Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 200931
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
431 AM EST Sat Jan 20 2018

.SHORT TERM...(Today and tonight)
Issued at 430 AM EST SAT JAN 20 2018

A quiet short term period is shaping up. Arctic cold front trailing
from vigorous low pressure tracking across Quebec, east of James
Bay, is currently just n of Lake Superior and drifting s. Ahead of
this front, fcst area is awash in Pacific air early this morning.
With exception of localized spots which have decoupled, allowing
temps to drop down into the 20s, much of the fcst area has temps
currently in the 30s, some close to 40F...unusually warm for what is
traditionally the coldest time period of the year. To the n of the
arctic cold front, temps drop down toward -20F in far northern
Ontario.

With mid-level flow across the Upper Lakes parallel to the arctic
cold front and with a weak shortwave tracking e and possibly
supporting a very weak sfc low pres wave along the front late
aftn/evening, the arctic front will only slowly drift s today,
aligning from near Isle Royale to Copper Harbor to n of Whitefish Pt
this aftn. So, under a Pacific air mass, it will be another warm day
for mid Jan, especially given the warm start to the day. Expect
highs in the mid 30s to lower 40s. There is low-level
moisture/stratocu across ne MN and portions of the Keweenaw. Low-
level winds suggests the stratocu should tend to expand across at
least the northern and eastern fcst area today. Should these clouds
become more dominant, highs will be a little cooler than expected.
On the other hand, if there is less stratocu/more sunshine, more
locations will top 40F.

Arctic front may drift slightly ne this evening in response to
possible weak low pres wave tracking along it. So, it will be a mild
night for mid Jan, though not as warm as it is early this morning.
Under baggy pres gradient, winds will be light/calm tonight,
supporting a better temp fall. Overall, expect min temps in the 20s
with at least considerable high cloudiness keeping temps higher than
they would be otherwise. 140-150kt upper jet will extend from ne MN
to Maine. Upper divergence in the right entrance of this jet and
corresponding fgen in the mid levels could support a narrow streak
of -sn across central MN to s central Upper MI late tonight.
However, models have been generally trending away from this idea.
For now, will only include slight chc pops far s central very late
tonight.

.LONG TERM...(Saturday night through Friday)
Issued at 406 PM EST FRI JAN 19 2018

...A winter storm remains possible Monday into Tuesday...

Overall, the main forecast concern remains with the possible winter
storm Monday into Tuesday. Those who have travel plans across Upper
Michigan should monitor the forecast over the up and coming days
closely, as the details in regards to this system and possible
impacts will be refined.

Potential Winter Storm Monday into Tuesday: Over the next few days a
longwave trough is progged to push onshore and track across the
western and central CONUS, favoring the development of a lee cyclone
across the central Plains which will gradually lift northeast across
northern Illinois and lower Michigan Monday through Tuesday. This
system will bring wintry precipitation to the region; however, at
this time the track of the axis for wet, heavy snow and the onset of
this wintry precipitation remains uncertain across Upper Michigan.
The GFS and the tail-end of the NAM favor a more western track with
the heavier band of system snow; whereas, the ECMWF and Canadian
track this band across central Upper Michigan. Forecast sounding
show some locations, mainly across the south-central and along Lake
Michigan, may see periods of freezing drizzle as we lose the deeper
moisture and lift. But to reiterate, this will be highly dependent
on the track of the system. Given the uncertainty, opted to hold off
on issuing a winter storm watch and opted to update the Special
Weather Statement to highlight and draw attention to this time
period. Over the next day or so, once we start to get better
sampling across the RAOB network the expected hazards and impacts
will become more clear.

After the system exits the region, we could see a brief period of
lingering lake effect snow through the middle of the week, but this
will be highly dependent on how cold 850mb temperatures get. We
should see a break in the wintry precipitation towards the end of
the week as high pressure tracks across the region, before another
round of warm air advection is progged to return and favor the
development of rain/snow.
&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1206 AM EST SAT JAN 20 2018

Mainly VFR conditions will prevail at all sites with mid to upper
level clouds although there may be a period of MVFR or near MVFR
cigs at KCMX this afternoon. A vigorous low-level jet will result
in LLWS at KSAW for a few more hrs.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 430 AM EST SAT JAN 20 2018

Strongest winds on Lake Superior during this fcst period will occur
Mon into Tue as low pres tracks from the Southern Plains, across
northern Lower MI and then ene from there. NE to N gales are
expected across most of Lake Superior Mon into Tue morning with
heavy freezing spray Mon night through Tue night.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Rolfson
LONG TERM...Ritzman
AVIATION...JLB
MARINE...Rolfson



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