Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 150951

Area Forecast Discussion
National Weather Service Marquette MI
451 AM EST Mon Jan 15 2018

.SHORT TERM...(Today and tonight)
Issued at 450 AM EST MON JAN 15 2018

...Moderate to heavy lake effect/enhanced snowfall potential
downwind of Lake Michigan this morning and then downwind of Lake
Superior late this afternoon through tonight...

Today: A surface low, centered over central and southern WI, is
continuing to allow southerly flow across Lake Michigan this
morning. This, along with an upper level closed low, is continuing
to provide support for lake effect/enhanced snow downwind of Lake
Michigan. 850mb temperatures are running around -14C to
-16C, which is cold enough for lake effect/enhancement. Radar
continues to show the very strong lake effect/convergence band
running from the Door Peninsula northward into Delta and far western
Schoolcraft county this morning. Some the heavier snow is even
making it into portions of Alger County. By mid to late morning and
into the afternoon hours, the aforementioned surface low is progged
to shift over southern Lower Michigan, which will allow easterly
flow to develop across all of the CWA. This will shift the lake
effect/enhanced bands to easterly wind favored snow belts over the
north central U.P. and Keweenaw off Lake Superior and south central
U.P. off Lake Michigan. South central will continue to see the
Winter Weather Advisory through this afternoon, while the north
central U.P. will see the Winter Weather Advisory come into effect
this evening as winds shift more northeasterly. Inversion heights
will continue to be around 10kft as the upper level low slides
overhead with fairly deep moisture lingering in the DGZ. This will
help to boost SLRs for the favored snow belts. The better system
forcing will exit to the east of the area; however, overwater
instability and upslope flow will allow for some heavier snowfall to
continue south central and develop over the Keweenaw and north
central U.P.

Tonight: As the surface low continues to shift off to the east,
winds will back from the east to northeast across the area. This
will effectively end any lake effect/enhancement off Lake Michigan;
however, lake effect snow will increase downwind of Lake Superior.
The increased upslope flow over the north central U.P. along with
the increased fetch on north to northeasterly winds will allow for a
period of heavier lake effect snow this evening into Tuesday
morning. 850mb temperatures will cool further, to around -16C to -
18C, with inversion heights around 8kft - 10kft, which will continue
to be favorable for lake effect snow. Locations over the higher
terrain could end up seeing totals approaching 8 inches by the time
the snow tapers off Tuesday morning.  Again, the high terrain would
see the heaviest totals as better upslope/convergent signatures are
showing up over those areas. This has led to the issuance of a
Winter Weather Advisory for both Baraga and Marquette counties
tonight through Tuesday morning. Wouldn`t be out of the question to
see a few warning snowfall totals in the highest terrain of
Marquette and Baraga Counties as well. As winds shift to the north
and northwest, the western U.P. will also see some lake effect snow;
however, the wind shifts look to occur quick enough that the more
focused bands should be transient enough to keep snowfall totals in
check, generally in the 3 to 6 inch range in a 24 hour period.
Again, similar to the north central, the heavier snowfall totals can
be expected over the higher terrain.

.LONG TERM...(Monday night through Sunday)
Issued at 346 PM EST SUN JAN 14 2018

Building ridge over the western CONUS will reach peak amplitude
tonight/Mon with 500mb heights upwards of 400m above normal over nw
toward n central Canada. This will force a shortwave se and
reinforce/maintain current cold conditions over the Upper Lakes thru
Tue. Advertised warmup for the last half of the week is still on
track as the ridge deamplifies and shifts to the E Coast by Sat in
in response to a trof swinging from the ne Pacific into the western
CONUS. As a result, Pacific air will push across the CONUS this
week. This pattern change is consistent with the signal from the
current active MJO over the Indian Ocean, in phase 3, which favors
western N America troffing and eastern N America ridging. Unless the
MJO weakens, it will be a forcing mechanism for mild
conditions/above normal temps over the Upper Lakes for the next few
weeks, suggesting cold spells thru the end of Jan will be short-
lived. In the end, pattern will likely be more variable btwn above
and blo normal temps with warmer conditions more frequently
occurring. As for pcpn, pcpn will be largely lake effect driven thru
Tue under cold air mass. Shortwave reinforcing the cold for the next
few days will provide a period of widespread light snow for the fcst
area into Mon along with mdt to hvy lake enhanced snow off Lake MI
and also off Lake Superior into Tue morning. LES will end midweek as
much warmer air arrives, then there may be some light mixed pcpn
late week. With Pacific energy moving across the CONUS in the
overall mild pattern during the last half of the month, there should
be more frequent opportunities for storm systems/pcpn to affect the
area, but unfortunately, that may include mixed ptypes. The first of
these systems should impact the Upper Lakes late this weekend/early
next week.

As deepening trof over the western Great Lakes on Mon begins to
shift e Mon night/Tue, e to ne low-level flow across the Upper Lakes
to start Mon evening will back to the n and then nw. Much of the
light synoptic snow from Mon should be out of the area by evening,
and any lingering/diminishing lake enhanced snow off Lake MI into
Menominee county will end early. The backing winds will shift
attention to lake enhanced/lake effect snow off Lake Superior. This
snow (potentially mdt to hvy) will already be ongoing into the
Keweenaw under easterly flow to start the evening. Under backing
winds, mdt/hvy snow will swing into the rest of western Upper MI and
also n central Upper MI Mon night into Tue morning. Deep layer
forcing for upward motion will be diminishing and slipping s and e
during this time, but deep moisture and well positioned DGZ in the
lake induced convective layer will likely support a period of hvy
snow Mon night/Tue morning. Temp/moisture profiles look favorable
for amounts to exceed warning criteria locally in high terrain where
upsloping is maximized. Otherwise, the steady backing of winds will
work as a limiting factor. With blsn not likely to be much of an
issue since winds aren`t strong and since snow-to-water ratios are
likely to be quite high given the well positioned DGZ (lower impact
snowfall), a watch or warning issuance at this time is not
warranted. Advys will likely be needed at a later time. The morning
commute on Tue will be impacted. With loss of deep layer forcing and
eventually deep moisture from w to e Tue/Tue evening, lake enhanced
snow off Lake Superior will diminish and transition to lighter pure
LES from w to e Tue aftn/night. Backing wind from n to w will also
shift the lingering snow showers which will continue to diminish
under the start of waa Tue night.

Strong waa will already be underway by Wed morning, and this will
raise 850mb temps sufficiently to end LES. The strong waa/isentropic
ascent could generate some -sn on Wed over the far eastern fcst
area, but that looks doubtful. Better potenital of -sn will be
farther ne, deeper into retreating cold air where it`s easier to
erode antecedant dry low levels. Although the upward temp trend
begins Wed, gusty w to sw winds will add a chill. Temps will then
push above normal Thu thru the weekend. There may be some spotty
light mixed pcpn at times Thu night thru Sat under continued waa
pattern with the potential of a couple of shortwaves to pass across
the area. Any pcpn would be light if it occurs.

Over the weekend, trof that moves into the western CONUS late week
will shift out over the Plains on Sun with an associated sfc low
lifting ne from the Southern Plains toward the western Great Lakes.
GEM/GFS ensembles show quite a bit of spread in low track and
intensity as would be expected at this time range, but there is a
decent signal for a deepening sfc low lifting ne from the Southern
Plains, a rare occurrence for this cold season. At this point, it
looks like this system will spread pcpn into Upper MI on Sun, and
pcpn could be a variety of ptypes.

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1235 AM EST MON JAN 15 2018

Conditions at all the TAF sites will alternate between MVFR and IFR
in light snow through Monday morning. LIFR visibilities will be
possible at KCMX Monday afternoon into Monday evening when winds
become easterly bringing lake enhanced snow into the terminal. When
winds turn northeast late Monday evening persistent IFR conditions
in lake enhanced snow will be likely at KIWD into early Tuesday

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 450 AM EST MON JAN 15 2018

As low pressure tracks southeast of the area across Wisconsin and
southern Lower Michigan winds are expected to be in the 20 to 30
knot range through tonight. There may be a brief period of gales
or gale force gusts to 35 knots over the west half of Lake
Superior as funneling occurs on northeasterly winds. This would
be mainly during the evening hours. Only moderate freezing spray
is expected through the first half of the week. Tuesday through
the end of the week, expect winds to remain between 20 to 30 knots
with a chance for gales Wednesday. &&

Upper Michigan...
  Winter Weather Advisory until 9 AM EST this morning for MIZ006-

  Winter Weather Advisory from 7 PM this evening to 1 PM EST
     Tuesday for MIZ004-005.

  Winter Weather Advisory until 6 PM CST this evening for MIZ011-

  Winter Storm Warning until 4 PM EST this afternoon for MIZ013.

Lake Superior...
Lake Michigan...


LONG TERM...Rolfson
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