Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 241203

Area Forecast Discussion
National Weather Service Marquette MI
703 AM 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 through Friday)
Issued at 522 AM EST SAT FEB 24 2018

...Winter storm exits early on Sun but strong winds are a concern
into Sun evening...

Low pressure that causes heavy snow and mixed precipitation moves
out quickly to the north of Lk Superior on Sun morning. Most
meaningful precip will be finished by 14z/9 am ET over northern
Upper Michigan. As low deepens to 985mb by time it reaches James Bay
late Sun morning, attn will turn to very strong west winds
developing across especially the Keweenaw Peninsula. Though cold air
advection is modest and there is really no isallobaric component to
the winds, forecast soundings indicate mixed layer winds will easily
reach 35 kts with 40-45 kts likely in gusts. Enough confidence to go
ahead and issue a wind advisory for Keweenaw for Sun. Main impact
could be possible downed tree limbs as the winds interact with
objects still covered in heavy/wet snow that occurs tonight.
Sporadic power outages could occur. Elsewhere, west winds will
become breezy and there may even be peak gusts toward 40 mph along
rest of the Lk Superior shoreline and also closer to Lk Michigan.
Any breaks in the clouds developing on Sun will help stronger winds
mix down to the sfc. Some light snow showers may linger over the
Keweenaw but don`t think blowing snow will be bigger issue as temps
rising into the 30s will make the snow on the ground wetter and not
prone to blowing around.

Rest of long term pretty quiet, but will have to keep focus on late
Wed night into Thu as there are indications another stronger storm
system could affect the Upper Great Lakes region. Previous EC showed
total qpf with that system over 2 inches. That is qpf, not snow. So
if that was even 10:1 snow, we would be looking at a major snowstorm.
00z EC backed off of this solution considerably. Recent GFS and GEM
model runs indicated well developed/deep low pressure system will
bring swath of very heavy precip across WI and lower MI and possibly
into at least southern forecast area. GEFS probabilities also
suggest a sharp gradient in qpf from north to south across the
region with decent probabilities showing up of 1+ inches of qpf in
the max axis of the system. Guess that suggests the 12z/23Feb EC
showing over 2 inches of qpf may not be too unrealistic. Early for
sure, but this time frame certainly bears watching.

With the active pattern continuing mostly due to larger scale
troughing over western half of Conus, temps through the long term
should end up at or above normal. Early this week could see daytime
temps pushing past 40F especially on days there is decent sunshine.

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 656 AM EST SAT FEB 24 2018

MVFR/IFR cigs at TAF sites will gradually scatter out later this
morning, leading to VFR conditions thru the rest of the day.
A fast moving low pres system will spread snow ne into Upper MI
tonight. All terminals will likely see a period of IFR to LIFR
conditions late tonight. &&

.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.

  Winter Weather Advisory from 1 AM to 7 AM EST Sunday for MIZ006-

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

  Wind Advisory from 10 AM to 7 PM 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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