Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 102140 AAE

Area Forecast Discussion...UPDATED
National Weather Service Marquette MI
440 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 night through Saturday)
Issued at 435 PM EST SAT DEC 10 2016

The medium range models suggest that the blocking ridge through
Alaska will favor pattern amplification with an intrusion of very
cold arctic air into the CONUS as the deep mid level low moves into
nrn Ontario. This will bring an extended period of wrly flow LES and
low wind chills across the region.

Sunday night, although the stronger isentropic lift will shift off
into the ern cwa during the evening a period moderate to strong 700-
300 mb qvector conv associated with the shrtwv moving out of the nrn
plains will help sustain the light to moderate snow through the
evening. In addition, convergent se winds off of Lake Michigan and
easterly winds on Lake Superior will bring some higher snow amounts
into s cntrl Upper Michigan and the Keweenaw. As the sfc trough
moves off to the east another period of lake enhanced snow may
affect the nw cwa. QPF values in the 0.10-0.15 inch range will
favor another couple of inches for most of the cwa with local
amounts of 5 inches or more over the Keweenaw.

Monday, once the lingering snow over the nw ends expect mainly dry
weather. Winds backing to the sw will keep most of the additional
LES potential west of the Keweenaw.

Monday night into Tuesday, the arctic front is expected quickly
move through the nrn Great Lakes. A period of light snow associated
with qvector conv ahead of the mid level trough may bring a period of
light snow through the cwa Monday night with heavier lake enhanced
snow or LES over the Keweenaw as winds veer to the west. Temps will
fall or remain steady through the single digits Tuesday.

Wednesday-Friday, after the initial surge of arctic air, a
reinforcing batch is expected to move in wed into wed night. This
will bring a slight veering trend with the low level flow which may
push the LES into a greater portion of the nrn cwa, especially from
p53 eastward. LES will continue through the period, but the
intensity will be limited as the very cold air limits snow growth.
However, low vsby will prevail through most of the period downwind
of the wrly flow. Wind chill values may approach 25 below both Wed
and Thu, especially inland west, farthest from any moderating
influence of Lake Superior.

Saturday, GFS/GEFS/ECMWF maintain the idea of that sw mid level flow
in response to trough into the Rockies will favor the development of
a broad waa pattern which could bring widespread snow into the
region. However, confidence in any details is low.

.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 PM Lake Superior forecast issuance)
Issued at 435 PM EST SAT DEC 10 2016

Expect NW winds up to 25 kts to diminish under 20 kts tonight but
may increase to around 25 knots as a trough lifts into Upper
Michigan Sunday. A steady WNW wind to 30 kts with potential for
brief periods of gales 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 feet.

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...


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