Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 081757 AAA

Area Forecast Discussion...UPDATED
National Weather Service Marquette MI
1257 PM EST Thu Dec 8 2016

Issued at 1256 PM EST THU DEC 8 2016

...Primary change was to issue lake effect warning for Alger

Even with northwest winds bringing sfc temps in the upper teens to
middle 20s across Lk Superior and MQT VWP showing depth of lake
effect convection up to near 10kft, the lake effect has been rather
disorganized to this point. Heavier snow showers, much more cellular
and convective looking versus traditional banding, generally lasting
less than 15 min a pop are dragging vsby down to 1/4-1/2sm but snow
amounts cannot add up as convergence is not persistent. Even so we
were able to accumulate 3.6 inches since our 7 am observation
bringing our total at the NWS office near Negaunee to 4.4 inches
thus far. Some shear is noted in RAP/HRRR wind fields up to h750 at
current and there is overall weak ambient sfc based cape analyzed as
well (some past studies have indicated that there is ambient cape
around it can be hard for lake effect banding to occur). RAP and HRRR
do show winds becoming unidirectional by late aftn into early evening
and the ambient cape diminishing. Overall expect the organization of
the lake effect to increase by this evening.

Vis satellite indicates convergence is increasing in the band
emerging from Lk Nipegon north of Lk Superior and expect this
convergence to help to develop a stronger band of snow fm tip of
Keweenaw to across eastern Marquette county this evening and moving
into western portions of Alger county tonight. Instability remains
very favorable with inversions to at least 8kft/lake induced capes
over 500j/kg and much of the dgz within the lake convective layer.
Overall once this band develops, helped along by increasing land
breeze convergence with W winds over cntrl Upper Michigan and NNW
over scntrl Lk Superior, expect a very fluffy lake effect snow to
result with several inches of accumulation with snowfall rates at
least to 2 inches per hour if not more. Since this band is expected
over western Alger county, opted to put a lake effect snow warning
out for Alger county into Friday and Friday night. Will look at the
other headlines this aftn and may do some tweaking to the end times
as in some areas the lake effect could end quicker that late Fri
night. Will not make those changes now though.

.SHORT TERM...(Today and tonight)
Issued at 523 AM EST THU DEC 8 2016

The SFC trough and associated band of heavy snowfall is currently
moving onshore from Marquette through Whitefish Point. Should see
very poor conditions right along the trough, then moderate to heavy
LES behind that. Elsewhere, NW winds LES will continue through the
short term. Most uncertainty in the short term is where the Lake
Nipigon enhanced band will be today through tonight. Models still
differ on exactly where to place the band and how transient it will
be...but it should be between Marquette and Munising. Best guess
right now is that the band will become more steady tonight when the
land breeze sets up...keeping the band possibly near the
Marquette/Alger border where some heavier snowfall totals will
result. Only change to winter headlines was to add a Lake Effect
Advisory for Delta County as bands get into the northern and eastern
portions of the County. Looks like bands will stay west and east of
southern Schoolcraft County, so left that out for now. See the
forecast and winter headlines for more details.

.LONG TERM...(Friday through Wednesday)
Issued at 412 AM EST THU DEC 8 2016

Nam shows a broad 500 mb trough over most of the U.S. 12z Fri with a
shortwave moving into the northern plains 00z Sun and into the upper
Great Lakes late Sat night. Nam brings in some deeper moisture and
strong 850-500 mb q-vector convergence Sat night across the area.
Went with persistence for the lake effect and made very few changes
to the going forecast. One change though is the system for Sat night
looks to be a bit further south now and lowered pops a bit for this.

In the extended, GFS and ECMWF show a 500 mb trough with 850 mb
temperatures from -15C to -19C over Lake Superior 12z Sun. There is
also a sfc low pressure system passing by to the south near Dubuque,
IA. The upper level trough at 500 mb broadens and deepens across the
U.S. on Mon with colder air poised to come down over the northern
plains and northern Rockies. This colder air sweeps across the upper
Great Lakes on Tue with a sfc cold front moving through the area.
850 mb temperatures drop down to -23C to -28C by then over Lake
Superior at 12z Wed with the core of the coldest air over the area
then. Slow modification takes places on Thu as the cold core moves
over the New England. Prolonged lake effect snow event during this
forecast period with temperatures well below normal.

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 642 AM EST THU DEC 8 2016

MVFR to IFR conditions with lake effect snow will persist through
the TAF period.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 523 AM EST THU DEC 8 2016

NW winds will gust up to 30 kts through Fri. Winds should diminish
to less than 25 kts through the weekend as pressure gradient
weakens. Freezing spray and heavy freezing spray is possible in the
middle of next week.

Upper Michigan...
  Lake Effect Snow Warning until 7 AM EST /6 AM CST/ Saturday for

  Lake Effect Snow Advisory until 7 AM EST Saturday for MIZ007-084-

  Lake Effect Snow Warning until 7 PM EST Friday for MIZ004-005.

  Lake Effect Snow Advisory until 7 PM EST Friday for MIZ013.

Lake Superior...
Lake Michigan...


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