Expert Forecast Opinion

045
FXUS63 KDTX 160809
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
409 AM EDT Fri May 16 2025

.KEY MESSAGES...

- Warm today with another round of showers and thunderstorms likely
late this evening. Isolated storms may be strong to severe, mainly
between 8 PM and 1 AM. Damaging winds and large hail are the main
threats.

- Cooler conditions this weekend, with westerly wind gusts 30 to 40
mph on Saturday.

&&

.DISCUSSION...

The cutoff upper low responsible for the early morning MCS continues
to meander over the upper Midwest today. Sunny conditions are
expected through the daylight hours as mid-level subsidence
dominates in the wake of the morning convection. Deep southwesterly
flow brings in a secondary warm sector with highs reaching the mid
80s. Strong daytime mixing will cause dew points to fall to the
lower to mid 50s - offering a less humid feel compared to yesterday.
Southerly wind becomes breezy to around 20 to 25 mph, eventually
advecting in dew points back into the mid to upper 50s by the
evening. Meanwhile, mid-level cooling commences late in the day as
the upper trough begins to pivot into the central Great Lakes,
allowing instability to build as 700-500mb lapse rates increase to
around 8 C/km. Forcing is disorganized through the early evening
hours suggesting little potential to overcome the resident cap near
700mb.

After 00z, upper flow becomes increasingly unbalanced at the nose of
a 90 kt jet streak as the trough takes on a negative tilt -
providing better support for synoptic lift and convective initiation
as a pre-frontal surface trough lifts northeast across the area.
Given the timing near and after sunset, there remains uncertainty
regarding whether the cap will erode and instability (~750 to 1000
J/kg MLCAPE) will become realized at the surface before storms move
through. Bulk 0-6km wind shear of 40 to 50 kt is supportive of a
broken line of strong to severe storms with damaging wind and large
hail the main threats. Severe potential is highest between 8pm and
1am before the trough sweeps through, then lingering showers and sub-
severe storms may persist into the morning hours as the cold front
trails behind. Most areas will receive around or less than 0.25" of
rain tonight, but localized areas may see up to around 1".

The stacked low pressure system slowly advances into northern Lake
Huron on Saturday with a much cooler air mass working in through the
day. Highs reach the 60s as a tight pressure gradient produces gusty
westerly winds to 30 to 40 mph. Moisture wrapping around the low and
weak instability will bring a continued chance for light showers at
times through the day. Mid-level ridging then begins to settle into
the area Sunday into the early work week to favor surface high
pressure with dry and cool conditions. The next period to watch will
be Tuesday night into Thursday as a closed low tracks from the
Midwest toward the Great Lakes and Ohio Valley. This will provide
the next opportunity for showers and storms.

&&

.MARINE...

Southerly 15-20kt winds develop today following the passage of last
night`s warm front as the surface low tracks over Lake Superior.
Stubborn areas of fog likely linger through at least the morning
though with dewpoints falling, expectation is the decreasing
humidity should allow for a gradual diminishing trend for the latter
half of the day. Respectable cold front is set to sweep across the
region late tonight supporting another round of showers and
thunderstorms in advance. Set up is not as favorable compared to
Thursday night with coverage likely limited to a broken line with
any strong to severe embedded storms being more isolated in nature.
Moderate west-southwest winds follow Saturday with the strongest
winds (20-30kts) expected over the southern half of the region where
the gradient is strongest. Small craft advisories are warranted for
most if not all nearshore waters as a result. Low fully departs
Sunday shifting winds to the northwest. Gusts peak near 20kts during
the day before weakening overnight as weak high pressure slides
overhead.

&&

.PREV DISCUSSION...
Issued at 1232 AM EDT Fri May 16 2025

AVIATION...

Squall line producing very strong winds, large hail, isolated
tornados, and persist downpours continues to work from west to east
across the terminals tonight. Gusts in excess of 60 knots and at
least one confirmed tornado have been reported upstream with this
system. Trends continue to favor MVFR visibility reductions in the
main rain band, with brief IFR reductions noted at MBS and FNT.
Timing the exit is the main forecast concern for the next TAF cycle
as the lingering back-edge will be slower to depart from DTW and DET
near the very beginning of the TAF window. The line should fully
clear east of all sites by 07Z. Post-frontal VFR conditions move in
early Friday and throughout the day. Surface flow weakens, backing
from southwest to southeast during the afternoon. Additional showers
and storms possible late Friday evening.

For DTW/D21 Convection... A decaying line of strong to severe
thunderstorms crosses DTW during the 05-06Z time window.

THRESHOLD PROBABILITIES...

* Medium for ceiling 5000 feet or less toward midnight through
sunrise the low through Friday.

* High for thunderstorms tonight, mainly 05-06Z Friday, then low
confidence after 00Z Saturday.


&&

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

$$

DISCUSSION...TF
MARINE.......KDK
AVIATION.....KGK


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