Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 040910

Area Forecast Discussion
National Weather Service Marquette MI
410 AM EST Sun Dec 4 2016

.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

.LONG TERM...(Sunday night through Saturday)
Issued at 322 PM EST SAT DEC 3 2016

Shortwave trough becomes negatively tilted while crossing the Upper
Great Lakes Sun aftn into Sun evening. Sfc-h85 trough crosses Upper
Michigan through this time switching winds from S-SE to W and
providing low-level convergence and lift. Main area of deeper layer
q-vector convergence stays mainly south and that should keep
widespread snow with the system later Sun into Sun night limited to
an inch or two. One exception though as S winds ahead of trough with
h85 temps of -7c would support lake enhanced snow downstream of Lk
Michigan. Similar to what has occurred last couple days with the
lake effect off Lk Superior, sfc temps in the low to mid 30s likely
will lead to rain/snow mix or only rain near the immediate shoreline
of Lk Michigan including at locations such as Manistique and the
east shore of the Garden Peninsula. Just inland where lake enhanced
snow is more widespread, it should be cold enough for mainly snow.
Run total qpf is all over the place over northern Lk Michigan and
into eastern cwa. Higher outliers are the GEM and WRF-ARW which show
totals nearing 0.80 inch late Sun aftn through late Sun night. Low
end values are 0.25-0.35 inches from the GFS and SREF mean. Since
stronger forcing remains south of Upper Michigan and higher qpf
values are very high outliers compared to SREF plumes and NCAR
ensemble qpf, will go more middle of road for qpf on the order of
0.3 to 0.5 inches and go with idea that there could be a few inches
of fresh snow which could result in slippery travel Sun evening on
untreated roads. Think the marginal temps in the mid 30s will
ultimately limit snow accums than what would otherwise occur with
the expected qpf totals. For now will mention this snowfall and
slippery roads in the Hazardous weather outlook.

Snowfall over the east cwa should taper off quickly after midnight
as larger scale q-vector divergence/subsidence and drying moves in
and with sfc winds backing west once the sfc trough exits to east.
Sfc high brings dry weather on Monday though not sure how much
clearing occurs as there could be moisture blo 925mb trapped beneath
subsidence inversion. High temperatures should only rise into the
mid to upper 30s, coolest where southwest winds upslope to the
higher terrain of cntrl Upper Michigan.

Mon night into Tue rather strong shortwave trough slides across
northern Plains and lifts into south central Canada. Sfc low deepens
blo 1000mb. GFS most aggressive in bringing swath of moisture into
Upper Great Lakes ahead of the low and even those soundings look dry
above h85 over all but far west cwa. Soundings do hint at low level
moisture with weak lift which would result in drizzle or freezing
drizzle over the central and east with some added moistening off Lk
Michigan. GFS looks like cold outlier with cold front over central
Upper Michigan by 12z Tue and h85 temps down to -12c over western Lk
Superior while ECMWF and GEM are not even down to -5c. Overall
though the GFS is quicker in bringing colder air in Tue and Tue
night, ECMWF does catch up by Wed and they have similar solutions as
both models keep shortwave trough and strong sfc low over Manitoba
and northern Ontario completely separate and unphased with shortwave
trough and sfc low sliding across the Ohio Valley. Whenever the sfc-
h85 cold front moves through there is some weak deep layer q-vector
convergence shown and there is also hint of another weaker wave
lifting across area along the cold front on Tue night. Otherwise,
large scale subsidence and drying takes hold into Wed as stronger
trough aloft remains over Manitoba and northern Ontario and southern
stream shortwave trough crosses the southwest Conus. Lake effect
during this time will likely be confined mainly to Keweenaw with sfc
to h85 winds from the W or WSW and h85 temps blo -12c as Lk Superior
temps are still 5-6c. Inversion heights around 5kft should limit
intensity of lake effect but could have several inches of fluffy
snow accum since the dgz will be within the lake convective layer.

Deep trough aloft with widespread cold air will continue to occupy
much of the eastern half of the Conus later Wed into Thu. Southern
stream wave should stay far enough southeast of Upper Great Lakes to
prohibit stronger storm to affect the region, though the lower
Michigan could see widespread snow as sfc low lifts across Lower
Great Lakes toward New England. ECMWF more in line with that idea
while GFS keeps system too sheared out to cause much snow until it
reaches northern New England late this week. Back over the Great
Lakes, lake effect snow will be the main story. Areas favored by NW
winds will see the the most snow as h85 temps continue to fall to
around -15c by late Thu into Fri. Sometime late in the week there
will be a reinforcing sfc-h85 cold front that could bring winds to
more N so lake effect could shift around to north flow areas for a
time. Plenty of deep moisture to h7/10kft with large scale trough
overhead so lake effect may be moderate to even heavy depending on
when shortwaves work through to enhance the snow further. Stronger
low-level winds will push snow showers farther inland than normally
seen and since low-level temps will be sufficeiently cold for snow,
should see snow all areas, even near the Great Lakes shorelines.
Lake effect will continue into Sat for NW flow areas, especially
over eastern cwa. Certainly by late next week it will look and feel
more like winter across most of Upper Michigan.

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1156 PM EST SAT DEC 3 2016

With sfc high pres ridge e of the area and southerly winds
developing, the downslope component to the wind should allow VFR
conditions to prevail at KCMX overnight with KIWD improving from
MVFR to VFR. Meanwhile, at KSAW, VFR conditions will likely fall
back to MVFR overnight as the upsloping southerly flow taps moisture
off Lake Michigan. An approaching disturbance will then spread -sn
across Upper MI today. Conditions will likely fall to IFR at
KCMX/KSAW in the aftn. At KIWD, while prevailing MVFR conditions are
expected with the -sn, there may be some periods of IFR. MVFR
conditions are expected in the evening as the -sn diminishes/ends,
though KSAW may remain IFR.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 409 AM EST SUN DEC 4 2016

Expect winds to remain 25 kts or less through Mon as the pressure
gradient remains relatively weak. An approaching low pressure trof
will tighten the gradient Mon night/Tue, resulting in sw winds up to
30 kts. There could be some w gales to 35 kts over mainly the
ncentral on Tue night into Wed under the tighter pressure gradient
on the southern flank of the deepening low pressure moving into nw
Ontario and with the arrival of colder air that will increase
overwater instability.

Upper Michigan...
  Winter Weather Advisory from 1 PM this afternoon to 1 AM EST
     Monday for MIZ007-014-085.

Lake Superior...
Lake Michigan...


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