Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 100558

Area Forecast Discussion
National Weather Service Marquette MI
1258 AM EST Sat Dec 10 2016

Issued at 1124 PM EST FRI DEC 9 2016

Dominant lake effect convergence band over the Keweenaw Peninsula
dropping snowfall rates of 3-4" per hour at some locations as
reported tonight on social media and by spotters. This convergence
band is also impacting Keweenaw County where we had no headline
going previously so have decided to issue a lake effect advisory.
Thought that band would move enough to generally keep snow totals blo
warning, but certainly is possible warning amounts could be reached
at a few locations. Continued the advisory through Saturday, but
would eventually expect the better convergence and focus for band to
shift south into Northern Houghton County by Saturday morning.

Rest of headlines still look good but did bump up snow totals
several more inches tonight over northern Houghton and eastern
Alger/Northern Luce given impressive nature of this dominant band as
model soundings show lake induced CAPE near 1000 j/kg, and a deep
DGZ throughout the convective layer which should lead to fluffy
snow totals approaching a foot or more.

.SHORT TERM...(This evening through Saturday)
Issued at 400 PM EST FRI DEC 9 2016

WNW flow aloft persists with a strong shortwave trough upstream over
southern Manitoba. This shortwave which enhances lift slides across
Upper Great Lakes tonight and will lead to significant lake enhanced
snow as temps at top of inversions are around -20c. Inversion
heights over western Lk Superior top out around 850mb/5kft while
longer fetch over eastern Lk Superior with the NW winds results in
inversions to around 700mb/10kft there through Sat. Strongest lift
within lake convective layer will be within the dgz so SLRs should
remain at least 20:1 if not over 30:1 as we have seen at times last
couple days. Instability will continue to be more than sufficient
for significant lake effect snow into Sat.

Sfc trough/lake induced troughing remains over Upper Michigan this
aftn extending from northern Lower Michigan to near Duluth.
Convergent westerly flow in the vcnty of the trough is where the
heavy lake effect snow is expected tonight with land breeze only
further increasing convergence. Temps inland west may drop toward
zero especially if there is some clearing. Still looks likely that
heavy snow will affect northern Ontonagon county into Houghton
county as enhanced snow band focuses off tip of Bayfield Peninsula.
Also have potential of mesolow/enhanced convergence band setting up
over eastern Lk Superior into far northeast cwa, further sharpened
by land breeze off Ontario. Wind obs over eastern Lk Superior are
already showing this idea is taking shape. This area will have added
factor of seeing nw winds flowing across long axis of Lk Superior
feeding into the mesolow circulation. Expect very heavy snow with
snowfall rates probably similar to what occured earlier today as
dominant band of snow dropped around a foot of fresh snow in
just a few hours over eastern Marquette into western Alger county.
Decent chance that some locations tonight in these two main
convergence areas will see snowfall toward a foot as well. Exact
locations where heaviest snow sets up still in question though.
Wherever the convergence snow bands develop, appears that they will
persist into much of Saturday as sfc trough remains anchored over
south shore of Lk Superior/northern Upper Michigan. Several inches
of additional accumulation is likely. Elsewhere along Lk Superior
other than the Keweenaw the snow should pretty much end as drier
airmass works in later tonight in wake of the shortwave moving

For the headlines, extended the lake effect snow warnings and
advisories for the northwest cwa in Ontonagon and Houghton through
Sat. Also extended the warning and advisory for Alger and northern
Schoolcraft through Sat as well. Did upgrade Luce county to a
warning with the expected dominant band affecting northern sections
though made sure to highlight lesser snow amounts toward McMillan
and Newberry as the heavier snow should stay north of those

.LONG TERM...(Saturday night through Friday)
Issued at 355 PM EST FRI DEC 9 2016

Although there wl be some moderation in temps late in the weekend
into Mon as a more zonal flow allows a lo pres to track farther to
the n and impact much of the cwa with at least a couple inches of sn
on Sun/Sun ngt, a flow of arctic air wl dominate the middle and end
of the coming week, resulting in sustained blo to well blo normal
temps. While no sgnft synoptic scale storms are likely to impact the
area during that 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
falling at least near advy thresholds away fm the moderating
influence of Lk Sup.

Sat ngt...A sfc hi pres rdg moving slowly thru the Upr Lks ahead of
a shrtwv rdg alf/dnva wl bring generally quiet wx to most of the
area. But despite these negative dynamics and the overall acyc
albeit lgt h925 flow, models show a lk induced trof stretching fm
the Keweenaw to near Whitefish Pt under thermal troffing with h85
temps ranging fm about -16C over the e to -19C near Isle Royale.
This trof, with llvl cnvgc enhanced by a weak land breeze flow,
should be the focus for persistent les, the intensity of which wl be
limited by a lowering subsidence invrn. But since the dgz wl be
present within the incrsgly shallow moist lyr, some places near the
trof axis could see a few inches of fluffy sn. Later at ngt, a
shrtwv over the nrn Rockies that is embedded in the wnw flow alf is
progged to streak ewd and aprch wrn MN by 12Z Sun. While the dpva/
deep lyr qvector cnvgc ahead of this disturbance wl remain to the w
of the cwa, general waa between the accompanying lower mslp to the sw
and the retreating sfc hi pres rdg wl bring some incrsg mid/hi clds
to the area overngt. The veering h925 flow toward the s wl also cause
the lk induced trof to shift to the n and clear all but perhaps the
nrn tip of the Keweenaw, ending most of the les. Since the pwat wl be
only about 0.10 inch and llvl winds wl be lgt, some places away fm
the lk induced trof/accompanying lo clds could see temps fall sharply
before the waa clds arrive later at ngt.

Sun/Sun ngt...The shrtwv nearing wrn MN at 12Z Sun is fcst to shift
into the wrn Great Lks on Sun ngt, impacting the cwa with a period
of dpva/deep lyr qvector cnvgc/upr dvgc. The models in general have
trended toward the n with the track of this disturbance and show
some fairly strong waa as well that supports raising pops into the
likely/categorical category. Although the 12Z ECMWF has trended a bit
flatter and farther to the s, recent NCEP discussion indicates a
preference for the deeper/farther n scenario shown by the 12Z GFS.
Despite the fairly strong waa, h7 specific humidity is fcst to only
aprch 2 g/kg, which would support a general 2-4" of synoptic sn
during the approximately 12hr period of larger scale forcing. One
concern would be the potential for some enhancement in the ese llvl
flow that could impact the scentrl cwa and the Keweenaw in the
presence of h85 temps arnd -10C. A deep dgz over 5k feet shown on the
fcst sdngs would also support hier sn/water ratios and sn totals.
Unless the models trend toward the 12Z ECMWF fcst, future shifts wl
need to consider a winter wx advy for at least a portion of the cwa.
Although the exit of the deep lyr qvector cnvgc later at ngt might wl
tend to cause the sn intensity to diminish, a persistent cyc ene flow
along some lk induced troffing hanging back over Upr MI fm the
departing sfc lo pres wl support lingering hier pops. Sfc temps
during this period wl be not far fm normal, with lo temps on Sun ngt
a bit above normal under the ovc skies/waa h85 thermal rdg.

Mon...Dnva/deep lyr qvector dvgc in the wake of the exiting shrtwv/
sfc lo pres and ahead of aprchg shrtwv rdg alf is fcst to bring some
mid lvl drying and weaken the lk induced trof that wl linger over the
area under h85 temps remaining near -10C. So although some sn showers
wl linger mainly near Lk Sup, the intensity of this pcpn wl be

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 06Z TAFS through 06Z Saturday night)
Issued at 1255 AM EST SAT DEC 10 2016

Lake effect will continue at CMX through the TAF period with IFR to
MVFR vsby and MVFR cigs. Lake effect will move out of IWD by Saturday
morning but bkn cigs will stay MVFR. SAW should stay out of the lake
effect for the most part through the rest of the TAF period with
mainly VFR cigs. &&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 355 PM EST FRI DEC 9 2016

Expect nw winds up to 25 to 30 kts into Sat to diminish under 20
kts for a time Sat night into Sun as a weak hi pres ridge moves
over the area. Then ese winds will increase back up to 25 kts on
Sun/Sun night under the tighter pres gradient between this slowly
departing hi pres and a lo pres moving through the Lower Lakes.
Although winds will diminish under 25 kts again for a time again on
Mon, a steady wnw wind to 30 kts will redevelop on Mon night into
Tue following a strong cold frontal passage that will introduce
arctic air into the Upper Lakes. Expect gales along with some heavy
freezing spray over at least portions of the Lake on Tue night/Wed
as this arctic air moves into the area and waves at the end of
fetch build to at least 10 feet.

Upper Michigan...
  Lake Effect Snow Warning until 7 PM EST this evening for MIZ002-

  Lake Effect Snow Advisory until 7 PM EST this evening for MIZ001-

  Lake Effect Snow Advisory until 1 PM EST this afternoon for

Lake Superior...
Lake Michigan...


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