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000
FXUS63 KDTX 272004
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
Issued by National Weather Service Grand Rapids MI
404 PM EDT Sat Apr 27 2024

.KEY MESSAGES...

- Southwest winds gust to 35 mph this afternoon.

- Dry through early tonight.

- Additional showers and storms are possible Sunday and Monday with
above normal temperatures before a cold front arrives on Tuesday.

&&

.DISCUSSION...

The overarching theme has been a delayed onset of precipitation
across much of southeast Lower MI. Water vapor imagery presentation
is quite harsh-looking with pronounced implied subsidence. Moreover,
upper flow upstream towards the southwest implies the presence of a
shortwave ridge possibly being bolstered by now-weakening convection
over the IL/KY border region.

To support the idea of prolonged weak to moderate upper subsidence
and indications that near-surface frontal convergence will be on the
weak side, it makes sense to expect a later onset of precipitation.
even farther northwest towards the Tri-Cities, it could be well
after midnight until that area receives measurable precipitation and
the Detroit Metro is now looking at 3am or later for the onset of
measurable precipitation. This will of course be well after the
diurnal instability peak so severe chances for southeast Lower MI
look a bit less than before.

As noted previously, we are looking at a prolonged unsettled
period from Sunday into Monday night thanks to a latitudinally
aligned quasistationary front across southern Lower MI with a slow
southward drift. Sufficiently robust and prolonged low-level
moisture convergence will replenish conditional instability and
provide modest forced ascent that necessitate a continued mention of
thunderstorms in the forecast. As noted before, highs south of the
front could be very warm with maximum temperatures towards the OH
state line reaching or exceeding 80F on Sunday.

Tuesday and Tuesday night currently look dry, but after that,
predictability really starts to suffer with the approach of a band of
strong upper southwesterlies capable of yielding episodic PV forcing
with details in position and timing remaining murky.

&&

.MARINE...

A healthy pressure gradient exists over Lake Huron through tonight
as strong low pressure crosses Lake Superior, but very warm airmass
over the cold lake is stabilizing the lower levels. As a result,
south/southwesterly winds peak through this evening at 20-25 kt,
diminishing thereafter as a cold front settles across the lake from
the north. This front is likely to touch off rounds of showers and
thunderstorms this evening into Sunday as it stalls, and continuing
into Monday as it lifts back north as a warm front. Easterly winds
increase on the cold side of the front over the northern half of the
lake Sunday night into Monday as the flow becomes constricted
between strong high pressure over Hudson Bay and low pressure
approaching from the southwest. Winds of 25-30 kt are expected
during this time, with internal guidance suggesting a 30%
probability of gales.

&&

.PREV DISCUSSION...
Issued at 112 PM EDT Sat Apr 27 2024

AVIATION...

Envelope of enhanced near surface moisture and associated MVFR
clouds is making steady progress across Southeast Michigan early
this afternoon. The cloud field is expected to slowly lift and scour
from south to north through the balance of the afternoon. While
complete clearing is not expected, expecting the integrity of the
cloud field to slowly degrade. Peak winds to 30kts from the
southwest have become common at all the terminals and will remain
the prevailing condition until sunset. As the surface flow decouples
this evening, low-level wind shear from the southwest will emerge
and continue through the night.

Aside from this afternoon`s winds, the other item of concern is the
prospects for convection tonight into Sunday. There is a low chance
for thunderstorms this evening across the Detroit terminals.
Meanwhile, anticipated convection over Northern Lower Michigan has a
shot at holding together into the Saginaw region late tonight.
However, the best chance for activity will be during the morning
Sunday, with the best opportunity at PTK, FNT, and MBS. Finally, the
lingering frontal boundary in the vicinity of FNT may initiate
additional convection Sunday afternoon.

For DTW/D21 Convection...there are three opportunities for
convection within the airspace. First, a limited window around 00z
this evening with the next surge of deeper moisture into the
building instability. Convective character would be widely scattered
and progressive. Second, around sunrise with an advancing warm front-
like feature. Coverage is expected to be greater across the northern
sections of the airspace with lesser chances at the airfield. Third,
during the mid to late afternoon on Sunday as the stalled front
serves as focus for new diurnal convective development. Coverage
with this activity looks limited and across the north third of the
airspace.

DTW THRESHOLD PROBABILITIES...

* Low in thunderstorms tonight into Sunday morning.

* Moderate for low-level wind shear tonight.

* High in ceilings aob 5000 feet this afternoon and Sunday morning.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until midnight EDT tonight for LHZ421-422.

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

$$

DISCUSSION...TJT
MARINE.......DBT
AVIATION.....Mann


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