Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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814
FXUS63 KDTX 191704
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
104 PM EDT Thu Sep 19 2019

.AVIATION...

Maintenance of a dry and stable low level environment held by high
pressure centered to the east ensures skies remain clear across the
lowest 5000 ft through the remainder of the daylight period. Winds
remain modest from the southeast during this time. A plume of
moisture will lift northward this evening, which may bring a brief
period of thicker cloud within the 4-6k ft level overnight. This
moisture then lifts to the east by Friday morning. Some shallow fog
also a possibility, but likely of limited coverage or duration.

DTW THRESHOLD PROBABILITIES...

* Low for cigs at or below 5000 ft tonight.

&&

.PREV DISCUSSION...
Issued at 331 AM EDT Thu Sep 19 2019

DISCUSSION...

Modest convective activity ongoing within the upstream corridor of
instability draped from the northern Great Lakes into the eastern
Great Plains early this morning. This action will struggle to
survive into the daylight hours while any potentially organized
convection remains tied to the instability gradient over the Midwest
anyway. Thus, with southeasterly return flow continuing to dominate
locally, expect little change from yesterday aside from the
potential for a partial coverage of high cirrus debris originating
invof the Upper MS River Valley early morning. Highs once again near
80 degrees.

Low to mid 60s dewpoints over the Lower OH Valley will
begin creeping into the area tonight into the weekend as the
prevailing pattern remains generally unchanged and light moisture
advection continues. This will place a rising a floor on overnight
lows each night while modest afternoon mugginess typical of late
September accompanies continued daytime highs in the 80s. Only item
of interest in the near term is potential for a weak MCV to trigger
isolated/scattered showers or t-storms on Friday as low-level
instability builds. 4-km NAM and NMM are aggressive in their
depictions of this scenario, but analysis of forecast soundings
reveals stout capping centered around 850mb and what appears to be
erroneous triggering of convective QPF. Nonetheless, there is a some
consensus among the various NWP, including the ECMWF, that a
convectively induced shortwave will propagate along the periphery of
the resident mid-level ridge potentially grazing the forecast area
Friday afternoon. A stronger outcome may therefore warrant an upward
revision to pops into the SCHC category, but maintained a dry
forecast for now. More likely scenario is simply a greater coverage
of lower-based diurnal cu than previous days, especially over
southern and eastern areas.

As the western US longwave trough runs its course and energy
releases into the central CONUS and northwest Ontario, subsequent
deamplification of the downstream ridge will allow the instability
gradient to be forced through Lower Michigan Sunday into Sunday
night warranting inclusion of showers/tstorms. High temps thereafter
settle closer to climatological average values.

MARINE...

Ridge of high pressure anchored over the Mid Atlantic will maintain
benign marine weather through the end of the week. Southeast winds
will veer to the south today, prevailing from this direction to
finish the week.

&&

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

$$

AVIATION.....MR
DISCUSSION...JVC
MARINE.......CB


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