Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 092055
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
355 PM EST Fri Dec 9 2016

.UPDATE...
Issued at 108 PM EST FRI DEC 9 2016

...Some headlines cancelled but other areas will see heavy lake
effect snow especially tonight...

Quite the convergence band that affected far eastern Marquette
county and western Alger county last night into this morning. Based
on radar estimates and the available isolated reports, likely that
at least a foot of snow occurred in narrow area from east side of
Harvey to Sundell/south of Deerton in western Alger county. Most of
that probably fell since daybreak this morning, especially for
Marquette county. Band of snow has shifted east into Alger so
dropped warning for Marquette and winds becoming west over far west
near IWD will also lead to improving conditions enough to drop the
warning for Gogebic.

Shortwave upstream over Manitoba moves across tonight with deep q-
vector convergence/lift noted. This forcing and cooling h85 temps to
near -20c will enhance where the snow is ongoing, probably in a
significant way. Sfc trough/lake induced troughing remains over
Upper Michigan this morning extending from northern Lower Michigan
to near Duluth. Convergent westerly flow in the vcnty of the trough
will produce more heavy lake effect snow tonight as land breeze only
further increases convergence. Appears 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. This area will have added factor of seeing nw winds
across long axis of north central to eastern Lk Superior. Expect
very heavy snow with snowfall rates probably similar to what occured
today with the dominant band eastern Marquette into western Alger
county. Pretty good chance some locations tonight in these two main
convergence areas will see snowfall toward a foot. Exact locations
where heaviest snow sets up still in question though. Beefed up
wording for these two potetntial heavy snow areas in latest wsw
statement.
&&

.SHORT TERM...(Today and tonight)
Issued at 544 AM EST FRI DEC 9 2016

NW LES continues, with the heaviest snow associated with the Lake
Nipigon band which is currently over far eastern Marquette and
western Alger County. The Nipigon band will shift east across Alger
County today, dropping up to 9 inches in spots there today. A ridge
pushing toward the area from the SW tonight will cause winds to
veer, which when combined with a shortwave moving through will
amplify the LES over northern Ontonagon and Houghton Counties. This
may lead to 6-9" of snow in that area. The LES out east will
continue to slowly shift east while diminishing some. Only headline
changes were to drop the warnings for Baraga and Keweenaw Counties
as only light LES is expected there. The Marquette County warning
may be able to be cancelled early today as LES shift east.

.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
lighter.

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 Saturday afternoon)
Issued at 114 PM EST FRI DEC 9 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 this
evening 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.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Lake Effect Snow Warning until 7 PM EST Saturday for MIZ002-003-
     006-007.

  Lake Effect Snow Advisory until 1 PM EST Saturday for MIZ084.

  Lake Effect Snow Advisory until 7 PM EST Saturday for MIZ085.

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

$$

UPDATE...JLA
SHORT TERM...Titus
LONG TERM...KC
AVIATION...JLA
MARINE...KC



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