Expert Forecast Opinion

861
FXUS63 KDTX 011736
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
136 PM EDT Tue Apr 1 2025

.KEY MESSAGES...

* Cooler temperatures and dry weather today with more mild weather
returning tomorrow into late week.

* Chance of light snow accumulations transitioning to a wintry mix
expected from roughly the M59 corridor and north tonight into
Wednesday morning.

* A conditional threat of severe weather exists Wednesday afternoon
and evening. Damaging winds and heavy rainfall will be the main
threats along with a conditional tornado threat.

&&

.AVIATION...

High pressure maintains VFR conditions through tonight. The next low
pressure system is set to arrive over Lake Michigan through tomorrow
which will initially result in an elevated front expanding across SE
MI. A band of precip arrives with this front early tomorrow morning,
bringing a window for snow to start across KFNT and KMBS, with lower
confidence of snow impacting KPTK. As warmer air progresses, a 1-3
hour window for a combination of freezing rain and/or rain will be
possible again favored across KPTK and locations north, before a
transition to all rain by the late morning to early afternoon.
Widespread rain showers and embedded thunderstorms then become likely
in the late morning to early afternoon time frame as wind gust
potential ramps up. Gusts ranging between 25 to 30 knots will be
possible.

For DTW...Rain showers with IFR/MVFR cigs quickly expand across the
terminal by the late morning hours tomorrow. The best window for
thunderstorms continues to be between the 15-19Z time frame, with
lower end thunderstorm chances continuing through the TAF period.

.DTW THRESHOLD PROBABILITIES...

* None

&&

.PREV DISCUSSION...
Issued at 438 AM EDT Tue Apr 1 2025

DISCUSSION...

Skies have cleared out early this morning with further drying
infiltrating in from the north as high pressure builds across the
north central Great Lakes. The resident cool airmass in place and
the clear skies is leading to cold start to the morning.
Observations are already down into the mid 20s across the Saginaw
Valley with similar temperatures expected across the southern border
by sunrise. Very dry airmass in place today will keep conditions dry
with limited cloud cover through the much of the afternoon. Despite
boost in sunshine today, still expect afternoon high temperatures to
top out in the mid 30s across the Thumb to low to mid 40s elsewhere
as flow will be veering from the northeast to east.

Commencement of lee cyclogenesis across the central plains today
will be triggered by western CONUS troughing and the associated
potent upper level wave. This highly dynamic system will be lifting
out of the central plains and over MN/WI by tomorrow afternoon
guided by a 140+ knot upper jet that extends from the TX Panhandle
to Lake Superior. Initial effects locally will begin tonight as the
lead arm of isentropic ascent arrives around 2 am bringing a chance
of snow with sub freezing forecast soundings to start. The M59
corridor north into the Saginaw Valley and Thumb will be favored for
potential accumulation through about 8 am Wednesday with a trace to
to around an inch possible. Greatest residence time of forcing in
combination with cooler thermal profiles will be across the Saginaw
Valley where the higher end of snow accumulation are expected. The
warm nose intrudes on the area in the 8 am to 11 am window as
surface temperature response is slower to warm above freezing. The
result will be a relatively brief period of wintry mix, which
includes freezing rain/drizzle. and be favored north of I69 where
better ascent pivots to during this transition period. The rapid
rise in surface temperatures into the early afternoon should limit
any impacts during this portion of the event as any ice and snow
accumulation will quickly melt. However, it will remain possible for
some areas to see slick roadways to develop for a brief period of
time before surface temperatures climb above freezing.

The strong 60+ knot low level jet with associated 850 mb moisture
transport will drive a very moist airmass with Gulf ties into the
Michigan. Forecast PWATs to 1.30-1.40" surge into central Michigan
by 5 pm Wednesday, which is well above climatological norms. The
morning and early afternoon surge of moisture will outrun the
surface based CAPE, but the quality of theta-e/elevated instability
will bring a chance of elevated thunderstorms. Favorable ascent
during this time results in QPF amounts of half inch to three
quarters inch from 8 am to 2 pm.

Focus then turns to the late afternoon and evening as greater severe
weather threat may emerge. Plenty of cloud cover and continued
rainfall throughout the afternoon puts into question the degree of
surface instability that is able to develop ahead of an advancing
cold front. This will be one of the main factors in how the severe
weather potential plays out. Local guidance points the best surface
based potential across Lower Michigan, though it does remain
relatively weak with only a few hundred J/kg or less being more
likely. The strength of the LLJ will result in 50+ knots of bulk
shear, thus the overall environment leans toward a high shear/low
CAPE event with damaging winds being the greatest threat given the
associated wind fields. Largely curved hodographs bring a tornado
risk if any thunderstorm can become surface based. High moisture
environment ahead of the cold front will provide a focus heavy
rainfall and possible flooding concerns. See hydrology section for
additional information.

Surface high pressure builds across the Great Lakes for Thursday
into Friday bringing a period of dry weather. West flow will
maintain mild conditions Thursday as the frontal boundary hangs up
across the Ohio River Valley. The next chance for rainfall, possibly
heavy, will be Friday night into Saturday as low pressure develops
of the frontal zone and lifts towards the southern Great Lakes.

MARINE...

High pressure has been building in overnight and will become
centered over the region today. Though the winds have decreased
generally less than 20 knots, persistent northeasterly winds will
keep waves elevated several more hours into the day so the Small
Craft Advisory will continue. There will then be a brief lull in
winds as the high passes over but will quickly increase once again
from the SE ahead of the next strong low pressure system that will
lift through the area Wednesday. A Gale Watch is in effect for Lake
Huron to account for the wind gusts up to around 35 knots through
the day Wednesday. The cold front will sweep through late Wednesday
evening which will flip the winds around to the southwest and though
they will remain elevated, will top out around the mid 20s. There
will also be potential for strong to severe thunderstorms across the
lakes late in the day on Wednesday.

HYDROLOGY...

Wednesday carries potential for heavy rainfall as a strong low
pressure system moves through the Midwest and increases PWATs to
1.30-1.40"by Wednesday afternoon. There will be potential for
widespread 1 to 2 inches of QPF over a 24 hour period, with a low-
end chance for localized higher amounts in excess of 2 inches. The
first wave of precipitation comes Wednesday morning and early
afternoon with average rainfall amounts of a half inch to three
quarters of an inch. Then a greater peak of heavy rainfall Wednesday
evening into Thursday morning associated with a cold front. Current
forecast calls for up to inch of rainfall possible and focused along
the I-75 corridor from Toledo to Detroit. Adjustments remain
possible in exact placement of heavy rainfall axis. This brings
increased flooding concerns, especially if the axis of heavier
rainfall sets up over the urban areas of Detroit. Rises in area
rivers will also be likely.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Gale Watch from late tonight through Wednesday evening for
LHZ361>363-421-422-441>443-462>464.

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

$$

AVIATION.....AM
DISCUSSION...AA
MARINE.......DRK
HYDROLOGY....AA


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