447
FXUS63 KDTX 120756
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
356 AM EDT Sat Jul 12 2025

.KEY MESSAGES...

- Showers and thunderstorms return this afternoon, capable of
  isolated severe gusts to 60 mph and torrential rainfall which could
  produce localized flooding.

- The combination of heat and humidity today will lead to max heat
  indices in the upper 90s for Metro Detroit, prior to the arrival of
  thunderstorms.

- Mainly dry and more seasonable temperature-wise Sunday, then
  warming back into the 90s midweek.

&&

.DISCUSSION...

Periodic convection with renewed potential for some severe
thunderstorms returns today as an active pattern holds firm over the
Great Lakes. Upstream convection exits into northern Lower through
the remaining morning hours while mid-level is underway over
Southeast Michigan. Thermodynamic profiles are still supportive of
an elevated mixed layer with over 500 J/kg of MUCAPE before deep-
layer southwest flow slides into the region. A shortwave trough with
a 50+ knot jet core at 500 mb ejects across western Lower today and
starts to phase with a more amplified trough tilting from neutral to
negative over the Upper Midwest.

Main corridor of CVA should largely reside west of the forecast area
as midday convection starts to initiate, likely between 16Z and 18Z.
This activity predominantly develops along the CAPE gradient, in the
vicinity of the western CWA border. Main plume of instability,
marked by MLCAPE of 1000-1500 J/kg, will quickly blossom and
overspread Southeast Michigan through the early afternoon hours.
Surface reflection from the parent wave takes a more north-
northeasterly track which slows the advance of its attendant cold
front. Wind progs indicate the more pronounced south-to-west wind
shift closer to 06Z (Sunday), thus the pre-frontal surface trough
axis will serve as the more important dynamic mechanism to amplify
convection. Perhaps more importantly, the majority of the latest NWP
suite supports surface-based free-convection with ELs above 35 kft
once surface dewpoints revisit the lower 70s and 2m temperatures
jump to near 90F within the expanding warm sector. Shear parameters
are not overwhelmingly impressive, but remain sufficient to help
organize some linear structures. Severe threat still mainly focused
on wind hazards (isolated gusts to 60 mph) and torrential rainfall.
For what it`s worth, ML data has carried higher severe wind
probabilities with run-to-run consistency. Also of note, prior to
the onset of precipitation, the greater Metro Detroit area could see
heat indices approach 100F, but it will be marginal since mid-70F
dewpoints appear to be the exception rather than the norm.

The front makes gradual inroads into Ontario late tonight which
corresponds to a drying locally, from west to east. Subset of CAMs
indicate a secondary storm response along the actually cold frontal
slope, but intensity should be significantly lower if this
materializes.

Post-frontal airmass characterized as cooler and drier for Sunday,
although temperatures should run near climatological averages (mid
80s). Can`t completely rule out a few showers for the extreme
southeast portion of the CWA with the slowed boundary. Longer
wavelength trough axis aloft then backs the temporarily zonal flow
aloft with little sensible fanfare. A rebound in geopotential
heights is in store for next week as synoptic-scale anticyclonic
gyre organizes over The Southeast. This promotes moderating thermal
profiles with negligible storm potential Monday and Tuesday. Zonal
jet centered over the 50th parallel delivers a weak wave extending
into southern Lower Michigan as soon as Wednesday that could spur
convective activity. Model divergence has emerged in the medium-
range solutions for the extent of thermal troughing over the state,
but NBM output exudes confidence with a cold FROPA by Friday.

&&

.MARINE...

Renewed chances for showers and thunderstorms today ahead of and
along a cold front, which brings chances for strong to severe
thunderstorm development capable of producing wind gusts aoa 35
knots. Winds veer toward the southwest then continue toward the west
after the passage of the front. Mainly dry conditions and light
winds expected in the wake of the front, and through early next
week.

&&

.HYDROLOGY...

Some heavy showers and storms are likely today as a hot and humid
airmass builds back into the region. The environment will support
pockets of heavy downpours with rainfall rates possibly exceeding 2
inches per hour. Localized flooding concerns exist for some areas
that experience clustering of cells. Flooding threat will largely be
for small streams, low-lying roadways, and otherwise poorly drained
areas. Activity should wane from west to east early tonight as drier
weather settles in for the rest of the weekend and early next week.

&&

.PREV DISCUSSION...
Issued at 1213 AM EDT Sat Jul 12 2025

AVIATION...

VFR skies should hold through the early morning period with
southeast Michigan in the warm sector and high clouds streaming in
downstream of a large convective line. Winds hold out of the south
and stay below 10 knots. Increasing southwest flow with gusts to
around 20 knots are expected by the afternoon ahead of an advancing
cold front. This front is expected to trigger increasing coverage of
showers and strong to severe thunderstorms, possibly by the early
afternoon hours.

For DTW/D21 Convection... There will be an advancing cold front that
will trigger a chance for strong to severe thunderstorms this
afternoon. Initiation looks occur around 17-18Z. Current timing for
activity to reach DTW looks closer to around 19-20Z. Adjustments in
timing remain possible.

THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less outside of thunderstorms today.

* Medium for thunderstorms this afternoon.


&&

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

$$

DISCUSSION...KGK
MARINE.......AM/KGK
HYDROLOGY....KGK
AVIATION.....AA


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.