992
FXUS63 KDTX 181701
AFDDTX

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

.KEY MESSAGES...

- Dry and seasonable conditions for much of today.

- A low chance of showers and thunderstorms starting late afternoon
across the Saginaw Valley and Thumb, with a greater potential for
showers with isolated thunderstorms for all of southeast Michigan
tonight.

- A few lingering showers possible early Wednesday, then turning
drier again with temperatures slightly below normal for the end of
the week.

&&

.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.

&&

.PREV DISCUSSION...
Issued at 333 AM EDT Tue Aug 18 2026

DISCUSSION...

Pleasant again today as the region starts the day under the
influence of departing high pressure. Subtle change from yesterday
is the establishment of deep layer westerly flow into southern lower
MI with the departure of said high. This nudges temps up a couple
degrees with highs around the mid 80s as well as a modest increase in
humidity with dewpoints creeping back to the lower to mid 60s.
Increasing afternoon cloud cover marks the arrival of a cold frontal
boundary dropping through the Great Lakes. High res models continue
to key on a prefrontal trough feature sliding over northern lower
MI/Lake Huron generating isolated to widely scattered
showers/thunderstorms. While the best potential stays north of the
area, the Saginaw Valley/Thumb hold on its southern fringe offering
some late afternoon rain chances, particularly north of M-46. Main
window for SE MI as a whole however comes late evening-overnight as
the surface cold front reaches the Straits/northwestern Lake
Michigan. Frontal boundary expected to generate a healthy coverage of
convection over the western Great Lakes however local arrival in the
western CWA looking to be between 00-03Z. Late in the diurnal window
in addition to signal convection outpaces driving instability,
increases uncertainty to what degree thunderstorms can maintain
themselves while crossing the state. Areas west of I-75/US- 23 stand
the best chance at thunder given the earlier timing supporting higher
residual CAPE. While an isolated stronger cell capable of gusty
winds can`t be ruled out due to marginally favorable kinematics
(unidirectional shear around 30kts), the thermodynamic setup (lapse
rates under 6.5 C/km & ~500 J/kg of elevated CAPE) is unfavorable for
severe storms.

Scattered to numerous showers with isolated thunder work across the
area for the rest of the night before the cold front clears to our
south first part of Wednesday morning. Passage of a secondary cold
front daytime Wednesday could generate a few afternoon showers,
though most of SE MI stays dry. Drier weather holds through the
remainder of the work week as surface high pressure slides directly
across lower MI. Unsettled pattern eventually returns Friday night
into the weekend as a mid-level shortwave dropping out of the
Canadian Prairie reaches the Great Lakes amplifying overhead upper
troughing.

MARINE...

Southwest flow briefly becomes established this morning as high
pressure washes out across the eastern Great Lakes. Winds remain
light for most locations through the afternoon, but localized
stronger gusts around 20 knots will be possible in the Saginaw Bay
given the more favorable fetch.

More active weather returns this afternoon and evening with the
passage of a cold front. Showers and thunderstorms will be likely
with the front as winds veer from southwest to northwest in the wake
of the front. A slight uptick in winds are expected along and behind
the front as cooler conditions filter in. Wind gust of 20 to 25
knots will be likely with the frontal passage. High pressure will
then fill back in on Thursday, tempering wind speeds for the day.

&&

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

$$

AVIATION.....MR
DISCUSSION...KDK
MARINE.......AM


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