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afddtx

Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1157 PM EST Thu Nov 14 2019



Aviation...

Stratus is locked in place over Southeast Michigan as very strong
midlevel subsidence inversion is down to approximately 2000 ft agl.
Strength of subsidence inversion supports persistence of stratus
throughout the first half of the night. Significant moisture
advection is then forecasted the latter half of the night with axis
of 900-775mb moisture streaming directly into the area in response
to sharp pv anomaly and low pressure system tracking across Canada.
The moisture will just reinforce cloud strong static stability in
place from 3.0 to 12.0 kft agl. Cloud to persist throughout Friday.
Surface wind shift to track through the area from approximately 19-
21z Fri with wind veering to the northwest.

For dtw...MVFR stratus to hold throughout the night. No drizzle
anticipated at this time. MVFR stratus Friday. Wind shift to northwest
(310) at approximately 20z.

Dtw threshold probabilities...

* high in ceilings below 5000 feet tonight and Friday.

&&

Previous discussion...
issued at 343 PM EST Thu Nov 14 2019

Discussion...

Light westerly flow around the periphery of the modified Arctic
airmass in which Southeast Michigan currently resides supporting
widespread lake enhanced stratus and patchy fog/freezing mist. With
forcing and moisture insufficient to generate actual hydrometeors,
nothing more than a very light glaze is expected on some elevated
surfaces. With no change to existing airmass or background forcing,
stratus will hold firm through at least the first half of tonight.

The lead energy ushering in the last hurrah of the aggregate polar
vortex that has been the prominent feature over the last week is
noted over northwest Ontario this afternoon. Eastward migration of
the occluding cyclone in the Gulf of Alaska during the previous 48
hours can be thanked for nudging the downstream waveguide just east
enough to steer this feature the attendant very cold air into
eastern Canada. Primary impact locally will be backing low level
winds that will diminish Overlake instability during the night
leading to a potential west-to-east clearing trend. The window for
clearing late tonight into early Friday will be short-lived,
however, as the cold front stretching from North Dakota into Ontario
settles through the lower peninsula during the day. Loss of forcing
over the central Great Lakes will allow the front to Orient parallel
to the mean flow, diminishing cold advection and slowing forward
progress. Even so, gradual veering of wind in the presence of slowly
deepening colder air will reintroduce potential for stratus as early
as Friday morning. Modest warming of the resident thermal profile
compared to today suggest high temps just a few degrees warmer, low
to mid 30s, under continued cloud cover. Temperatures, especially
highs, remain below normal into the weekend as the strong Arctic
high drives flow from northerly by late Friday to northeast by
Saturday.

Dissipation of the Aleutian low relaxes the downstream flow over
North America, and the polar low is noted pivoting back into the
high latitudes as as result. Jet streak racing across the northeast
Pacific today is shearing off a piece of the resident deep pv
Reservoir there. This energy will amplify in the Lee of The Rockies
late this weekend, with limited potential given relatively fast-
moving flow. A round of unimpactful snow showers seems most likely
at this time - perhaps an inch or so across the north. The more
noteworthy development is the the 12z ec/GFS flooding this
developing trough with Pacific energy and reestablishing a longwave
trough over the eastern US to start next week. Even as West Coast
height falls threaten to pump up height falls over the central Continental U.S.
Midweek, global nwp funnel more high latitude energy into the
northern US as around building Alaska ridging. The modeled
transition out of and back into blocked flow over the North Pacific
and the seeming dependence on model handling of high latitude energy
doesn't inspire confidence in medium range model performance, but
certainly no discernible signal can be teased out for a return to
normal temps at this time.

Marine...

Small craft advisories will continue until 10am Friday as southwest
flow begins to relax. Winds will then veer to the northwest
throughout the day Friday as a cold front pushes across the central
Great Lakes. Winds will continue rotating to northeasterly Friday
night due to the presence of a high pressure moving southeast across
Ontario. Gusts in the immediate wake of the cold front Friday night
may approach gale force, but generally expect 30 knots to be the
rule. Building waves in this developing flow will likely lead to
additional Small Craft Advisory conditions by Friday evening as
onshore flow pushes this high wave action into the nearshore waters.
Winds will weaken during the weekend as broad high pressure setups
over the central Great Lakes region.

&&

DTX watches/warnings/advisories...
Michigan...none.
Lake Huron...Small Craft Advisory until 10 am EST Friday for lhz421-422-441.

Lake St Clair...none.
Michigan waters of Lake Erie...none.
&&

$$

Aviation.....Cb
discussion...jvc
marine.......SC

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