Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 141802
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
102 PM EST Wed Feb 14 2018


.AVIATION...

VFR conditions to start this TAF period with southwest winds of
mostly around 5-12 knots. Conditions will begin to deteriorate
through the day as lowering CIGS and VSBYs will arrive as a plume of
moisture continues to move northward and takes hold of southeast
Michigan. Widespread MVFR to IFR ceilings will move in this evening
and persist into tomorrow morning. Periods of drizzle and IFR fog
will accompany the IFR ceilings as much milder air moves over the
current snowpack. Winds will remain out of the southwest around 5-12
knots into tomorrow morning.

For DTW... Clear skies through the late afternoon will become
overcast by this evening with ceilings below 5000ft as moisture and
cloud shield moves northward. IFR fog and drizzle will accompany the
moisture surge and continue into tomorrow morning.

/DTW THRESHOLD PROBABILITIES...

* High for ceilings below 5000 ft this evening through tomorrow
  morning.

&&

.PREV DISCUSSION...
Issued at 331 AM EST Wed Feb 14 2018

DISCUSSION...

Radiating under clear skies has proven effective this morning in
spite of a steady light southwest wind. Some stations have begun to
rebound during the predawn hours while several others remain firmly
in the mid teens. Regardless, ongoing warm advection under clear
skies will favor a healthy rebound in temperatures today with the
bulk of 00z guidance coming in near inherited forecast highs in the
upper 30s/low 40s - more than reasonable given full insolation for
the balance of the daytime hours.

A northward push of Gulf moisture in progress as southwest gradient
organizes over the southern and central US in response to western US
height falls and high pressure situated over the East Coast. An
abundance of low clouds is noted over the southern plains, MS River
Valley, and even some creeping north toward the southern Michigan
border at 08z this morning. The bulk of the latter will shift east
of the area during the morning, possibly scraping the southern
counties for a few hours. Otherwise, and in contrast to the majority
of NWP forecast soundings, expect low cloud to arrive this evening
coincident with low-level jet forcing and the lead edge of higher
theta-e airmass. Solid overcast progged to arrive in the southern
counties around 6 pm local time. The best surge of moisture along
the nose of the LLJ will be over the eastern half of the CWA, the
strengthening westerly wind response noted at 850mb coming out of
Wisconsin after about 03z will likely provide a sufficient boost of
convergence to ensure overcast envelops all locations before
ushering low cloud east of the area by sunrise Tues. Even with NWP
likely embellishing boundary layer moisture over melting snowpack,
added LLJ-related shear near the inversion has the potential to
force enough mechanical mixing to elicit some drizzle 03-09z tonight.
Confidence is not necessarily high, but there is certainly no
justification to removing it. The only noteworthy changes to the
forecast tonight were therefore refinements to timing of
stratus/drizzle. In light of typical model biases over snow, fog
continues to be omitted pending observational evidence this
afternoon.

Progressive northern stream wave digging over the western US today
into tonight will set the pieces into motion for weather over SE
Michigan on Thursday. As this wave effectively kicks out whatever
remains over California this afternoon, the upper mass gradient will
strengthen tonight into Thursday and elicit a more noteworthy LLJ
response during the daytime hours Thurs. PV anomaly itself will
remain displaced to the north, but strong moist isentropic ascent
and mid-level convergence as the frontal slope tilts will yield
widespread light rain Thursday. The daytime floor on temps will be
near 40 degrees owing to the high dewpoint airmass, with a higher
end potential near 50 degrees conditional on intensity/duration of
rain. Renewed troughing behind a weakly forced fropa late Thursday
will allow temperatures to settle near normal for the end of the
week.

MARINE...

Moderate southwest wind will bring increasingly mild air into the
Great Lakes today resulting in areas of drizzle and fog expanding
over the region tonight and Thursday. The mild air will also produce
very high stability over marine areas which will limit wind gusts to
25 knots or less and limit wave growth on the remaining open water
of central Lake Huron. Passage of the cold front Thursday night will
bring strong low level cold advection and possibly a short period of
gales in the initial northwest flow. The short duration is the main
limiting factor for headline consideration. Gusts around 30 knots
will otherwise be more common before high pressure arrives Friday
afternoon.

&&

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

$$

AVIATION.....AA
DISCUSSION...JVC
MARINE.......BT


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