184
FXUS63 KDTX 242305
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
705 PM EDT Tue Jun 24 2025

.KEY MESSAGES...

- Additional chances for thunderstorms will persist Wednesday
through Friday, including the return of heat indices in the mid 90s
Friday.

&&

.AVIATION...

Steady decline in convective potential going forward late this
evening, as earlier activity offers improving stability amidst a
standard reduction thru loss of daytime heating. There remains low
potential, particularly in the vicinity of FNT, as a boundary
lingers near the area. Winds become northeasterly in the wake of
this boundary, lending some potential for lower stratus to emerge
from north to south with time overnight. Lower confidence yet on the
possibility and will await a greater signal via observational trends
before moving more aggressively toward predominant MVFR. Any stratus
development would lift into a broader VFR diurnal cu field with
daytime heating Wednesday. The lingering frontal boundary will again
provide a focus for shower and thunderstorm development. This will
position the DTW/YIP corridor most favorably, although development
may remain just to the south and west depending on the frontal
positioning.

For DTW/D21 Convection...Higher stability now in place from earlier
thunderstorm activity makes additional development unlikely through
tonight. Potential for thunderstorms will again exists Wednesday
from mid afternoon through early evening.

 THRESHOLD PROBABILITIES...

* Low for thunderstorms Wednesday afternoon and early evening.

* Low for cigs aob 5kft late tonight through Wednesday.

&&

.PREV DISCUSSION...
Issued at 300 PM EDT Tue Jun 24 2025

DISCUSSION...

After starting the day in the low to mid 70s, midday heat indices
are peaking in the upper 90s to lower 100s ahead of an approaching
front since surface dewpoints haven`t really mixed-out and 2m
temperatures have stalled in the low to mid 90s. Modest relief is
pending after a multi-day stretch of +90F highs once the forecast
narrative transitions from heat and humidity focus to convective
impacts this afternoon as a cold front drops through Southeast
Michigan. GOES imagery shows pre-frontal convective initiation well
underway with precipitation echoes blossoming in KDTX reflectivity
products. Mesoscale environment remains favorable for scattered to
numerous thunderstorms amidst uncapped SBCAPE building into the 1500-
2500 J/kg through the remaining daylight hours. Per HREF, ensemble
minimum SBCAPE values, south of I-69, range from 750-1750 J/kg which
ensures the presence of necessary instability for storm development.
Main limiting factor will be the lack of meaningful shear, marked by
0-6 km magnitudes of 20-25 knots. Still, expect some heavy water-
loading in the most robust multicellular updrafts which could lead
to isolated severe gusts/microbursts, in addition to efficient
rainfall rates. At issuance time, several SPSs and one SVR were in
effect with the most productive initial storm activity, located
along the instability gradient. Early observational data (PTK
gusting to 25 knots) reinforces the belief in winds as the primary
threat. Outflow boundaries are already organizing which should lead
to additional pre-frontal convective development, especially at
intersecting boundaries and lake breeze interactions.

Current heat headlines (Extreme Heat Warning and Heat Advisory) will
be allowed to expire on-schedule (8 PM) given the reduction in
temperatures due to the transition in diurnal cycle, expected
rainfall, and FROPA. Storms gradually decrease in coverage and
intensity overnight as the surface front settles near/south of the
MI/OH border Wednesday morning allowing for the first reprieve of
overnight lows to less deviant levels (mid-upper 60s, and 70F near
the state-line).

Shift to a light ENE gradient wind develops in the wake of the
boundary with a comparatively cooler airmass filtering in. 850 mb
temperatures drop into the mid teens (Celsius) which caps highs AOB
80F for most locations, aided further by a higher cloud fraction
throughout the day. Synoptically, the 598 dam sampled 500 mb ridge
will continue to flatten and fill-in Wednesday as the upper level
jet streak presses through southeastern Canada. Did raise MaxTs a
bit as guidance hints at minor reversal of the cold front as a warm
front which could bring highs into the upper 80s south of I-94.
Minor height falls are forecast for the local area Wednesday which
sustains additional chances for thundershowers at times Wednesday.
Latest CAMs are notably drier than the coarser solutions suggesting
a narrower footprint, generally south of I-96/696. This coincides
with the better residual moisture and proximity to the surface
convergence axis. Not expected much in the way of severe potential,
but can`t rule out an isolated marginally severe gust given a less
unstable airmass.

Lower Michigan set to reside between a northern stream ridge rolling
east across the Canadian Prairies and the decaying Southeast CONUS
mid-level anticyclone to close out the workweek. This keeps the
region positioned within a more perturbed/cyclonically active height
field. Meanwhile, the stalled boundary lifts north as a warm front
Thursday with a sensible uptick in surface dewpoints. This
environment favors fresh convective activity with renewed CAPE,
although weak capping will need to be overcome/eroded for surface-
based parcels. 850 mb temperatures creep back into the upper teens
Thursday and Friday, perhaps even into Saturday providing above
normal readings into the weekend. A weak surface low tracks into the
Great Lakes Friday dragging a decaying cold front with. Expect it.
This serves as the next focus for convection Friday into Saturday
with a low-end severe threat. However, dynamics should be
unimpressive, and the front eventually washes out, undercutting
advection of meaningfully cooler air. Shortwave ridging passes
through aloft Saturday into Sunday for a brief period of higher
confidence drying before the next longwave trough digs into The
Midwest early next week with more showers and storms to follow.

MARINE...

A warm and unstable airmass persists over the Great Lakes this
afternoon, which will be the catalyst for shower and thunderstorm
development through the evening. The greatest coverage of
thunderstorms will be south of Port Huron, in which stronger storms
will be capable of wind gusts over 34 knots, heavy downpours, and
cloud to ground lightning. Storms wane with loss of daytime heating
while high pressure builds over Lake Superior. This eases winds to
the north-northeast by Wednesday morning as the high takes hold. SE
Michigan will still reside on the northern fringe of a strong ridge
axis with warm and unstable conditions, which affords the
opportunity for both nocturnal and afternoon storms with low
predictability. A broad trough of low pressure then tracks into the
region to end the work week, bringing another round of shower/storm
potential and enhancements to the wind field.

HYDROLOGY...

Initial round of showers and thunderstorms are underway this
afternoon as a slow moving cold front capitalizes on a moist and
unstable airmass. Deep column moisture makes for efficient rainfall
rates that could briefly approach two inches per hour. This may
result in localized flooding, predominantly in low-lying and flood-
prone areas. Locations which receive repeated rounds of showers and
thunderstorms are most susceptible, but confidence in specific
locations is low. The humid airmass remains in place through the end
of the week offering several additional opportunities for more
showers and storms, some of which could produce further instances of
isolated flooding.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 8 PM EDT this evening for MIZ060-062-063-068-
     075-082-083.

     Extreme Heat Warning until 8 PM EDT this evening for MIZ061-069-070-
     076.

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

$$

AVIATION.....MR
DISCUSSION...KGK
MARINE.......MV
HYDROLOGY....KGK


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