Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 051151

Area Forecast Discussion
National Weather Service Marquette MI
651 AM EST Tue Dec 5 2017

.SHORT TERM...(Today and tonight)
Issued at 502 AM EST TUE DEC 5 2017

WV imagery and RAP analysis indicated an amplified pattern with a
mid/upper level trough from Manitoba into the cntrl CONUS. A vigrous
shortwave trough was lifting north through wrn Upper Michigan. The
comma head snow area with this feature from nw WI and wrn Lake
Superior into the wrn cwa was steadily diminshing and also quickly
lifting to the north. Snowfall of a few inches from IWD into
Ontonagon county has produced snow covered roads with hazardous
travel conditions. Otherwise, sct -shra near KMQT were also moving
away as drier air moves in from nrn WI. At the surface, a 978 mb low
was located over the north end of Lake Superior. The strong pres
gradient behind the low supported wsw winds gusting to around 35 kt
from nrn WI into most of Upper Michigan.

Today, although the snow near IWD and Ontonagon will continue to
diminish, snow that has moved into the Keweenaw will persist and
intensify as 850 mb temps drop to around -15C by this afternoon as
deep moist cyclonic flow remains over the area. Snowfall amounts in
the 3 to 7 inch range are expected along with strong winds gusting
to around 50 mph at times. Blowing and drifting will become more
signficant as temps drop and snow available on the ground increases.
Although the stronger isallobaric gradient will move out by 12z,
increasing mixing depths with the strong pres gradient will still
support wind gusts to around 45 mph at times, per momentum transfer
fcst, over all but the ern cwa until this evening. Temps will drop
through the day into the teens west and the mid 20s east.

Tonight, gradually veering winds to wnw will bring the heavier lake
effect snow from the Keweenaw peninsula and Ontonagon county by late
afternoon back into Gogebic county overnight. 250-260 winds over the
se lake will keep the snow bands offshore. Favorable deep moisture
with 850 mb temps around -16C will support moderate to ocassionaly
heavy snow with additional accumulations in the 3 to 7 inch range
for the Keweenaw and 2 to 6 inches from IWD to Rockland.

.LONG TERM...(Wednesday through Monday)
Issued at 457 AM EST TUE DEC 5 2017

Switch to winter has been a messy one in the last 12-24 hours with
heavy rain, thunderstorms with small hail and strong winds and now
wet sloppy snow over western Upper Michigan. However, once the
pattern changes for the entire area to winter, it looks like we stay
in a prolonged period of active winter weather both near the Great
Lakes and even inland throughout the entire length of the long term
and beyond.

Broad upper troughing will be fully in place on Wed morning with sfc
low around 976mb spinning near James Bay. WNW winds and H85 temps
-15c to -17c will support widespread lake effect near Lk Superior on
Wed. Snow showers will be enhanced due to widespread deep moisture
to H7 or 10kft AGL. Will be a pure LES setup over west but hint of
shortwave/lift aloft over eastern forecast area. DGZ remains firmly
in the lake convective layer so snowfall will be efficient. Only
negative for really high SLRs toward 30:1 is mixed layer winds over
25 kts which will fracture snowflakes. Expect WNW-NW flow areas to
see moderate to heavy lake effect into Wed evening west and over
east late on Wed night. Probably looking at 12 hour snow amounts Wed
of 3-5 inches to 4-7 inches due to ideal placement of DGZ and higher
inversions up to 10kft. Moderate snow accums could continue over the
eastern areas on Wed night too. Current headlines over the west go
through 00z Thu and that will probably work out well. We will
eventually need headlines for snowbelts of eastern forecast area but
since the snow showers don`t move onshore there until very late
tonight or Wed morning, will hold off on any headlines farther east
attm. This also keeps the immediate messaging focus on the strong
winds currently ramping up in those areas. Gusty northwest winds
will also lead to areas of blowing snow near Lk Superior, especially
where the more persistent snow showers occur.

Lake effect slowly diminishes into Thu, hanging on longest in the
east with inversions to 5kft AGL and steady NW flow persisting off
Lk Superior. Another 1-3 inches of snow could occur over the east on
Thu. Models remained locked onto clipper system diving south across
the Upper Great Lakes Thu night into Fri. Widespread light snow even
inland should occur as with cold airmass already in place it will
not take much forcing to generate at least some light snow. That
cold air already in place increases concern for potential heavy lake
effect snow over west Thu night. Strong forcing, inversions up to 10-
12kft AGL and a WNW flow with H85 temps around -16c point to heavy
lake effect snow. Trended upward on pops/qpf and snow, probably not
enough, but at least started the trend. Used local lake effect and
lake enhanced snow checklist guidance to make those adjustments to
the model output. Eventually the clipper will result in winds
turning N later Fri into Fri night. Should see moderate to heavy
lake effect snow for north wind snow belts during these times.

GFS and ECMWF indicate pattern stays very active with more clippers
dropping through late in the weekend into early next week in a very
amplified larger scale troughing pattern. H85 temps drop to sub -20C
early next week will lead to several bouts of lake effect/enhanced
snow. Expect at least a few chances to see minor snow accumulations
inland. If the really cold air times out behind one of these
clipper systems, we could even be dealing with near advy wind
chills early next week. Talk about a complete switch of a weather

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 648 AM EST TUE DEC 5 2017

Very gusty west winds will prevail today behind a deep low pressure
system. Gusts to near 50 knots at KCMX are expected while gusts of
35-40 knots are expected at KSAW and KIWD. Mainly MVFR cigs with IFR
vsby is expected at KIWD while heavier sn/blsn will keep vsby aob
1/2sm into tonight at KCMX. After a period of light snow early at
KSAW the Lake effect snow will remain to the west and north of the
site with cigs at or just above the MVFR threshold.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 457 AM EST TUE DEC 5 2017

Active period on Lk Superior continues until further notice. Storms
expected over most of Lk Superior today into tonight. Winds diminish
to gales into Wed and Wed night. Storm warnings up at this time and
those will need to be transitioned to gale warnings later today or
tonight. Should be down blo gales by daybreak Thu as deep low
pressure in the Lk Superior region moves farther away into northern
Quebec. Winds will stay in the 20-30 kt range into Fri but a clipper
surging through may bring a brief return of N gales Fri night. Most
of weekend will stay with 20-30 kts for winds but more gales from
the NW are possible late Sun as another clipper works through. Bouts
of freezing spray are expected Today into Thu, late Fri and again
late Sun. Air temps staying mainly in the 20s throughout the
weekend should prohibit heavy freezing spray.

Upper Michigan...
  Wind Advisory until 8 PM EST /7 PM CST/ this evening for MIZ002-

  Winter Storm Warning until 5 AM EST Wednesday for MIZ001-003.

  Lakeshore Flood Advisory until 8 AM EST Wednesday for MIZ001>003.

  Winter Weather Advisory until 9 AM CST this morning for MIZ009.

  Winter Weather Advisory from midnight tonight to 6 PM CST
     Wednesday for MIZ009.

  Lakeshore Flood Advisory until 5 PM EST this afternoon for

  Winter Weather Advisory until 7 PM EST Wednesday for MIZ002.

Lake Superior...
  Storm Warning until 11 PM EST /10 PM CST/ this evening for

  Gale Warning until 4 PM EST Wednesday for LSZ249>251.

  Storm Warning until 7 PM EST /6 PM CST/ this evening for LSZ162.

Lake Michigan...
  Gale Warning until 7 AM EST Wednesday for LMZ221-248-250.



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