981
FXUS63 KDTX 300348
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1148 PM EDT Tue Jul 29 2025

.KEY MESSAGES...

- Increasing chance of showers and possible thunderstorms Wednesday
night into Thursday, with a narrow swath of heavy rain possible.

- Dry weather, with much cooler and less humid air in place on
Friday, lingering into the weekend.

&&

.AVIATION...

Limited cloud cover overnight and early Wednesday, aided by slightly
drier and stable conditions as a weak frontal boundary settles south
of the state. Winds will emerge from the north-northeast in the wake
of this boundary on Wednesday. VFR conditions maintained throughout
the day, as high based cloud thickens atop a standard coverage of
diurnal cu. A mid level wave tracking along this boundary will bring
the potential for rain Wednesday night. A few embedded thunderstorms
also possible should greater instability materialize.

For DTW/D21 Convection...Dry conditions favored through Wednesday
afternoon. Shower potential increases Wednesday night, with embedded
thunderstorms plausible should greater instability develop.

THRESHOLD PROBABILITIES...

* Low for thunderstorms Wednesday evening and overnight.

&&

.PREV DISCUSSION...
Issued at 240 PM EDT Tue Jul 29 2025

DISCUSSION...

Another very warm day across southeast Michigan as temps haven risen
into the upper 80s with surface dew pts mostly in the upper 60s to
around 70 degrees.

Jet core tracked through northern Lower Michigan/Lake Huron this
morning, with 0-6 km bulk shear of 50 knots. However, leftover shear
values over CWA generally around 30 knots per latest SPC mesoscale
analysis. Meanwhile, remnant inactive (thus far) MCV tracking through
southeast Michigan late this afternoon. Fortunately, instability is
mostly lacking over southeast Michigan, as 12z DTX sounding indicated
very dry mid levels and warm temps, extending down to 900 MB. Still,
as temps approach the convective temp of 90 degrees, there may be
enough low level moisture pooling to get areas of MLcapes at or
slightly above 1000 J/kg. Will carry just a slight chance of a
thunderstorm into the evening hours. Slightly better shear is over
northern Thumb region where there is little in the way of cape.
Toward the southern Michigan border is where the moderate cape
resides due to the better surface dew pts, but still some MLCIN in
place.

Upper level energy coming out of the northern Rockies, with modest
height falls tracking through southern Lower Michigan tomorrow
afternoon-night. Main moisture axis (PW values ~1.5 inches), 850-700
MB Theta-E ridge currently over Lower Michigan will be sinking south
tonight into Wednesday. The baroclinic zone/south to north moisture
gradient will be tightening up significantly. The 12z NAM has
trended fairly extreme with surface low/wave riding along the front
for Wednesday night-Thursday. Regardless if it is a flatter wave,
see Canadian model, prospects for showers looks very high for
Wednesday night-Thursday morning at the very least. The strength of
the wave/surface reflection will determine where the axis of heavy
rain lines up, and NAM is likely too far north, as euro ensembles
suggests highest amounts along and south of I-94 corridor. Still, a
mid level fgen flare up for areas between the M-59 and I-69
corridors is in play, and with tropical like 700 MB dew pts of 5-7
C, heavy rain is a concern. This forecast is still a bit in flux
with the inconsistent solutions, and NBM pops have at least
continued to trend upward Wednesday night into Thursday, but still
likely not enough.

Drying out to end the work week as the west-northwest upper level
flow takes hold with the expanding broad upper level trough axis
developing over the Great Lakes region on Friday. Significantly
cooler and drier airmass, which looks to persist into the weekend as
the surface high is slow to retreat eastward. Temps slightly below
normal trending close to normal by Sunday.

MARINE...

A weak disturbance passing through the Great Lakes maintains a
chance for widely scattered showers and thunderstorms through this
evening. Ambient wind remains below 10 kt and disorganized, but may
be locally stronger within any storms. Wind then becomes more
organized out of the north overnight into Wednesday at around 10 to
15 kt as cooler air begins to filter in from Canada. Chances for
additional showers and storms Wednesday into Wednesday night will be
focused across southern Lake Huron, Lake St. Clair, and Lake Erie.
Stronger NE wind develops Thursday and may necessitate Small Craft
Advisories around the Thumb due to wave heights building within the
onshore flow. High pressure then spreads in from the upper Midwest
late week into the weekend to support a period of benign marine
weather.

HYDROLOGY...

A frontal boundary lingering around the southern Michigan border
Wednesday night into Thursday will bring a threat of heavy rain.
However, the exact location remains uncertain, as the swath of
potential heavy rain (1-2 inches) looks to be narrow. The favored
location at this time suggests I-94 corridor and points south, with
the bulk of the rainfall during the early morning hours of Thursday.
With the rainfall likely falling in a longer period (4-6 hours), any
flooding should be minor in the typical low lying/flood prone areas.

&&

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

$$

AVIATION.....MR
DISCUSSION...SF
MARINE.......TF
HYDROLOGY....SF

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