Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 170800

Area Forecast Discussion
National Weather Service Marquette MI
300 AM EST Sat Feb 17 2018

.SHORT TERM...(Today and tonight)
Issued at 300 AM EST SAT FEB 17 2018

Upper air pattern consists of a 500 mb broad trough over the central
U.S. with a ridge off the west coast. There is also a shortwave over
the northern plains this morning. This shortwave heads east and
moves through the area today. Pretty dry conditions exist upstream
of the area as evidenced by 00z MPX sounding and there is an awful
lot of dry air to overcome. For this reason, kept pops pretty low
for the west half today. Overall, did not make too many changes to
the going forecast.

.LONG TERM...(Saturday night through Friday)
Issued at 344 PM EST FRI FEB 16 2018

...Active period of winter weather expected starting Sunday...

Broad upper trough across northern half of the Conus transitions to
more of a western Conus trough and southeast Conus ridge most of the
upcoming week. That can be an active pattern across the Great Lakes,
but at least not a significantly cold one. Lead shortwave/sfc low
move in Sun and another more complex weather system moves through
Mon and maybe another system affects the area Tue before things
settle down for mid week. WV loop and modeled H5 heights indicate
the Sun system traces to shortwave trough currently dropping across
British Columbia while the Mon system traces to much stronger
shortwave and sfc low currently along southern coast of AK. After a
very quiet period of winter weather first part of this month, these
two systems will bring return of active synoptic weather.

Main trend in model guidance for the first system is for quicker
arrival of snow on Sun. Main time of snow for most areas will be
late Sun morning through early Sun evening. Shortwave and H85 low
start out sharper over northern Plains then shear out while moving
into more confluent flow aloft. Even with that negative factor,
could see several inches of snow over Upper Michigan as right
entrance region of jet and H85-H7 frontogenesis support swath of
snow moving west to east across Upper Michigan, mainly over north
half. Generally looking at total amounts by midnight Sun night of 2
to 4". Little snow is expected south central, south of Iron Mountain
and Escanaba. Banded enhancement of snow possible due to negative
EPV atop the fgen layer. SLRs near 20:1 result in fluffier snow.
Best chance for high end advisory snowfall (4-6") will occur over
far west and Keweenaw. Given the high SLRs and banded snow potential
from the system though, could see snow amounts end up higher than
these projections in some areas. No real strong winds expected so
the snow will be the main hazard from this first system. Pinning
down the stronger fgen/banded snow areas will be main key for the
system and that will be more of a near term forecast issue later
this weekend.

Next system is a bit more complicated in its dynamic makeup as
appears that there will be two jet streams (polar and sub-tropical)
coming together late Sun night into Mon to bring the system into the
Upper Great Lakes. Most of the precip initially upstream of Upper
Great Lakes will be along sub-tropical jet in form of rain/freezing
rain across mid Mississippi River Valley while the main area of snow
will be expanding across the northern Plains on front side of larger
troughing aloft and along axis of polar jet. Should see snow spread
into Upper Michigan from the west as mid-level fgen develops to the
north of H85 low that moves from Omaha daybreak Mon to Green Bay by
Mon evening. Though main sfc low and trough is forecast to stay to
the south of Upper Michigan, fgen forced snow, helped by divergence
aloft from upper jet, should expand as H85 low and moisture
advection (H7 mixing ratios over 3g/kg) moves in through the day.

That said, strongest moisture advection will stay south and east of
Upper Michigan though, closer to the sfc low/trough. For a more
certain heavy snow event, especially with lower SLRs as expected,
would like to see either a stronger shortwave trough/deformation
area over our region and/or strongest moisture advection pointed
into Upper Michigan. Neither is shown at this point and think the
models all along coming in with 0.25-0.50 inch of qpf supported by
ensembles makes sense. Latest GEM seems to be running hot with qpf
compared to other guidance for both Sun and Mon events. The GEM
would easily support warning amounts on Mon as it shows almost 0.80
inch of liquid in 12 hours from 12z-24z. On the other end of the
spectrum is the ECMWF which barely cracks 0.30 inch of qpf during
that time. GFS is more toward ECMWF but does push qpf totals up to
around 0.5 for some areas. Given the negatives mentioned already
with how the forecasts for this system are coming together and
consistent signals of lower qpf from ensembles, will not head toward
the wetter GEM idea attm. Overall looks like a wetter 2-4"/3-5" type
snowfall over much of Upper Michigan. Impact could still be higher
though due to the wetter nature of the snow and timing as it will
impact the evening commute on Mon. Also still looks breezy along Lk
Superior with some blowing snow. At this time, greatest potential
for mixed precip, including freezing rain, would occur late Mon
afternoon into Mon evening along Lake Michigan as there is decent
agreement of H85 warm layer up to 1-2c briefly pushing into the

Things get tricky for late Mon night into Tue across the region as
with larger scale upper level trough still well upstream over
western Conus, additional waves of precip are expected to lift into
the Great Lakes. Pretty decent indication of stronger low pressure
wave/heavier qpf lifting across mainly central Great Lakes on Tue.
Main impact from this system probably will stay south and east of
Upper Michigan though ECMWF would suggest glancing blow could occur
for south and east forecast area. Will have to keep eye on this
though as indications there could be freezing rain/significant icing
on northern fringe of this system with warm layer aloft over 5C
progged while sfc temps are progged 25-32F. Spells trouble no matter
how you look at it.

Generally looks quiet behind all of the early week winter weather.
Could be another system affect the region late in the week as broad
trough stays in place over west half of the Conus. And with that
upper level pattern staying in place, no real cold intrusions are
expected through the next week.

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1157 PM EST FRI FEB 16 2018

VFR conditions will prevail at KIWD/KCMX/KSAW overnight. Ahead of an
approaching disturbance, low-level winds have strengthened just off
the sfc, and this will lead to LLWS into the morning hrs. As the
disturbance moves across the area today, some light snow will be
possible. Best chance of MVFR cigs and light snow will be at KCMX.
Clouds will scatter out during the evening.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 300 AM EST SAT FEB 17 2018

A few southwest gale force gusts to 35 knots could still be possible
today. Otherwise, winds are expected to stay below gales through the
rest of the forecast period.

Upper Michigan...
Lake Superior...
Lake Michigan...


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