504
FXUS63 KDTX 010841
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
441 AM EDT Tue Sep 1 2026

.KEY MESSAGES...

- Hot and humid conditions today and tomorrow.

- Favorable conditions for potential severe weather exist today
  through tomorrow. A Marginal Risk for severe weather is in place
  today with Wednesday a Marginal to Slight Risk for tomorrow.

- More rain and thunderstorm chances during the late week.

&&

.AVIATION...

A brief period of fog development remains possible prior to daybreak
as high clouds exit the region, given the light winds and abundant
low level moisture. Otherwise outside of a low chance for a stray
isolated shower, dry conditions continue this morning. This
afternoon and evening will showcase a highly conditional
thunderstorm environment. A capped environment is expected to limit
shower and thunderstorm coverage throughout the day. However, there
remains low end chances for isolated to scattered development in the
late afternoon and evening hours, possibly derived with lake
convergent boundaries. The boundary derived from Lake Erie would
place the Metro terminals as the most favorable location for
development, thus will retain a PROB30 group for this potential. Any
thunderstorms would have the ability to rapidly intensify given the
high instability in place.

D21/DTW Convection...There will be a low chance (20-30%) for
isolated to scattered thunderstorm development this afternoon and
evening. Strong to severe thunderstorm development will be possible
with any thunderstorm development today.

.DTW THRESHOLD PROBABILITIES...

* Low this afternoon and evening.

&&

.PREV DISCUSSION...
Issued at 352 AM EDT Tue Sep 1 2026

DISCUSSION...

Southeast Michigan will reside on the northern periphery of a high
pressure ridge slowly migrating east across the OH/TN Valleys to the
Atlantic Coast over the next several days. A warm and humid airmass
will settle into the area and persist and support chances for
multiple rounds of showers and thunderstorms with some storms
possibly becoming strong to severe. Models struggling to come to a
consensus with this pattern and predictability remains low over the
next 2-3 days.

For today, an 850-500 mb theta-e ridge axis containing deep moisture
will hover around lower Michigan today and pivot northward later in
the day. Surface dewpoints have already climbed to the 70 marks in
parts of the area this morning. The 00Z RAOB from last evening
observed PWAT at 1.60 inches with PWATS approaching 2.00 inches
expected to pivot northward with the theta-e ridge. Temperatures at
850 mb have also climbed to 20C and are forecast to hold around there
over the next couple days, which would support high temperatures up
to around 90 degrees. Presence of a cap with warming mid-levels along
with some drying aloft is bringing some confidence that any
widespread convection is becoming less likely today. This leans the
forecast towards the higher temperature outcome putting heat indices
up toward 100 degrees in parts of Lower Michigan. It still looks
borderline for prolonged heat indices to 100 degrees or greater, so
will hold off on any headlines for now. Regardless, a warm and muggy
day will be in store. While widespread convection looks unlikely
during much of the day, the underlying environment will be supportive
of strong to severe thunderstorms if any cells are able to overcome
any capping via local boundaries. SBCAPE values will be up to 2000+
J/kg with the NAM advertising 4000-5000 j/kg by late afternoon.
Effective shear will be up to 40+ knots and mid-level lapse rates
will be up to 6-7 C/km. Late this afternoon into the early half of
tonight appears to be the best opportunity for potential convection
to develop while a shortwave also rounds the ridge across Lake
Michigan. Confidence remains low on where convection may develop, but
the parts of the Saginaw Valley close to Saginaw Bay looks favored
by some of the latest guidance. Will also need to keep an eye on any
upstream development that may try and roll into the forecast area.
Any cells or clusters of cells that can develop will be capable of
strong to severe winds and hail along with heavy downpours that could
lead to localized flooding, thus the entire CWA is in a Marginal
Risk for severe weather.

For tomorrow, a shortwave within a belt of strong mid-level westerly
along with a potential nearby cold frontal boundary will be the
items of interest for another round of potential strong to severe
thunderstorm development. Models again not offering much consensus
on how Wednesday may play out, as some point to an early afternoon
uptick in convection while others point toward convection not
occuring until late in the day into Wednesday night. Timing of
convection ultimately will determine overall severe weather threat.
Parameter space though bulk of the day will again be supportive of
isolated to scattered severe weather if timed well in the diurnal
cycle (MLCAPEs to 1000-3000 J/kg, effective shear to 40+ knots, and
mid-level lapse rates 6-7 C/km). Severe wind and hail with locally
heavy rain will again be the main threats with a low end tornado
potential. The other item of note for Wednesday will be the heat and
humidity bringing heat index values back up to around 100 degrees,
which will be dependent on how convection eventually plays out.
Headlines may be possible if early day convection does not pan out
and less cloud cover allows for max heat index values to be realized.

Aforementioned cold front will eventually be pushed southward
keeping shower and thunderstorm chances in the forecast late
Wednesday night into Thursday morning. Though, instability will be
decreasing throughout the night. The frontal boundary hanging around
lower Michigan Thursday morning/afternoon will again provide a focus
for additional isolated strong to possibly severe convection as
another shortwave is advertised to crest the building ridge axis.
Post frontal airmass does look to cool daytime temperatures back
down into the 80s for the late week period.

MARINE...

A low pressure system over southern Manitoba will track through
Ontario today resulting in periods of active weather locally. There
is an occluded front reaching down into northern Minnesota with a
warm front then extending east through the straits and northern Lake
Huron. A series of mid level disturbances have been initiating
rounds of showers and thunderstorms which will continue to occur
through Wednesday until the cold front drops through the region. Any
break in the rain will be short lived as the front lifts back north
on Thursday providing additional chances of storms. Winds will be
fluctuating alot this week with the frequency of frontal passages.
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.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Dense Fog Advisory until 2 PM EDT this afternoon for LHZ361.

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

$$

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


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