Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 082010

Area Forecast Discussion
National Weather Service Marquette MI
310 PM EST Thu Dec 8 2016

.SHORT TERM...(This evening through Friday)
Issued at 309 PM EST THU DEC 8 2016

WV loop shows deep troughing across eastern Canada and the Great
Lakes. Cold airmass continues to pour across Upper Great Lakes with
h85 temps of -13c to -16c lowering to -16c to -19c by Fri aftn. IR
satellite loop showed colder cloud tops this morning with shortwave
working through then that faded this aftn but more hints of larger
scale forcing is showing up this aftn north of Lk Superior so lake
effect late this aftn into tonight should get a boost from this
forcing. Lake effect thus far today has been cellular instead of
banded, likely due to some shear present in the lake convective
layer and lingering sfc based instability over the land areas.
Earlier enhanced snow over the Keweenaw has shifted more over scntrl
Lk Superior and ncntrl Upper Michigan since 19z/2 pm ET while what
looks like convergence band off Lk Nipigon is quickly developing
ncntrl Lk Superior. Seems the combination of the subsidence to west
of the enhanced snow showers moving over ncntrl Upper Michigan and
lack of larger scale forcing for a time has put crimp on lake effect
over western Upper Michigan with vis sateliite showing less vertical
extent to the clouds there. Overall this event thus far at least
during the day is behaving much more like a fall or spring hybrid
type instead of a more typical setup with multiband and embedded
dominant bands.

RAP and HRRR do show winds becoming unidirectional late this aftn
into early evening and the ambient cape diminishing. Overall expect
the organization of the lake effect to increase through the evening.
Instability into later tonight and Fri 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. Decent agreement that
enhanced snow will continue to swing across ncntrl Upper Michigan
mainly Alger county late aftn then additional snow showers will
orient toward eastern Marquette into western half of Alger county
this evening. Elsewhere inversions to 5kft and some shear within
convective layer will limit lake effect to moderate instensity.
Stronger convergence will be over far west near IWD.

Later this evening stronger convergence band with origin off Lk
Nipigon and tip of Keweenaw peninsula should setup vcnty of far
eastern Marquette county into western half of Alger county. This
band of snow will be helped along by increasing sfc convergence with
W winds over cntrl Upper Michigan and NNW winds over scntrl Lk
Superior. Expect 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. This heavy band of snow should persist over
western Alger county on Fri morning before shifting to the east
through the day. Elsewhere on Friday, expect similar setup to the
lake effect with inversions to 5kft and most of that convective
layer within the dgz. Thus, expect additonal fluffy accumulations to
continue. Winds diminish near Lk Superior so blowing snow so become
less of an issue as the day goes on. Since the dominant band is
expected to persist over western Alger county later tonight into Fri
morning, put a lake effect snow warning out earlier today for Alger
county into Friday and Friday night. Otherwise, will let all other
headlines continue as planned at this time.

.LONG TERM...(Friday night through Thursday)
Issued at 309 PM EST THU DEC 8 2016

A flow of arctic air wl dominate the medium/extended range fcst
period, resulting in sustained blo to well blo normal temps. While
no sgnft synoptic scale storms are likely to impact the area during
this time, persistent les thru the period wl likely result in some
sgnft accums over time in areas that see the most persistent snow
showers. The coldest air wl invade the area beginning next Tue, with
wind chills much of the second half of the week at least falling
near advy thresholds away fm the moderating influence of Lk Sup.

Fri ngt/Sat...A cold wnw llvl flow ahead of slowly aprchg sfc hi
pres rdg moving into MN on Sat wl advect h85 temps as lo as -18C to
-20C into the Upr Lks and bring persistent les in the favored sn
belts and aob normal temps. As the rdg shifts slowly to the e on Sat
and the llvl flow becomes more acyc and backs toward the wsw, much of
the les may end expect over the Keweenaw and the far e toward
Whitefish Pt. But a lk induced trof and enhanced llvl cnvgc
accentuated by a land breeze flow may result in some persistent mdt
sn fall in these areas despite the negative larger scale trends.
Presence of the dgz within the llvl moist lyr wl support hi sn/water
ratios 20-30:1 and greater albeit fluffy sn accums. Wl cont with
going les headlines in the favored wnw winds sn belts on Fri ngt over
the w and to the e of Marquette. Future shifts may need to consider
extending the les headlines over the Keweenaw and the far e on Sat.

Sat ngt/Sun...Most of the medium range models, except the 12Z NAM,
continue to track a shrtwv passing thru the ncentral Plains on Sat
toward the Lower Lks by 12Z Sun, with accompanying dynamic forcing
and deep mstr remaining to the s and brushing just the scentral with
some sn Sat ngt into Sun mrng before the shrtwv exits to the e. The
12Z NAM shows a farther n track with widespread lgt pcpn impacting
the entire cwa, including some lk enhanced sn over the e in the
stronger sly flow ahead of the aprchg farther to the n shrtwv. But
considering the persistent wnw flow aloft that would tend to shear
out this shrtwv and force a more srn track, suspect the NAM is on the
wrong track. The other models hint some les may linger near Lk Sup
with a relatively flat synoptic scale pres gradient/lgt llvl winds in
the presence of h85 temps slowly moderating toward -12 to -14C
allowing a lk induced trof to persist and focus this pcpn. The
locations most likely to be impacted by this les would be the
Keweenaw and far ern cwa near Lk Sup. Temps wl remain blo normal. If
the shrtwv tracks farther to the s and accompanying mid/hi clds on
its nrn flank are thinner on Sat ngt, min temps could fall sharply in
some areas.

Sun ngt/Mon...The medium range guidance indicates another shrtwv wl
track thru the Lower Lks during this period, with the sn on its nrn
flank impacting mainly the scentral cwa under the ely flow off Lk MI
to the n of accompanying sfc lo track near Chicago that could allow
for some lk enhancement. While a general acyc h925 flow and h85
temps moderating to arnd -10C wl suppress the pcpn farther to the n,
some lgt les wl probably linger near Lk Sup even as temps ease back
closer to normal on Mon.

Extended...The longer range models show a deepening upr trof over
central and ern NAmerica downstream of a bldg rdg along the w coast
during this period, which wl allow a very cold arctic airmass/well
below normal temps to invade and dominate the Upr Lks. The cold fnt
that wl introduce this very cold air into the area is progged to pass
on Mon ngt, accompanied by only sct-nmrs sn showers in the absence of
meaningful mstr inflow. As h85 temps fall toward -25 to -30C under a
steady w-nw flow on Tue thru Fri behind the fropa, expect wdsprd les
in the favored sn belts and wind chills to at least fall toward advy
thresholds away fm lk moderation.

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 103 PM EST THU DEC 8 2016

Lake effect snow continues. Some blowing snow as well but with winds
less than 20 kts, main vsby reduction is from the snow. Overall
expect the snow showers to produce IFR vsby with MVFR cigs. Vsby
may trend toward MVFR later tonight into Fri at IWD and SAW.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 309 PM EST THU DEC 8 2016

NW winds will reach 30 kts through Fri with gale gusts to 35 kts
still possible over central and eastern sections, especially in the
vcnty of stronger lake effect snow showers over cntrl sections.
Winds diminish to less than 20 kts Sat through Mon. W to NW winds
increase to 30 kts by later Tue with gales possible Tue night into
Wed as bitter cold air arrives. There is a good chance of heavy
freezing spray by 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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