Area Forecast Discussion
Issued by NWS Marquette, MI

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000
FXUS63 KMQT 132043
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
443 PM EDT Fri Apr 13 2018

...Significant Winter Storm Expected This Weekend...

.SHORT TERM...(This evening through Saturday)
Issued at 410 PM EDT FRI APR 13 2018

Sharp upper level trough is present this aftn over the Plains
with strong sfc low of 990mb near Omaha. Sharp warm front extends
over northern Ill to northern Ohio. A bit farther south than was
projected at this time yesterday. Mid level front has also set up
farther south, mainly across central WI to lower Michigan. Plenty
of instability along and south of the mid- level front has
resulted in clusters of thunderstorms with some lightning as far
north as Green Bay and Gaylord. Though it has been pretty calm
over Upper Michigan today, there has been interesting day in the
region with thundersnow at Gaylord in northern lower Michigan and
a seiche down across central Lake Michigan. Precip has been slow
to arrive over scntrl Upper Michigan due to dry air north of the
mid level front and rain has finally developed at Menominee in the
last hour.

For tonight, cross sections of frontogenesis and associated
circulation point to narrow ribbon of lift only making it into
mainly Menominee county. Lift will be enhanced by negative epv atop
the fgen layer so there could be heavier banded precip. Ptype though
starting as rain should quickly turn to snow by late evening.
Continued to highlight southern Menominee county for 3 to 5 inches
of snow overnight. Isolated higher totals, maybe over 6 inches,
would be possible well south of US-2 toward Menominee. Snow should
be finished up around daybreak Saturday. High dwpnt depressions and
sharp cutoff to the north edge of fgen should result in minimal if
any snow farther north of US-2.

Not much change to forecast for Sat. Generally the quiet before the
storm as upper low and sfc lows remain well to the southwest of
Upper Michigan through most of the day. Main issue will be gusty
northeast winds, possibly with gusts over 30 mph near the Great
Lakes. Beneath a mostly cloudy sky and in cold air advection regime
to the north of sharper front that moves to the south tonight, temps
will be significantly below normal with readings only reaching the
mid 20s to near 30F. Have some slight chances for snow returning
very late in the day near the WI border.

.LONG TERM...(Saturday night through Friday)
Issued at 435 PM EDT FRI APR 13 2018

Saturday night through Sunday night:

Well-advertised, aforementioned (above) strong low pressure system
will move into the lower Great Lakes region on Sunday, with a slower
trend in its progression depicted in the latest model runs. Concern
at this point is not whether or not the forecast area will see
moderate to heavy snow, but attempting to hone in on the finer
details, such as timing of onset of precip, as well as QPF amounts
and subsequent snowfall totals. Parent upper-level trough will
become increasingly negatively tilted overnight Saturday into
Sunday, with Upper Michigan poised to reside in the deformation zone
of the low. Exactly where the low ends up tracking will be what
defines the final snow totals that will end up falling.

12Z GFS has come more in line with the recent runs of the ECMWF,
with some notably different tracks between the four lower-res
models in the 48hr to 60hr (based on 12Z run) time frames. That
said, there is enough continuity at this point to conclude that
the GFS does not appear to have the greatest handle on the
deformation zone precip that is expected to be the primary driver
of the heaviest snowfall, in addition to the localized impacts of
the terrain playing a factor in snow totals, leading to having
greater uncertainty in the western extent of the snow band`s
impacts and amounts.

Bottom line is that highest snow amounts currently look to reside
primarily east of U.S. Hwy 141 and west of Schoolcraft and Alger
counties. Part of this is due to upsloping effects considering the
backing ENE to NE winds prevailing on Sunday, which could produce a
bullseye of highest amounts in central Marquette County. However, it
cannot be stressed enough that there is still ample time for this
forecast to change, especially given that higher-res models haven`t
picked up the system yet, and a number of factors, including snow
ratios, could significantly impact snow totals. Therefore, it`s
critical to focus more on the impacts of the expected winter
weather rather than the amounts. Those impacts include difficult
travel conditions given the wetter snow (thanks to lower snow
ratios, looking to range in the mid teens) with breezy conditions
expected as compared to what`s more typically seen in the winter
season.

Monday through Monday night:

As the low crosses the Great Lakes region, drier air aloft feeding
into the backside of the system looks to throw a wrench into
precipitation type. Essentially, for the eastern portions of the
Upper Peninsula, mixed precipitation, primarily snow and/or freezing
rain/drizzle, could be the dominate type, especially during the
daytime hours Monday as highs attempt to rise above the freezing
mark. Overall though, while an additional inch or two of snow could
be possible for typical lake effect locations on Monday, total
wintry precipitation amounts look to be minor, with little to no
ice accumulations anticipated (thanks to the increasing April sun
angle). Same caveats apply to this time period given that there
is still ample opportunity for the forecast to change.

Tuesday onward:

Tuesday, the Upper Peninsula will be between systems, with brief
local ridging keeping conditions dry during the daytime. Another
shortwave and associated sfc low pressure system is expected to
deepen as it moves out of the Plains and into the Great Lakes
Wednesday. GFS has come more into agreement with the EC track,
bringing the center of sfc circulation ENEward across southern WI
into central Lower MI, although the CMC actually tracks the low more
from the WNW to the ESE into the Ohio River Valley. If the GFS/EC
win out, this would be a widespread 2-5" snow event, although
daytime temperatures may warm up enough to mix in a little rain
south-central. Some additional light lake effect is possible behind
the system Wednesday night and Thursday. Indications are that we
should dry out on Friday with broad high pressure building over the
central CONUS, and may finally warm back towards seasonal highs.
&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 146 PM EDT FRI APR 13 2018

Expect IWD and CMX to remain VFR through midday Sat. SAW will see
some sct-bkn MVFR stratus. Uncertain in whether we`ll see enough
moisture for a ceiling to develop so kept it above more critical
threshold of 2kft AGL. Could see a few flurries at IWD and SAW
late today into this evening. Northeast winds will be increasing
through the period ahead of a low pressure system.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 410 PM EDT FRI APR 13 2018

As a strong low pressure system slides toward the area through the
weekend, winds will continue to increase across Lake Superior. Gales
of 40-45 knots are expected over western Lake Superior possible late
tonight through Saturday night. Gales around 35 kts are expected for
the rest of Lake Superior for the same time period. Gales will
slowly diminish to 30 kt winds on into Monday. Winds for the rest of
next week should settle down below 25 kts. Heavy freezing spray will
be an issue through the weekend as a winter time pattern prevails.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Storm Watch from Saturday evening through Monday morning
     for MIZ001>006-009-084.

  Winter Storm Watch from Saturday evening through late Sunday
     night for MIZ007-010>014-085.

  Winter Weather Advisory from 7 PM this evening to 7 AM CDT
     Saturday for MIZ012.

Lake Superior...
  Heavy Freezing Spray Warning from 6 AM to 4 PM EDT Saturday for
     LSZ243>251-263>267.

  Gale Warning from 2 AM Saturday to 2 AM EDT Monday for
     LSZ243>251-264>267.

  Gale Warning from 8 PM EDT /7 PM CDT/ this evening to 2 AM EDT
     /1 AM CDT/ Monday for LSZ162-240>242-263.

Lake Michigan...
  Gale Warning until 8 PM EDT Sunday for LMZ221-248-250.

&&

$$

SHORT TERM...JLA
LONG TERM...lg/KCW
AVIATION...JLA
MARINE...JLA



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