Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 182341

Area Forecast Discussion
National Weather Service Marquette MI
641 PM EST Sat Nov 18 2017

.SHORT TERM...(This evening through Sunday)
Issued at 301 PM EST SAT NOV 18 2017

The main forecast concerns through the short-term forecast is the
potential for light lake effect snow and blowing snow potential for
mainly northwest wind favored snow belts.

Tonight through Sunday: A shortwave is progged to slide into the
Upper Great Lakes tonight. As this happens, expect colder air to
slide into the Upper Peninsula both at the surface and aloft. This
will act to lower the DGZ enough to place the moist lower levels
within the DGZ and take away the freezing drizzle potential. This
will keep precipitation in the form of lake effect snow for mainly
northwest wind favored locations. 850mb temperatures are expected
drop to the -14C to -17C range through this time period, giving
delta-t values in the 19C to 22C range. More than enough for lake
effect snow potential. Inversion heights are progged to be around
5kft to around 8kft when accounting for lake surface temperatures;
however, soundings indicate that the convective cloud layer would
mainly be below 6kft. In addition, drier anticyclonic flow at the
surface will begin to make for a more hostile lake effect snow
environment over the western portions of the U.P. by late tonight
and effectively ending the lake effect snow chances for most of the
day Sunday. The exception may be over the Keweenaw Peninsula, where
winds become more westerly during the day Sunday allowing for
increase low level moisture on an increased fetch.

This will also begin to shift the snow bands northward over the
eastern U.P., placing most of the snow closer to the shoreline and
over eastern Lake Superior. This all basically points to a light
lake effect event through this time period. The best chance of
seeing a few inches of snow would be as the aforementioned wave
moves overhead tonight into Sunday morning. Generally looks like 1
to 3 inches possible in the northwest wind favored snow belts,
with the greatest totals expected over the higher terrain of the
west and over the eastern Upper Peninsula. There are some
indications that a more dominant band may set up by late Sunday
afternoon as winds become more west to west northwesterly. This
may give a bit higher totals over the Keweenaw and over eastern
portions of the U.P., specifically east of Munising closer to Lake
Superior. It may take a some time for the band to orient with the
w/wnw winds, so the heavier precip with that band may occur
closer to the evening hours. If this happens portions of the
aforementioned locations could see totals reaching closer to 3 to
5 inches locally. Again, this would be the total for a 24 hour
period, tonight into tomorrow evening.

In addition to the lake effect snow, winds may gust as high as 20 to
30 mph along the Lake Superior shoreline, which may result in some
blowing snow. The gusty northwest winds will also allow waves to
build as high as 10 feet over eastern portions of Lake Superior.
This may cause minor lake shore flooding and beach erosion for
locations east of Marquette along Lake Superior.

.LONG TERM...(Sunday night through Saturday)
Issued at 328 PM EST SAT NOV 18 2017

Lake effect snow will be ongoing for the WNW wind snow belts Sunday
evening. High resolution guidance suggests the eventual formation of
a somewhat dominant LES band crossing the southern Keweenaw before
extending eastward to Grand Marais to Whitefish point. A subtle
700hPa trough shifting southeastward across the CWA during the
evening hours will likely enhance convergence into this band via
backing surface flow. Modest inversion heights and the lack of DGZ
growth should limit accumulations, but several inches of LES will be
possible late Sunday afternoon through Sunday night for the
aforementioned locations. Much of the remainder of Upper MI will
remain dry Sunday night.

LES will diminish and shift northward over Lake Superior amid warm
air advection and backing surface winds on Monday. Much of the area
will likely see sunshine for the first time in over a week,
producing temps slightly above normal.

Then, a somewhat stagnant pattern with persistent deep troughing
near and over Hudson Bay will result in primarily west to northwest
flow across the Upper Great Lakes into the weekend. A period of lake
effect snow with gusty northwest winds will take hold late Monday
night into Tuesday night. Moderate accumulations will be possible
for the NW-wind snow belts, primarily Tuesday afternoon into the

LES will wane through the day Wednesday as inversion heights lower.
A brief round of LES is then expected on Thanksgiving night behind a
trough that clips the area to the northwest. A clipper system will
then cross the region Friday night into Saturday, but indications at
this time are that the bulk of the precip will remain north of the

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 641 PM EST SAT NOV 18 2017

Increasingly colder air flowing across Lake Superior on nw winds
tonight will result in lake effect -shsn becoming more numerous,
affecting KIWD/KCMX more so than KSAW. On a prevailing basis,
conditions should hold in the MVFR category, but as is typical for
lake effect, conditions will be variable with some brief IFR
possible at KIWD/KCMX. Winds will also be gusty tonight, strongest
at KCMX where gusts may approach 30kt. Backing winds should allow
KIWD to break out to VFR late Sun morning or early aftn as overlake
wind trajectory is lost. KSAW will also become VFR as downwsloping
increases. KCMX will likely remain MVFR with -shsn at times.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 301 PM EST SAT NOV 18 2017

Northwest winds of 20 to 30 knots are expected through Sunday
evening. There may be a few gale force gusts for the south central
portion of Lake Superior, but not expecting anything sustained
enough to support a gale warning. South gales are possible Monday
night before shifting to northwest gales Tuesday into Tuesday night.
Otherwise, winds are generally expectedt to be in the 15 to 25 knot
range, with a few gusts approaching 30 knots on Thursday.

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


LONG TERM...Kluber
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