054
FXUS63 KDTX 271950
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
350 PM EDT Wed Aug 27 2025

.KEY MESSAGES...

- Showers increase Thursday morning with a chance of non-severe
  thunderstorms, mainly during the afternoon hours.

- Temperatures will remain below average for late August through the
  end of the week.

&&

.DISCUSSION...

SE Michigan remains on the northern fringe of surface high pressure
this evening. The 12z DTX RAOB sampled a very dry airmass, with a
PWAT of 0.37". Moisture has since increased, which has aided in the
development of a scattered cumulus deck, but dry conditions are
expected through most of tonight. Temperatures in the low 70s at
issuance characterize another pleasant evening across SE Michigan.

Meanwhile, an upper low (currently located over James Bay) will
plunge south toward New England tonight and Thursday, driving a cold
front through the Great Lakes as it does so. Already starting to see
the frontal response ongoing across the Upper Peninsula and northern Lake
Huron where showers have increased in coverage. Frontal convergence
will be the primary forcing mechanism, with a broken band of showers
reaching the Saginaw Valley and Thumb regions around daybreak
Thursday morning. The front will then gradually settle through SE
Michigan during the course of the day, expanding shower coverage
south of M-59 by mid-day. A compact mid-level wave trails closely
behind the front, pivoting around the upper low and trending the
trough axis toward a neutral tilt. This adds a second layer of
ascent during the afternoon hours. Afternoon destabilization further
aids shower activity, with an increasingly convective nature and
increasing thunder chances during the afternoon. Updrafts will
struggle to become organized amidst a weakly unstable environment and
modest mid-level flow (< 30 knots). Instability will be bound to a
relatively narrow corridor between moisture convergence/cold
advection near the front and trailing subsidence behind it. All of
these factors contribute to a General Thunder designation from SPC
for SWODY2. Max PoPs are categorical with this event reflecting very
good model consensus as all LREF members generate QPF (interquartile
range between 0.2" and 0.5"), although some convective enhancement
could generate locally higher totals.

Subsidence squashes convective depths and strips away enough
moisture to bring an end to shower chances late Thursday afternoon-
evening from north to south. The exception to this will be downwind
of Lake Huron, where northerly flow and warm lake temperatures
maintain lake induced CAPE and thus shower chances into Friday. The
broader impact of the fropa is a strong surge of cold advection into
SE Michigan which drops 850mb temperatures to 3-5 C and holds
daytime highs in the 60s on Friday. High pressure returns for the
weekend, ensuring mainly dry conditions although some enhancement to
boundary layer moisture is likely as moisture flux continues off of
the lakes. This will be reinforced by periods of northerly flow and
longwave troughing that maintain fall-like temperatures in the 70s
this weekend.

&&

.MARINE...

Rain showers will move in across northern Lake Huron this afternoon
and evening before a more robust line of showers with possible
embedded thunderstorms fills in late tonight along a progressing
cold front. This front will sag south across the Great Lakes through
the morning and early afternoon hours tomorrow, bringing the
continuation of shower and thunderstorm chances. Convergence along
the frontal boundary coupled with the rush of cooler air behind the
front does bring the chance for waterspout generation through the
day tomorrow as wind direction backs from southwest to north-
northwest. Better mixing depths behind the front with the cooler air
will increase over lake instability, allowing sustained winds around
20 knots with gust potential around 25 knots to then persist through
early Friday morning.

Small Craft Advisories will be needed for at least the outer Saginaw
Bay and Lake Huron shoreline Thursday afternoon through Friday
morning for both wind and wave concerns. High pressure quickly fills
in Friday through the day, alleviating the more active conditions.

&&

.PREV DISCUSSION...
Issued at 130 PM EDT Wed Aug 27 2025

AVIATION...

Trailing influence of high pressure maintains modest west flow under
VFR skies today. High cloud thickens through the latter part of the
day/tonight ahead of an approaching cold front dropping out of the
northern Great Lakes. Associated showers expand north to south over
the course of Thursday morning bringing MVFR to IFR cigs. A few
embedded thunderstorms are likely, focused towards afternoon,
however coverage and timing are too nebulous at the current time to
warrant more than a Prob30 highlight.

For DTW/D21 Convection...Showers arrive late morning over the
airport. A few embedded thunderstorms are expected during the
afternoon with best chances currently looking to fall closer to the
18-22Z timeframe.

THRESHOLD PROBABILITIES...

* High for ceilings below 5,000 feet Thursday morning.

* Low to moderate for thunderstorms Thursday afternoon.


&&

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

$$

DISCUSSION...MV
MARINE.......AM
AVIATION.....KDK


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