Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 032023

Area Forecast Discussion
National Weather Service Marquette MI
323 PM EST Sat Dec 3 2016

.SHORT TERM...(This evening through Sunday)
Issued at 322 PM EST SAT DEC 3 2016

12Z raobs/latest wv imagery and RAP analysis show shrtwv rdging
moving e thru the wrn Great Lks and supporting a sfc hi pres rdg
axis stretching fm nw Ontario into WI. Although the larger scale
subsidence/mid lvl drying associated with these feature are
suppressing any larger scale pcpn, some lk effect snow showers
linger under h85 temps arnd -8C and primarily along a lk induced
trof stretching fm the ern cwa acrs scentral Lk Sup and the Keweenaw
into wrn Lk Sup. However, lo subsidence invrn base arnd h85 and near
absence of a dgz within the moist lyr under the invrn base are
limiting the sn intensity. Looking upstream, plenty of lo clds
linger thru MN despite presence of llvl acyc flow. Farther to the w,
there are a pair of shrtwvs of interest. The first is lifting enewd
thru SDakota while the second is out of the Rockies into the
ncentral Plains.

Main fcst concerns in the short term wl focus on pops/qpf on Sun
associated with pair of upstream shrtwvs.

Tngt...As the shrtwv rdg/sfc hi pres rdg axis shift slowly to the
eand allow the gradient flow to shift to the s, expect only some sct
light snow showers to persist along the weak lk induced sfc trof
axis that wl become oriented fm near Isle Royale acrs ecentral Upr
MI and into nrn Lk MI. The wshft to the s in the presence of h85
temps still arnd -7C may result in some weak enhancement off Lk MI.
With considerable lo clds likely to linger thru the ngt over most of
the cwa, opted to raise fcst min temps a couple of degrees. Although
the incrsg downslope s wind later might cause the lo clds to break
up over the far w, the steadier wind and arrival of some waa mid/hi
clds ahead of the first shrtwv moving enewd fm the Plains would tend
to hold temps up there as well.

Sun...The first shrtwv lifting newd fm the Plains is fcst to shear
out and bring mainly just some thickening mid clds as the dynamic
support wl be inadequate to saturate the lingering dry lvls
associated with the rdg axis passing to the e. However, the s wind
btwn the departing sfc hi pres rdg axis and falling mslp to the w wl
still allow for some snow showers psbly mixed with rain to stream
into the ern cwa off Lk MI. During the aftn, the second shrtwv now
moving into the nrn Plains is progged to shift toward the Lower
Great Lks by 00Z Mon. The arrival of some dpva/deep lyr qvector
cnvgc/upr dvgc on the nrn flank of this feature wl allow for a some
steady light snow, primarily over the se half of the cwa closer to
the stronger forcing and where there wl be some lingering
enhancement of the pcpn off Lk MI. Although this pcpn wl fall mainly
as snow except perhaps right near the shore, warming of the sly flow
off the waters that lift temps above 32 wl tend to limit snow accums.

.LONG TERM...(Sunday night through Saturday)
Issued at 322 PM EST SAT DEC 3 2016

Shortwave trough becomes negatively tilted while crossing the Upper
Great Lakes Sun aftn into Sun evening. Sfc-h85 trough crosses Upper
Michigan through this time switching winds from S-SE to W and
providing low-level convergence and lift. Main area of deeper layer
q-vector convergence stays mainly south and that should keep
widespread snow with the system later Sun into Sun night limited to
an inch or two. One exception though as S winds ahead of trough with
h85 temps of -7c would support lake enhanced snow downstream of Lk
Michigan. Similar to what has occurred last couple days with the
lake effect off Lk Superior, sfc temps in the low to mid 30s likely
will lead to rain/snow mix or only rain near the immediate shoreline
of Lk Michigan including at locations such as Manistique and the
east shore of the Garden Peninsula. Just inland where lake enhanced
snow is more widespread, it should be cold enough for mainly snow.
Run total qpf is all over the place over northern Lk Michigan and
into eastern cwa. Higher outliers are the GEM and WRF-ARW which show
totals nearing 0.80 inch late Sun aftn through late Sun night. Low
end values are 0.25-0.35 inches from the GFS and SREF mean. Since
stronger forcing remains south of Upper Michigan and higher qpf
values are very high outliers compared to SREF plumes and NCAR
ensemble qpf, will go more middle of road for qpf on the order of
0.3 to 0.5 inches and go with idea that there could be a few inches
of fresh snow which could result in slippery travel Sun evening on
untreated roads. Think the marginal temps in the mid 30s will
ultimately limit snow accums than what would otherwise occur with
the expected qpf totals. For now will mention this snowfall and
slippery roads in the Hazardous weather outlook.

Snowfall over the east cwa should taper off quickly after midnight
as larger scale q-vector divergence/subsidence and drying moves in
and with sfc winds backing west once the sfc trough exits to east.
Sfc high brings dry weather on Monday though not sure how much
clearing occurs as there could be moisture blo 925mb trapped beneath
subsidence inversion. High temperatures should only rise into the
mid to upper 30s, coolest where southwest winds upslope to the
higher terrain of cntrl Upper Michigan.

Mon night into Tue rather strong shortwave trough slides across
northern Plains and lifts into south central Canada. Sfc low deepens
blo 1000mb. GFS most aggressive in bringing swath of moisture into
Upper Great Lakes ahead of the low and even those soundings look dry
above h85 over all but far west cwa. Soundings do hint at low level
moisture with weak lift which would result in drizzle or freezing
drizzle over the central and east with some added moistening off Lk
Michigan. GFS looks like cold outlier with cold front over central
Upper Michigan by 12z Tue and h85 temps down to -12c over western Lk
Superior while ECMWF and GEM are not even down to -5c. Overall
though the GFS is quicker in bringing colder air in Tue and Tue
night, ECMWF does catch up by Wed and they have similar solutions as
both models keep shortwave trough and strong sfc low over Manitoba
and northern Ontario completely separate and unphased with shortwave
trough and sfc low sliding across the Ohio Valley. Whenever the sfc-
h85 cold front moves through there is some weak deep layer q-vector
convergence shown and there is also hint of another weaker wave
lifting across area along the cold front on Tue night. Otherwise,
large scale subsidence and drying takes hold into Wed as stronger
trough aloft remains over Manitoba and northern Ontario and southern
stream shortwave trough crosses the southwest Conus. Lake effect
during this time will likely be confined mainly to Keweenaw with sfc
to h85 winds from the W or WSW and h85 temps blo -12c as Lk Superior
temps are still 5-6c. Inversion heights around 5kft should limit
intensity of lake effect but could have several inches of fluffy
snow accum since the dgz will be within the lake convective layer.

Deep trough aloft with widespread cold air will continue to occupy
much of the eastern half of the Conus later Wed into Thu. Southern
stream wave should stay far enough southeast of Upper Great Lakes to
prohibit stronger storm to affect the region, though the lower
Michigan could see widespread snow as sfc low lifts across Lower
Great Lakes toward New England. ECMWF more in line with that idea
while GFS keeps system too sheared out to cause much snow until it
reaches northern New England late this week. Back over the Great
Lakes, lake effect snow will be the main story. Areas favored by NW
winds will see the the most snow as h85 temps continue to fall to
around -15c by late Thu into Fri. Sometime late in the week there
will be a reinforcing sfc-h85 cold front that could bring winds to
more N so lake effect could shift around to north flow areas for a
time. Plenty of deep moisture to h7/10kft with large scale trough
overhead so lake effect may be moderate to even heavy depending on
when shortwaves work through to enhance the snow further. Stronger
low-level winds will push snow showers farther inland than normally
seen and since low-level temps will be sufficeiently cold for snow,
should see snow all areas, even near the Great Lakes shorelines.
Lake effect will continue into Sat for NW flow areas, especially
over eastern cwa. Certainly by late next week it will look and feel
more like winter across most of Upper Michigan.

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1235 PM EST SAT DEC 3 2016

As a sfc hi pres rdg shifts to the e and the s wind component
increases, expect lo clds impacting IWD and CMX to dspt with the
stronger downsloping and give way to VFR conditions. As this flow
taps more mstr off Lk MI late tngt, lo clds and MVFR cigs wl impact
SAW. More lo clds/MVFR cigs wl arrive at IWD late in the TAF period
ahead of an area of -sn that wl be aprchg fm the w.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 322 PM EST SAT DEC 3 2016

Expect winds to remain 25 kts or less through Mon as the pres
gradient remains relatively weak. An approaching lo pres trof will
tighten the gradient Mon night/Tue, resulting in sw winds up to 30
kts. There could be some w gales to 35 kts over mainly the ncentral
on Tue night into Wed under the tighter pres gradient on the
southern flank of the deepening lo pres moving into nw Ontario and
with the arrival of colder air that will increase overwater
instability. Depending on how quickly the Ontario lo pres deepens
and how fast it moves away, there could be some nw gales late this
coming week as colder air surges into the Upper Lakes. There is
likely to be some freezing spray as waves build.

Upper Michigan...
Lake Superior...
Lake Michigan...


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