165
FXUS63 KDTX 260349
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1149 PM EDT Fri Apr 25 2025

.KEY MESSAGES...

- Showers and scattered thunderstorms expanding in coverage this
afternoon and evening.

- Heavy rainfall and localized flooding is the primary but an
isolated thunderstorms may be marginally severe in the afternoon.

- High pressure this weekend brings dry conditions. Cool Saturday
before returning to near normal Sunday.

- Temperatures back into the 70s on Monday before another cold front
arrives on Tuesday, which will bring renewed chances for
thunderstorms.

&&

.AVIATION...

Shallow cold advection in the wake of a cold front will bring a
lowering inversion and a likelihood for MVFR stratus tonight. There
does remain a potential for IFR cigs with some chance at reduced
visibilities in light br, however, forecast soundings have trended
more optimistic. Confidence is low on fog with a lack of clearing.
MVFR conditions at daybreak are expected to transition to VFR
ceilings for Saturday afternoon.

.DTW THRESHOLD PROBABILITIES...

*  High for ceiling at or below 5000 ft tonight.

&&

.PREV DISCUSSION...
Issued at 338 PM EDT Fri Apr 25 2025

DISCUSSION...

A pair of longwave troughs will impact the region the rest of today
through tonight. The first trough of note is a weaker southern
stream trough with very little jet support, but several weak
shortwave embedded within it. The stronger trough is lagging a bit
to the west dropping into the Midwest this afternoon before
strengthening and becoming more closed off while passing over Lake
Huron Saturday afternoon.

The leading southern stream trough complex will lift through SE MI
this afternoon/evening bringing the chance showers and thunderstorms
to the area. We were able to clear out most of the clouds for a good
chunk of the day helping to destabilize the boundary layer a bit. In
addition, a stalled frontal boundary lifted north of the state line
from and is draped along the I69 corridor which allowed mid 70s to
surge northward through the region with dewpoints into the mid 50s.
deeper moisture will lift north over the next few hours as low
pressure tries to come together along the front with dewpoints
rising into the low 60s. In addition, PWATs are expected to rise to
around 1.25 inches so moisture will be ample for storm/shower
development and heavy rain. CAPE values per SPC Meso Analysis has
already climbed to around 1500 J/kg south of M59 and 1000 up to Port
Huron. Low level lapse rates will become strong but mid level lapse
rates are weak, as is overall shear profile. Without stronger upper
level or low level jet support, shear will struggle to help organize
storms. You have to get up to around 20kft to get winds over 30
knots. Models are advertising a brief window this evening where the
low level convergence of the surface front and the deformation of
the surface low come together over the Irish Hills helping to
enhance the storms coverage and intensity before the low peals off
to the east pulling the cluster of storms eastward through St Clair,
Macomb, and Wayne Counties. Main threat with these storms will be
heavy rainfall with storm motions around 20 knots and slow movement
to the cluster as it pivots around the low so we remain in a
Marginal Risk of excessive rainfall from the WPC. Gusts look to
largely remain in the 40-50 mph range but can`t rule out a stray
gust to 60 mph. Trough pushes east of the region between 00-03Z
which will end the threat of storms.

Second northern stream trough then pushes through the region tonight
into Saturday. A cold front will push through Saturday morning with
pretty good cold advection behind it with 850mb temps down to -3C
behind it. Northerly cold flow through the day will help limit max
Ts to the 50s. Model soundings mix up to around 4kft which will tap
into winds of 25-30 knots so should be a gusty afternoon. Precip on
the trailing trough may stay north of the area during the day, but
could also brush southward into the Thumb producing light rain. Will
lean dry with this forecast with high pressure actively building
across the Great Lakes.

High pressure then holds across the region Sunday and Monday with a
warming trend back into the 60s Sunday and 70s Monday as ridging
amplifies over the eastern conus. Attention in the long term remains
on Tuesday as the next cold front sweeps through the region
presenting the next chance of strong to severe storms.

MARINE...

A low pressure system lifts through Lower Michigan today offering
opportunities for showers and thunderstorms this afternoon and
evening within the system`s warm sector. Localized higher winds and
waves are possible with any isolated strong to severe storms that
move through. Relatively light non-convective winds back with time
before strengthening from northern Lake Huron down to the southern
waterways, tied to the progression of the system`s cold front
tonight. Cold advection and northwest flow promote an uptick in
gradient winds, into the 15 to 20 knot range early Saturday which
results in increased wave action along the southern Huron
nearshores. As such, the Small Craft Advisory will remain in place.
It has been expanded to include Inner Saginaw Bay given sufficiently
steep low-level lapse rates mixing down 25-30 knot winds from
between 2-4 kft AWL. The surface low then spins into the eastern
Great Lakes Saturday while the back edge of the system lingers over
the Huron basin. It will take some time for the gradient to relax as
high pressure builds in, eventually leading to weaker and more
variable winds. A much more potent low pressure system organizes out
west Monday into Tuesday featuring a pre-frontal warm sector with
gusty winds, followed by a strong cold front. Expect a period of
thunderstorms and gusts in excess of 30 knots.

HYDROLOGY...

Increasing daytime instability and surface low pressure arriving
this afternoon will support showers and scattered thunderstorms, as
PW values rise aoa 1.25 inches. Increased coverage of shower and
storm potential will be possible into the evening hours. Although
basin average rainfall is generally expected to be a half an inch or
less, slower storm motions along with the potential for heavy
downpours will bring the highly localized rainfall totals of 1.0-
1.50 inches or higher in a short period. Highly localized flooding
in low-lying and/or flood prone locations will be possible.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 10 PM EDT Saturday for LHZ421-441.

     Small Craft Advisory until 10 PM EDT Saturday for LHZ422-442-443.

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

$$

AVIATION.....CB
DISCUSSION...DRK
MARINE.......KGK
HYDROLOGY....AM


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