144
FXUS63 KDTX 121900
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
300 PM EDT Tue Aug 12 2025

.KEY MESSAGES...

- Scattered-numerous showers and thunderstorms to re-develop
through tonight.

- The strongest storms will be capable of producing locally heavy
rainfall. In addition, isolated wind gusts of 50 to 60 mph will be
possible through this evening.

- High pressure brings near normal temperatures and less humid
conditions to close out the work week.

- Heat returns for the weekend.

&&

.DISCUSSION...

Very moist airmass in place, as indicated by the 6 C dew pt at 700
MB indicated by the 12z DTX sounding, with surface dew points
currently in the upper 60s to lower 70s. Mid level jet max which was
responsible for bulk of convection across Lower Michigan today is
exiting the Central Great Lakes at the present time.

Additional, more subtle shortwaves tracking through the rest of day
into the evening hours before main trough axis/height falls swing
through early Wednesday morning, making for a complicated forecast.
Mid level temps/500 MB barely budge over southern Lower Michigan, as
tight gradient is displaced over northern Lower Michigan. Notable
shortwave over northwest Missouri, but it appears this feature is
lagging the northern stream and will not become absorbed, and will
track slowly through the western Ohio Valley. Notable 850 MB Theta-E
ridge (355-357 K) around the Detroit Metro Area late this
afternoon/early this evening with pre-frontal trough or outflow
boundary potentially leading to sufficient convergence to generate
heavy rain producing storms with SBcapes in the 1500-3000 J/kg
range.

Overall wind shear across southeast Michigan remains weak (effective
shear under 30 knots), but isolated precip loaded downburst winds of
50-60 mph remain on the table with downdraft capes around 1000 J/kg.

The surface cold front looks to moving through very slowly tonight,
and additional redevelopment is likely with the modest southwest 850-
700 MB speed max tracking through with some lingering instability
leftover.

Any lingering showers around Wednesday morning should dissipate as
westerly upper level confluent flow and low level drying takes hold
during the day, but perhaps still enough near surface moisture/instability
toward the south Michigan border in the afternoon to trigger isolated
activity, along with areas downwind of Lake Huron with moisture flux
boost from warm waters.

Broad troughing for Wednesday night into Thursday, with subtle
shortwave tracking through, potentially sufficient to trigger a
isolated shower over the Central Great Lakes. However, mid levels
will likely be too dry with 30 C dew pt depressions, and the NBM is
going out with pops of 10 percent or less.

Upper level ridge (594+ dam at 500 MB) then builds back over the
Midwest to end the work week, allowing for heat (90+ degrees) to
return for the Weekend, as 850 MB temps reach toward 20 C.
However, there are a couple opportunities for ridge riders to come
over the top and track into Lower Michigan as the ridge folds over
and sinks south to end the weekend.

&&

.MARINE...

Low pressure tracks across Hudson Bay tonight, dragging a cold front
across the Great Lakes Wednesday. Ahead of the frontal passage,
multiple waves of showers and storms will be possible. A combination
of outflow and lake breeze boundaries have already been a catalyst
for convection this afternoon, with the outflow sinking south across
Lake St. Clair and western Lake Erie through roughly 00z (8pm
local). This will be the best timeframe to see an isolated wind gust
over 40 knots. Showers and a few thunderstorms continue overnight
until the cold front begins to clear the Great Lakes early Wednesday
morning. The fropa will be marked by a shift to northwest flow for
Wednesday and Thursday, with sustained winds of 10-15 knots and
gusts of 15-20 knots. Winds gradually veer to the south by Friday as
the high pressure center moves overhead, relaxing winds below 10
knots.

&&

.HYDROLOGY...

Scattered-numerous showers and thunderstorms are expected to persist
into tonight. A very moist environment will create favorable
conditions for locally heavy rainfall, with rainfall rates briefly
in excess of 2"/hr under the strongest storms. Basin average
rainfall rates between one half and one inch are possible, with
locally higher amounts in excess of one inch where slow moving or
training cells develop. Localized flooding of urban, low-lying and
poor drainage areas along with rises in area rivers will be
possible.

&&

.PREV DISCUSSION...
Issued at 144 PM EDT Tue Aug 12 2025

AVIATION...

Organized moisture advection ahead of a deep Canadian midlevel
trough will lead to shower and thunderstorm activity across
Southeast Michigan today and tonight. Currently observing a
composite outflow just north of Metro Detroit that is currently
funneling shower activity over the I 69 corridor. SCT-BKN low VFR
cumulus activity has developed to the south of this boundary within
a pristine diurnally heated airmass. IFR to occasional VLIFR
conditions in heavy rainfall will be possible with any this
afternoon through 06Z tonight. There is uncertainty with much
activity will impact the Detroit terminals specifically as there is a
model signal that suggests storms will not be favorably aligned to
the wind shear.

For DTW/D21 Convection...The likely time window for thunderstorm
activity is 23z and 03z this evening.

 THRESHOLD PROBABILITIES...

* Low for thunderstorms this afternoon. Moderate for this evening.


&&

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

$$

DISCUSSION...SF
MARINE.......MV
HYDROLOGY....SF
AVIATION.....CB


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