916
FXUS63 KDTX 162255
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
655 PM EDT Wed Jul 16 2025

.KEY MESSAGES...

- Areas north of I-69 could see some additional storms late tonight.

- A cold front works through Thursday producing some additional
morning showers/storms, then cooler and less humid air filters in
through Friday.

- Additional storms possible Saturday with temperatures near
seasonal normals.

&&

.AVIATION...

While a few scattered showers/storms are still around this evening,
the coverage is waning as we lose diurnal heating. Between 03-07Z,
the remnants of convection over WI/MI/IN will track across southeast
Michigan. Current radar trends and high-resolution guidance show a
gradually diminishing trend with this activity as it gets closer.
Have PROB30 mentions for -RA/TSRA between roughly 03/07Z, with
higher confidence in seeing overnight storms up near MBS/FNT. A cold
front moves through early Thursday morning, allowing south winds to
become westerly and northwesterly between 10-13Z. Along and behind
the cold front, wind gusts up to around 20-25 knots are expected
along with the arrival of MVFR stratus.

For DTW/D21 Convection...Convection is becoming more isolated this
evening as we lost daytime heating. The next round of decaying
showers and storms arrives between 04-07Z.

THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less late tonight, and especially on
  Thursday.

* Low to moderate for additional thunderstorms through 07Z tonight.

&&

.PREV DISCUSSION...
Issued at 350 PM EDT Wed Jul 16 2025

DISCUSSION...

Moist antecedent conditions are in place across Southeast Michigan
with surface dewpoints in the low to mid 70s and Precipitable Water
values exceeding 2.00 inches. Heavy rainfall and localized flooding
remains the main threat this afternoon with rainfall rates of 0.75
inch in 30 minutes being observed. Difficult to gauge exactly how
widespread the rainfall amounts will be with no larger scale focus
mechanism. There is some signal in the hires solutions that suggests
some southwest to northeast convergence boundary over portions of
Metro Detroit up into the Thumb, that could possibly be orographic
and coincident to the windward side of the Irish Hills. Models do
suggest that convection will gust out, which has been observed with
little to no organization in the ongoing storms. It still remains
possible that as the afternoon wears on and the depth of the
convection increases there could be a gravity wave that develops
(reference the morning update discussion). Thus, will monitor for
the development which could cause different storm behavior with
storm mergers.

The arc of discrete cells across Wisconsin has been modeled to
transition into a bowing cluster or line segment in vicinity of
Lake Michigan by this evening. Latest consensus of many NPW sources
suggests the convection or convective remnants will push eastward
northeastward into the Saginaw Valley or immediately north of the
cwa sometime between 02z-06z. This fits the conceptual model of the
convection favoring the northeast quadrant of the MCV and localized
vorticity anomaly. However, there is an outlier solution namely the
consistent HRRR runs that brings the center of the bow farther south
down into the I69 corridor before weakening overhead. This remains
plausible because there could be an acceleration of the line
cluster/feature eastward into the surface based CAPE reservoir
during the evening transition. With that stated there is a healthy
amount of convection ongoing over portions of western and central
Lower Michigan that could disrupt the available instability. A strong
to severe threat for damaging wind gusts will exist as long as the
convective line remains organized.

A surface dewpoint front or cold front is forecasted to push
southward Southeast Michigan mainly between 12-15z Thursday. Plan
views and forecast soundings support isentropic downglide and very
active subsidence in the 3.0 to 8.5 kft agl layer. This will
effectively shut down any lingering precipitation chances over
Southeast Michigan Friday away from any small chances near Lake
Erie. There is some indication that higher dewpoints could mix
downward from aloft during the day which could elevate surface
dewpoints in a shallow layer at the surface. Heat indices over Metro
Detroit could again reach the middle 80s.

A shallow, cool airmass  will be in place over Southeast Michigan
Friday supporting high pressure and comfortable weather
(temperatures 3 to 5 degrees below normal). The next warm advection
surge will be quick on the heels bringing rain and thunderstorm
chances again Friday night and Saturday. Difficult to offer much
definitive timing with the zonal jet configuration.

MARINE...

Moist, unstable conditions continue to provide fuel for scattered to
numerous showers and thunderstorms through this afternoon and
evening. Some of the thunderstorms could be strong, producing
localized wind gusts in excess of 40 knots. Compact low pressure
tracks east across Lake Michigan this evening before reaching
Saginaw Bay and central Lake Huron by early Thursday morning. This
brings additional showers and storms overnight. The cold front
pushes across the area through the rest of the morning with gusty
northwest wind ensuing in its wake. This will reach the 20 to 25 kt
range during the late morning and afternoon with waves in excess of
4 feet developing over parts of Lake Huron. These waves may impact
parts of the nearshore around the tip of the Thumb and will monitor
the need for a Small Craft Advisory. Winds then veer around to the
north-northeast Thursday evening while decreasing to 15 knots or
less. Broad high pressure builds into the area on Friday, promoting
light and variable winds.

&&

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

$$

AVIATION.....JA
DISCUSSION...CB
MARINE.......TF


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