Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 202010

Area Forecast Discussion
National Weather Service Marquette MI
310 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 through Monday)
Issued at 224 AM EST TUE FEB 20 2018

Upper air pattern consists of a 500 mb trough in the western U.S.
and a strong 500 mb ridge over the sern U.S. 12z Wed. The trough in
the western U.S. tries to advance eastward, but the shortwaves that
eject out of it get sheared out as the ridge remains over the sern
U.S. this forecast period. 850-500 mb q-vector convergence and some
deeper moisture arrives Thu night. Looks pretty quiet until Thu
night when next system arrives. Did not make too many changes to the
going forecast.

In the extended, GFS and ECMWF show a 500 mb trough over the western
U.S. 12z Fri extending up into the Canadian Prairies and a 500 mb
ridge across the sern U.S. The trough ejects into the southern
Rockies 12z Sat and into the Great Lakes Sat night. More troughing
moves into the area 12z Mon into Mon night. Temperatures stay above
normal for this forecast period. System moves out Fri with another
coming in Sat night and another on Mon.

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1238 PM EST TUE FEB 20 2018

Light freezing drizzle with its accompanying LIFR to IFR ceilings
and visibilities continue this afternoon across all terminals.
Expect this trend to continue through the afternoon hours, before
precipitation gradually transitions over to light snow at KCMX and
KIWD later this afternoon/evening. Tonight, as a cold front pushes
across the area, breezy west-northwesterly winds will fill in behind
the front. There is the potential we could see some light snow
showers along this front, especially at the western terminals as the
colder air will take advantage of some open waters for light lake
effect. By Wednesday, ceilings will improve into at least the high-
end MVFR 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.

Upper Michigan...
  Winter Weather Advisory until 7 PM EST this evening for MIZ007.

Lake Superior...
Lake Michigan...


SHORT TERM...Ritzman
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