Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 042000
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
300 PM EST Sun Dec 4 2016

.UPDATE...
Issued at 1018 AM EST SUN DEC 4 2016

Delta and Alger Counties added to winter weather advisory. With
some enhancement off Lake MI likely to impact mainly the e half of
Delta and Alger Counties, opted to include those counties in the
winter weather advisory that was issued earlier for Schoolcraft and
Luce Counties. In fact, many of the hier res models show some heavier
wet snow bands influencing the e half of Delta and Alger Counties. As
is the case for Schoolcraft County, some rain may mix with the snow
near the shore of Delta County. &&

.SHORT TERM...(Today and tonight)
Issued at 409 AM EST SUN DEC 4 2016

Upper air pattern consists of a 500 mb shortwave over the northern
plains and a closed low over the southern Gulf of California. This
shortwave moves through the area this afternoon and evening. Deeper
moisture and 850-500 mb q-vector convergence moves through the cwa
through this evening, then both move out late tonight.

Made one big change to the forecast. Looks like there will be a Lake
Michigan lake effect snow component to the system for this afternoon
and evening. With Lake Michigan water temperatures around 6C and 850
mb temperatures forecasted to be around -6C, this is enough lake-850
mb delta-t with a south-southwest wind to get some lake enhanced
snowfall across Luce and Schoolcraft Counties. Could see up to 5
inches of snow in those places and issued a winter weather advisory
for snow for that reason. Mesoscale models in particular were
showing a mesoscale band of snow focusing over that area and for
that reason bumped up pops and qpf a bit for that reason in the ern
cwa. Overall though, that was the only big change made to the going
forecast. Did not change temperature much. Forecast hinges a lot on
a mesoscale narrow band of heavier snow affecting the ern cwa.
Otherwise, cwa will see anywhere from 1 to 3 inches of snow. Lesser
amounts will be along the Lake Michigan and bay of Green Bay
shorelines.

.LONG TERM...(Monday night through Sunday)
Issued at 258 PM EST SUN DEC 4 2016

Late Mon into Mon night the Great Lakes will be within shortwave
ridging btwn the shortwave trough (bringing the snow to Upper
Michigan this aftn) exiting across New England and rather strong
shortwave trough crossing the northern Plains and pivoting north
into southern Manitoba and northwest Ontario. Could see light snow
showers into far west cwa Mon night as h7 moisture/h7-h5 q-vector
convergence pass by mainly to the west. Associated sfc low deepens
blo 1000mb along the SE Mantioba/Ontario border by 12z Tue which
sends a sfc cold front toward western Upper Michigan. Could be light
rain/snow around on Tue over parts of Upper Michigan as the front
crosses especially if the GEM and ECMWF are on track showing
stronger shortwave/h7-h5 q-vector convergence lifting across WI and
Upper Michigan Tue aftn into Tue evening. Temps should be steady or
even fall slightly over the west as colder air works in from the
northern Plains. Could be lake effect on the Keweenaw but should be
light as inversion remains less than 5kft and winds are more SW than
W.

Shortwave trough becomes more of an upper low Tue night into Wed
with sfc low slowly crossing northern Ontario. As this occurs,
another shortwave trough will be tracking across the southwest conus
to the southern Plains with a sfc low crossing vcnty of northern
TX/OK. On Wed, expect lake effect to affect more of the northwest
cwa as colder air moves in with h85 temps down blo -12c and as sfc-
h85 winds veer more W or even NW if the more aggreesive GFS is
correct. Inversion heights around 5kft increase to 6-8kft bringing
dgz into much of lake convective layer so there should be moderate
les. Snow showers over the west could become heavy at times if
stronger low-level convergence develops. Away from the lake effect
the cooldown will be well underway with daytime highs in the 20s
most areas. Could be breezy especially near Lk Superior.

Deep trough aloft with widespread cold air will continue to occupy
much of the eastern half of the Conus late this week with the cold
reaching the deep south and Gulf coast by Fri. Over the Great Lakes,
lake effect snow will be the main story. Areas favored by NW winds
will see the the most snow across Upper Michigan as h85 temps
continue to fall to around -15c by late Thu into Fri. Plenty of deep
moisture to h7/10kft with large scale troughing and low level
cyclonic flow so lake effect may be moderate to even heavy depending
on when shortwaves work through to enhance the snow further. Though
the TX/OK wave and sfc low look to stay south of Upper Lakes
limiting widespread system snow, once that system lifts across New
England late Thu into Thu night it should help a reinforcing cold
front drive across the Upper Great Lakes. GFS continues to be on the
faster side with the fropa (Thu aftn) and ECMWF is slower (Fri
morning into early Fri aftn). As this front moves through winds
could become more NNW or N so lake effect could shift around from
the northwest flow areas to the northerly flow areas for a time.
Unlike the regime we have been in the last week or so with only
marginally cold low-level temps, low-level temps late this week will
be sufficiently cold for snow, so should see snow all areas, even
near the Great Lakes shorelines.

Lake effect will continue at least into Sat morning for NW flow
areas, especially over eastern cwa. Another shortwave works across
north central Conus by next Sun. Sfc low should accompany the
trough. Have to wait on specifics in terms of system snow across
Upper Lakes, but just from a pattern recognition standpoint, should
see lake enhanced snow off Lk Michigan since h85 temps are blo -10c
as the system approaches. Certainly by late next week and next
weekend it will look and feel more like winter across most of Upper
Michigan.
&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1243 PM EST SUN DEC 4 2016

Expect a period of IFR conditions at all the TAF sites this aftn and
evng associated with a band of sn crossing Upr MI. The best chc for
the more persistent IFR conditions wl be at SAW, which wl be closer
to some moistening off Lk MI and not experience the downslope wind
that wl tend to limit the duration of the lower vsbys at CMX and
especially IWD. Later tngt into Mon mrng, the closer aprch of a hi
pres rdg/more acyc flow wl result in lingering MVFR cigs improving
to VFR. A wly upslope flow at CMX wl slow the improvement at that
location.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 258 PM EST SUN DEC 4 2016

S to SW winds 20-30 kts through Mon then as low pressure trough
moves in Mon Night then deepens into to a low pressure system on Tue
northwest of Lk Superior, the tightening pressure gradient will
result in SW gales to 35 kts, especially over the west and north
central portions of Lk Superior. NW winds to 30 kts continue Wed
into Fri as colder air moving in increases over water instability.
The colder air and building waves will result in some freezing spray
by late in the week. &&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory until 1 AM EST Monday for MIZ006-007-013-
     014-085.

Lake Superior...
None.
Lake Michigan...
None.
&&

$$

UPDATE...KC
SHORT TERM...07
LONG TERM...JLA
AVIATION...KC
MARINE...JLA



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