277
FXUS63 KDTX 160425
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1225 AM EDT Wed Sep 16 2026

.KEY MESSAGES...

- Rain and thunderstorm chances continue into the midweek period.

- A first look at the weekend indicates showery weather but mild
  temperatures Saturday and Sunday.

&&

.AVIATION...

Thunderstorm clusters exiting the DTW corridor at forecast issuance
are followed by the cold front that also exits south and east before
sunrise. The forecast focus then turns to cloud conditions along
with any stray showers or rumble of thunder post front through the
morning. Expansion of MVFR stratus with a fog component are
maintained in light and variable wind that turns NE off Lake Huron
in the low levels, and as breaks in mid/high clouds allow some
boundary layer radiational cooling. Borderline MVFR/low VFR ceiling
then continues through the afternoon, especially toward DTW with the
cold front still nearby to the south. This is also where the
potential for showers and a rumble of thunder are greatest, although
timing predictability is on the low side. Farther north, the inbound
high pressure air mass has just enough dry air to combine with
daytime heating and nudge the cloud edge south of MBS mid to late
afternoon.

D21/DTW Convection... A rumble of thunder lingers during the late
night as the cold front moves through the region before sunrise.

.DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less late tonight and Wednesday.

* Moderate for thunderstorms before sunrise.

&&

.PREV DISCUSSION...
Issued at 910 PM EDT Tue Sep 15 2026

UPDATE...

An arc of instability has built into SW Lower Michigan and is
expanding into portions of SE Michigan as of 9 PM local time. This
has led to blossoming convection along a line from roughly Jackson
to South Bend to Kankakee with cells moving east-northeast. A couple
of these cells have acquired stronger updrafts with latest radar
scans showing echo tops over 40.0 kft arl, and will likely cross the
CWA border within the hour and remain along/south of I-94 as they
march east-northeast.

These cells have quickly grown upscale, materializing into a heavy
rainfall threat if they can hold together upon crossing the
instability gradient. Rainfall rates may exceed 1" per hour in any
thunderstorm activity, but the overall eastward progress of the line
is encouraging for limiting duration at any one location. Will
monitor for localized flooding concerns, particularly in low-lying
and urban areas as discussed in the Hydrology section from earlier
today. The deeper convective cells also warrant monitoring for a
severe threat, but are competing against waning daylight and the low
level subsidence bubble that was sampled in the 16.00z KDTX
sounding. Main concern continues to be isolated gusts that could
approach severe limits, more likely toward the Ohio border where
dewpoints are flirting with 70 degrees. Storms however are moving
into an environment that is more supportive of elevated convection.
No major changes to thinking from the afternoon package.

PREV DISCUSSION...
Issued at 353 PM EDT Tue Sep 15 2026

DISCUSSION...

Expansion of high pressure across the upper Midwest will progress a
cold front into southern Michigan where the boundary is then
expected to slow and stall out tonight. This will retain an area of
enhanced theta-e across southern Michigan overnight, characterized
by PW values nearing 2" closer to the MI/OH border along with 850mb
dew points ranging between 12-14C. Low level convergence and weak
shortwave impulses within this region of higher moisture will be the
focal point for renewed showers and possibly thunderstorms this
evening through at least tomorrow morning.

For tonight, expansion of renewed showers and isolated thunderstorms
will be more favorable around and south of M59. Any arrival of
convection between 23Z - 02Z may be able to capitalize on a brief
increase in surface instability along the nose of enhanced theta-e
ahead of the cold front. This coupled with moderate low to mid level
lapse rates and 0-6km bulk shear around 35 knots will bring some low
end chances for an isolated strong to severe thunderstorm. Any
stronger development will be capable of producing localized stronger
wind gusts from a wet microburst. SR-hodographs also show a modest
streamwise component from 0-3 km, highlighting potential for some
better organization, but all said, poor buoyancy with unfavorable
timing of convective potential will be a major hindrance to any
robust convection. SWODY1 highlights a marginal risk for several
weather for this activity.

Severe chances are then mitigated overnight once surface instability
wanes and conditions turn more elevated. Zonal low to mid-level flow
will bring continuation of shower and storm potential overnight
through tomorrow afternoon. Any repeated shower and thunderstorm
will have the low potential to bring localized flooding in flood
prone locations. See the hydrology section for additional details.

The frontal boundary will waver across southern Michigan late
Wednesday into Thursday, providing additional chances for showers
and thunderstorms through the midweek period. Some respite from rain
chances will be likely late Thursday into Friday as the southern
periphery of high pressure builds in across the Great Lakes, but
additional chances for showers and storms, possibly heavy rain, will
re-enter on Saturday as storm complex derives from the Plains
progresses into a stronger baroclinic zone. There is uncertainty
this far out regarding where any enhanced forcing will align, with
mid-range models highlighting anywhere from central Michigan to
locations south into the Ohio Valley as potential zones for elevated
QPF.

MARINE...

An occluded low pressure system tracks into Hudson Bay this evening
with its southwesterly low-level jet easing out of the northern
Great Lakes with time. The core of the strongest winds has already
exited the area and the Gale Warning will be allowed to expire on
time at 4 PM. The system pushes a cold front across the area
overnight, causing southwesterly wind to quickly veer to north and
northeast by Wednesday morning. Ahead of the front this evening and
overnight, additional scattered showers and a few thunderstorms will
be possible mainly for Lake St. Clair and western Lake Erie. An
isolated storm may be strong to severe with wind in excess of 34 kt
the main threat. High pressure passes to the north of the lakes on
Wednesday, sustaining continued northeasterly flow of 10 to 15 kt. A
chance of showers and storms lingers around the southern Great Lakes
through Wednesday and Thursday as the cold front stalls in the
vicinity.

HYDROLOGY...

Redevelopment and expansion of rain showers with some embedded
thunderstorms will be possible tonight and overnight, most favorable
along or south of M59. Any thunderstorm development will be capable
of producing brief but heavy downpours. New rainfall totals from
this afternoon through tomorrow morning are expected to range between
a quarter-inch to a half-inch, however, any thunderstorm development
will likely produce highly localized totals that reach or exceed one
inch. This will bring a low chance for localized road flooding or
minor flooding of low-lying and urban area through tomorrow.

&&

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

$$

AVIATION.....BT
UPDATE.......MV
DISCUSSION...AM
MARINE.......TF
HYDROLOGY....AM


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