974
FXUS63 KDTX 170143
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
943 PM EDT Fri May 16 2025

.KEY MESSAGES...

- Thunderstorms remain likely tonight. The potential exists for
  storms to become strong to severe between 10 pm and 2 am, capable
  of producing damaging winds and large hail.

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

&&

.UPDATE...

Ongoing storms from central Lower Mi into southern Lake Mi continue
moving eastward while new development is likely out ahead and
farther east into SE Mi late this evening. Expanding convection is
boosted by height falls and DCVA on the leading edge of the 500 mb
low which then feed off MUCAPE holding in the 1000-1500 J/kg range
and effective bulk shear in the 30-50 kt range. This has already
been supportive of the large hail producing supercell exiting
Isabella county at forecast issuance. Hourly mesoanalysis and RAP
projections maintain favorable 700-500 mb lapse rate near 8 C/km as
the moisture axis sweeps through Lower Mi ahead of the cold front.
This is combined with the 00Z DTX sounding that shows both the lapse
rate and dry air centered around 700 mb along with a dry inverted-V
profile below cloud base. Bottom line here is that we continue to
expect strong to severe storms, with large hail as the primary hazard
and damaging wind also possible, in SE Mi until the cold front
sweeps activity into Ontario around 2 AM.

&&

.PREV DISCUSSION...
Issued at 705 PM EDT Fri May 16 2025

AVIATION...

Early evening VFR and lake breeze enhanced SE wind leads to another
round of thunderstorms with scattered to numerous coverage that is
on schedule to move across Lower Mi from mid evening until exiting
into Ontario around 2 AM. The activity is associated with strong
Midwest low pressure drawing moisture and instability back northward
into Lower Mi ahead of the trailing cold front. Storms are expected
to affect all SE Mi terminals with a few reaching strong to severe
intensity with strong wind gusts and brief MVFR/IFR restriction.

A few hours of VFR occur in the system dry slot after the
storms/cold front move east later tonight. This precedes MVFR
ceiling as it expands eastward from the Midwest where coverage is
widespread within the low pressure pattern. Gusty wind also becomes
a weather highlight late tonight and especially in the morning
through Saturday afternoon. West gusts well in into the 30 knot
range are expected as the boundary layer builds which also helps
ceiling break into low end VFR in the afternoon into Saturday
evening.

For DTW/D21 Convection... A few showers percolate nearby to the
south and east of the terminal early this evening. Otherwise,
clusters of storms ongoing from Upper Mi, WI, and IL/IN are on
schedule to reach the DTW area after 02Z. A few could be strong to
severe with strong wind and hail possible.

THRESHOLD PROBABILITIES...

* Medium for ceiling at or below 5000 feet with storms tonight, then
  high Saturday morning and midday.

* Moderate for thunderstorms after 02Z tonight.

PREV DISCUSSION...
Issued at 344 PM EDT Fri May 16 2025

DISCUSSION...

Southeast Michigan holding position late this afternoon immediately
downstream of a closed mid level pivoting across Wisconsin. A warm
but drier profile now entrenched, with a brief window of deeper
stability in residence now evident by a simply a limited coverage of
diurnal cu. Dry and stable conditions to hold through at least 00z,
with attention tonight shifting to a mid level perturbation shearing
out ahead of the main height fall center. Noted increase in forced
ascent attendant to this feature set to sweep across the local area
01z-07z. Renewed boundary layer moistening will commence at the same
time, offering at least a weakly unstable low level environment.
Mixed signal yet across the model solution space on possible degree
of destabilization, with variability noted in dewpoint recovery by
as much as 8-10 degrees. This will impact both prospective coverage
and vigor of any convective development within this window. Assuming
the upward vertical motion field can overcome residual capping
issues, then potential exists for cells to attain greater updraft
depth given very steep mid level lapse rates. Background wind field
more than sufficient to offer organization to any vigorous updrafts.
This conditional setup carries enough potential should greater
instability materialize to warrant an upgrade in the Day 1 SPC
outlook to a slight risk for southern portions of the area,
highlighting a damaging wind gust and hail threat. A secondary
window exists for sub-severe convective development with the actual
cold frontal passage late tonight.

Mid level low offers greater influence on conditions to start the
weekend, with the circulation center passing thru northern lower MI
during the daylight hours Saturday. Cold front exits to the east
Saturday morning, with ensuing cold air advection battling daytime
heating throughout the day. Minimal thermal recovery expected off
morning lows. Temperatures parked in the upper 50s to lower 60s.
Notably breezy conditions as mixing capitalizes on a firm west-
southwest gradient. Gusts in excess of 30 mph Saturday afternoon.
Moist cyclonic flow engaging daytime heating will maintain a chance
of showers. Seasonably cool conditions persist Sunday under deeper
layer northwest flow. Aside from a broad, thicker diurnal stratocu
field, generally benign weather conditions to finish the weekend as
general subsidence takes control.

Cooler and drier profile maintains residence Monday as low level
northeast flow governs conditions under building high pressure from
the north. A high amplitude, slowly evolving large scale pattern
emerges for the midweek period. Southeast Michigan likely holds
position between the high to the north and organizing low pressure
to the west. Potentially unsettled conditions at times this period,
depending the pace and trajectory of the closed low. Maintenance of
east flow with prospective cloud/shower potential on the rise will
keep temperatures on the cooler side of average through the rest of
the week.

MARINE...

Low pressure tracks over Lake Superior this evening sweeping a
respectable cold front late this evening. A broken line of showers
and storms likely develops in advance with isolated embedded strong
to severe thunderstorms possible. 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 have been issued for all nearshore waters
daytime Saturday 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.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...None.

Lake Huron...Small Craft Advisory from 8 AM to 10 PM EDT Saturday for LHZ421-422-
     441>443.

Lake St Clair...Small Craft Advisory from 8 AM to 10 PM EDT Saturday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 8 AM to 10 PM EDT Saturday for LEZ444.

&&

$$

UPDATE.......BT
AVIATION.....BT
DISCUSSION...MR
MARINE.......KDK


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