408
FXUS63 KDTX 291924
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
324 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 along or 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.

&&

.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.

&&

.PREV DISCUSSION...
Issued at 208 PM EDT Sat Jun 29 2024

AVIATION...

Low VFR to MVFR ceilings persist this afternoon. Daytime mixing
should continue to lift these ceilings towards VFR by this evening,
but areas of BKN MVFR ceilings may continue to linger further into
the afternoon. Mixing will also yield gusty southwest winds. Peak
gusts should largely come in at around 20-25 knots. An isolated
shower or two are present one radar at press time just south of I94.
Any thunderstorm potential is low for this afternoon and chances
look even less favorable this evening towards DTW. Will monitor any
need to tempo in rain showers over the next few hours. This evening
into tonight will see wind gusts weaken while a cold front drops
south and leads to a wind shift out of the northwest along with
increasing low clouds. MBS will stand the best chance to see a
thunderstorm between 00-06Z, but confidence is too low to mention at
this time.

For DTW/D21 Convection...Thunderstorm potential is low this
afternoon. Placement in current isolated showers also looks to hold
just south of DTW. An amendment for a brief tempo shower may be
needed.

DTW THRESHOLD PROBABILITIES...

*  Medium for ceiling aob 5000 ft this afternoon. High early
   tomorrow morning.

* Low for thunderstorms this afternoon.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422.

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

$$

DISCUSSION...AM
MARINE.......BC
AVIATION.....AA


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at www.weather.gov/detroit.