Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 182001
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
301 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 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 18Z TAFS through 18Z Sunday afternoon)
Issued at 1238 PM EST SAT NOV 18 2017

Upslope flow off Lake Superior combined with moisture trapped under
inversion will lead to prevailing lowered CIGs today. There could be
some very light dz/fzdz at each of the TAF sites; however, coverage
is expected to be very low. Have left this out of the TAF at this
point, due to the aforementioned coverage and confidence in this
actually occuring. As colder air moves in this evening into Sunday,
any dz/fzdz will transition to lake effect snow. First at IWD and
CMX and then at KSAW. Generally expecting only light snow; however,
gusty winds may lead to some blowing snow causing reduced visbility
at times into Sunday morning. Winds becoming westerly through the
day Sunday will shift the main focus of any remain light lake effect
snow to the KCMX TAF site, while KSAW and KIWD see improving
conditions Sunday morning and afternoon.
&&

.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.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...KEC
LONG TERM...MZ
AVIATION...KEC
MARINE...KEC



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