928
FXUS63 KDTX 262242
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
642 PM EDT Sat Jul 26 2025

.KEY MESSAGES...

- Rounds of showers and thunderstorms continue late this afternoon
through this evening. Heavy rainfall and flooding remain the primary
hazards, although a few storms could generate damaging wind gusts.

- Heat and humidity build Sunday and Monday as high temperatures
return to the lower 90s with heat index near 100 through early next
week.

- Heat breaks with passage of a cold front around the Tuesday night
period followed by much cooler and less humid air for the late week
period.

&&

.AVIATION...

The airspace is relatively free of convection early this evening
with only a few residual showers churning across the far north near
MBS. A remnant wave from prior convection is inducing some
development over Southwest Lower Michigan. This wave and any
associated activity will plod through the immediate region in the
hours prior to midnight. Coverage of deep convection will remain
rather limited - but enough so to handle the characterization with a
tempo group across the south and a prob window north.

The moisture rich environment will once again support MVFR to
occasional IFR ceilings to expand in the overnight hours and some
visibility reductions at terminals that experience rainfall this
evening. Drier air works into the region on the heals of northwest
flow Sunday morning and lower clouds will quickly clear out from
northwest to southeast during the mid to late morning hours.

For DTW/D21 Convection...a small window of opportunity for deeper
convection will occur from roughly 01-04z. Expecting scattered
convection within the D21 airspace with less confidence regarding
impacts to specific terminals as upstream activity will undergo a
fair amount of modification over next couple of hours.

THRESHOLD PROBABILITIES...

* Moderate to high in ceilings aob 5000 feet overnight and early
  Sunday.

* Low in thunderstorms tonight.

&&

.PREV DISCUSSION...
Issued at 403 PM EDT Sat Jul 26 2025

DISCUSSION...

Thunderstorms and heavy rainfall remain the forecast highlight for
late today and this evening, set up by a few mesoscale features that
have taken control of convective trends this afternoon and are set
to persist through the evening. Morning convection in central Lower
Mi morphed into a mini MCV to help focus surface based storms along
the outflow-warm front hybrid west to east near the M-46 corridor at
forecast issuance. Backed low level flow produced a few mini
supercell structures in the stronger updrafts which remain a concern
while the boundary sets up favorably to focus additional storms as
the southern Lake Michigan MCV moves across Lower Mi this evening.
Heavy rain is still the primary hazard in this area as training
clusters are favored along the west to east boundary. A similar west
to east boundary has more of a differential heating origin toward
the Ohio border but also poses a heavy rain threat with a boost of
additional activity possible off the south flank of the Lake Mi MCV.
Scattered convective clusters fill in between the two boundaries as
some thinning of mid/high clouds occurs and MLCAPE briefly gets into
the 1000-1500 J/kg range. All of these smaller scale scenarios are
feeding off the very high moisture content within a broad 2 inch PW
axis along and south of the front. Better prospects for the Marginal
Risk of severe intensity are shifting farther south into IN/OH while
a stray precip loaded damaging wind gust remains possible in the
strongest SE Mi storms this evening.

Remaining convection and showers within the frontal zone slide
through SE Mi mid to late evening changing the forecast focus toward
a new round of heat and humidity to finish the weekend. The
composite outflow/front settles south of the Ohio border after
midnight and dissipates toward sunrise bringing an end to this round
of convection. The frontal passage is facilitated by eastward
passage of the 500 mb short wave/MCV combo followed by convincing
larger scale subsidence during the late night into Sunday morning.
This is indicated with good model consensus by the short wave ridge
centered on the upper MS valley at 12z, and by a corresponding
pocket of dry 850-500 mb mean RH. Weak surface high pressure follows
Sunday but with little to no air mass change leaving morning clouds
breaking up into a shallow cumulus in the afternoon. A mostly sunny
peak heating scenario helps lift temperatures toward 90 while Td
holds at least in the lower 70s for peak index in the upper 90s.
Light and variable wind becomes SW to then help temperatures take a
step up into the Lower 90s Monday bringing afternoon heat index
toward the 100 F Head Advisory threshold.

Monday is set up to be the peak day for heat and humidity but the
temperature is also vulnerable to convective debris clouds or even a
stray afternoon shower/storm. SE Mi remains on the southern storm
track periphery tied to northern Ontario low pressure and the front
trailing into the northern Plains. This system is expected to
generate clusters of convection with a broad model signal for
propagation downstream along the larger scale instability gradient.
It is favorable from a conceptual model perspective but still has
low predictability so far downstream from the larger scale low
pressure and frontal system Monday and Monday night. Storm potential
increases Tuesday into Tuesday night as the Midwest cold front moves
through Lower Mi followed by much cooler and less humid weather for
the late week period.

MARINE...

Multiple waves of showers and thunderstorms are expected through
tonight across the Great Lakes. A warm front is draped across the
Saginaw Valley and Thumb regions, which has led to some rotating
thunderstorms near the waters. A waterspout cannot be ruled out in
these locations. Otherwise, the best opportunity for strong storms
with wind gusts over 40 knots will be for Lake St Clair and Lake
Erie where instability is greatest. The warm front will continue to
lift north overnight and shift flow to the southwest by Sunday
morning. A drier day is in store on Sunday as high pressure builds
in briefly, which generally caps thunderstorm chances. Unsettled
weather continues into early next week before a pattern transition
is expected as a cold front tracks through the area.

HYDROLOGY...

Warm and humid air continues to fuel showers and thunderstorms this
afternoon and tonight. The anomalously moist airmass carries 2 inch
PW in addition to warm cloud depths supporting efficient rainfall
rates. The greatest coverage of storms occurs generally north of the
I-69 corridor and toward the Ohio border. These areas have greater
potential for torrential rainfall threats due to this moisture-laden
airmass. Rainfall rates in excess of 2"/hr are likely under the
strongest storms (even weaker storms will be capable of rates at or
above 1"/hr). Localized flooding is expected especially in urban and
low lying/flood prone areas. More impactful flooding is possible
should storms train over the same locations.

&&

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

$$

AVIATION.....Mann
DISCUSSION...BT
MARINE.......MV
HYDROLOGY....BT


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