Expert Forecast Opinion

949
FXUS63 KDTX 141931
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
331 PM EDT Wed May 14 2025

.KEY MESSAGES...

- Scattered showers with some embedded thunderstorms continues
through the evening.

- A Slight Risk for severe thunderstorms exists tomorrow night to
Friday morning primarily between 10 pm and 3 am. Large hail and
damaging winds will be the main threats, although a tornado cannot
be ruled out.

- Cooler and less humid weather by this weekend.

&&

.DISCUSSION...

The meandering closed low over the Ohio Valley has opened up this
afternoon placing the broad trough axis over the Great Lakes with
embedded weaker vort maxes. Periods of isl/sct showers and some
embedded thunderstorms remain likely with vort passages, under a
moderately unstable environment where LI/showalter values hold
negative. Deep layer shear aob 10 knots inhibits the chance for
organized convection. Decreasing coverage of shower potential will be
likely overnight outside of southern Michigan into the Metro region,
where weak convergence along an elevated warm front retains
continued low (30%) chances for showers and storm potential through
the night.

Passage of a warm front tomorrow will retain muggy conditions as dew
points creep up into the mid 60s with the boost of thermal advection
propelling temperatures into the low 80s for a daytime high. Outside
of some low-end shower potential mainly focused across the Thumb and
Tri-Cities, the afternoon and evening hours will see mid-level lapse
rates steepen significantly while 700-500mb RH values drop,
signifying the advection of an EML eastward into the region. This
will lead to an increasingly capped environment through peak heating
hours, suppressing ci development for most of the day. Shower and
organized thunderstorm potential then becomes increasingly more
likely late tomorrow night into Friday morning along a prefrontal
convergence zone where upscale growth brings the potential for
organized strong to severe activity.

Once initiated, convection has the potential to organize quickly
along the boundary, supported by deep-layer shear vectors and strong
0-6 km bulk shear. Storm mode favors quasi-linear evolution despite
the orthogonality of wind and shear vectors due to broad frontal
ascent. Being said, some embedded supercell structures or
mesovortices remain possible within any developing line, especially
where mesoscale enhancements briefly support more discrete updrafts.
One of the questions for this setup is the degree of erosion of the
cap and supporting stable layer. Latest hi-res guidance has many
members with a relatively stable near surface layer, which would
limit tornado potential and keep any supercell development elevated.
However, if surface parcels can be tapped as the boundary layer
cools, the environment does support some tornado potential. This may
be slightly more probable across the southern third of the cwa where
the nose of a llj supports ageostrophic flow just ahead of any
linear upscale growth and where better MLCAPE potential resides.
Otherwise, strong updraft generation bring damaging wind gusts and
large hail as the main hazard potential, noting strong mid-level
lapse rates near 8C/km. There is uncertainty with degree of
instability that can be squeezed in just ahead of any developing
line, but potential for aoa 1,500 j/kg is there in a high-end
scenario. Timing for convection is centered 02Z (10PM) to 07Z (3AM)
Fri.

Storm potential will promptly end by the mid-morning hours once a
dry slot filters in. Little change in the thermal field on Friday
with 850mb temperatures holding around 15C, which will bring the
warmest temperatures of the week as highs increase into the mid 80s
for most locations, potentially into the upper 80s across the Metro
region. Additional shower and storms re-enter Friday night into
Saturday morning ahead of a cold front, with the passage of the front
then support temperatures back to near normal values back into the
upper 60s to lower 70s for highs Saturday and into the early week
period.

&&

.MARINE...

A broad Gulf-originating trough continues to linger over the Great
Lakes/Ohio Valley this evening into tonight supporting isolated to
widely scattered shower and storm chances as well as lighter (less
than 15kt) southeast flow. Humid airmass atop the cooler lakes will
also support the redevelopment of areas of fog tonight. Strong
surface low pressure developing over the northern Plains lifts a
warm front across the central Great Lakes late Thursday night
setting up modest, 15-20kt, southwest winds in its wake for Friday.
A line of strong to severe thunderstorms is expected to develop in
advance of this front early Thursday night with all hazards (wind,
hail, waterspouts) in play, though winds in excess of 40kts will be
the primary threat. Aforementioned low gradually tracks over Lake
Superior late Friday-Saturday driving a cold front through central
lakes Saturday morning bringing additional shower/storm chances and
westerly turning northwesterly flow for the weekend.

&&

.PREV DISCUSSION...
Issued at 218 PM EDT Wed May 14 2025

AVIATION...

Stubborn MVFR cloud field persists this afternoon ahead of
blossoming isolated to scattered convection. Overall forcing remains
quite weak with uninspiring dynamics aloft, paired with weak surface
wind speeds, generally from the southeast. Do expect an increase in
coverage of showers and storms with time, starting first over the
southern terminals (YIP/DTW) per latest radar trends. PROB30s were
included for the afternoon period, followed by another possible
convective window this evening as the moisture-laden airmass holds.
May have been too optimistic in ceiling recovery, therefore
amendments may be needed to capture uncertainty with VFR timing
later today.

For DTW/D21 Convection... Isolated thunderstorms increasingly likely
this afternoon and again this evening. Added PROB30s. Storms will be
narrow in diameter, thus low confidence in any direct hits to the
airfield.

THRESHOLD PROBABILITIES...

* High for ceiling aob 5000 feet through the forecast.

* Low to medium for thunderstorms this afternoon and evening.


&&

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

$$

DISCUSSION...AM
MARINE.......KDK
AVIATION.....KGK


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