Area Forecast Discussion
Issued by NWS Marquette, MI

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154
FXUS63 KMQT 101954
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
254 PM EST Tue Dec 10 2019

.SHORT TERM...(Today and tonight)
Issued at 506 AM EST TUE DEC 10 2019

WV imagery and RAP analysis indicated a mid/upper level trough from
Hudson Bay into the north central CONUS. The next significant
upstream shortwave trough was dropping southeast from northern
Manitoba. At the surface, nnw winds prevailed between low pressure
over northern Quebec and high pressure building into the Northern
Plains. CAA has dropped 850 mb temps to around -20C supporting light
to moderate LES. With the high building toward the area, winds have
gradually backed, shifting the LES over north central Upper Michigan
mainly in locations from Alger County eastward. The shorter fetch
into the west with the influx of very dry air and lowering inversion
heights has limited LES intensity with mainly light snow.

Today, winds will continue to back to the west as the Manitoba
shrtwv approaches. This will shift the LES into locations mainly
east of Munising and toward the Keweenaw in the west. Although the
stronger low level conv is not expected to linger in any one place very long
as it shifts eastward, additional accumulations in the 2 to 5
inch range will be possible over the east. Lower amounts in the 1
to 3 inch range are expected over the west.

Tonight, As the shrtwv moves through the northern Great Lakes,
climbing inversion heights should support an increase in the LES
for west flow favored locations. This should move the heavier snow
offshore from northeast Upper Michigan by late evening. The high
res models suggest that the convergent wrly flow could result in
dominant band into the Keweenaw that could bring a period of
heavy snow. However, there is uncertainty where the band might
develop and how long it would persist. Nevertheless, higher
amounts are likely over the Keweenaw, mainly north of M-38. In
addition, gusty winds to around 25 mph could produce areas of
blowing snow in open areas.

Temps dropping into the -5 to -12 range along with winds of at least
5 to 10 mph will result in wind chills in the -20 to -30 range over
much of the inland west half overnight.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 253 PM EST TUE DEC 10 2019

Forecasted upper level pattern hasn`t changed much, with a deep long
wave trough extending south from Huron Bay with a ridge in place
over the west coast. The ridge will shift east, creating a quasi-
zonal flow over the region with a shortwave embedded moving through
Thursday. This is followed by long wave troughing again this weekend
before it shifts east as deeper troughing extends across the central
US by early next week. This pattern will keep cold arctic air in the
forecast overnight Wednesday but as the flow becomes more zonal, the
lake effect will turn off and temperatures will increase going into
the weekend ahead. The shortwave passing through Thursday followed
by the weekend`s storm, will keep snow in the forecast at least
through the weekend.

Overnight Wednesday, with brief ridging building in across the
region followed by increasing warm air advection, the lake effect
regime for the W and NW snow belts will come to end sometime close
to midnight. As the ridge builds in, it`ll give us another cold
night. Overnight lows -5 to -10F will be possible in the interior
west/central and near 0F elsewhere. Wind chill -20 to -10F will be
possible for the coldest interior areas.

Thursday, isentropic lift and warm air advection ahead of shortwave
will help create some widespread snow across the region.  Right now
the better forcing looks in place over northern Lake Michigan into
the eastern UP so snow totals will likely be higher close to 5-6
inches during the day there. Elsewhere expect at least 2-3 inches
CWA-wide during the day Thursday. With the return flow and warm air
advection, high temps look to rebound into the mid-teens in the
interior west/central and climb into the low to mid 20s elsewhere.

Friday looks largely drier, with most moisture associated with
Thursday`s shortwave exiting by the morning hours. There are some
inconsistencies in lingering moisture and a system to the north, so
at the moment keeping slight chances for POPs. Better moisture with
some isentropic enhancement arrives Saturday so widespread snow is
likely.  Some models, namely the GFS, appear to be outliers,
suggesting upwards of 0.25-0.5" of QPF over the central UP so
certainly something to keep an eye on.  Sunday after this system
exits, some lake effect NW snow showers look possible until high
pressure over the northern Plains settles in overnight Sunday into
Monday.
&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1250 PM EST TUE DEC 10 2019

Cold high pressure dropping south through the Northern Plains will
make the wind west enough to keep lake-effect snow mostly out of SAW
and IWD (though some LES -SHSN are lingering the next 1-2 hours at
IWD). Therefore, conditions are expected to become VFR at both IWD
and SAW by this evening. However, as winds turn more NW, MVFR lake-
effect cigs will return to IWD late tonight. Some models advertise
IFR cigs at IWD but did not go below 1 kft for now because
confidence is not there for prevailing IFR.

Now, at CMX... lake-effect snow showers continue throughout the TAF
period with IFR or worse conditions expected more or less
continuously. The period to watch will be tonight, from about 00z to
about 10z (give or take an hour) when a more intense snow band is
expected to develop over CMX and then shift back and forth to the
north and south through the night. There will likely be a period of
1/4 mile vis with +SN in this band but given that the band will be
shifting around, it may not be continuous enough to warrant a
prevailing line. Therefore, went with a TEMPO instead. This heavy
band shifts south and/or breaks apart before sunrise Wednesday, but
lighter LES -SHSN continue into the day with prolonged IFR vis
expected.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 409 AM EST TUE DEC 10 2019

Arctic air as begun to spill across the Upper Great lakes, with
northwest winds between 20 and 30 knots today, tonight expect the
winds to back westerly at similar speeds. Could see a few gale force
gusts to 35 knots overnight. Another bout of stronger cold air
advection arrives Wednesday, bringing back northwest winds 20 to 30
knots with gales to 35 knots possible across the east half of the
lake. Confidence wasn`t high enough to issue a gale watch at this
time for Wednesday, given the brief nature. However, if gales look
to hold on longer headlines may be needed. As the colder air arrives
tonight through Wednesday, moderate freezing spray will ramp up and
become heavy across much of the lake. Heavy freezing spray warnings
are in effect for these expected conditions. Winds diminish by
Thursday morning to speeds generally between 15 and 25 knots, and
linger through Friday backing southerly as high pressure moves over
the area. Warmer air moves back into the region as well, shutting
down any freezing spray threats.

Another round of colder air looks to arrive over the weekend. This
round of colder air won`t be as cold, but will bring back 20 to 30
knot north-northwest winds and moderate freezing spray.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Wind Chill Advisory from 9 PM EST /8 PM CST/ this evening to
     noon EST /11 AM CST/ Wednesday for MIZ004-005-009>013-084.

  Winter Weather Advisory until 10 PM EST this evening for MIZ006-
     007-085.

  Winter Weather Advisory until 7 AM EST Wednesday for MIZ001>003.

Lake Superior...
  Heavy Freezing Spray Warning from 7 PM EST /6 PM CST/ this
     evening to 7 PM EST /6 PM CST/ Wednesday for LSZ162-240>244-
     263>267.

Lake Michigan...
None.
&&

$$

SHORT TERM...JLB
LONG TERM...JP
AVIATION...RJC
MARINE...Ritzman



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