471
FXUS63 KDTX 272245
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
645 PM EDT Sat Apr 27 2024

.KEY MESSAGES...

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

&&

.AVIATION...

Convective development is forecast across northwest Lower Mi this
evening as instability expands along/in advance of a southward
moving cold front. While upscale growth of this convection is
anticipated during the evening hours, it is expected to decrease in
coverage/intensity as it slowly sinks southward toward MBS in the 05
to 08Z time frame. Meanwhile, recent ACARS soundings out of DTW and
FNT show a weakly capped environment which will likely keep deep
convection isolated over most of the area through the evening.
Decoupling of the boundary layer this evening will lower sfc wind
speeds, however increasing winds just atop the nocturnal stable layer
will be supportive of some low level wind shear during the night.

A secondary influx of moisture and instability from the south
overnight will support another round of showers with a few embedded
thunderstorms late tonight through Sun morning. This added moisture
influx and showers will contribute to widespread MVFR and IFR based
clouds.

For DTW/D21 Convection...There appears to be some weakening of the
cap across the southern portions of the airspace. So some of these
showers may gain enough depth to support an isolated thunder risk
this evening. Otherwise, another round of moisture and elevated
instability advection overnight will drive scattered to numerous
showers across the area Sunday morning with some embedded
thunderstorms. The risk for thunderstorms to the airspace will be
greatest in the 09Z to 15Z time frame.

DTW THRESHOLD PROBABILITIES...

* Low in thunderstorms tonight. Moderate Sunday morning.

* High in ceilings aob 5000 feet overnight and Sunday morning.

&&

.PREV DISCUSSION...
Issued at Issued by National Weather Service Grand Rapids MI

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.

&&

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

$$

AVIATION.....SC
DISCUSSION...TJT
MARINE.......DBT


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