Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 242009

Area Forecast Discussion
National Weather Service Marquette MI
309 PM EST Sat Feb 24 2018

.SHORT TERM...(Today and tonight)
Issued at 522 AM EST SAT FEB 24 2018

...Winter storm to impact Upper Michigan tonight into Sunday...

Shortwave over the southwest CONUS as noted on water vapor imagery
is fcst to lift ne into the Upper Great Lakes late tonight and early
Sunday bringing the potential for moderate to heavy snow and some
minor ice accumulation to much of Upper Michigan.

Today, sfc high pressure will dominate the area resulting in dry
conditions and light winds across Upper Mi today. Skies will be
sunny at least through the morning hours, but then mid-upper clouds
will gradually increase from the southwest ahead of the approaching
storm system organizing over the southern/central Plains. Max temps
will be above normal with highs in the lower to mid 30s.

Models show lee cyclogenesis taking place over the southern Rockies
today with rapid deepening of the sfc low this afternoon and tonight
in coupled upper jet structure as the approaching shortwave takes on
a negative tilt. Model consensus indicates sfc low deepening to
around 988 mb over central Upper Mi late tonight. Consensus track of
the 850 mb low for all models except the NAM suggests heaviest qpf
(in excess of .5 inch) and snowfall should occur over western Upper
Mi. SREF data also support heavier qpf/snowfall over the western
counties of the U.P. With the system expected to move through
quickly we are expecting only a 6-8 hr window for the heaviest pcpn,
and with SLRs expected of 12/13-1 still expecting 5-8 inches of wet
heavy snow over the western counties beginning late evening into
early morning Sunday. Snow amounts will taper off slightly heading
east into Baraga, Iron, Marquette and Dickinson as qpf amounts will
be closer to .4 inch and SLRs closer to 11/10-1 resulting in
snowfall amounts more in the 3-5 inch range.  Pcpn becomes a bit
more mixed heading into the east half of the U.P in the warm sector
of the sfc low so expect snow amounts in the 1-4 inch range with
some minor ice accumulation possible over the east half.

Bottom line as far as headlines: Decided to go with a winter storm
warning for wet heavy snow in Gogebic, Ontonagon, Northern Houghton
and Keweenaw counties beginning late evening into Sunday morning and
have issued advisories for all the rest of the counties for moderate
wet snow and possible minor ice accumulation late this evening into
Sunday morning. As the storm lifts rapidly ne of Lake Superior,
strong winds on its southern periphery will impact the Keweenaw on
Sunday, so in addition to the winter storm warning, a wind advisory
has been issued for the Keweenaw on Sunday as well.

.LONG TERM...(Sunday night through Saturday)
Issued at 308 PM EST SAT FEB 24 2018

Pretty tranquil, even early spring-like, stretch of weather expected
through the early part of the extended forecast.  With mean trough
position over the western U.S. and west southwesterly flow into the
Great Lakes temperatures will remain above normal for much of the
week. Temperatures will climb into at least the lower 40s inland
from the ice covered nearshore areas of the Lakes through Wednesday.
If any of those days end up being full sun days...temperatures could
go even higher.

The only time period for any impactful weather this week will occur
late Wednesday night through Thursday.  Models are still having some
consistency issues with the handling of energy ejecting out of the
trough in the southwest but they are suggesting an upper low closing
off somewhere over the upper midwest or lower Great Lakes with an
associated surface low moving eastward through these areas. How far
north and west the precipitation shield gets will be the forecast
challenge over the next couple of days. There will be plenty of
moisture for the system to work with but if the track stays over the
southern Lakes any significant precipitation would be confined to
the southern U.P. or further south. Precipitation type would also be
an issue with not much cold air wrapped into the system.

Upper ridging will build back into the Great Lakes by late in the
week into next weekend with temperatures continuing to run at or
above normal.

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1233 PM EST SAT FEB 24 2018

There is a narrow area of scattered to broken MVFR ceilings just
south of KSAW this afternoon, but do not expect much of an impact
from these clouds as they continue to thin. Otherwise, VFR
conditions will persist across all terminals through the remainder
of this afternoon. However, as we progress through the overnight
hours conditions will deteriorate rapidly as moderate to heavy wet
snow is expected to impact all terminals as a surface low tracks
northward across the region. Expect visibilities to be sharply
reduced for at least a 3-6 hour time period as this band of snow
pushes northward. The potential is there for snow to mix with sleet
and/or freezing rain at times at KSAW, but confidence was not high
enough to include mentions of this wintry mix at this time.

While ceilings and visibilities will improve by mid-Sunday morning,
strong and very gusty westerly winds, especially at KCMX, will pick
up behind the exiting surface low. With the snow expected to be wet
and heavy, confidence is not high if we will see blowing snow and
resulting reduced visibilities on Sunday.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 522 AM EST SAT FEB 24 2018

Winds will remain below 15 knots, but will quickly ramp up to
easterly gales of 35 to 40 knots later tonight then become westerly
gales Sunday into Sunday evening as a deepening low pressure system
lifts across the Upper Great Lakes region. High-end gales look
likely for Sunday behind the exiting system. Winds will fall below
30 knots by Monday morning and remain so through the first half of
the week.

Upper Michigan...
  Winter Weather Advisory from 11 PM EST /10 PM CST/ this evening
     to 7 AM EST /6 AM CST/ Sunday for MIZ004-005-010>013-084.

  Wind Advisory from 7 AM to 7 PM EST Sunday for MIZ001>005-084.

  Winter Weather Advisory from 1 AM to 10 AM EST Sunday for MIZ006-

  Winter Storm Warning from midnight tonight to 10 AM EST Sunday
     for MIZ001-003.

  Winter Storm Warning from 10 PM EST /9 PM CST/ this evening to 7
     AM EST /6 AM CST/ Sunday for MIZ002-009.

Lake Superior...
  Gale Warning from 1 AM Sunday to 1 AM EST Monday for LSZ266-267.

  Gale Warning from 9 AM EST /8 AM CST/ Sunday to 1 AM EST
     /midnight CST/ Monday for LSZ162-263>265.

Lake Michigan...
  Gale Warning from 7 AM to 7 PM EST Sunday for LMZ248-250.



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