Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 191925
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
325 PM EDT Thu Oct 19 2017

.DISCUSSION...

Ideal Autumn weather will continue into the weekend. Dewpoints have
tumbled into the mid 20s and 30s behind a weak cold front supporting
a dry boundary layer while steadily increasing subsidence ensures
clear skies through the column. Dewpoints will stabilize in the 30s
areawide upon the onset of nocturnal cooling, setting a low floor
for overnight lows in a nearly ideal radiating environment.
Amplifying ridge downstream of surging Pac energy will force a
strong surface high pressure across the Ohio Valley. High confidence
that the southern half of the CWA will decouple with temperatures
falling toward the cooler MET/MAV numbers. Potential for mid to
upper 30s exists across the north where a slightly stronger PGF may
prevent maximum radiating. In any case, a cool, crisp night and
early Friday morning with negligible wind is in store.

Thermal profile rebounds again on Friday as longwave pattern
amplifies over the CONUS. Friday and Saturday will be nearly
identical as southerly flow advects H85 temperatures well into the
teens. Freshly developing return flow will be predominantly
southerly on Friday, placing the eastern third of the CWA squarely
in Lakes Erie and Saint Clair lake shadows. Limited mixing depths
will contain highs to the upper 60s with chillier readings
immediately downstream of the lakes. The western half of the CWA and
southern tier of counties should have no issues mixing into at least
the low 70s under full sun. The airmass will remain essentially
unchanged into Saturday as wind veers to the SW and cirrus begins
spilling into the area behind the ridge axis. Progged temps in the
low to mid 70s everywhere seems reasonable as warm SW flow persists
and lake shadow effects are eliminated for most of the area.

Warm and pleasant conditions continue on Sunday, highs again
reaching the low 70s, though clouds will increase through the day as
the next front approaches from the west. Rain to move into the area
late Sunday into Monday morning as this front progresses across
Michigan.

Models continue to diverge on how the pattern will evolve Monday.
The ECMWF shows this front stalling over SE Michigan before a low
pressure system develops and lifts through the Ohio Valley to the
Great Lakes early Tuesday - this solution would keep rain chances
higher for our area through Tuesday. The GFS solution suggests
Monday`s front will continue eastward and clear the region by the
afternoon. However, both models advertise an upper trough digging
through the Great Lakes and eastern CONUS by late Tuesday which will
lead to cooler, below average temps and a chance of showers
Wednesday. The trough will move out Thursday, resulting in a slight
rebound in temperatures and a better chance for dry conditions.

&&

.MARINE...

Westerly winds of 15-20 knots will decrease throughout the afternoon
into the tonight before dropping to 5-10 knots by tomorrow morning.
High pressure will drift across the eastern Great Lakes through the
beginning of the weekend bringing dry conditions. Winds will begin
to increase back into the 10-20 knot range tomorrow afternoon out of
the south as a tightening pressure gradient from approaching low
pressure system will keep winds elevated through the end of the
weekend. Rain chances will return on Sunday night and remain for at
least a couple days. Cold front looks to arrive early next week as
well and will bring some gusty winds out of the W/NW.

&&

.PREV DISCUSSION...
Issued at 150 PM EDT Thu Oct 19 2017

AVIATION...

VFR conditions will prevail for this TAF period with westerly winds
of 10-15 knots through this afternoon. Expect winds to decrease
later this evening before backing to the south by tomorrow morning in
response to a high pressure drifting through the eastern Great
Lakes. Little in the way of clouds this afternoon besides a thin
layer of cirrus streaming in from the northwest.

//DTW THRESHOLD PROBABILITIES...

* None.


&&

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

$$

DISCUSSION...JVC/TF
MARINE.......AA
AVIATION.....AA


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