Expert Forecast Opinion

211
FXUS63 KDTX 021115
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
715 AM EDT Wed Sep 2 2026

.KEY MESSAGES...

- Hot and humid today. A Heat Advisory is in effect for portions of
SE MI.

- There will be a Slight Risk for severe weather today. Most
favorable timing for severe weather will be this afternoon and
evening.

- Additional shower and thunderstorm chances Thursday and Friday.

&&

.AVIATION...

A lull in thunderstorm activity looks to follow through this morning
with renewed thunderstorm chances arriving this afternoon first
across MBS and FNT again and then progressing southward into tonight.
Uncertainty does exist with respect to coverage of any thunderstorm
activity heading into this evening and tonight across southern
terminals. Have added a prob30 for the potential. Predominately VFR
skies will prevail through bulk of today outside the morning fog and
any thunderstorms that would bring a reduction to MVFR or below VSBYs
given the heavy downpour potential. Cold front makes inroads from
the north late in the TAF period.

D21/DTW Convection...The best chance for thunderstorms is north of
DTW toward the northern fringe of D21 this afternoon, but
thunderstorm chances may develop after 00Z this evening.

.DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less Wednesday afternoon.

&&

.PREV DISCUSSION...
Issued at 345 AM EDT Wed Sep 2 2026

DISCUSSION...

Ongoing convection across southern Minnesota and central Wisconsin
will continue to progress east-northeast through the morning, with
primary convective concerns holding across northern Lake Huron,
northern lower MI, and the U.P. Very moist low-level conditions
remain in place across SE MI with surface dewpoints in the low 70s,
which will support intermittent stratus and isolated showers through
the morning. Showers or an isolated thunderstorm will be most
favorable along or north of M59 this morning.

For this afternoon, any lingering low clouds are expected to erode
quickly with enhanced boundary-layer mixing. With the projected
convection and thicker cloud canopies holding north of the cwa, h850
temperatures aoa 20C, and some early day sunshine, daytime highs
peak in the low 90s across a greater portion of the cwa. Mixing may
temper the dew points slightly during peak heating, but the high
boundary layer moisture should still support heat indices aoa 100
degrees across southern Michigan. This will be most favorable from
the MI/OH border and up through the M-59 corridor, noting the usual
enhanced potential across the urban Metro corridor. As a result, a
Heat Advisory is now in effect from Noon through 8 PM EDT. Conditions
still remain hot and muggy north of the advisory zones with heat
indices ranging in the mid to upper 90s. The higher potential for mid
to high level clouds and earlier arrival of potential showers and
storms (more below) precludes the issuance of heat advisories farther
north.

Attention then turns to the potential influence of a convectively
generated outflow from the activity that is projected to traverse
across northern Michigan this morning. This boundary would be slated
to arrive across the Tri-Cities and Thumb late this afternoon and
evening, coincident with peak daytime heating. MLCAPE values between
2500-3000 J/kg along with strong kinematics characterized by bulk
shear values of 40-45 knots will be likely by the afternoon. Any CI
generated off an outflow/pseudo cold front could result in organized
convection capable of generating strong to severe thunderstorms. The
greatest confidence for this scenario resides across the Thumb where
several hi-res solutions depict a more pronounced southward-moving
boundary. This potential may extend west into the Tri-Cities for
initial development before progressing southward toward the I-69
corridor and Port Huron through the evening.

If strong to severe thunderstorms develop, storm mode may briefly
start as semi-discrete but would likely quickly amalgamate to multi-
cell clusters or a linear mode. Strong 1-3 and 1-6km shear values of
30-40 knots could support supercell development with any initial
discrete formation under modest streamwise vorticity within the
midlevels. The likely hazards would likely be damaging wind gusts
with any bowing segments from cold pool generation or microbursts
given deep layer CAPE. Large hail is also possible noting the CAPE
values and strong mid-level lapse rates. Last, ML output does
highlight chances for a tornado, most favorable within the Thumb.
Uncertainty is higher with tornadogenesis. Again any initial discrete
development would would make this possible noting 0-1km shear around
20 knots, but with current thinking hedged towards multi-
cell/linear, ambient shear profile would be altered. Some guidance
suggests secondary boundaries capable of propagating farther south
into the evening through the Metro region. However uncertainty is
higher in southern extent of any convection as timing of this
coincides with loss of daytime heating. Overall, SWODY1 places all of
SE MI in a slight risk for severe weather with all storm hazards
possible.

Slightly cooler temperatures projected for Thursday but very humid
conditions remain as dew points hold in the 70s. Quasi-zonal flow
ushers in warm and humid conditions into the Great Lakes from the
Plains, which will again support the chance for showers and
thunderstorms tomorrow. SWODY2 clips a portion of southern Michigan
for a Marginal risk for severe weather. Persistence forecast holds
into Friday, with the overall pattern starting to breakdown into the
weekend as ridge amplification commences across the Plains.

MARINE...

A low pressure system over Ontario will control the weather across
the Great Lakes through mid week. The warm front is now east of Lake
Huron with the cold front approaching Lake MI leaving us in the hot
and humid warm sector. Though the airmass is mostly stable at this
time, it hasn`t taken much mid level energy to spark clusters of
storms the last few days. The cold front will slowly enter lower MI
and drift SE today leading to additional rounds of storms possible
through tonight and even into Thursday if the front stalls over the
area. The weak gradient will keep speeds down through the week
though with max wind gusts rarely touching 20 knots. The slightly
cooler air over the waters brings chances of waterspouts with any of
the storms over the lakes this week. The very humid airmass over the
lakes will also lead to fog development over the waters, mainly the
north half of Lake Huron which will need to be watched for another
possible Dense Fog Advisory through this morning.

HYDROLOGY...

A humid air mass will bring a chance of heavy rainfall within any
strong thunderstorm that develops. However, areal coverage and exact
timing remains elusive across Lower Michigan. Periodic chances of
storms will exist right through Friday. Any strong thunderstorm will
have the potential to quickly produce 1-2 inches of rain, which can
lead to localized minor flooding of roads and poor-drainage areas.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory from noon today to 8 PM EDT this evening for
MIZ068>070-075-076-082-083.

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

$$

AVIATION.....AA
DISCUSSION...AM
MARINE.......DRK
HYDROLOGY....AM


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