Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 261008

Area Forecast Discussion
National Weather Service Marquette MI
508 AM EST Sun Feb 26 2017

Issued at 840 PM EST SAT FEB 25 2017

With very dry airmass shown on the 00Z GRB raob /00Z pwat was 0.10
inch/ moving over the Upr Lks under sfc rdg axis, temps have fallen
quickly below the previous fcst near the WI border where winds have
decoupled. Lowered fcst min temps accordingly, but steady pres
gradient well to the n of the hi center over the srn CONUS and the
arrival of some clds ahead of a disturbance in MN that wl bring some
sn showers to the w overngt should prevent temps fm falling too far.

.SHORT TERM...(This evening through Sunday)
Issued at 322 PM EST SAT FEB 25 2017

Upper air pattern consists of a 500 mb trough over the lower Great
Lakes this morning and a shortwave in the Canadian prairies. The
trough will continue to move away from the area and this shortwave
will head southeast and affect the area late tonight into Sun. Nam
shows some 850-500 mb q-vector convergence along with deeper
moisture moving through the area on Sun before moving out by Sun
evening. GFS and ECMWF are similar with the 850-500 mb q-vector

Going forecast has things well in hand. Did not make too many
changes to the going forecast. Lake effect snow continues to wind
down with temperatures still staying cold enough for lake effect
snow for this forecast period. Only thing is winds back to the wsw
and this would put the Keweenaw peninsula into play with several
inches of snow possible late tonight into Sun with convergence and
lake enhancement helping to focus a band across that area. This
would be where the heaviest snow will fall with up to 4 inches in 18
hours. Could be a little lake enhancement from Lake Michigan with a
southwest wind and could see 2 inches of snow there. Did not make
too many changes to temperatures either.

.LONG TERM...(Monday through Saturday)
Issued at 506 AM EST SUN FEB 26 2017

Models suggest that a progressive pattern will prevail through
next week as a mid/upper level trough over the west moves through
the north central CONUS and Great Lakes into the northeast by the
end of the week. A transition toward a more zonal pattern is
expected next weekend.

Monday and Monday night. Scattered snow showers will be possible
early over the Keweenaw early with wrly low level flow and 850 mb
temps climbing from around -14C. Otherwise,  WAA ahead of the next
trough will boost temps into the mid 30s under partly to mostly
cloudy skies.

Tuesday into Tuesday night, as southwest mid/upper level flow
develops ahead of a trough into the wrn CONUS, the models have been
consistent in bringing a shortwave, bands of fgen, moderate
WAA/isentropic ascent toward the nrn Great Lakes. Although the
forcing remains somewhat unorganized and confidence in the details
remains low, it should be strong enough to support QPF into the
0.10 to 0.25 inch range, greatest over the northwest half.
Precipitation type also remains uncertain. Wet-bulb zero heights
favor mainly snow over the northwest and a mix or mainly rain
changing to snow over the southeast half as highs climb into the
upper 30s in most areas. There be a mix with freezing rain of
freezing drizzle early as a warm layer aloft develops. In
addition, there may also be a period where ice nuclei are absent.
With temps marginal for snow, any accumulations to near an inch
should remain confined to the Keweenaw.

Wednesday, model trends and the more consistent ECMWF suggest that
the large area of precipitation associated with a shortwave and sfc
trough along the stronger baroclinic zone will remain to the south
of the cwa. Slowly backing northeast winds and 850 mb temps in the
-8C to -10C range may support some light snow showers or fzdz into
locations downstream of Lake Superior.

Thursday-Saturday, weak clipper shortwaves may affect the region in
the developing nw mid/upper level flow. Confidence is higher that
enough cold air will slide into the area for increasing nw flow LES
from late Thursday into Friday as 850 mb temps drop to around -21C
by Friday morning. A stronger Pacific shortwave and sfc moving
toward Manitoba will bring increasing WAA Saturday with a chance of
light snow along with moderating temps into the 30s.

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1238 AM EST SUN FEB 26 2017

As an aprchg lo pres trof moves closer early this mrng, some -shsn
wl impact mainly the wrn CMX/IWD sites, and cause lingering VFR
conditions to deteriorate to MVFR, at least temporarily. The VFR
conditions are likely to linger longer at SAW and thru 12Z farther
fm the band of forcing. Some -shsn wl continue at both IWD and CMX
much of the day, especially at CMX, where vsbys wl probably end up
in the IFR range a good portion of the time. The best chc for the
lower vsbys wl be under more focused shsn along a lo pres trof that
wl move w-e acrs Upr MI in the aftn. Expect at least a brief period
of lower IFR vsbys associated with the heavier sn showers that occur
along this trof that wl clr SAW arnd 27/00Z. The arrival of much
drier air behind this trof wl then bring a return of VFR conditions
this evng.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 322 PM EST SAT FEB 25 2017

NW gales to 35 knots are expected over the east half of Lake
Superior into this evening. Winds will stay 25 kts or less through
Sun and then increase to 30 knots Sun night behind the next system
that moves through on Sun. Winds will become NE to 30 kts Tue night
into Wed behind another low pressure system crossing Great Lakes.
Winds diminish to 25 kts or less into Thu as the low moves toward
New England and a high pressure ridge builds from western Canada to
the central Conus.

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


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