408
FXUS63 KDTX 181947
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
347 PM EDT Tue Aug 18 2026

.KEY MESSAGES...

- Some showers and a few thunderstorms tonight with isolated
  marginally severe gusts possible.

- A few lingering showers are possible early Wednesday, then turning
  mainly dry through the end of the week.

- The next chance for showers and storms arrives Friday night,
  continuing into Saturday.

&&

.DISCUSSION...

Surface high pressure influence exits this evening as a cold front
continues to advance toward Lower Michigan tonight. A disjointed
line of showers and thunderstorms currently positioned along the
front should persist and grow in scale as the boundary approaches
Southeast Michigan. This results in a period of nocturnal convection
which should become more organized as the evening wears on, possibly
containing some multicell clusters and linear segments. One limiting
factor will be timing since the diurnal cycle will have already
peaked, but regardless, low-level CIN should inhibit the path of
most surface-based parcels. Aloft, mid-level lapse rates are more
supportive of instability, but with limited density as MUCAPE values
should only reside within the 200-500 J/kg range. SPC`s latest
SWODY1 added a Marginal Risk to more of Lower Michigan, extending
all the way across The Plains, and up into Montana. Main concern
will be a rogue downdraft or two, resulting in a low-end chance for
isolated marginally severe gusts. Machine learning datasets are
mixed on any severe potential.

The front slows Wednesday, becoming quasi-stationary over the Ohio
Valley as the governing longwave composite trough axis aloft becomes
stalled. The placement of the surface convergence zone favors a
mainly dry forecast for Wednesday, after any morning remnants clear
south. The post-frontal airmass will only be slightly cooler,
hindered by unfavorable WNW flow trajectories that delay the onset
of more robust cold advection. Some evidence of a secondary weak
backdoor cold front trying to move in off Lake Huron, but diffuse
pressure field limits the cohesiveness of a material northeasterly
wind shift. Between the backdoor front over The Thumb, and the
stalled boundary just to the south, potential exists for additional
convection Saturday. The 12Z HRRR is the most aggressive CAM in
generating Wednesday afternoon convection along/north of I-69,
although it`s in the extreme minority as NBM PoPs are about zero
between 18Z and 00Z Wednesday. Note that the 18Z HRRR fell in-line
with the rest of the Hi-Res space. Mid-level perturbation within the
mean flow does offer weak synoptic support. Areas to the far south
may see diurnal convection spill just north of the Michigan/Ohio
state line. No severe weather expected with any conditional
convection Wednesday.

Surface high pressure attempts to build more aggressively into Lower
Michigan on Thursday, in spite of persistent vicinity longwave
troughing. Lower column stability/drying and subtle warming aloft
make for a difficult setup for any shower activity to materialize.
Temperatures persist near or a couple degrees above normal, in the
lower 80s. The next chance for showers and storms arrives Friday
night, continuing into Saturday as the next wave digs across the
High Plains toward the Ohio Valley. Thermal troughing fills in
afterwards, delivering slightly cooler than normal conditions into
early next week as 700 mb temperatures dip near/below 0C.

&&

.MARINE...

A cold front will pass from north to south across the Great Lakes
this evening and into the early morning hours which will veer wind
direction from southwest to northwest. Showers and thunderstorms
will be likely with the passage of the front. There will be a low
chance for a stronger isolated thunderstorm capable of producing a
wind gust aoa 34 knots. This will be most favorable across Lake
Huron.

High pressure fills back in behind the front which will
maintain lighter wind speeds through Thursday. Additional chances
for showers and storms will return Friday into the weekend with the
passage of a warm and subsequent cold front.

&&

.PREV DISCUSSION...
Issued at 101 PM EDT Tue Aug 18 2026

AVIATION...

Pockets of high based cloud atop a scattered to briefly broken
coverage of diurnal cu will mark conditions through the late
afternoon hours. Prevailing wind from the west-southwest. A weak
frontal boundary lifting across the region will bring increasing
potential for shower development late this evening and overnight.
Isolated thunderstorm potential also exists, but confidence in
occurrence remains low and precludes a defined mention. Window
exists within the immediate post-frontal environment for lower
stratus to increase coverage, leading to some intervals of MVFR
cigs. Forecast will continue to highlight this potential for late
tonight. Lingering low cloud lifts into a standard VFR cu field for
Wednesday. Post-frontal winds becoming northwesterly Wednesday.

D21/DTW Convection...Very low chance of a thunderstorm tonight.

DTW THRESHOLD PROBABILITIES...

* Low for ceiling at or below 5000 feet this afternoon into the
  evening, medium tonight, and high tomorrow morning.

* Very low for thunderstorms tonight.


&&

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

$$

DISCUSSION...KGK
MARINE.......AM
AVIATION.....MR


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