Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 212109

Area Forecast Discussion
National Weather Service Marquette MI
409 PM EST Tue Nov 21 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 407 PM EST TUE NOV 21 2017

WV imagery and RAP analysis indicated an amplified pattern with a
mid/upper level trough from Hudson Bay through the western Great
Lakes into the mid MS valley. 700-300mb Qvector div and subsidence
developed over Upper Michigan in the wake of a shrotwave trough to
the east of Lake Superior. However, another weaker shrtwv was
sliding into nrn Ontario (north of KINL). At the surface, gusty nw
winds prevailed over the region bewteen a 990 mb low se of James Bay
and 1033mb high pres building into the nrn plains. Radar indicated
that multiple wind parallel LES bands have gradually diminished this
afternoon as inversion heights drop to 4k-5k ft.

Tonight, 850 mb temps around -14C will provide enough instability
for continued LES even as 850-700 mb moisture moves out this
evening. The shrtwv moving through may provide a brief boost to the
LES. Winds backing to wnw overnight will shift the best chance for
additional accumulations from Munising eastward. Expect additional
accumulations of 1 to 3 inches in the favored nw flow locations.
Otherwise, only a few flurries or light dusting will be possible.

Wednesday, backing winds push the remaining LES bands in the east
offshore by afternoon. Mid/high clouds will increase in the aftrnoon
ahead of the next clipper shrtwv. Even with WAA, temps will only
climb into the mid to upper 20s.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 217 PM EST TUE NOV 21 2017

...Temps on roller coaster with lake effect snow at times...

Upper air pattern heading into Thanksgiving features trough over
northeast Pacific to western Canada and another trough over Hudson
Bay. Appears that polar jet stream/arctic air intrusion stays just
north of Lk Superior for Thanksgiving. Weaker shortwave working
through may bring lgt snow/flurries even inland on Wed night then
could see some light lake effect snow or rain/snow from Keweenaw to
eastern forecast area on Thanksgiving Day. Possible there may not be
enough moisture around at times for ice so there could also be
drizzle or freezing drizzle. Not a big risk right now so just kept
ptype snow.

Attn Thu night into Fri turns to H25 130 kt jet streak pushing over
Pacific Northwest which will push upper troughing eastward toward
central Canada and northern Plains. Associated sfc low deepens to
lower than 980mb as it reaches central Manitoba on Fri morning. Warm
air moving in ahead of the low along with some mid-level moisture
could support some light mixed precipitation (light snow changing to
sleet and freezing rain) late Thu night into Fri morning, especially
northwest where sufficient saturation for precip looks like better

Fri will be breezy with temperatures rising above normal (well into
the 40s some areas) as Upper Lakes is within warm sector of the deep
sfc low crossing into northern Ontario. Shortwave driving in from
northwest through the day will eventually spread precip back over
the forecast area in the aftn. Ptype should stay rain through Fri
evening, then as sfc temps fall blo freezing late Fri night expect
any rain to change to snow. Upper level trough deepens over Great
Lakes on Sat with colder air (H85 temps as low as -14c) moving
across the region. After the warmer temps on Fri, high temps on Sat
will be in the 20s west to low 30s east. Temps may fall through the
day in some areas. WNW-NW winds will result in lake effect snow.
Snow showers could be heavy at times early Sat as cold air first
charges in, but lake effect should diminish later in the day as
synoptic moisture exits and inversions fall with arrival of
anticyclonic flow as high pressure builds from central Canada to
the Upper Great Lakes and middle Mississippi River Valley.

Differences show up by Sun in how quick cold air departs. ECMWF
keeps cold air locked in longer and at stronger intensity compared
to GFS on Sun (H85 temps at 12z on Sun range from -15c on 00z ECMWF
to -3c on GFS). 12z ECMWF has now moderated somewhat. GEM provides
slight compromise. NAEFS and ECMWF ensembles, though not as cold,
look more like ECMWF compared to GFS. Overall, think operational GFS
may be too aggressive in getting rid of the cold and will lean
toward colder ECMWF idea with highs mainly in the 20s and some lake
effect snow continuing into the aftn. Warming will eventually win
out by early next week as upper ridging builds across much of the
eastern Conus. Sfc low over the plains will also support warming
with S to SW return flow. Eventually though the cold returns middle
of next week as the temperature roller coaster continues.

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1243 PM EST TUE NOV 21 2017

The gusty winds leading to some blsn at KIWD/KCMX will diminish this
afternoon. While MVFR conditions should prevail, expect some periods
of IFR and possibly some LIFR vsby at KCMX where winds will be
strongest, producing more blsn. Conditions will improve to VFR at
KSAW late this evening and by Wed morning at KIWD/KCMX.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 407 PM EST TUE NOV 21 2017

NW gales across much of Lake Superior will end by late evening.
Winds will diminish to under 25 knots while becoming westerly
through Wednesday morning, before backing to SW winds of 20 to 30
knots Wednesday night. Westerly winds of 20 to 30 knots Thursday
will back to the south on Friday. Another strong low pressure system
will then bring the potential for northwest gales of 35 to 40 knots
Friday night into Saturday.

Upper Michigan...
  Lakeshore Flood Advisory until 9 PM EST this evening for MIZ006.

Lake Superior...
  Gale Warning until 10 PM EST this evening for LSZ243>245-248>251-

  Gale Warning until 5 PM EST /4 PM CST/ this afternoon for LSZ162-

Lake Michigan...


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