512
FXUS63 KDTX 292316
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
716 PM EDT Sat Jun 29 2024

.KEY MESSAGES...

- There remains a very low chance for an isolated strong to severe
thunderstorm late this afternoon into the late evening.

- The first low end (15%) t-storm chance will be confined south of I-
94 through the evening, where wind gusts and locally heavy rainfall
are the main threats. The second low end (15%) chance will be
confined north of I-69 late tonight, where hail is the main threat.

- High pressure builds in behind a cold frontal passage on Sunday
and brings cooler and drier weather for early next week.

&&

.AVIATION...

Convection early this forecast will fire off to the south and
southeast of the terminals with VFR conditions expected. Additional
showers/storms now sweeping into northern lower MI may clip KMBS
later this evening before dissipating, but confidence is too low to
include in forecast at this time. Cold frontal passage late tonight
will bring veering winds to the northwest with MVFR/lower VFR cigs.
These conditions persist through Sunday with just a gradual lifting
and breaking up of ceilings expected with main clear expected to
hold off until 00z Sunday evening or beyond.

For DTW/D21 Convection...Thunderstorms are not expected during the
upcoming forecast as main low level convergence settles south to
southeast of the terminal as the forecast period begins.

DTW THRESHOLD PROBABILITIES...

*  High in ceilings aob 5kft early Sunday morning (10z), medium
   Sunday afternoon.

&&

.PREV DISCUSSION...
Issued at 324 PM EDT Sat Jun 29 2024

DISCUSSION...

For the remainder of the afternoon and evening... Most locations are
expected to remain dry as weak cap starts to build around h800. Two
low-end chances (~15%) for a shower or thunderstorm will still
exist... The first will be confined along or south of the I-94
corridor, where a ridge of enhanced theta-e may provide support for
showers or storms to extend from northern Indiana and northwest Ohio,
clipping far southern Michigan. Most model output holds chances
south of the state line, however, in the low end chance a thunderstorm
clips southern Michigan, a marginal risk for severe weather holds,
with damaging wind gusts to 60 mph as the primary threat. An
isolated tornado cannot be ruled out, but this threat remains very
low. Please see the morning update for the additional information as
the information pertaining to severe weather hazard types remains
valid. Only changes noted were the geographical location of the
severe threat and the extended timing, which will now last through
about 01Z (9PM).

The second window for low-end chances (~15%) will reside north of
I-69 as a cold front starts to drop across the cwa. An isolated
shower or thunderstorm from northern lower Michigan may clip a
portion of the Tri-Cities or northern Thumb between the 01-05Z time
frame. Severe weather chances for this activity remains low
especially as daytime instability rapidly wanes. Still, strong mid-
level winds fill in with the front which will elongate hodographs,
and with lingering instability holding on, the marginally severe
threat will remain, with hail to an inch as the primary threat. Storm
modes for both areas are expected to be pulse.

Although limited convection is expected with the frontal passage,
the drop in temperature and humidity will certainly be felt. H850
temperatures presently around 17C will drop between 5-8C this time
tomorrow. Likewise, surface dew points now in the 70s will drop down
into the lower 50s. Expecting a fair amount of stratu-cu production
tomorrow with the thermal trough in place, which will promote steep
low-level lapse rates while working with saturated near surface
conditions. Rapid erosion of cloud cover is expected through the
evening and overnight hours as mixing with the dry air aloft works
in, coupled with loss of daytime heating and continuous dry air
advection. Clear overnight skies leading into Monday will bring cool
overnight lows in the mid 40s to lower 50s. This will lead into very
pleasant conditions on Monday -- copious amounts of sunshine, light
winds, low humidity, and highs in the mid 70s.

High pressure will gradually depart into the continental northeast
while an upper-level trough fills in over the Dakotas. This will
bring the heat and moisture back into the Great Lakes by Tuesday
with temperatures returning to the 80s. The return of rain and
thunderstorm chances return Tuesday with the boost in humidity, but
will be conditional on the location of prefrontal shortwaves.
Wednesday will offer better chances for rain and thunderstorms with
a weak cold frontal boundary passing over the state. Of higher
confidence, near normal to above normal temperatures are expected to
return by the midweek period. The latest NBM output highlights highs
in the mid to upper 80s by Wednesday.

MARINE...

Low pressure system moves through today bringing chances for showers
and storms through the rest of the afternoon and evening today.
Ahead of the cold front, southwesterly winds up to 20 knots will
remain in place this evening. Wind gusts have underperformed and are
forecasted to decrease further through 10 PM, so the Small Craft
Advisory for Saginaw Bay has been canceled. Cold front moves in
tonight and veers winds to the northwest, speeds up to 20 knots and
gusts to 25. Direction of flow will allow waves to reach Small Craft
Criteria near the Thumb on Sunday. As the low departs, high pressure
fills in behind and allows for drier conditions and gentle winds
to take over on Monday.

&&

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

$$

AVIATION.....DG
DISCUSSION...AM
MARINE.......BC


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at www.weather.gov/detroit.