Expert Forecast Opinion

353
FXUS63 KDTX 251635
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1235 PM EDT Fri Apr 25 2025

.KEY MESSAGES...

- Showers and scattered thunderstorms expected this afternoon and
evening. 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...

Mostly clear skies and moisture transport from south to north,
helping to destabilize the atmosphere. Expecting shower and
thunderstorm development around 20-21z in the Detroit Metro Area, as
frontal boundary is in place to help provide the focus, with ripple
of low pressure tracking through. Activity likely persists into the
early evening hours. Tougher call farther north at FNT and
especially MBS, where showers and activity could miss altogether,
keeping VFR conditions locked in through the evening hours.
Increasing northwest winds tonight with the cold advection behind
the departing low/frontal boundary brings high confidence in an MVFR
deck of clouds (short period of IFR not out of the question)
spreading in form northwest to southeast late tonight and persisting
through Saturday morning. Diurnal mixing and further low level
drying tomorrow should lift cloud bases into low VFR for the
afternoon hours. Frequent northwest gusts in excess of 20 knots
expected late tonight through early tomorrow afternoon.

For DTW...Afternoon convection is forecast to initiate across the
northern and western portions of the airspace during the mid
afternoon. Coverage is expected expand across the metro airspace in
the 20Z to 00Z time frame. Overall slow motion of thunderstorms and
potential redevelopment should result in thunderstorms impacting at
least portions of the airspace for several hours late this afternoon
and early evening.

.DTW THRESHOLD PROBABILITIES...

* Low for ceiling at or below 5000 ft early this afternoon, then
medium late this afternoon through 9z Saturday, followed by
high.

* Moderate to high in thunderstorms late this afternoon and early
evening.

&&

.PREV DISCUSSION...
Issued at 345 AM EDT Fri Apr 25 2025

DISCUSSION...

Positively tilted trough now over west Ontario extending through
North Dakota will deepen as it moves across Lake Michigan late
tonight. Upstream of the approaching trough, shortwave features will
ripple over the southern Great Lakes this afternoon and evening, with
an ill-defined low pressure system becoming more organized across
the state as a result. Timing of these aforementioned features will
intersect peak destabilization, initially producing widely scattered
showers and thunderstorms with then increasing coverage by the
evening.

SE MI will reside under a marginally strong storm environment
characterized by CAPE aoa 1000 j/kg and steep lllr. Limiting factors
for more organized severe potential is the lack of shear through 3km
(1-3km bulk shear of 15 knots) and modest mid-level lapse rates.
Given the overall kinematics, shear does increase through 6km, so
single to multicell development will be the main storm mode for the
afternoon hours. The biggest risk for thunderstorm activity will be
wet microbursts capable of producing wind gusts of 50-60 mph with any
stronger storm development. An isolated severe storm cannot be ruled
out. Increased coverage leading into the evening hours will be
possible once the low and better moisture arrives over the state,
which then introduces the low end chance for highly localized
flooding potential. This is reflected within the HREF LPMM QPF output
and within very few of the higher- end EPS QPF outputs. Please see
the hydrology section for additional details. Any of this stronger
storm potential will be confined south of the Tri- Cities and
northern Thumb due to the sharp drop off of sbCAPE across the
northern reaches of the cwa. Instability wanes after sunset, but the
lingering shower and storm complex can last through Midnight as low
pressure ejects into Lake Erie and Ontario.

A cold front moves over the state Saturday morning in the wake of
the low which will drop temperatures back into the 50s for a high
while high pressure begins to fill in from the west. Mixing depths
intersect the 25-28 knots wind field aloft, supporting gust
potential around 30 mph during daylight hours. Outside of lower end
brief shower potential through the Thumb in the afternoon, most
locations stay dry with the build up of higher pressure. High
pressure centers over the state by Sunday afternoon.

Tuesday will be the next potential day of interest as medium range
models show strong thermodynamics and kinematics in place across the
Midwest through the Great Lakes along with an eventual passage of a
strong cold front, a setup conducive for strong to severe storms.
EPS mean cape values increase towards 1500 J/kg through the day and
EFI CAPE/SHEAR parameter displays a nice signal. It is too soon to
get into specifics this far out, but worth a mention at present time.

MARINE...

Easterly flow increases this morning ahead of low pressure that
tracks in from the Midwest through the day. This system will bring
scattered to numerous showers across the area today with embedded
thunderstorms. Wind direction backs to northerly late this afternoon
and evening, increasing in magnitude tonight as the low deepens and
departs into the eastern Great Lakes. Frequent gusts are forecast to
peak in the 25 to 30 kt range overnight into midday Saturday as
showers gradually move out. This will cause wave heights to build
into the 4 to 6 ft range in the southern Lake Huron nearshore
waters, prompting a Small Craft Advisory. North flow persists
through Saturday but gradually weakens as strong high pressure
builds in from the west. This high promotes lighter winds and waves
through Sunday. A warm front then lifts into the region Monday with
additional showers and storms becoming likely Tuesday.

HYDROLOGY...

Increasing daytime instability and surface low pressure arriving
today will support showers and scattered thunderstorm development
starting this afternoon, 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 1-1.50 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 from 10 PM this evening to 10 PM EDT Saturday
for LHZ421-441.

Small Craft Advisory from 2 AM to 10 PM EDT Saturday for LHZ442-443.

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

$$

AVIATION.....SF
DISCUSSION...AM
MARINE.......TF
HYDROLOGY....AM


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