Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 201137

Area Forecast Discussion
National Weather Service Marquette MI
637 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

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

.LONG TERM...(Sunday through Friday)
Issued at 529 AM EST SAT JAN 20 2018

...Impacts from potential winter storm likely Monday into Tuesday...

Sunday into Sunday night: Several models suggest a fgen band forming
across south central Upper Mi on Sun in response to upper divergence
in the right entrance region of a 150+ kt 250 mb jet max across
eastern Ontario/western Quebec. Models however indicating fairly
light pcpn with this band (only the NAM printed out a few hundreds
QPF) mainly in form of wet snow which would amount to half an inch
of snow accumulation or less. Max temps on Sunday will remain above
normal with highs in the lower to mid 30s. Models now trending
slower with arrival of pcpn Sun night in advance of approaching
system from the Plains. If any areas see snow Sun night it looks
like it would be late along the Wi border counties.

Attention turns to the approaching winter storm from the Central
Plains expected to impact the Upper Great Lakes Monday into Tuesday.
00Z GFS/NAM and GEM runs in fairly good agreement taking the
developing storm system from the Central Plains late Sunday across
central/northern Lower Mi late Monday night/early Tuesday. The 00z
ECMWF is farther north with sfc low track than GFS/NAM/GEM consensus
but is fairly consistent with these models showing the swath of
heavier system snow across central and eastern Upper Mi Monday
afternoon into Monday evening with dry slotting moving into south
central and eastern Upper Mi overnight Mon night which could result
in some frdz or fzra mixing in with lighter snow over these areas of
the cwa. Given continued model uncertainty, trends toward a slower
arrival of system pcpn on Monday and the threat of a mid-level dry
slot potentially cutting into total snow amounts across portions of
the fcst area later Mon night, have decided to hold off on issuing
winter storm watches for this system.  Instead, will update the SPS
and continue to highlight uncertainty with the storm track and where
the heavier system snowfall will occur. This will also allow the day
shift to look at a model run where hopefully the main shortwave
associated with this system can be better sampled by RAOB and sfc
observing networks as it moves onshore this morning off the southern
CA coast.

As the storm system departs east late Tue and sfc ridging moves
behind it Tue night into Wed, lake effect snow should taper off
and/or become confined to the Keweenaw and far eastern shoreline
areas of cwa. After a period of quieter and milder trending weather
Thu into Fri under a mid-level ridge, models indicate that a trough
will move in from the Plains and impact the western Great Lakes
region with another low pressure system for next weekend.

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 636 AM EST SAT JAN 20 2018

MVFR cigs have spread into much of nw and n central Upper MI early
this morning. Expect these MVFR cigs to continue at KCMX/KSAW thru
the morning hrs though the clouds may scatter out at times. Less
confidence in how long the MVFR cigs may persist in the aftn, but
expect clouds to scatter out at KSAW by mid aftn and at KCMX by late
aftn. KIWD should remain VFR thru the day. Diminishing winds toward
calm tonight along with elevated dwpts may lead to radiational fog
and perhaps stratus development tonight, but expectation of
considerable high and mid clouds should preclude development. For
now, maintained VFR conditions thru the end of the fcst period at
all terminals.

.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.

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


SHORT TERM...Rolfson
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