Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 191943

Area Forecast Discussion
National Weather Service Marquette MI
243 PM EST Mon Feb 19 2018

Issued at 1049 AM EST MON FEB 19 2018

Western counties have been added to winter wx advy. Ongoing fgen is
leading to band of fairly hvy snow extending from nw WI to around
Houghton. While models don`t suggest this band will remain well-
defined thru the day, radar indicates additional snow development
filling in farther s. For now, expect snow accumulations of at least
2-4in thru this aftn, warranting advy issuance. Will carry advy into
Tue morning for the combination of lighter snow and some light
icing, especially se portions of the new advy area. No meaningful
changes have been made to the rest of the fcst area.

.SHORT TERM...(Today and tonight)
Issued at 458 AM EST MON FEB 19 2018

Short term forecast is dominated by complicated mixed precip, so
will be general with exact timing of various precip type changes and
focus on amounts.

Precip will spread from W to E today while intensifying. Primary
ptype will be snow over roughly the NW half of the U.P and freezing
drizzle/rain with some snow mixed in over the SE half. Greatest
impacts today will be this afternoon and early evening when precip
will be most intense. Expect 2-3 inches of snow over the N-central
and western U.P. today and an inch or less elsewhere. Ice amounts
are forecast to range between 0.10 inches over the E half and S-
central to a couple hundredths of an inch from near Iron River to

For tonight, have generally light precip all night, but with
gradually reducing intensity through the night. Expect a mix of snow
and freezing drizzle over roughly the NW half, favoring snow earlier
in the night and a mix or more freezing drizzle later in the night.
Over the SE half, mainly freezing drizzle will be favored. Only 1-2
inches of snow expected over the NW half with ice amounts ranging
from a glaze over the far W and Keweenaw to 0.10 inches over
Marquette and Dickinson Counties. Exact precip amounts especially
over the NW half will depend on exact moisture levels in the DGZ and
microphisical processes that are difficult to predict. Over the S-
central and E half, generally 0.10-0.20 inches of ice is forecast.

No changes were made to headlines.

.LONG TERM...(Tuesday night through Monday)
Issued at 242 PM EST MON FEB 19 2018

More active winter weather possible late this week into next weekend
as general troughing over west half of Conus contiues to send systems
toward Great Lakes.

Active weather occurring early this week settles down considerably
as early as Tue night as sfc low exits into Quebec and quasi
stationary boundary moves to the lower Great Lakes. High pressure
over northern Plains then builds over western Great Lakes through
Wed. Colder air (h85 temps down to -18c) works in on northwest low-
level winds so there may be light lake effect for northwest to west
flow snow belts. However, do not expect much LES this time around
since area is within dry slot of H85 low lifting toward James Bay
resulting in minimal large scale low-level moisture. Another
negative for LES is expansive ice on western Lk Superior. Will only
have slight chance pops for mainly the Keweenaw late Tue night into
Wed morning. Expect partly to mostly cloudy skies along Lk Superior
and east for much of the day but skies should clear out Wed night.
High pressure and light winds along with pwats less than 0.10 inch
point to min temps dropping well below zero inland. Used colder WPC
and GEM bias corrected guidance.

High pressure will keep conditions dry over Upper Michigan on Thu
though increasing high clouds will signal the return of another
system lifting into the region from the central Plains. Shortwave
and area of q-vector convergence with H85 wave and moisture
advection appear to be main drivers for the light snow. Not much
enhancement coming from upper level jet as its primary lifting
influence stays south and east of here closer to sfc front and
baroclinic zone. Real good agreement from model qpf and GEFS
ensembles for a 6-12 hour period of light snow with QPF amounts
staying less than 0.25 inch. SW flow ahead of H85 low tries to bring
warmer air into the western Great Lakes, but right now looks like it
stays cold enough for just snow as ptype across all of Upper

After a break on Sat, another system could move in late Sat night
into Sun as shortwave trough rides across the Great Lakes downstream
of broad trough aloft over west half of Conus. There are expected
model differences that far out though. Main difference is GFS taking
shortwave/sfc low farther south across the Ohio valley while
ECMWF/GEM and GEFS would bring system farther north across central
Great Lakes. Latest GFS continues to keep U.P. dry on Sun while
other guidance has at least light qpf over much of Upper Michigan.
ECMWF would even bring moderate qpf over 0.25 inch across parts of
Upper Michigan. Probably stays cold enough for just snow for this
system as well. Another weaker system may move in on Monday, but
there are too many differences to go with anything more than slight
chances. Other than chilly night Wed night, temps through the long
term should be normal or even above normal.

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1227 PM EST MON FEB 19 2018

IFR conditions (vis and/or cigs) will mostly be the rule thru this
fcst period at KIWD/KCMX/KSAW as waves of pcpn move ne across the
Upper Lakes. While pcpn should be only snow at KIWD/KCMX, snow at
KSAW will likely mix with or change to -fzdz at times tonight thru
Tue morning. May even be a period of only -fzra Tue morning.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 242 PM EST MON FEB 19 2018

May see northeast gale gusts to 35 knots over western sections of Lk
Superior through tonight. Otherwise, winds are expected to stay
below gales the rest of the forecast period. &&

Upper Michigan...
  Winter Weather Advisory until midnight EST /11 PM CST/ Tuesday
     night for MIZ006-007-012>014-085.

  Winter Weather Advisory until 7 PM EST /6 PM CST/ Tuesday for

  Winter Weather Advisory until 1 PM EST /noon CST/ Tuesday for

Lake Superior...
Lake Michigan...


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