NWS Forecast Discussion

054
FXUS63 KDTX 151032
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
632 AM EDT Tue Sep 15 2026

.KEY MESSAGES...

- Scattered showers and a chance of thunderstorms return to the area
today. The best chance of storms and heavy rainfall is late
afternoon and evening south of I-69.

- A chance of showers lingers Wednesday, again mainly south of I-69,
until becoming more likely again Wednesday night and Thursday.

- Dry weather with temperatures around normal are projected for
Friday.

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

&&

.AVIATION...

Synoptic scale baroclinic zone will steadily organize today along
the southern edge of the upper level jet. Persistent convergence
will lead to lowering ceilings, predominately VFR, and rain showers
at times. Loss of nocturnal outgoing radiative cooling support
should lead to a downtick in activity across the region during the
late morning and afternoon hours. Persistent model signal exists for
convective redevelopment and thunderstorms this evening between 02-
05z for the Detroit terminals.

D21/DTW Convection...Thunderstorm development within the airspace
will probable between 02-5z this evening.

.DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less Tuesday afternoon and evening.

* Low for thunderstorms Tuesday evening.

&&

.PREV DISCUSSION...
Issued at 358 AM EDT Tue Sep 15 2026

DISCUSSION...

A large and strong low pressure system is developing on schedule
while entering NW Ontario early this morning. The system moves
toward James Bay while drawing a band of showers with a few
thunderstorms across Lower Mi this morning followed by additional
activity along the the trailing cold front tonight. The cold front
then becomes the forecast subject for continued shower/storm
prospects through Wednesday and Thursday.

Early morning observations indicate the primary band of
showers/storms aligned with strong low level jet forced moisture
transport. The eastern fringe is tied more to elevated sections of
the warm front still moving in from the mid MS valley. Shower
clusters continue to develop NE with some enhancement due to
increasing nocturnal/elevated instability. The northward displacement
from the surface warm front also means there is still a substantial
layer of dry air in the low levels for these showers to overcome
through the morning. The 00Z DTX sounding shows this as it was last
evening and which model soundings indicate will remain a limiting
factor until the larger scale moisture axis moves in from the NW mid
to late morning. This primary moisture axis, and the showers/storms
within, continues to sink into central Lower Mi and toward the I-69
corridor by noon. As this occurs, there is still a considerable
weakening trend depicted across the range of model solutions which
passes the eye test considering changes in the larger scale setup.
The advective process shifts into Canada and leaves the moisture axis
overhead where it loses nocturnal/elevated instability while also
moving farther away from support provided by the upper jet and parent
mid level short wave.

Other than a rumble of thunder this morning, a greater chance for
thunderstorms in SE Mi is held during the late afternoon and
evening. Early to mid afternoon showers remain scattered within the
moisture axis while a narrow surface based warm sector builds into
Lower Mi ahead of the cold front. SW flow gusting near 30 mph
carries in a resurgence of surface Td back up into the 60s to around
70 with southward extent. Afternoon highs in the lower to mid 80s
toward the Ohio border help projections of HREF mean surface based
instability reach 1000 J/kg after 21Z, but just barely up into
Lenawee and Monroe counties although also with 30-40 kts of 0-6 km
bulk shear. The range of hi-res models then depict a late peak
heating cycle convective initiation mainly 21Z to 00Z along or just
ahead of the cold front which lasts through the evening. This is a
slower/later trend on initiation timing which is a limiting factor
for development farther north from the Ohio border. The updated SPC
Marginal Risk up toward the I-94 corridor looks good in that regard,
and which highlights an isolated storm capable of some entry level
wind organization, or a precip-loaded gust, until the line exits
south and east after midnight.

A chance of showers lingers toward the Ohio border late tonight and
Wednesday as the passing cold front stalls through central to
southern IN/OH. The position of the surface front and active zones
aloft are slightly farther south compared to recent model cycles
which is reflected in the NBM carrying POPs mainly south of the I-69
corridor until later Wednesday night. This is when the next low
amplitude mid level wave and surface low are projected to slide
along the frontal zone, however the new 00Z model run maintains the
increased spread in QPF solutions noted in yesterday`s forecast.
Consensus of GFS, NAM, Canadian is mostly south of the IN/OH border
while the ECMWF is well north over southern Lower Mi. ECMWF ML/AI
runs suggest the deterministic solution is too far north, but this
uncertainty remains in the NBM with likely POPs brushed across all
of SE Mi later Wednesday night and early Thursday.

Extended time range models build surface high pressure southward
enough to give us a break of dry weather Friday, in the subsidence
wake of the passing short wave. However, model trends are faster
bringing moisture back into Lower Mi Friday night into Saturday
leading to concerns that showers then remain active through Sunday.

MARINE...

An occluded low pressure system advances across northern Ontario
today, directing a strong southerly low-level jet across the Great
Lakes. A Gale Warning remains in effect for Lake Huron north of
Alabaster through 4 PM where gales of 35 to 40 kt are forecast.
Farther south, gusts of 20 to 30 kt will be more common through this
afternoon and Small Craft Advisories remain in effect for the Lake
Huron nearshore waters. A band of showers with a few embedded
thunderstorms works across the area this morning with the highest
coverage across Lake Huron. Additional scattered showers and
thunderstorms then become possible across Lake St. Clair and western
Lake Erie during the late afternoon and evening ahead of a cold
front. This front eases across the area tonight, bringing the end to
showers and causing wind to shift from south/southwest to
north/northeast by Wednesday morning. High pressure passes to the
north of the lakes on Wednesday, sustaining continued northeasterly
flow of 10 to 15 kt.

HYDROLOGY...

Showers and a chance of thunderstorms increase across Lower Michigan
as a moisture rich airmass surges back into the region today. The
warm and humid air moves in ahead of a cold front which tracks
through late in the afternoon and this evening. The front then
stalls out across the northern Ohio Valley before lifting back north
later this week. This will result in multiple opportunities for
widespread rainfall throughout the week. In the near-term, the best
opportunity for heavy rain will be south of I-69 this evening where
thunderstorm development may enhance rainfall rates to over an inch
per hour. Depending on where the front stalls, rain may linger
overnight to produce storm totals over one inch by Wednesday morning
with training storms not out of the question. This pattern presents
a chance for localized road flooding, or minor flooding of low-lying
and urban areas during the mid to late week period.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Gale Warning until 4 PM EDT this afternoon for LHZ361>363.

     Small Craft Advisory until 4 PM EDT this afternoon for LHZ421-422-
     441>443.

Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....CB
DISCUSSION...BT
MARINE.......TF
HYDROLOGY....BT


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NWS DTX Office Area Forecast Discussion