096
FXUS63 KDTX 261717
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
117 PM EDT Thu Sep 26 2024

.KEY MESSAGES...

- Mostly sunny today with daytime highs in the mid to upper 70s.

- Next opportunity for rain showers (30-40 percent chance) arrives
Friday night into Saturday for areas along/south I-96/696.

- Lower chances for rain persist through the weekend with a
rumble of thunder possible.

&&

.AVIATION...

Surface high pressure holds across the airspace today while
deformation aloft has led to a northward expansion of high cloud.
Low level moisture has been meager so far, with any diurnal cu
response likely to remain FEW-SCT through the rest of the afternoon.
Light NE flow persists through the overnight before strengthening as
the pressure gradient tightens in response to Helene`s extratropical
transition. Winds strengthen toward 12 to 15 knots by 18z Friday
afternoon with gusts approaching 25 knots, highest across the DTW
corridor. Pockets of low level moisture may develop during the
morning-afternoon, although cigs aob 5000 feet will be transient and
do not warrant inclusion in the TAF at this time.

For DTW/D21 Convection...Thunderstorms are not expected this period.

DTW THRESHOLD PROBABILITIES...

*  Low for ceiling at or below 5000 feet Friday morning-afternoon,
   medium Friday evening.

&&

.PREV DISCUSSION...
Issued at 318 AM EDT Thu Sep 26 2024

DISCUSSION...

An aggressive high pressure response is underway this morning as a
1017 mb surface ridge currently centered near the MN/WI/IA border
exerts its influence further east across Lower Michigan. The
statically stable airmass and accompanying subsidence is well
evidenced in morning satellite imagery as a dense poleward cirrus
plume struggles to make significant inroads beyond I-69 which will
keep the majority of Southeast Michigan exposed to more sun than
clouds today. A sparse diurnal cumulus field is then possible early
this afternoon, but consensus RH progs are not conclusively
representative of such. Forecast soundings do indicate slight
moderation of the column today (both in the advective and adiabatic
sense) which supports broad coverage of daytime highs approaching
the upper 70s. This takes into account a much cooler start over the
Tri-Cities (upper 40s) compared to the Metro area (closer to 60F)
given uninhibited solar insolation for the former and cirrus
obscuration for the latter.

Confidence in a dry forecast continues to trend upward for the
daylight hours Friday as Hurricane Helene accelerates north-
northwestward across The Southeast before it rapidly deteriorates
into a Tropical Depression. Latest solutions converge toward a
forecast track that favors a sharp westward turn midday Friday
leading to eventual residence over western Kentucky once the
tropical wave engages an orphaned trough currently stalled over the
Mid-Mississippi Valley. Such an evolution carries higher
predictability in the core ThetaE plume holding south of the state-
line, along with the associated heavy rainfall. Duration and
magnitude questions persist regarding the extent of shearing rain
bands that migrate into the southern part of the forecast area.
Deflecting FGEN helps activate initial ascent/moistening over Monroe
and Lenawee Counties Friday night before system-relative isentropic
ascent reinforces shower activity along the northern fringe of the
system. Will continue to advertise light QPF of a few hundredths of
an inch Friday night into Saturday for the southern third of the CWA.
Still expecting a more notable gust response Friday afternoon as
east-northeast winds peak around 30 mph by late evening with the
glancing LLJ core.

Automated NBM PoPs for this weekend fell within the Chance range (25-
40 percent) up to I-69 which is probably a bit too aggressive for
the northern edge. However, (light) rainfall still largely depends on
the secondary and tertiary spokes of forcing aloft within an
increasingly saturated environment as wrap-around Gulf moisture
transport persists. Eventually, the propagation of a progressive
Pacific wave dislodges the remnant system eastward Monday into
Tuesday. Temperature readings remain on-track to peak a few degrees
above climatological averages during this time with highs in the mid
70s and lows in the upper 50s (low 60s for the more urban areas).
Next area of commanding high pressure builds into the Great Lakes
behind a cold front for the middle of next week resulting in a
transition to below normal temperatures and drier conditions.

MARINE...

High pressure will expand eastward across the region today resulting
in northerly winds which will veer more northeasterly though the day
while remaining below 15 knots. As the high pushes off to the east
Friday, an area of low pressure will lift north out of the
Southeastern United States and is forecast to stall over southern
Illinois and Indiana late Friday. The pressure gradient between the
high and approaching low will be tightest over Lake Erie, and gusts
of 25 to 30 knots appear likely Friday-Saturday morning which would
necessitate Small Craft Advisories. Winds will decrease heading
northward toward Lake Huron but any shift north or south by the low
will lead to a shifting wind field as well which will be watched for
in the next 24-36 hours.

&&

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

$$

AVIATION.....MV
DISCUSSION...KGK
MARINE.......DRK


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