Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 090529
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
1229 AM EST Sat Dec 9 2017

.SHORT TERM...(This evening through Saturday)
Issued at 337 PM EST FRI DEC 8 2017

Not much change in forecast thinking from the previous shift and no
significant headline change were needed. While a persistent LES band
into Alger County this afternoon continues to weak and will shift N,
synoptic snow ahead of a shortwave (NW of Lake Superior) is moving
into the western CWA. May see 2" to may 3" of snow over the S-
central tonight as the shortwave passes, but think impacts will not
justify any headlines. LES, enhanced by the shortwave and colder air
down to -20C behind it, will strengthen this evening from W to E.
Winds will be out of the N to NNW tonight into Saturday, which will
favor the far W and the N-central for the greatest snowfall amounts.
In these favored areas, have generally 4-8" with some greater totals
up to 10" near Ironwood. However, snowfall amounts over the N-
central will be more dependent on the placement and evolution of the
Lake Nipigon band that models show developing into eastern Marquette
County late tonight into Saturday. Do expect that strong band to set
up, so it`s more of a question of exactly where and for how long.
Could see higher totals if it sits over one area for long.

LES gradually diminishes Saturday, slowing in doing so over the N-
central. Will still see snow in all the NNW wind snowbelts by late
tomorrow, but it won`t amount to much by the end of the day.

.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/Sun...next 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 06Z TAFS through 06Z Saturday night)
Issued at 1228 AM EST SAT DEC 9 2017

Lake effect snow will impact all terminals through the morning
hours. This snow has already begun at KIWD early this morning, and
will continue to move into the KCMX/KSAW terminals. Expect ceilings
to remain MVFR, with improving conditions later in the afternoon.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 337 PM EST FRI DEC 8 2017

No gales expected through the weekend, but could see some N gales to
35kts over the eastern half of Lake Superior Mon night into Tue.
Occasional freezing spray is likely into the middle of next week.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory until 5 PM EST this afternoon for MIZ006-
     007-085.

  Winter Weather Advisory until 1 PM EST /noon CST/ this afternoon
     for MIZ001>005-009-084.

Lake Superior...
None.
Lake Michigan...
None.
&&

$$

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



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