Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 091136
AFDMQT

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

.SHORT TERM...(Today and tonight)
Issued at 422 AM EST SAT DEC 9 2017

A clipper system charged across the region during the overnight
hours and is currently centered over southeast Wisconsin this
morning, with an inverted surface trough draped across central and
eastern portions of the area. With enhanced convergence along this
inverted surface trough, and fairly weak synoptic flow a few
mesolows have developed - one over the northern half of the Bay of
Green Bay and a couple across the southern shore of Lake Superior.
Otherwise, unidirectional flow out of the north continues to push
eastward across the area, as evident on IR satellite imagery showing
colder cloud tops becoming more prevalent across Lake Superior this
morning. Lake effect snow has already begun impacting the west this
morning.

Today: We`re still looking at accumulating lake effect snow this
morning across the north wind snow belts as flow behind the exiting
surface low becomes northerly across the region. There are multiple
different aspects to this lake effect snow event, including mesolows
coming on shore this morning across the north central and east,
followed by more numerous and widespread lake effect snow expected.
As these mesolows come on shore, primarily looking at Marquette
County early this morning and then Alger/Luce counties later this
morning, expect a quick burst of snow where snowfall rates may
approach 1 to 2 inches an hour. Then, behind these leading mesolows,
an additional 3 to 6 inches is expected through the rest of the day;
however, as we progress into the afternoon hours the focus for
additional lake effect snow will transition to the northwest,
and west wind snow belts.

Across the west, the lake effect snow has already begun and will
continue through the morning hours. As we progress through the
afternoon hours surface ridging will begin to build in the western
half of Upper Michigan. This will allow flow to transition from north
to west-northwest, as well as the lingering lake effect snow.

Tonight: With yet another wave digging south across the region,
another surface trough is progged to develop across Lake Superior.
This trough will enhance low-level convergence across the ongoing
lake effect snow in the west to northwest wind snow belts.
Therefore, have opted to extend the winter weather advisory into
Sunday for the northwest and eastern portions of Upper Michigan.
Given the enhanced lift along the surface trough, forecast soundings
show strong lift through the DGZ and inversions deepening to around
10k feet. Therefore, like the current thinking of the high-res
models with higher QPF tonight into Sunday morning mainly across the
Keweenaw and around/east of Munising. Have increased QPF and snow
ratios over those areas as the snow should be highly efficient. It
is possible that snowfall accumulations during this time period may
top 8 inches in some locations, so the ongoing advisory may need to
upgraded to a warning.

.LONG TERM...(Sunday through Friday)
Issued at 422 AM EST SAT DEC 9 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, north
to northwest wind favored snow belts will be the favored lake effect
areas; however, there some clipper systems that will drop 850mb
temperatures to around -20C and allow winds to shift. At this point
the heavier snowfall time period are expected Monday into Tuesday
and again Wednesday into Thursday.

Sunday into Sunday night: Another quick moving, very weak, 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 much 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
mainly light to possibly moderate lake effect snowfall along Lake
Superior. At this point, not really expecting too much in the way of
accumulation outside of early Sunday morning, where 2 to 4 inches of
snow could occur for locations along Lake Superior, mainly east of
Marquette.

Monday into Tuesday: Yet another, much stronger shortwave will slide
through the Upper Peninsula Monday through Tuesday. At the same
time, a low pressure system is progged to slide just south of the
Upper Peninsula as another low tries to form over eastern Lake
Superior. This would help to give more north to northwesterly winds
across the area, allowing for enhanced lake effect conditions for
those snow belts. Ahead of the low, there may be a brief period of
southerly winds Monday morning, which could allow some lake
enhancement downwind of Lake Michigan; therefore, have adjusted
snowfall totals a bit higher for locations east of Escanaba along
Lake Michigan. Otherwise, as lapse rates steepen and moisture
increases Monday afternoon, a very deep snow growth layer is progged
to slide across the Upper Peninsula with the stronger shortwave.
Soundings would suggest the DGZ would be moist from 3kft up to 8kft
Monday into Monday night along with a decent forcing and lake
induced instability through that layer. This would allow for
increased snow to liquid ratios and allow for moderate to heavy snow
rates. Most locations along Lake Superior will see a period of
moderate to heavy snowfall during this time period, but pinning down
exactly what location see the heaviest snowfall totals will depend
on the surface pressure pattern and associated wind direction.
Current thinking is the north to northwest wind favored locations
could pick up several inches of snow from Monday afternoon through
Tuesday afternoon. This time period will likely need a headline,
possibly meeting warning criteria for some locations north central
and east, depending upon the exact wind direction. For southern
locations, the low pressure system would have enough moisture to
provide at least a couple inches of snow Monday, with a few higher
totals possible downwind of Lake Superior on Monday morning. Much
colder air will filter in for Tuesday, with many locations only
seeing low teens for highs. Stay tuned for updates for this time
period.

Rest of the Extended: Active cold weather pattern continues through
much of the work week with some moderation expected toward the end
of the week. Another strong shortwave is progged to slide through
the area Wednesday night into Thursday, which will allow for another
time period of enhanced lake effect snow. This being farther out in
the forecast time period makes it difficult to pin down the exact
locations that would see moderate to heavy lake effect snow. At this
point, will stick with a consensus of the models, giving good
chances of lake effect snow all along Lake Superior. Again, like all
lake effect events, the surface feature developments will help
refine the heavier snow bands as we get closer to the event. The end
of the week into the weekend models are hinting at southerly flow
developing across the Upper Great Lakes, which would allow for a
break in the lake effect snow for Friday into the first part of the
weekend. Additionally, this would allow for some modification in
temperatures as well with highs warming into the upper 20s to near
30.
&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 635 AM EST SAT DEC 9 2017

Lake effect snow will impact all terminals this morning with MVFR
ceilings and reduced visibilities. At times heavier snow may cause
visibilities to drop lower than currently reflected in this TAF
cycle, especially at KSAW. However, confidence in where the band of
heavier snow will set up later this morning was not high enough to
include such mentions. Snow will gradually diminish across the
KIWD/KSAW later today and tonight, but expect the snow to linger at
KCMX. In fact, late tonight into early tomorrow the potential is
there for a heavy band of snow to impact the terminal. Left mentions
of impacts out as there is uncertainty in the timing right now.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 422 AM EST SAT DEC 9 2017

Wind gusts will primarily remain between 20 and 30 knots through the
weekend before a brief decreased to less than 15 knots Sunday night
into Monday. However, late Monday into Tuesday gales of 35 to 40
knots look possible, especially across the central and eastern half
of the lake. Winds will drop below 30 knots by Tuesday night, and
further decrease to around or below 15 knots on Wednesday.
Occasional freezing spray is likely into the middle of next week. We
could see heavy freezing spray develop Monday night into Tuesday,
especially across the north central portions of the lake.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory until 2 PM EST Sunday for MIZ006-007-085.

  Winter Weather Advisory until 11 AM EST Sunday for MIZ001>004-
     084.

  Winter Weather Advisory until 1 PM EST /noon CST/ this afternoon
     for MIZ005-009.

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

$$

SHORT TERM...Ritzman
LONG TERM...KEC
AVIATION...Ritzman
MARINE...Ritzman


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