364
FXUS63 KDTX 181958
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
358 PM EDT Fri Apr 18 2025

.KEY MESSAGES...

- Warm and breezy today with high temperatures well into the 70s to
near 80 degrees.

- 30 to 50% chance for storms to spread over the Saginaw Valley and
Thumb this evening between 6 and 10PM. An isolated severe storm
capable of 1 inch hail and damaging wind gusts will be possible.

- Additional showers and thunderstorms are likely across all of
Southeast MI overnight. Severe weather is not likely but cannot be
fully ruled out.

- Mainly dry and mild weather this weekend with the next round of
showers and storms arriving Sunday night into Monday.

&&

.DISCUSSION...

Subsidence behind the morning convection and EML induced capping
becoming evident in recent ACARS soundings should suppress
convection through the rest of the afternoon, even as surface based
instability is progged to increase to 1000-1500 J/kg beneath the
inversion. Low pressure over northern IL lifts northeast across Lake
Michigan into northwest and mid MI this evening, with convection
already starting to percolate near the low center near Rockford. As
a weak shortwave and relatively nebulous frontal forcing lift
northeast from the Mississippi Valley, this convection is shown in
much of the hi-res guidance to track northeast along the instability
gradient toward the Saginaw Valley and Thumb this evening. This
window from roughly 22z to 02z appears to be the most favorable
chance for any severe weather before instability begins to wane
through tonight. Isolated storms may be capable of producing large
hail and damaging wind gusts as the primary threats. Confidence in
severe weather occurring remains low and SPC continues to maintain
the Marginal Risk (1 out of 5) for the area.

Given the positive tilt to the driving upper trough and deep layer
southwesterly flow parallel to the boundary, forward speed of the
cold front will be slow overnight. This sustains scattered showers
and thunderstorms through the night into the pre-dawn hours. Lapse
rates weaken considerably as deeper layer moisture arrives and
severe weather becomes increasingly unlikely later in the night. The
environment will support pockets of heavy downpours with PWAT
nearing 1.50", deep warm cloud layer, and potential for backbuilding
storms given weak corfidi upshear vectors. The limiting factor
appears to be relatively weak forcing along the front which keeps
convective coverage on the lower end locally. The showers and storms
should depart most of the area by around sunrise, but the Monroe and
Downriver areas may see additional light showers as remnant lower
Ohio Valley LLJ forcing creeps in at times through the morning.
Otherwise, drying westerly flow through the day Saturday offers dry
and seasonable conditions with highs in the mid 50s to mid 60s.

Shortwave ridging amplifies overhead on Sunday in between systems,
promoting high pressure with light wind and cool weather. There will
be a slight chance for showers as elevated warm advection grazes the
western half of the state, otherwise mainly dry conditions prevail.
The next mid-level wave ejects from the southern Plains toward the
western Great Lakes on Monday, nearing occlusion as it passes over
Lake Michigan. Numerous showers and storms will be likely through
the day as this system passes through. There is uncertainty where
the triple point will set up and track, but if the warm sector
creeps in some stronger storms would be possible before the cold
front moves through by the evening. Placement of the warm sector
also brings higher uncertainty to the high temperature forecast
which may range from the lower 60s to the lower 70s. After this
system departs, zonal flow aloft sets up through midweek with the
jet stream slowly migrating northward across the Great Lakes.
Overall mainly dry and mild conditions are favored but there will be
low-end chances for rain at times as smaller scale waves ripple
across the northern lakes.

&&

.MARINE...

A warmer and drier airmass settles in for the early evening period
while increasing stability begins to limit wind gust potential.
Given that wind gusts have generally underperformed today and wave
heights have subsided below 5 feet, all Small Craft Advisories will
end at 4 PM. Additional clusters of showers and thunderstorms are
possible tonight, especially north of the warm front which has
stalled just north of Saginaw Bay. These storms are likely to remain
elevated, which limits impacts to large hail and heavy rainfall.
Additional showers and storms may fill in ahead of a slow-moving
frontal zone overnight, before this front settles south of the Ohio
border Saturday morning. Northwest flow prevails in the post-front
regime, with benign marine conditions expected through the better
part of the weekend. The next low pressure to bring rain chances and
increased winds/waves arrives Monday.

&&

.PREV DISCUSSION...
Issued at 251 PM EDT Fri Apr 18 2025

AVIATION...

The line of shower and thunderstorm activity driven by inertia
gravity wave dynamics is currently tracking eastward out over Lake
Huron. A few surface wind gust observations of 35 to 60 mph were
associated with this activity. Surface winds are now forecasted to
uniformly respond out of the southwest 20 to 35 knots this afternoon
ahead of approaching cold front. Low confidence exists on the
expected timing and duration of additional shower and thunderstorm
activity this evening and tonight. Convective inhibition from warm
air aloft is expected to limit activity possibly until sometime 04-
09Z. There is some model signal that suggests thunderstorm activity
could split the area to the north and south.

For DTW...Uncertain time window for thunderstorm development with
the passage of a cold front between 07z and 09z tonight.

DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less through this evening, then high
  tonight.

* Low for thunderstorms after midnight Friday night.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 4 PM EDT this afternoon for LHZ421-422-
     441>443.

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

$$

DISCUSSION...TF
MARINE.......MV
AVIATION.....CB


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