Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 222044

Area Forecast Discussion
National Weather Service Marquette MI
Issued by National Weather Service GAYLORD MI
344 PM EST Thu Feb 22 2018

.SHORT TERM...(This evening through Friday)
Issued at 341 PM EST THU FEB 22 2018

Initial forecast problem for tonight will deal with anticipated
widespread snowfall that is expected to develop as the evening
progresses.  Isentropic ascent combined with increasing moisture
(precipitable water values above 0.50 inch) on the nose of an
increasing low level jet (and subsequent moisture convergence) and
some increasing divergence aloft ahead of a subtle short wave
trough.  Weak mid level static stability won`t hurt the cause either
(700-500mb lapse rates around 7C/km overnight into Friday morning)
Focus for heaviest QPF tonight into Friday morning looks to be
across the western half of Upper Michigan...with some enhancement
across the higher terrain along the spine of the Keweenaw Peninsula.
22/12z HREF snowfall probabilities show a decent shot of more than
8"/12h ending 12z Friday morning over parts of the
least fairly confident in a 4-6 inch swath of snow across Ontonagon/
Houghton/Keweenaw Counties through 12z Friday..with 3-5 inch amounts
west of an IMT-MQT line where best low level frontogenetic forcing
will be focused...and 1-3 inches east of that line where snow will
start latest (as low level dry air will take some time to overcome).
 Push of warmer air into the upper Great Lakes will have an impact
on snow ratios...with forecast soundings implying a deep layer (on
the order of 300-400mb) of temperatures warmer than -10C...which
support more riming/aggregation of snowflakes and tend toward a
wetter/high density type of snowfall (SLR in the 9-14:1 range???).
This type of snowfall...though perhaps not of "cement mixer"
consistency...will still be more difficult to drive through
especially with system timing (during morning drive time to

Snow will still be ongoing at daybreak Friday morning...but is
expected to taper off from west to east as the morning wears on as
drying/subsidence take hold (though low level moisture/cloudiness
may persist).  Can`t rule out snow tapering off to drizzle/freezing
drizzle during the afternoon...some weak QPF signals especially in
the high-res guidance though usually prefer to see more of a low
level warm advection/convergence signal (though low level lapse
rates to steepen as cold advection kicks in).  Additional snowfall
for Friday expected to be in the 1 to 2 inch range (higher east)...
for event totals of 5 to 8 inches for Ontonagon County northeast
through the Keweenaw...3 to 6 inches west of IMT-MQT line and 2 to 4
inches east.  As for headlines...seems to make sense to expand
current advisory to encompass remaining central U.P. counties
(Alger/Schoolcraft/Luce) given similar snowfall amounts and concerns
about snow density (will simply shift the start/end times about 3h
forward).  This has been coordinated with our "friends" at APX
(since I`m staring at them from above my workstation).  Other
headlines look fine...including the Keweenaw warning.

.LONG TERM...(Friday night through Thursday)
Issued at 341 PM EST THU FEB 22 2018

Next forecast problem arrives for the latter half of the weekend as
a more substantial short wave trough lifts northeast out of the
southern Plains Saturday night...and pushes a deep but compact
surface low probably across the Upper Peninsula Sunday morning. The
threat for precipitation will increase ahead of the low late
Saturday into early Sunday...possibly starting as snow but could
become mixy as warm air surges north.  Potential snow amounts will
depend on the evolution of this warm push...but at this point
another round of wintry headlines may be in the offing.  A glancing
blow of cold air on the backside of this system to start next
week...but lake effect pattern overall not looking impressive at
this distance.  Gusty west winds Sunday afternoon especially across
the Keweenaw.

No other impactful weather systems on the horizon next week as low
amplitude ridging aloft takes hold of the eastern CONUS.  There is
some mischief possible in the southern branch of a split flow
pattern that will need to be monitored.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1248 PM EST THU FEB 22 2018

VFR conditions this afternoon with increasing mid cloud...but am
anticipating worsening flight conditions as the evening
progresses as ceiling heights fall and eventually snow overspreads
the western and central U.P. after 03z. LIFR conditions expected
overnight and into the first part of Friday morning at
IWD/CMX/SAW...visibilities expected to improve as the morning
progresses and snow winds down.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 341 PM EST THU FEB 22 2018

Relatively light winds tonight with high pressure ridge giving way
to a wave of low pressure expected to lift northeast across the
upper Lakes Friday.  Winds will increase from the northwest Friday
afternoon in the wake of the front...gusts may kick up to 30 knots
over the eastern half of Lake Superior.  More substantial winds are
likely Sunday as a sub 985mb low is forecast to lift northeast
across Lake Superior.  Some easterly gales may occur Saturday night
to the north of the approaching surface low...with winds veering to
west Sunday with more gale force gusts likely especially over the
eastern half of Lake Superior.


Upper Michigan...
  Winter Weather Advisory from 1 AM to 1 PM EST Friday for MIZ006-

  Winter Weather Advisory from 10 PM EST /9 PM CST/ this evening
     to 10 AM EST /9 AM CST/ Friday for MIZ002-004-005-009>013-

  Winter Storm Warning from 10 PM this evening to 10 AM EST Friday
     for MIZ001-003.

Lake Superior...
Lake Michigan...


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