Area Forecast Discussion
Issued by NWS Marquette, MI

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000
FXUS63 KMQT 100902
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
402 AM EST Sun Dec 10 2017

.SHORT TERM...(This evening through Sunday)
Issued at 327 PM EST SAT DEC 9 2017

LES will continue to gradually weaken through this evening while
shifting N due to winds becoming more westerly. A more dominant LES
band will develop across the Keweenaw and into NE Upper MI as a
shortwave and SFC trough advance toward the area. This heavy snow
band will shift onshore as the SFC trough moves onshore, likely
resulting in a short burst of very heavy snow along the lakeshore
Sun morning. Behind the trough, moderate LES in NNW wind snowbelts
will result. Snowfall tonight and Sunday will be greatest near the
base of the Keweenaw and E of Munising with 6-8" (possibly as high
as 10") forecast. Elsewhere near Lake Superior, totals will
generally be in the 2-5" range. Night shift may need to add an
Advisory for Marquette County for late tonight and Sun, but didn`t
want to do so now since we have an advisory currently in effect.
Otherwise, headlines should work as they stand now.

.LONG TERM...(Monday through Saturday)
Issued at 401 AM EST SUN DEC 10 2017

Overall, we`re not looking at much of a pattern shift through the up
and coming weekend as longwave troughing remains anchored across the
central and eastern CONUS. As a result, multiple embedded shortwaves
will dig across the region bringing chances for periodic area-wide
snow and then lingering lake effect behind these systems. The main
forecast concern in the near-term is the potential for a heavy lake
effect snow across the north wind snow belts beginning Monday
afternoon and running through at least Tuesday night into Wednesday.
Temperatures will start off well below normal early this week, but
should gradually warm towards normal by the end of the weekend.

Monday: Initially we will split two shortwaves, one well south of
the region and the other rapidly digging south across Lake Superior.
As a result, a clipper system will track across the region, possibly
lingering a bit and/or deepening as height falls associated with the
approaching northerly wave arrive. The warm air advection ahead of
the secondary wave looks like it will be enough to produce
widespread snow across the area on Monday, with lake enhanced snow
possible north of Lake Michigan. This snow looks like it will impact
the west during the morning commute and then gradually transition
eastward through the mid-morning and afternoon across the central
and east, respectively. While QPF is low per the high-res and medium
range models associated with the system snow, forecast soundings
continue to show some depth through the DGZ along the leading edge
of the warm air advection. Therefore, expect the snow to be somewhat
efficient, but probably closer to 15-20:1 as thermal profiles
hugging the -10C line. 1-3``, with localized amounts up to 4`` look
possible Monday morning through the afternoon. As the secondary wave
charges south across the area Monday afternoon, lake effect snow
will pick up in the north wind snow belts across the west and north
central during the afternoon and evening, respectively. This will be
the beginning of the LES event expected to persist through Wednesday.

Monday night through Wednesday: Moderate to heavy LES will
overspread the north wind snow belts through Monday night and is
expected to linger into Wednesday. The medium-range models continue
to consistently show strong unidirectional north-northwest flow
through much of the time period as the main 850mb low associated
with the secondary shortwave slowly pushes over the eastern Great
Lakes. The combination of unidirectional flow and increasing cold
air advection, with 850mb temperatures expected to drop down to
around -20C, will allow the LES machine to kick in full force during
this time period. Forecast soundings show ample lift through the DGZ
as a result, with inversion heights/equilibrium levels reaching 8-
12k feet. This seems reasonable given the lingering weak vort maxes
expected to rotate across the region during this time period.
Therefore, the synoptic setup coupled with the mesoscale and
microphysics details support highly efficient LES, with SLRs of at
least 30:1, across the north wind snow belts. Certainly headlines
will be needed during this event; however, confidence was high
enough given the model-to-model and quasi run-to-run agreement
(mainly the only difference being the onset and longevity of the
event), to issue a winter storm watch for LES for Marquette and
Alger counties as a warning for heavy LES definitely looks possible.
The main concern is for areas east of a line from Big Bay to
McFarland across Marquette county and much of Alger county as a very
strong/highly efficient LES band is expected to develop and linger
across the area for upwards of 24-36 hours. In fact, with this wind
direction the air mass upstream of Lake Superior will already be pre-
conditioned by Lake Nipigon, which will inhibit drier air from
working into the region and prolonging the LES. It is difficult to
pinpoint exactly where this band will develop and linger; however,
areas that do remain under this band for long periods of time may
pick up at least a foot to a foot and a half of snow, if not more.
This thinking is further supported by CIPS Analog Guidance.

Wednesday night through Sunday: We will see additional chances for
accumulating LES with periodic system snow through this time period
as we remain in a highly active pattern across the central CONUS.
&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1228 AM EST SUN DEC 10 2017

Lake effect snow will ramp back up later tonight mainly at KCMX
in a convergent westerly wind flow resulting in IFR conditions. As
a lake-induced trough moves onshore late tonight and Sun morning
winds will shift to a northwest to north direction bringing lake
effect snow showers into KIWD and KSAW with a period of MVFR to
IFR conditions. Lake effect snow showers should diminish or end
Sun afternoon with improving conditions at the TAF sites as high
pressure builds in from north of Lake Superior.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 327 PM EST SAT DEC 9 2017

Northeasterly winds will gust to 20 to 30 knots tonight and into
early Sunday with light freezing spray possible, especially across
the eastern half of Lake Superior. Late Sunday, winds will weaken to
below 20 knots but then increase Monday afternoon and evening with
gale force gusts to 35 knots and heavy freezing spray possible. A
few gale force gusts to 40 knots are possible across the eastern
half of Lake Superior late Monday. Winds will then weaken to 20 to
30 knots on Tuesday and below 20 knots on Wednesday.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory until 11 AM EST this morning for
     MIZ001>004-084.

  Winter Weather Advisory until 2 PM EST this afternoon for MIZ006-
     007-085.

  Winter Weather Advisory until 2 PM EST this afternoon for MIZ005.

  Winter Storm Watch from Monday afternoon through late Tuesday
     night for MIZ005-006.

Lake Superior...
  Gale Watch from Monday evening through late Monday night for
     LSZ266-267.

  Gale Watch from Monday evening through late Monday night for
     LSZ265.

  Gale Watch from Monday afternoon through late Monday night for
     LSZ244-245-263-264.

Lake Michigan...
None.
&&

$$

SHORT TERM...Titus
LONG TERM...Ritzman
AVIATION...Voss
MARINE...BB



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