Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 082024

Area Forecast Discussion
National Weather Service Marquette MI
324 PM EST Fri Dec 8 2017

.SHORT TERM...(Today and tonight)
Issued at 453 AM EST FRI DEC 8 2017

A band of moderate to heavy lake effect snow associated with the
axis of a slow moving surface trough has pushed onshore east of
Marquette this morning. Across the west, lake effect snow has
begun to diminish in intensity as visibilities have improve
through the early morning hours. The light synoptic driven snow
across the interior portions of Upper Michigan has diminish from
north to south as the main forcing continued to dig southward.

Expect moderate to at times heavy lake effect snow mainly across the
east as the above mentioned band of lake effect snow continues to
push onshore. At times this band of snow may produce 1-2`` per hour
snowfall rates, resulting in reduced visibilities and deteriorating
travel conditions during the morning commute. With flow becoming
northwesterly behind the surface trough, expect this single band to
transition to multiple bands with impacts becoming a bit more
intermittent through the afternoon hours across the east. A few of
these bands may try to sneak into Marquette county, but due to the
northwest flow expect only the far northeast portions of the county
to be impacted, if at all. Out west, expect the light lake effect to
linger through the morning hours before diminishing in intensity.

Late this afternoon into the evening hours, expect the lake effect
snow to linger in the northwest wind snow belts. However, a clipper
system will dig across the region and bring widespread chances for
accumulating snow across the area, along with the potential for
moderate to heavy lake enhanced snow in the northwest to north wind
snowbelts late today through the overnight hours. While this clipper
system will be quick hitting, given the potent shortwave energy and
the left exit region of the northern jet tracking across the area,
ample synoptic-scale lift will be present. Therefore, we could be
looking at a sneaky event across the interior; however it does look
like SLRs will remain fairly high given the extent of the colder air
aloft. Near the shore of Lake Superior, initially we`re looking
across the western half of the area late this afternoon into the
overnight hours for the potential for moderate to heavy lake
enhanced snow, especially after the surface trough pushes through.
Into the overnight hours, flow behind the exiting clipper system
will veer northerly and allow lake enhanced/effect snow to
transition over the north wind snowbelts. This is especially notable
in the 1000-850mb omega fields as strong vertical motions are
present. Forecast soundings show a deep convective layer, with
equilibrium levels climbing to nearly 10k feet and much of the cloud
depth spanning the DGZ. This should be more than sufficient to
produce 2-3`` an hour snowfall rates in some locations, but it is
hard to discern where exactly these stronger bands will setup
tonight. Therefore, especially across the north central and east,
conditions will need to be monitored closely as winter weather
advisories may need to be upgraded to warnings.

.LONG TERM...(Saturday night through Friday)
Issued at 324 PM EST FRI DEC 8 2017

Strong ridge remains set up along the w coast of N America with
impressive positive height anomalies in excess of 350m at 500mb
centered over BC. This ridge will remain in place thru next week,
forcing a trof over eastern N America. However, the ECMWF ensemble
notably deamplifies the western ridge late next week, leading to
downstream deamplification of the trof. While this is seen in the
GFS and CMC ensembles as well, both of these ensemble systems show
some rebuilding of western ridging and some raising of heights over
Arctic which in turn strengthens troffing again over central/eastern
Canada into the n central to ne CONUS beyond 10 days. This pattern
will favor persistence of blo normal temps for Upper MI, but nothing
unusually cold for this time of year. There may be a tendency for
relaxing of the cold late next week into the early part of the
following week (week of the 17th), but restrengthening of
central/eastern Canada troffing suggests colder conditions will
follow. As for pcpn, this pattern will not favor any significant
winter storms for Upper MI for the foreseeable future. A series of
clipper type shortwaves will provide frequent opportunities for
widespread light snow over the next 7 days, but more importantly,
they will generate brief periods of mdt/hvy LES as each passes.
Aforementioned temporary relaxation of the ridge/trof may support
somewhat more active pcpn producing shortwaves beyond 7 days, but
that remains to be seen.

Beginning Sat night/ shortwave will be dropping se thru
northern Ontario, causing winds to back more westerly Sat night.
Typical for this type of flow, convergence will strengthen in a w-e
band across Lake Superior, likely cutting across the Keweenaw, as
land breeze further backs wind off Upper MI/nw WI and veers wind off
Ontario. The setup will be similar to what occurred last night. Will
likely see an advy event for the Keweenaw as there will be deep
moisture and a very deep DGZ, though much of the DGZ won`t be within
the upward motion to make it more ideal. Then, similar to today, sfc
trof will drop s, pushing convergent LES band s and bringing a
period of mdt/hvy snow into areas e of Marquette Sun morning. After
the convergent band moves onshore, nnw flow LES will gradually
diminish thru the day from w to e as deep moisture exits though LES
may be mdt at times for much of the day e of Marquette as DGZ
dominates the convective layer.

Sun night thru Mon night, a pair of shortwaves will drop se. One
vigorous wave will track from the Northern Plains to Indiana while a
second will follow from Manitoba into the western Great Lakes. The
former will generate a swath of snow from northern MN across WI into
Lower MI under vigorous deep layer forcing per q-vectors, left exit
of accompanying upper jet and band of isentropic ascent. NE portion
of this snow band will brush the fcst area late Sun night/Mon, and
may provide an inch or 2 of snow accumulation. If sfc low pres wave
is sufficiently organized, winds may swing around off Lake MI to
provide a lake enhancement opportunity for Menominee county.
Keweenaw could get into lake enhancement as well if winds become
easterly. As sfc wave passes by s and se of the area, ne then n
winds will develop off Lake Superior at the same time forcing from
second wave arrives. This wave will be followed by CAA dropping
850mb temps to at least -20C by 12z Tue. All of the counties
bordering Lake Superior should see at least a brief period of
mdt/hvy LES late Mon aftn into Mon night.

Light to mdt LES will continue Tue while winds back to the nw. LES
may be hvy at times e of Marquette where sharper convergence is fcst
along with longer fetch/Lake Nipigon preconditioning. Tue will
likely be the coldest day of the week with highs in the teens, maybe
only just above 10F over the interior nw half.

Timing of shortwaves becomes more problematic during the middle and
end of next week as is normally the case at this time range into
model runs, especially when features are more subtle. Air mass will
likely remain cold enough to maintain LES off Lake Superior, and the
LES will shift based on timing/track of shortwaves. Right now, there
is reasonable agreement for another shortwave/sfc low pres wave to
drop across the western Great Lakes on Thu, providing a better chc
of widespread light snow at that time as well as another round of
mdt/hvy lake enhancement off Lake Superior.

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1251 PM EST FRI DEC 8 2017

A clipper system, and lake effect with N-NW winds with cooler air
behind it, will lead to deteriorating conditions this evening and
tonight. Good confidence in overall flight category, but will likely
see more variability with conditions as is normal with lake effect.
Conditions will gradually improve Saturday.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 453 AM EST FRI DEC 8 2017

Winds are expected to remain between 20 to 30 knots through the
weekend. With numerous clipper systems expected to dig south across
the lake, the winds will be in and out of westerly to northerly flow
through the weekend. Sunday night into Monday, a weak surface ridge
will move across the lake and allow winds to briefly drop down to 10
to 15 knots. However, expect the winds to ramp back up to around 20
to 30 knots Monday through Tuesday as another system tracks across
the region. Through the rest of the week, winds look to remain below
25 knots. Occasional freezing spray is likely through early next
week; however, no heavy freezing spray is expected at this time.

Upper Michigan...
  Winter Weather Advisory until 5 PM EST Saturday for MIZ006-007-

  Winter Weather Advisory until 1 PM EST Saturday for MIZ001>004-

  Winter Weather Advisory from 10 PM this evening to 1 PM EST
     Saturday for MIZ005.

  Winter Weather Advisory until noon CST Saturday for MIZ009.

Lake Superior...
Lake Michigan...


SHORT TERM...Ritzman
LONG TERM...Rolfson
MARINE...Ritzman is the U.S. government's official web portal to all federal, state and local government web resources and services.