Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 180821

Area Forecast Discussion
National Weather Service Marquette MI
321 AM EST Sat Nov 18 2017

.SHORT TERM...(This evening through Saturday)
Issued at 335 PM EST FRI NOV 17 2017

...Heavy snow possible through early evening on the Keweenaw...
...Wintry mix will lead to slippery travel into Sat...

Large scale trough expands across Great Lakes through Sat. Stronger
shortwave and jet streak in base of trough will support stronger sfc
low spinning up from mid Mississippi River Valley late tonight to
the lower Great Lakes by late Sat aftn. Widespread precipitation
that moved in this aftn will diminish from west to east tonight as
sfc trough tied to low over northern Ontario continues to cross
Upper Michigan. Warm layer aloft 850-800mb or 3-4kft AGL led to
wintry mix of ra/fzra/sleet and snow earlier today but that mostly
has changed to rain now for central and east. Out west, already
seeing signs that cold air is slipping back into the region as rain
has changed back to snow at KCMX and has mixed with mixed with snow
at KIWD.

Attn is on h8-h7 fgen band in right entrance of jet streak causing
moderate to heavy precip over northeast MN and over western Lk
Superior. This forcing/precip slides across Keweenaw this evening.
RAP and HRRR are locked on to period of heavy precip, all snow,
through 00z with tapering to dz/fzdz afterwards. Will put out a
short duration winter wx advy for evening across Keweenaw Peninsula
for a brief period of moderate to heavy snow occurring right during
the evening commute.

Elsewhere, expect rain/snow mix over mostly scntrl and east forecast
area to gradually change to mainly dz or fzdz late evening into the
overnight hours. Will have to watch out for potential for some more
rain/snow scntrl and east as late as a bit after midnight as one
last push of precip tied to left exit of jet streak over central
Plains moves through. N to NW winds in wake of the sfc trough will
lead to best chance of dz/fzdz later tonight over higher terrain of
west, northwest and ncntrl Upper Michigan.

Other than the winter weather advy for evening on the Keweenaw
Peninsula, another SPS will be issued for the west half of Upper
Michigan to cover continual wintry mix and possible icy roads
tonight into Sat morning. Already hearing of icy roads in the
interior west U.P. as temps are just above freezing. Would expect
more of the same this evening and overnight as temps fall below

Into Sat, precip for most of the day will be dz/fzdz, mainly west
and ncntrl higher terrain. Approaching shortwave from Manitoba and
northern Ontario that eventually helps carve out deeper troughing
and brings in colder air aloft on Sat night could also lead to
enough ice introduced aloft to lead to ptype becoming mostly snow in
the afternoon for the west half. Any ice and snow amounts on Sat
will be light.

.LONG TERM...(Sunday through Friday)
Issued at 321 AM EST SAT NOV 18 2017

Progressive northern stream will persist for much of the upcoming
week. Light lake effect snow will be ongoing Sunday morning for
northwest wind favored areas with over lake 85H temps in the -13 to
16C range.  Over lake anticyclonic flow along with generally dry
airmass should limit additional accumulations to no more than an
inch or two.  In fact...warm advection sets in pretty quickly by
late morning over the western lake as winds become more westerly
ahead of next clipper system.

Surface low associated with next clipper will pass north of Lake
Superior late Monday into Tuesday. Significant warm advection ahead
of the low should boost temperatures to a few degrees above normal
over the western U.P. on Monday and back to near normal elsewhere.

Cold surge behind the clipper for Tuesday into Wednesday will
reinvigorate northwesterly flow lake effect snow with 85H temps
falling back to -15C or so. Quick transition from cyclonic to
anticyclonic flow and limited moisture will once again keep snowfall
accumulations in check.

Overall travel conditions across the U.P. and through the Great
Lakes should be pretty tranquil from Wednesday afternoon through
Thanksgiving Day. Temperatures will modify back to their late
November normals...perhaps even a little above...for Thanksgiving
and Friday ahead of next clipper and bout of lake effect snow for
next weekend.

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1206 AM EST SAT NOV 18 2017

Upslope flow off Lake Superior combined with moisture trapped under
inversion will lead to prevailing IFR conditions at KCMX/KSAW
overnight with LIFR conditions more likely at KIWD. In addition,
there may be some -dz or -fzdz at times with temps hovering around
the freezing mark. As gradually colder air arrives during the day
today, cigs will lift to MVFR at all terminals. Late in the aftn and
into the evening hrs, some lake effect -shsn may develop off Lake

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 335 PM EST FRI NOV 17 2017

Gales will diminish this evening as cold front to the south of low
over northern Ontario moves through. However, northwest winds
increase to gales again late Sat into Sat night. Not quite sure if
we`ll see prevailing gales though so will keep just gusts for now
and not issue a Gale warning. Winds diminish to 30 kts Sun into Mon
but more gales are possible late Mon night through Tue night as
active pattern continues.

Upper Michigan...
Lake Superior...
Lake Michigan...


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