Expert Forecast Opinion

882
FXUS63 KDTX 050157
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
957 PM EDT Fri Apr 4 2025

.KEY MESSAGES...

- Widespread rain overnight through Saturday morning.

- Dry with cooler conditions for the latter half of the weekend.

- Cooler conditions persist early next week with rain/snow showers
likely on Monday.

&&

.UPDATE...

Ohio valley convective trends and potential northward extent into
Lower Mi remain the forecast focus for SE Mi tonight and Saturday
morning, although evening observational evidence suggests
expectations for a manageable rainfall event remain intact. Upstream
radar/satellite/surface observations indicate a band of showers and
storms extending from the lower Ohio valley to east Texas along a
broad surface frontal structure. The pattern is capitalizing on deep
SW flow moisture transport consolidated east of the northern stream
upper level trough and southern stream closed low that extends from
central Canada to northern Mexico. New thunderstorm development is
occurring east of the main line from the central Ohio valley into
central Ohio as the low level jet ramps up north of the surface warm
front making the surface to 925 mb frontal zone most active with new
convection. This trend is expected to continue while the northern
end of line extends NE toward western Lake Erie and as low pressure
ripples northward from AR/MO. The surface low track is projected to
reach very near the west end of Lake Erie which maintains a late
night time window for elevated thunderstorms to graze the corner of
SE Mi prior to sunrise. Overnight rainfall totals around 0.75 inch
remain possible up to about the I-94 corridor while clusters of
lighter showers activate farther north/higher up the frontal slope
over most of southern Lower Mi. The initial 6 hours of the 00Z NAM
and the latest runs of the RAP/HRRR concentrate this activity
generally north of the I-69 corridor where totals around 0.5 inch
are possible until about mid morning when the surface low exits east
of Lake Erie.

&&

.PREV DISCUSSION...
Issued at 740 PM EDT Fri Apr 4 2025

AVIATION...

The leading edge of light rain has reached the DTW corridor at
forecast issuance and will spread the remaining way across SE Mi
during the evening. Dry easterly flow at low levels is able to delay
onset of MVFR and the transition to IFR/LIFR until later in the
night as showers increase coverage intensity, and then as the
surface low approaches NW Ohio late tonight. A rumble of thunder
remains possible near to the south of DTW and more likely south of
the Ohio border during the late night. This will be monitored as the
surface low ripples along the warm front south of a TOL to CLE line
early in the morning. Passage of the low brings wind around to the
NW across Lower Mi leading to a slow ceiling improvement through
Saturday.

DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 feet or less tonight and Saturday.

* Low for thunderstorms tonight.

PREV DISCUSSION...
Issued at 337 PM EDT Fri Apr 4 2025

DISCUSSION...

High pressure anchored north of the region maintains cool and dry
conditions through the evening period. Temperatures easing into the
40s during this time. Another widespread rainfall event then becomes
the focus for the overnight period. Wave of low pressure ejecting
northeast across the Ohio valley will draw an elevated warm frontal
boundary into the local area during this time. This occurs in
conjunction with deep northward moisture transport governed by
increasing magnitude to low level southwest flow and characterized
by pw in excess of 1.25 inches across southern sections. Combination
of pronounced isentropic ascent along the advancing frontal slope
and strengthening frontal forcing in the presence of increasing
deformation effectively yields an axis of moderate to potentially
brief heavy rainfall, with some probability for the northern expanse
to develop across areas mainly south of M-59. Model guidance
offering lower spatial predictability than desired at this stage in
providing greater insight in location of heavier rainfall. Consensus
with the HREF suggests convection across the warm sector will have
greater influence on prospective moisture transport across the cold
side of the frontal slope, maintaining a manageable qpf of generally
less than 0.75" under limited mid level destabilization. Assessment
of EPS membership, NAM output and local probabilistic information
highlight the uncertainty, indicating greater potential with a
roughly 50% chance of achieving an inch south of I-94 and a 25%
chance of 1.5". Should forced ascent ultimately capitalize on
greater theta-e advection and mid level instability, then a focused
region of higher precipitation rates will be possible. Peak
rainfall rates centered 04z-10z, with pockets of light showers
lingering into Saturday morning as mid level forcing slowly peels
away from west to east.

Increasing deep layer stability with time heading into Saturday
afternoon as emerging low level northwest flow affords greater
drying throughout the column. Limited insolation potential given the
lingering stratus canopy, as weak cold air advection solidifies a
below average temperatures for the day. Highs capped at upper 40s
north to mid 50s south. Energetic mid level southwest flow maintains
a stream of shortwave energy along and north of the frontal zone
easing southward across the Ohio valley. Tremendous moisture
advection along the frontal slope in the presence favorable entrance
region upper jet support will elicit another axis of heavy rainfall
Saturday night, but expectation remains for this moist plume to
mainly hold south of the region. Low end precip chances maintained
across the far south to capture some uncertainty yet on the northern
fringes of the qpf axis. Notably colder conditions to finish the
weekend period, as a period of greater heights falls offer renewed
cold air advection characterized by 850 temperatures of -5 to -7c.
Highs peaking the 40s.

Compact mid level wave of polar origin projected to pivot across the
great lakes Monday. Potential for a narrow but pronounced axis of
forced ascent to arrive tied to associated frontal forcing and dcva.
Despite the daytime arrival, suppressed freezing levels afford a
high probability for precipitation type of snow, particularly given
the likelihood for some higher precipitation rates. Significant
component of melting as surface temperature lift from lower 30s into
the 40s, but some accumulation potential will exist on grassy
surfaces. Another downturn in temperatures as high amplitude
troughing takes control Tuesday. Inbound airmass will leave
temperatures roughly 15 degrees below average, with readings
struggling to climb out of the 30s.

MARINE...

High pressure over Lake Huron this afternoon leading to light and
variable winds which will give way to light easterly this
evening/tonight with a warm front lifting into southern Michigan.
Widespread rain showers will develop, with embedded weak
thunderstorms possible over Lake St. Clair and Lake Erie. A wave of
low pressure will ride along the front Saturday morning, with
increasing northwest winds following for Saturday afternoon-night.
Good surge of low level cold advection, as 850 MB temps drop to
around -10 C over northern Lake Huron, promoting deep mixing and
wind gusts around 30 knots for a short period during early Saturday
evening. A brief period of wind gusts near 25 knots over Saginaw Bay
and northern tip of the Thumb region. Light winds return for Sunday
before a clipper system tracks through on Monday producing a period
of snow and rain showers. Even colder air will follow this system
and northwest wind gusts around 30 knots appear likely over much of
Lake Huron for Monday evening.

HYDROLOGY...

A warm front will bring widespread rain to all of SE MI late tonight
through tomorrow morning. Rainfall totals are expected to range
between 0.25" and 0.75" for most of the forecast area, with highest
totals south of I-94. There remains potential for some repeated
areas of higher intensity rainfall, particularly with any
thunderstorms, to lead to locally higher rainfall totals possibly in
excess of one inch. Given prior widespread rain activity and
saturated soil, some ponding of water on roadways and localized
flooding in low-lying and poor drainage areas may still be possible.

&&

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

$$

UPDATE.......BT
AVIATION.....BT
DISCUSSION...MR
MARINE.......SF
HYDROLOGY....MR


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