757
FXUS63 KDTX 040704
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
Issued by National Weather Service Gaylord MI
304 AM EDT Wed Jun 4 2025

.KEY MESSAGES...

- Breezy and increasingly humid today. Cooler north and warmer south.

- Shower chances across the Tri Cities area yield thunderstorm
  development largely along and south of I-69 this afternoon.
  Potential for severe weather and localized torrential rainfall.

- Slowly drying out from north to south tonight into Thursday, with
  lingering shower potential south into Friday.

&&

.DISCUSSION...

Cold frontal intrusion well underway upstream, with embedded mesolow
processes ongoing across northern Lake Michigan, driving rounds of
stratiform rain across Grand Traverse Bay, with tailing
precipitation stretching south and west along the cold frontal
boundary through the western Corn Belt into the southern Plains.
Expecting this frontal boundary to continue passing through the
region throughout the day today, as a noticeably more humid airmass
makes its presence know across the board... with surface dewpoints
ballooning well into the 60s.

Lack of instability initially brings about more of a stratiform rain
regime, first intruding into the Tri Cities this morning, eventually
sagging southward into the I-69 corridor around midday. Some
lingering low level jet driven influences may drive some heavier
showers early this morning across the Tri Cities, with some
localized totals of 0.50"+ certainly on the table, though much of
this rain likely remains lighter. Certainly quite the temperature
contrast across southeast Michigan into the Bay area this
afternoon... thicker clouds and the progressing front will lead to
temps in the 70s north, and most spots along / south of I-69 should
warm anywhere from 80 to 86 degrees amid that continued
southwesterly flow (some 25+ mph gusts again possible today). The
warmer temperatures across the southern part of the CWA will set the
stage for afternoon thunderstorm development as moisture intrusion
allows for instability to materialize, which could bring about a
marginal, yet, rather complex severe storm and heavy rain risk.

Ahead of the progressing area of showers, instability balloons to
750 to 1000 J/kg MLCAPE. Couple this with bulk shear pushing 45kts
courtesy of ample speed shear throughout the profile, and the recipe
is there for strong to even severe storms after 17z, mainly south
and east of a Fowlerville to Port Sanilac line. Considering shear
vectors are parallel to the boundary, this screams more of a
damaging wind threat at first (hail is less likely but still
possible), and with this amount of shear, certainly gives potential
for any storms that initiate to quickly grow upscale and become
outflow dominant (perhaps leading to a bow echo or two materializing
as storms exit to the ENE into Canada, which could lead to a more
potent wind threat)... and any stronger updrafts that materialize in
the wake of these initial storms will need to be watched as
saturation lowers cloud bases, which could bring a closet tornado
threat if outflow boundaries start laying all over the place...
though confidence in this particular scenario remains very low at
this time. Additional concerns arise with the potential for the
aforementioned training storms to materialize. PWATs exceeding 1.50,
could certainly produce some impressive rain totals in places, which
could prove problematic in the event that this occurs in the
immediate Metro Detroit area (urban areas drain poorly). So after
all that... it should be noted that there is some uncertainty with
this setup... though wind fields are favorable for severe storms and
heavy rain, it all depends on the instability materializing, and
being able to break through the cap this afternoon. Most CAMs are on
board with this scenario, but for now, the Day 1 Severe Storm and
Excessive Rainfall outlooks carry a Marginal Risk across southeast
Michigan.

Thunderstorm concentration will begin to be suppressed southward
toward Ohio with time through the evening, with some lingering
stratiform rain anticipated through the night, especially along and
south of I-69. The front looks to stall out across northern Ohio
late tonight into Thursday, which will prolong the potential for
rain showers, largely south of I-96 / I-696, as another wave rides
along the frontal boundary. Most of this activity should taper later
into the day, yielding a drier evening. Temps on Thursday will be a
little backwards from the usual status quo... sunnier skies near
Saginaw Bay should promote highs well into the 70s, while clouds and
showers may stunt areas south of I-69 into the mid-to-upper 60s. The
lack of progression made by the front into Friday will yield another
shower chance, particularly along and south of I-94. When all is
said and done, some areas may see quite impressive rain totals, with
some guidance trying to paint totals well in excess of 2.50" across
Lenawee and Monroe counties by Friday. Surface high pressure builds
for Saturday, returning drier conditions to the region. The next
rain chances after this look to be later Sunday into Monday, as
another cold front passes through the area... coupled with potential
for an upper level low to dig into the Great Lakes region next week,
which may set off another run of unsettled weather.

&&

.MARINE...

Cold frontal passage set to commence through the day today, with
shower coverage increasing from north to south on Lake Huron,
reaching the Saginaw Bay through this morning. Showers and
thunderstorms will be possible at times across southern Lake Huron
this afternoon, spreading southward toward Lake St. Clair and into
Lake Erie this evening. SW winds ahead of this cold frontal boundary
will remain elevated, sustained 10 to 15kts, with some 25+ kt gusts.
As such, Small Craft Advisories have been extended for the Saginaw
Bay and Lake Huron nearshores, with an expansion into Lake St. Clair
and the Lake Erie nearshore waters of Michigan. In the wake of the
front, winds will flip northerly and turn lighter with time as we
progress into Thursday, with continued shower potential across Lake
St. Clair and points southward.

&&

.PREV DISCUSSION...
Issued at 120 AM Jun 4 2025 by National Weather Service Gaylord MI

AVIATION...

VFR conditions are expected to persist through 12Z at all TAF sites.
CIGs are then expected to lower from northwest to southeast
Wednesday morning into the afternoon in association with rain
showers and isolated thunder chances along/ahead of a cold front
dropping across the state. As discussed by the previous forecaster,
thoughts still align with these rain/thunder chances arriving at MBS
first (most likely before 18Z), and then the other TAF sites around
18Z and after. Similar timing is expected with lowered CIGs,
although low MVFR/IFR CIGs may not reach DTW/DET/YIP until after 00Z
Thursday. Strong winds off the surface w/ weaker winds at the ground
also keep LLWS in the TAF through tonight before south-southwest
surface winds increase through the morning ahead of the front.

For DTW Convection: Aforementioned front will help generate showers
and isolated storms later this afternoon, potentially impacting DTW.
Best chances for any strong storms appear to be between 19Z-00Z, but
shower/storm chances look to continue through tonight. Will continue
with PROB30 in the TAF given uncertainty in timing and storm
coverage at this time. Lightning, hail, and gusty winds will be
possible with any strong storms.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 6 AM EDT early this morning for LHZ421-
     422-441>443.

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

$$

DISCUSSION...HAD
MARINE.......HAD
AVIATION.....DJC

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