316
FXUS63 KDTX 031031
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
631 AM EDT Wed Sep 3 2025

.KEY MESSAGES...

- A bit warmer and breezier with showers and a few thunderstorms
moving in throughout the day.

- Most of the rain should fall between 5 PM and 1 AM this evening.

- Cooler weather settles in Thursday, becoming briefly warmer
Friday, before trending below normal again over the weekend.

&&

.AVIATION...

Increasing south-southwest winds will precede an approaching cold
front today, with a solid region of 20 to 25 knots in the lowest 5k
feet. Deepening of the daytime mixed layer will lend itself to
increasing gustiness to the sfc winds. The approaching cold front
will be driven eastward across Se Mi tonight as a deep upper low
rotates into the northern Great Lakes. Weak instability along a
prefrontal trough axis this afternoon and evening will support
initial convective initiation as a line of showers and scattered
thunderstorms. The main cold front will progress eastward across Se
Mi tonight, resulting in widespread showers. A axis of moisture
along the front and the initial influx of post frontal cold air
advection will support widespread MVFR based clouds tonight, with
some areas of IFR possible.

For DTW/D21 Convection...Prefrontal forcing will align late
afternoon/evening convection into linear segments. Given the weak
instability, coverage of thunderstorms is expected to remain isolated
to scattered. Thunderstorm potential will be best after 23Z and
diminish after 02Z as instability wanes.

THRESHOLD PROBABILITIES...

* Moderate in thunderstorms this evening.

* High in ceilings aob 5000 feet tonight.

&&

.PREV DISCUSSION...
Issued at 345 AM EDT Wed Sep 3 2025

DISCUSSION...

Significant adjustments aloft are underway early this morning as an
extended period of dry weather concludes with the departure of
persistent ridging. A longwave trough encompassing the eastern two
thirds of CONUS remains stationary today with its axis of neutral
tilt extending from the Gulf Coast to Hudson Bay. An embedded
upstream shortwave becomes increasingly dynamic today as solutions
show this feature tracking from the Canadian Prairies into the
northern Great Lakes as a 548 dam closed low at 500 mb. The wave`s
cyclonic flow field extends through the depth of the troposphere
with the lower column circulation encroaching on Southeast Michigan
after 15Z. A ribbon of ThetaE extends along the LLJ which primes the
column for potential convective activity, as early as 18Z for
Midland and Bay Counties. This pre-frontal troughing may not suffice
with southeastward extent as it could outrun the supporting moisture
and instability profiles. Metro Detroit will be relatively cloud-
free until midday allowing for peak insolation and temperatures
breaking the 80F mark while cooler and breezier conditions reside
north of I-69.

The system`s cold front trails this initial line of shower/storms,
delaying the better forcing until the evening/overnight hours. CVA
moves in over the frontal slope with continued influx of moisture
along southwesterly flow trajectories. Expect a more widespread
precipitation response from 21Z to 09Z Thursday with the FROPA and
better shear parameters. Not expecting any severe weather given
mismatched timing for necessary shear and instability. The surface
front should exit into the southern Ontario peninsula between 06Z
and 09Z Thursday, preceding the onset of northwest flow and
deepening cold advection.

Forecast soundings indicate a shift to zonal flow throughout the
column by midday Thursday with a period of cooling and drying. 850
mb temperatures retreat from the low teens to the low-mid single
digits (Celsius) by 18Z Thursday, 24 hours later, as the cold-core
upper low takes residence over central Ontario. A speed max
currently ejecting across Canada`s Yukon Territory is expected to
dig into the High Plains Thursday and amplify over the Midwest
Thursday night with resultant 125+ knot jet streak. This supports
rapid cyclogenesis of a 990 mb surface low tracking racing across
The Straits on Friday. The system`s precipitation shield likely
extends into part of the local area with most of the shower activity
reserved for the Tri-Cities and Thumb. The entire forecast area will
be subject to substantially gustier weather should mixing depths
break into the 4-5 kft AGL range. Some 35+ mph gusts cannot be ruled
out. With preceding southwest flow and readings back in the 70s, a
dry FROPA veers winds westerly by the evening hours. Post-frontal
airmass sends highs back into the 60s for the weekend with mainly
dry conditions.

MARINE...

Weather will deteriorate today as a low pressure system and cold
front drop south into the Central Great Lakes, beginning with Small
Craft Advisories for gusty SW wind this 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 with a few embedded thunderstorms move across Southeast
Michigan today and tonight, ahead of a southeast moving cold front.
For most areas, the bulk of the rainfall will occur between 21Z
today and 06Z Thursday with 0.25 to 0.50 inches expected. Localized
1 inch rainfall totals cannot be ruled out. The front`s steady
forward progress, combined with subtropical moisture, should limit
minor flood potential to typical poor drainage areas. Drier
conditions filter in from west to east Thursday morning.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory from 10 AM this morning to 10 PM EDT this
     evening for LHZ421-422.

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

$$

AVIATION.....SC
DISCUSSION...KGK
MARINE.......SF
HYDROLOGY....KGK


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