900
FXUS63 KDTX 150757
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
357 AM EDT Tue Jul 15 2025

.KEY MESSAGES...

- Sunny and warm today with high temperatures around 90 degrees and
  heat indices in the low 90s.

- Shower and thunderstorm chances begin Wednesday and increase Wednesday
  night through Thursday with potential for heavy rainfall.

- A cold front sweeps through the area Thursday night followed by
  cooler and less humid air Friday and to start next weekend.

&&

.DISCUSSION...

Weak high pressure is centered over Lower Mi to start the day and
begins more of an eastward move this afternoon and tonight. In the
meantime, it combines with a plume of deep dry air aloft to ensure
one more dry weather day across the region. Calm to light west wind
surface through mid levels backs and increases from the south, and is
expected to displace the forest fire smoke layer that had an
impressive impact on temperatures yesterday. Full sun then helps
readings reach guidance highs around 90 while surface Td lingering in
the 60s keeps humidity in the moderate range. Heat index projections
only tack on a couple degrees through peak heating.

Progression of the larger scale pattern gains traction tonight as
northern Ontario low pressure develops along the broad frontal zone
reaching from northern Quebec to the upper Midwest and then into the
central Plains. This system starts a weak process of low to mid
level moisture transport from the Ohio valley and pulls the surface
front back into Lower Mi late tonight and Wednesday morning. A
hybrid short wave/MCV also moves up from mid MS/TN valleys to
provide of boost of forcing, mainly south of the Mi border through
sunrise. The lack of anything resembling a low level jet otherwise
limits the northward reach of showers/storms in Lower Mi and reduces
effectiveness of the mid level theta-e gradient through Wednesday
morning. After that, the 15/00Z HREF advertises a more pronounced
flare-up of surface based convection across SE Mi during afternoon
peak heating as warm sector Td rises back into the 70s. The 70s Td
footprint also outlines coverage of PW rising into the 1.5 to 2 inch
range indicative of the moisture depth favorable for slow moving
convection capable of heavy rainfall with a few moisture laden
downbursts possible.

The Wednesday phase of events in the Great Lakes helps set the
larger scale moisture axis in place ahead of the Midwest frontal
system by Wednesday night. Convection ongoing upstream late tonight
runs the length of the front from western Lake Superior into the
Rockies. This supports the 15/00Z deterministic models that offer
broad agreement on similar cycles of surface based storms refiring
each afternoon as the frontal system moves closer to Lower Mi. Timing
is set for Wednesday afternoon activity across the Midwest to reach
SE Mi late Wednesday night into Thursday morning, and then flare up
again as the front moves through the region during Thursday.
Convective clusters arrive with nocturnal timing affecting lower
downstream instability but with an incrementally improved wind
profile. This is highlighted by model 500 mb wind increasing from sub
20 knots Wednesday afternoon to around 35 knots Thursday morning, in
line with the SPC marginal risk through 12Z Thursday.

Model consensus on the frontal passage Thursday night, before
midnight, is 6-12 hrs faster than the last few forecast cycles.
Surface high pressure is then building solidly into Lower Mi by
Friday morning with cooler and less humid air, but also giving way
to the next low pressure system more quickly during the weekend.

&&

.MARINE...

Light, mostly southerly winds, continue into Wednesday supporting
warm temperatures and increasing moisture. The next chance for
showers and thunderstorms will enter Wednesday through early Friday
as a series of upper-level disturbances and cold front pass over the
Great Lakes. This brings the chance for some localized stronger wind
gusts with any thunderstorm development, but otherwise winds remain
light given the weaker pressure gradient in place.

&&

.PREV DISCUSSION...
Issued at 1200 AM EDT Tue Jul 15 2025

AVIATION...

Predominately VFR conditions are expected through this TAF period
with minimal clouds and light winds. High pressure moves directly
over southeast Michigan and to the east tomorrow turning winds out
of the south. Main item of note remains the presence of wild fire
smoke near the surface that is bringing occasional periods of MVFR
haze. The other item is, some models want to develop areas of fog or
patchy fog across parts of southeast Michigan during the early
morning hours. Confidence in a widespread fog is low, so will leave
out for now and monitor trends through the morning hours.

For DTW/D21 Convection...No thunderstorms expected this TAF period.

THRESHOLD PROBABILITIES...

* None.


&&

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

$$

DISCUSSION...BT
MARINE.......SF
AVIATION.....AA


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