Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 102109

Area Forecast Discussion
National Weather Service Marquette MI
409 PM EST Sat Dec 10 2016

.SHORT TERM...(This evening through Sunday)
Issued at 409 PM EST SAT DEC 10 2016

...Lake effect snow ends tonight then widespread system snow moves
in on Sunday...

Lake effect snow continues but the areas affected have become less
over the last 24 hours. Persistent sfc trough over southern Lk
Superior is main focus with one or two dominant bands of snow over
parts of Keweenaw and multiple dominant bands with some connection
to Lk Nipigon converging over eastern Alger and northern Luce. Over
water instability remains favorable for lake effect with inversions
over western Lk Superior around 5kft/h85 with inversion top temps to
-20c and up to 8kft/h75/-25c over eastern Lk Superior. Winds back
steadily to the WSW-SW this evening over Keweenaw so expect heavier
snow to remain on the move and will not extend the warning or advy
there. However, convergence remains strong into far eastern Alger
and northern Luce so extended warning there until midnight when HRRR
indicates blyr winds turn SW enough to push heavier lake effect
offshore. Away from the lake effect this evening skies should be
mostly clear allowing temps to fall off toward zero this evening for
the interior west. Mid-high clouds increase overnight as low
pressure system over eastern WY and CO this aftn pushes across the
central Plains. Min temps will depend how quickly the clouds move in
but a few zero to 5 below readings for favored cold spots seems

Low pressure system crosses IA and WI/northern IL on Sun morning.
WNW flow aloft and lack of very tight baroclinic zone at h85 should
keep stronger isentropic ascent snow mainly south of cwa into Sun
morning. However by aftn shortwave trough that is currently over
Pacific NW moves across Dakotas and northern MN. Deep layer q-vector
convergence increases markedly through the aftn and that forcing
along with increasing moisture advection ahead of low pressure
trough over WI (mixing ratios at h7 up to 2g/kg) running into cold
airmass should start to produce light to moderate snow. H85 low
tracking across northern WI as the shortwave moves through also
increases larger scale lift and there is some mid-level fgen on
northern edge of this low. That forcing along with SE winds off Lk
Michian and E winds off Lk Superior should result in lake
enhancement with h85 temps -8c to -10c and water temps around 5c.
Overall snow amounts with this system should fall into advy range of
3 to 5 inches in 12 hours (12z-24z/7 am ET to 7 pm ET) along WI
border, but lake enhancement could add to the totals for scntrl
Upper Michigan and across the Keweenaw Peninsula. Highlighted this
potential in the WSW statement and it is possible eventually could
need warnings but will start with advy for now. Does look like after
this event all areas of Upper Michigan will have at least light
snow cover.

.LONG TERM...(Sunday through Friday)
Issued at 441 AM EST SAT DEC 10 2016

Main theme for the extended periods will continue to be on the
arctic air that will arrive early in the week and linger through the
bulk of the extended. Prior to the much colder air arriving, the
late weekend shortwave will be lifting northeast across Chicago late
Sun evening, but the effects will be overspreading the U.P. in the
late afternoon hours and continue through Monday, as strong
isentropic ascent through a moist column will likely push
accumulating snow to the area. Winds will be southeasterly, and
there could be enough cold air to see some minor enhancement off of
Lake Michigan to the snow. Operational solutions then lift the
shortwave northeast towards Toronto by daybreak Mon, with the
surface flow turning northeasterly then northerly Mon afternoon.

Surface ridge will slide southeast across the Missouri Valley, which
will place the Upper Midwest/Northern Great Lakes in a Northwest
flow in the lower-levels Mon in the wake of the departing surface
low. Upstream 500mb robust vort max will be starting to bleed south
from the Canadian Rockies, helping to sharpen the baroclinic zone
across the Northern Plains Mon aftn/eve.

Ensembles continue to show minimal spread amongst members in the
medium term with respect to the arctic frontal boundary approaching
the Upper Midwest late Mon ngt, then reaching the U.P. by early Tue.
An elongated surface trough will have a couple weak surface lows
from Wisconsin to just west of Hudson Bay, but expect these to
consolidate over Ontario early Tue. Much colder air will quickly
advect south/southeast from Canada towards the Great Lakes region,
with a potent 850mb thermal trough of -20 to -25 deg c air. This
will likely set the stage for high temps struggling to warm beyond
the single digits above zero, with the exception possibly being
areas immediately downwind of Lake Superior. As for LES, expect
several periods of light accumulating snow to occur in the extended;
however, the favored dendritic growth zone will be crashing towards
the surface and could limit flake size or accumulations but on the
flip-side visibilities could be impacted due to the abundance of
snow crystals. But again the main theme of the extended will be the
bitter cold temperatures in the single digits for highs and sub-zero
overnight lows.

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1252 PM EST SAT DEC 10 2016

Lake effect will be in and out of CMX into early this evening. IFR
vsby mainly through brief reduction to VLIFR is possible late this
aftn as heaviest band of snow moves back across. Conditions improve
to VFR late tonight into Sun morning. At IWD expect mainly MVFR to
VFR cigs until system snow with IFR vsby/MVFR cigs moves in on Sun
morning. SAW will remain VFR until midday Sun when system snow moves
in. Expect all sites to drop to LIFR/IFR conditions on Sun aftn as
low pressure system crosses the region.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 524 AM EST SAT DEC 10 2016

Expect NW winds up to 25 kts to diminish under 20 kts Sat night
through Mon as a weak high pressure ridge moves over the area. A
steady WNW wind to 30 kts will redevelop on Mon night into Thu
following a strong cold frontal passage that will introduce arctic
air into the Upper Lakes. Expect some heavy freezing spray over at
least portions of the Lake on Tue night/Wed as this arctic air moves
into the area and waves at the end of fetch build to at least 10

Upper Michigan...
  Winter Weather Advisory from 10 AM EST /9 AM CST/ Sunday to 1 AM
     EST /midnight CST/ Monday for MIZ002-004>007-009>014-084-

  Lake Effect Snow Warning until midnight EST tonight for MIZ006-

  Winter Weather Advisory from 1 PM Sunday to 7 AM EST Monday for

  Lake Effect Snow Warning until 7 PM EST this evening for MIZ003.

  Lake Effect Snow Advisory until 7 PM EST this evening for MIZ001-

Lake Superior...
Lake Michigan...


LONG TERM...Beachler
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