Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 070939

Area Forecast Discussion
National Weather Service Marquette MI
439 AM EST Thu Dec 7 2017

Issued at 956 PM EST WED DEC 6 2017

Considerable/dramatic drying was noted on KINL/CWPL soundings from
12z/6 Dec to 00z/7 Dec. Models have a good handle on bringing this
drier air southward across the area overnight into Thu morning. Per
obs and webcams, it appears LES has been light over the Keweenaw for
the last several hrs. Given the incoming dry air, opted to drop
Keweenaw advy. Across the rest of western Upper MI, it`s still
snowing at a decent clip locally, and will allow ongoing headlines
to expire as scheduled. To the e, deeper moisture is a little slower
to depart. Opted to extend Marquette county advy out to 12z though
extension is in reality just for a small part of the county. Area in
question relates to potential of land breeze aided convergence band
to set up and stream from around Big Bay into the area btwn Harvey
and Shot Point. That said, setup is not as favorable as desired
since winds won`t be more northerly across the lake to provide
stronger convergence near the Marquette county shoreline. Ongoing
headlines farther e are on track. LES from Marquette county eastward
will rapidly diminish late tonight/Thu morning as sharp drying

.SHORT TERM...(This evening through Thursday)
Issued at 416 PM EST WED DEC 6 2017

...Significant lake effect snow will continue into tonight as winds
gradually diminish...

Strong storm system over James Bay will continue to fill/weaken as
it moves slowly ne into northern Quebec later tonight. As a result
winds which have shifted from w to nw with a trough moving south
across Lake Superior will gradually weaken into tonight. Already
seeing signs of gradual weakening of winds over the Keweenaw and
expect further diminishment of winds across the area later tonight
as sfc ridging builds in from Ontario and the Northern Plains.

This evening into Tonight, troughing and deeper moisture along with
a shortwave moving across the Upper Great Lakes (as noted on water
vapor imagery) is supporting wnw wind flow moderate to heavy lake
effect shsn into Upper Mi. Winds continuing to veer nw into tonight
will push les bands farther inland this evening. As winds shift more
nw into this evening, best low-level wind convergence will shift
focus for heavier les bands into Gogebic-Ontonagon and Alger-Luce
and northern Schoolcraft counties as suggested by much of the high-
res model guidance.  850 mb temps close to -16C, deeper moisture
into this evening, weak enhancement by shortwave and favorable snow
growth with much of lake convective layer placed within DGZ should
result in moderate to heavy les bands through at least this evening
with typical accumulations of 3-5 inches with locally higher accums
near 8 inches over favored higher terrain areas, especially the
Porkies over the west.

As for headlines, since best les bands have for the most part
shifted south of the Keweenaw Peninsula and vsbys have improved
there due to weaker wind and less snow have decided to drop the
winter storm warning and transition to a winter weather advisory
into this evening. Advisories for Gogebic-Ontonagon and Baraga-
southern Houghton still look good through this evening for
moderate to occasionally heavy les. Also included Marquette County
in an advisory into early overnight mainly for the potential of
higher accums near 7 inches over the highlands of western
Marquette County and for areas over far eastern MQT county. The
city of Marquette will probably see closer to 3 inches total
accumulation. Not expecting much accumulation from Gwinn southward
given nw wind direction. Eastern counties will have potential for
les to last longer through night and possibly into Thu morning
with the potential for a more dominant band setting up around
Munising area as Lake Nipigon connection over Ontario lengthens
fetch across eastern Lake Superior. Kept advisory up there through
tonight and expect accums of 4 to 8 inches with locally higher
amounts of 10 inches or more into Thu morning before les
dissipates and shifts east with ridging and drier working in from
the west.

Thursday, weak sfc ridging into the nrn Great lakes will bring
backing winds and lowering inversion heights to around 3k ft even as
850 mb temps remain around -16C. With nw winds shifting to the west,
expect diminishing LES with additional accumulations of 1-3 inches
over western counties and eastern counties along shoreline east of

.LONG TERM...(Friday through Wednesday)
Issued at 439 AM EST THU DEC 7 2017

The extended forecast will continue the trend of near to below
normal temperatures along with a very active lake effect snow
pattern through the entire period.

Generally expecting northwesterly flow aloft into the Upper Great
Lakes region, bringing the continued cold air into the area. 850mb
temperatures are expected to be in the -12C to -18C range through
much of the extended, which will be plenty cold enough for continued
lake effect snow downwind of Lake Superior. For the most part, west
to northwest wind favored snow belts will be the favored lake effect
areas; however, there are a couple clipper systems that will drop
850mb temperatures to around -20C and help to turn the winds a bit.

Friday into Saturday: A couple quick moving clipper systems will
slide through during this time period. This will allow 850mb temps
to drop down near -20C, helping to steepen the overwater
instability. The surface pressure pattern would initially favor west
to northwest wind favored snowbelts Friday; however, as a surface
low shifts off to the south of the U.P. Friday night through
Saturday, winds will turn more northerly. This would give most
locations along Lake Superior a good shot at at least moderate lake
effect snow. Snow ratios look to be a little better during the
Friday night into Saturday time period as the wave slides through
with fairly light winds through and below the snow growth layer.
Good forcing and instability in the snow growth layer along with
inversion heights reaching close to 10 kft also point to an uptick
in the snowfall intensity Friday night into Saturday morning. At
this point, blending some hi-res qpf guidance gives several inches
of snow from Friday night into Saturday morning especially for north
wind favored snow belts. The heaviest snowfall totals are expected
over the high terrain of the west and over the high terrain of the
north central U.P. Current thinking is that 4 to 8 inches of fluffy
snow may fall in the aforementioned areas with locally higher totals
possible by early Saturday afternoon. Elsewhere along Lake Superior
will likely see totals around 3 to 6 inches. A headline will likely
be need for this time period, Friday night into Saturday morning.

Sunday into Sunday night: Another quick moving clipper-type system
is progged to slide through the Upper Peninsula. This will again act
to steepen the lapse rates enough to enhance the lake effect snow
downwind of Lake Superior. This will be a similar type setup as the
Friday night into Saturday setup, except not quiet as strong and a
little quicker. Initially the lake effect snow would be confined to
the west wind favored snowbelts Sunday morning; however, as the low
shifts to the east of the U.P., winds are expected to once again
shift to the north and northwest, giving most areas light to
moderate snowfall along Lake Superior.

Monday into Tuesday: Yet another fairly strong shortwave, in the
active weather pattern, will slide through the Upper Peninsula
Monday through Tuesday morning. Winds look to be north to north-
northwest through this time period, allowing for yet another period
of enhanced lake effect snowfall downwind of Lake Superior. Again,
moderate lake effect snow is possible for the north to north-
northwest wind favored snow belts and as is typical, the greatest
totals are expected over the higher terrain of the north central
U.P. and over the higher terrain of the west.

Rest of the Extended: Active cold weather pattern is expected to
continue with another shortwave progged to slide through the area
Tuesday night into Wednesday. At this point, will stick with a
consensus of the models, giving good chances of lake effect snowfall
along Lake Superior, especially in the north to northwest wind
favored snowbelts.

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1157 PM EST WED DEC 6 2017

Much drier air spreading s across the area overnight into the
morning hrs will cause lake effect shsn to diminish from w to e.
At KIWD, expect prevailing MVFR conditions to improve to VFR this
aftn, then fall back to MVFR this evening as next disturbance
approaches. At KCMX, MVFR conditions should mostly prevail into the
aftn. There may be some brief periods of IFR overnight, then w winds
and an approaching disturbance should lead to an increase in lake
effect shsn at KCMX late this aftn/evening, dropping conditions back
to prevailing IFR. At KSAW, conditions should vary btwn VFR and MVFR
thru the morning hrs before becoming VFR.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 439 AM EST THU DEC 7 2017

Winds are expected to remain in the 20-30 kt range into early next
week as an active weather pattern keeps a fairly tight gradient
across Lake Superior. Freezing spray is expected through Friday
night and again late Monday into MOnday night. Air temps staying
mainly in the 20s should prohibit heavy freezing spray through this
time period.

Upper Michigan...
  Winter Weather Advisory from 3 PM this afternoon to 10 AM EST
     Friday for MIZ001>004-084.

  Winter Weather Advisory until noon EST today for MIZ006-007-085.

  Winter Weather Advisory until 7 AM EST this morning for MIZ005.

Lake Superior...
  Gale Warning until 5 AM EST early this morning for LSZ244-245-

Lake Michigan...


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