240
FXUS63 KDTX 121103
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
703 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.

&&

.AVIATION...

Warm and humid air entrenched across the area governS aviation
conditions today and at least through this evening. Patchy MVFR fog
to start is short-lived as mid July daytime heating quickly ramps up
this morning. Full VFR then leads to another round of thunderstorms
expected to blossom and feed off the heat and humidity this
afternoon and evening. Weaker showers/storms could begin by late
morning toward MBS and then expand in coverage and intensity through
the afternoon eventually affecting all terminals by late afternoon.
Expect numerous overall coverage with clusters of severe intensity
bringing potential damaging wind in addition to IFR/MVFR restriction
in heavy rainfall. This activity occurs ahead of the primary cold
front which could bring a stray shower or storm late tonight
followed by a short period of MVFR ceiling leading up to sunrise
Sunday morning.

For DTW/D21 Convection... An afternoon time window for thunderstorms
remains on schedule. Earlier initiation is possible toward MBS and
the northern reaches of D21 while timing of more direct impacts at
DTW is still closer to 21Z.

THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less outside of thunderstorms today and
  this evening. Moderate with the cold front late tonight.

* Moderate for thunderstorms this afternoon.

&&

.PREV DISCUSSION...
Issued at 356 AM EDT Sat Jul 12 2025

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.

&&

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

$$

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


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