Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 202346
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
646 PM EST Tue Feb 20 2018

.SHORT TERM...(This evening through Wednesday)
Issued at 309 PM EST TUE FEB 20 2018

Low pressure tracked across central and western Upper Michigan this
afternoon bringing widespread impacts to roadways as a wintry mix of
sleet, freezing rain, and snow lifted northeast across central and
eastern Upper Michigan earlier today. Across the western half of
Upper Michigan, snow transitioned to freezing rain, and eventually
freezing drizzle through the early/mid morning hours.

Tonight as the main surface low continues to lift northeast, exiting
the region, colder air behind the system will begin to filter into
the region. This will allow lingering light freezing drizzle to
transition over to light lake effect snow, mainly across the
Keweenaw Peninsula. As this colder air mass begins to track eastward
tonight, a few models show subtle hints of a narrow band of snow
developing along the weak cold front. Confidence was not high enough
to include mentions of this additional snow associated with this
front any further east than the north central, but we should start
to see any lingering fog and/or light freezing drizzle dissipate as
this colder and drier air works in from the west. As an enhanced
surface pressure gradient pushes eastward across Upper Michigan
behind the exiting system, this coupled with pressure rises, will
also allow for breezy westerly winds to develop overnight.

Lingering light lake effect snow across the west will diminish
through the early/mid morning hours as surface ridging begins to
work into the region. Cloud cover will gradually diminish away from
Lake Superior during the day on Wednesday, but expect at least some
diurnal cumulus to develop during the afternoon given the colder air
aloft and increasing insolation. The colder air progged to be in
place tomorrow will knock temperatures down about ten degrees
compared to today`s high temperatures.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 407 PM EST TUE FEB 20 2018

For a winter that has had a notable lack of synoptic pcpn events for
Upper MI, we are currently in somewhat of an anomaly, considering
the pcpn that has occurred over the last 24-36hrs, the fcst of 2
more events in the next 7 days, and potentially another event late
next week. In the next 7 days, one will occur Thu night/Fri and the
second over the weekend. At this time, neither looks significant,
but the second will be one to monitor. Currently, a deep trof
exists over the western CONUS (500mb height anomalies of 260m)
while strong ridging is centered just off the E Coast (500mb
anomalies of 350m over New England). Deep sw flow btwn these
anomalies has transported incredible moisture northeastward with
the 12z raob at DTX/APX indicating precipitable water at
500pct/426pct of normal, both setting new record high values for
the entire month of Feb. Over the next 7 days, a mean trof will
persist over the western CONUS while the strong ridge just off the
E Coast will tend to deamplify next week. With the persistence of
the western trof, something not seen this winter, there will be
opportunities for ejecting shortwaves to bring pcpn into the Upper
Lakes. Pattern is certainly favorable for significant pcpn
events, but whether something significant occurs for Upper MI
remains to be seen. The first wave, a weak one, will affect the
area Thu night/Fri, bringing what should be a widespread light
snow event, perhaps a few inches of snow. The second will occur
Sat night/Sun. This second wave looks more significant in all the
guidance, and it will likely be a better pcpn producer. With the
mean western trof, there should be additional shortwaves affecting
the area next week. For now, there is broad agreement for another
system during the last half of next week. As for temps, with a
mean western trof dominating, temps thru next week will be running
near normal or above normal each day with above normal likely on
the majority of days. Farther down the line, longer range guidance
has been indicating the NAO to go negative, which normally favors
a cold pattern for the Upper Lakes. While temp signals from the
guidance have not really indicated that to be the case, there
should be a trend toward a period of colder weather in early Mar.

Beginning Wed night...high pres will be situated right over Upper
MI, providing a clear/tranquil night. Favored the low side of
guidance for mins. Traditional cold spots likely to fall to at least
-5F.

Thu...sfc high pres will slip e on Thu, but still ridge back into
the area. Expect an increase in high and mid clouds as waa regime
develops upstream and entrance region of upper jet overspreads area.

Thu night into Fri...a shortwave will shear ne into the Upper Lakes,
bringing a period of waa/isentropic ascent. Mixing ratios up to
2.5g/kg are avbl in the 700-750mb layer, suggesting potential of 2-
4in of snowfall for 6-9hrs of main ascent. Snow ratios will be on
the lower side with relatively narrow DGZ at or above 10kft. So
probably looking at "wetter" snow accumulation mostly on the order
of 1-3in across the area. Snow will develop sw to ne Thu night then
diminish and/or end sw to ne during Fri. Snow may mix with or change
to a little -fzdz as the pcpn diminishes/ends on Fri. Probably won`t
be cold enough for any LES behind this wave. So, a quiet period of
weather will return Fri night/Sat.

Sat night/Sun...attention turns to the next shortwave ejecting from
the mean western trof. Medium range models show this shortwave being
stronger than its predecessor. Last 3 runs of the GFS spin up a
fairly strong low pres system (980s mb) with a hvy snow band to the
nw of the low track as it lifts into the Great Lakes. Majority of
the GFS ensembles are as strong or stronger than the operational run
with 24hr qpf in the 0.5 to over 1 inch range nw of the low track.
GEM and ECMWF are notably weaker and there are only a few GEM
ensembles supporting a strong sfc low pres similar to the GFS. At
this point, a strong system seems unlikely given the lack of support
from the ECMWF/GEM. On the other hand, given the abundance of
unseasonable warmth/moisture that will remain avbl over the Lower
Mississippi Valley to Ohio Valley, won`t take much of a shortwave to
generate fairly significant pcpn. Ptypes could be an issue given the
lack of arctic air avbl and the unseasonable warmth to the s. Looks
like Sat night/Sun morning will be the main time period for pcpn.

Once again, probably won`t be cold enough for any LES behind this
system heading thru late Sun into Mon. Dry weather will then likely
prevail from Mon into Tue.
&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 638 PM EST TUE FEB 20 2018

Lingering -fzdz should end this evening as drier air pushes in
behind a cold front. Breezy west-northwesterly winds will bring in
colder air for some possible light snow showers in the wake of the
front tonight, especially at the western terminals. By Wednesday,
ceilings will improve into at least the high-end MVFR to low end
VFR category, with VFR visibilities expected. &&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 309 PM EST TUE FEB 20 2018

Winds will remain between 20 and 30 knots through the day on
Wednesday, before subsiding to less than 20 knots Thursday through
the weekend. There may be a few pockets of heavy freezing spray in
areas that have more expansive open waters, mainly across the far
east late tonight through Wednesday. However, ice cover is far too
expansive to warrant any headlines at this time.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory until 7 PM EST this evening for MIZ007.

Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Ritzman
LONG TERM...Rolfson
AVIATION...Voss
MARINE...Ritzman



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