Area Forecast Discussion
Issued by NWS Marquette, MI

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000
FXUS63 KMQT 170716
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
316 AM EDT Sun Mar 17 2024

.KEY MESSAGES...

- Lake effect snow into Monday, especially over the western U.P. near
  Lake Superior. Highest snow amounts of 5-9 inches possible
  across mainly the western counties. Elsewhere in the northwest
  wind snow belts, 2-5 inches is possible.
- Gales continue into tonight on Lake Superior.
- Blustery northwest to north winds continue today.
- The snow, combined with blustery winds, will result in some
  hazardous driving conditions.
- Light snow possible Tuesday followed by another lake effect
  snow event through early Thursday.
- Blustery winds return Tuesday night and Wednesday.
- Northwest gale force winds and heavy freezing spray possible
  Tuesday night and Wednesday across eastern Lake Superior.

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 243 AM EDT Sun Mar 17 2024

Upper air pattern consists of a 500 mb ridge in the Pacific NW, a
closed 500 mb low in the desert sw and a closed 500 mb low over
eastern Ontario. Several smaller shortwave are embedded in the upper
low over Ontario and will continue to rotate through the upper Great
Lakes and help to continue the LES snow event this period. 850 mb
temperatures will continue to fall today to -11C across the east to
-15C across the west and this will continue the LES snow. Did not
make many changes to the going forecast and continued persistence
with this forecast. Inversion heights stat in the 3000-5000 foot
range looking at various soundings with the DGZ in the layer and
some omega, so LES snow amounts look reasonable with a fluffy snow
and did not change much with this either.

&&

.LONG TERM /TONIGHT THROUGH SATURDAY/...
Issued at 312 AM EDT Sun Mar 17 2024

Guidance packages continue to present a consistent representation of
the pattern for a majority of the extended forecast period. The
broad ridge extending up the west coast and downstream troughing
extending down the east coast will position Upper Michigan within
northwest flow early in the extended period, subjecting the forecast
area to the impacts of any clipper system riding the ridge southeast
into the trough. In terms of sensible weather, this means snow
chances, more winter like temperatures, and gusty winds. Toward the
end of the week, there`s a potential for the pattern to shift to
more zonal flow; however, confidence is low given the broad and
longitudinally elongated negative height anomaly stretching across
most of Canada and an eastward progressing deep trough into the west
coast. Overall, this results in less confidence in the forecast for
this weekend.

Tonight, Upper Michigan will continue to be under the influence of
mid-upper level cyclonic flow as a deep trough digs southeast into
the Ohio Valley. This will maintain the colder airmass aloft and
sustain the ongoing lake effect snow event for the forecast area.
Through the night, surface high and mid-level ridging will inch
across the Northern Plains. Given the timing of it`s progression
into the area though, suspect the snow shower activity downwind of
Lake Superior will persist into the early morning hours. However, by
sunrise, activity should begin waning as inversion heights fall due
to increasing subsidence and increasing mid-level dry air. By
afternoon, most, if not all show showers save for some isolated ones
in the east should be diminished. Guidance suggests additional
snowfall amounts on the order of 1 to 5 inches tonight into early
Monday morning for the northwest wind snow belts, with the higher
amounts being in Alger County and the Michigamme Highlands of
Baraga/Marquette counties.

Monday evening, a shortwave/clipper system will exit Canada into
northern Minnesota. As it moves into the Upper Great Lakes, light
snow will move in from northwest to southeast. Through the day on
Tuesday, a secondary surface low will slowly move eastward just
north of Lake Superior while a secondary shortwave drops into the
region. As this pulls away, a tighter pressure gradient will develop
over the region as cold air advection sweeps south. In effect, this
will develop lake effect snow showers and support blustery
conditions late Tuesday into Wednesday. An inverted surface trough
should gradually take form across eastern Lake Superior, sustaining
shower activity across eastern Upper Michigan into early Thursday.
High pressure shifts east through Ontario during the day Thursday,
working to diminish snow shower activity.

At this point, guidance begins to vary as the broad trough over the
east coast begins lifting while another closed low drops into
northern Manitoba, reinforcing the negative height anomaly across
Canada. Given the differences in timing and influence presented in
18 and 0z guidance, its unclear if a shortwave ejecting out of the
northern Rockies will get caught up in this broad circulation. If it
does, another round of precip could move into the region Thursday
night; if it doesn`t, then this impulse should remain too far south
to impact us. The same level of uncertainty exists for another wave
Friday night into Saturday.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 121 AM EDT Sun Mar 17 2024

An increasingly favorable lake enhanced snow regime will be setting
up off of Lake Superior thru this aftn under nw to nnw low-level
winds. At IWD, expect varying MVFR and IFR to become prevailing IFR
overnight thru today. Some brief periods of LIFR will be possible
late in the night thru at least the morning hrs. Improvement to MVFR
may occur at IWD this evening. At CMX, expect varying MVFR and IFR
to become prevailing IFR overnight thru this aftn. Some periods of
LIFR will be possible at times late in the night thru this aftn.
Expect improvement to MVFR this evening at CMX. At SAW, expect
fluctuations btwn MVFR and VFR overnight, then prevailing MVFR for
today though some brief IFR will be possible. A slight veering of
winds this evening should bring somewhat heavier shsn to SAW,
dropping conditions to IFR. Expect gusty winds to 20-35kt at all
terminals throughout this fcst period with the stronger gusts at
CMX.

&&

.MARINE...
Issued at 312 AM EDT Sun Mar 17 2024

A low end northwest gale event has been ongoing overnight, with
lightening winds observed across western Lake Superior. As we
progress through the night and Sunday, expecting the east half to
continue to see gales of 35-40kts. Winds should lighten by Monday
morning, with the lake being below 30kts near sunrise. Across the
west half, some stray gale force gusts will be possible, with
chances increasing as you move west toward Copper Harbor, but
otherwise.

Light winds should persist afterwards through Tuesday morning.
Another system moving through the region then will leave behind
another punch of colder air and tighter pressure gradient. There has
been a slight upward trend between previous and current guidance
packages, suggesting the threat for gales across the east half is
increasing. Additionally, with this trend and the colder airmass,
heavy freezing spray is appearing to be more likely. Winds decrease
Wednesday night, coming in at or below 20 knots the rest of the
week.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory until 2 AM EDT /1 AM CDT/ Monday for
     MIZ002>004-006-009-084-085.

Lake Superior...
  Small Craft Advisory until 2 PM EDT /1 PM CDT/ Monday for
     LSZ240>242.

  Gale Warning until 2 AM EDT Monday for LSZ243>251-264>267.

Lake Michigan...
  Small Craft Advisory until 11 AM EDT Monday for LMZ221-248-250.

&&

$$

SHORT TERM...07
LONG TERM...JTP
AVIATION...Rolfson
MARINE...JTP


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