRK


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at www.weather.gov/detroit.