Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 212013

Area Forecast Discussion
National Weather Service Marquette MI
313 PM EST Sat Jan 21 2017

.SHORT TERM...(This evening through Sunday)
Issued at 211 PM EST SAT JAN 21 2017

Upper trough from northern Plains to Upper Great Lakes will lift
north to Manitoba and Northern Ontario through Sun while stronger
shortwave trough develops from the southern Plains to the southeast
Conus. Sfc low with northern shortwave trough is currently over
southern MN and that will weaken as it moves toward western Upper
Michigan tonight into Sun morning. The stronger low pressure system
will be tied into the southern stream shortwave trough and will stay
well to the south of Great Lakes into Sun. Expect waves of scattered
to at times widespread showers over WI to lift across cwa this aftn
into early this evening. Kept mention of sleet over western Upper
Michigan for rest of day as heavier showers could result in enough
cooling aloft to produce sleet. Just a slight chance. After the
showers move out this evening, there is only very weak large scale
forcing to support additional precipitation so will have pops
diminishing steadily by the overnight hours and on into Sun. Could
not completely rule out some drizzle at times though.

The weakening sfc low/light winds along with dwpnts rising into the
middle 30s advecting across the melting snowpack will result in more
fog tonight into Sunday morning. Already extended the dense fog advy
til midday Sun and will go ahead and expand it into the western U.P.
as well since the downslope flow that saved that area from the dense
fog last night is not as strong and dwpnts will be higher. N to NW
winds increase on Sun aftn over west cwa as sfc low lifts across Lk
Superior so should see vsby begin to improve some by that time.

.LONG TERM...(Sunday night through Saturday)
Issued at 310 PM EST SAT JAN 21 2017

Sunday night through Monday night...Inverted trough extending into
the Great Lakes from a significant low pressure system moving into
the southeast and Atlantic Coast States will lead to continued low
cloudiness, fog, and chances of precipitation through the period.
Any precipitation Sun night will mostly be in form of dz/fzdz as
model soundings show shallow moisture well below height of -10c
isotherm. Only exception could be eastern counties late Sun
night...where model soundings indicate deeper Atlantic moisture
wrapping back into area from se CONUS system resulting in rain.
Combination of deeper Atlantic moisture and modest forcing from
shortwave approaching the area from the west will bring a better
chance for rain/snow mix across the area Mon into Mon
night...possibly mixed with sleet at times over central counties.
Expect very little diurnal swing in temps under cloud cover with
mins generally in the lower 30s and maxes on Tuesday in the mid to
upper 30s.

Tuesday...After some lingering morning snow showers east from
shortwave moving through the area Mon night, expect most of Tuesday
to be dry as weak ridging moves in behind the shortwave. Looks like
clouds and possibly fog (dew points still in the lower 30s) will
remain over the area though as low-level moisture remains trapped
under mid-level subsidence.

Models indicate a more significant shortwave ejecting ne from the
broad western CONUS trough will reach the Great Lakes midweek.
Continued falling heights and cooling column will mean ensure ptype
of just snow, by Tue night/Wed. The operational GFS remains quicker
and farther north than either the operational ECMWF or the Canadian
model. The Canadian remains the farthest south of the models taking
the sfc low through far southern Lower Mi and the Lower Great Lakes
while also being much slower (12-18 hours slower than the ECMWF).
The 12Z GFS track is similar to the GFS ensemble track but about 6
hours slower.  The operational ECMWF is probably closer to the GFS
ensemble mean with sfc low in terms of track/timing. In any event,
it would seem there is a decent potential for a period of widespread
synoptic snow at some point Tue Night into Wed/Wed night time frame.
The positive tilt of the large scale trough in which the stronger
shortwave is embedded suggests that a wrapped up strong sfc low is
unlikely. So, synoptic snow accumulations midweek should not be
significant, generally in the light to moderate range.  Expect light
to moderate les in the nw Lake Superior snowbelts behind the system
into Thu, with les tapering off sometime on Fri as h85 thermal
trough shifts east and surface ridging moves in behind it.

Models indicate a clipper shortwave moving down across the Upper
Lakes which will bring in a modest reinforcing shot of colder air to
generate another round of les for the n-nw wind snowbelts sometime
Sat into Sat night.

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1220 PM EST SAT JAN 21 2017

IFR to VLIFR conditions will continue in fog through Sun. The worst
conditions will be at CMX and SAW where winds will continue to
provide upslope lifting. The low visibility may improve at times
this aftn as rain showers lift across the area.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 211 PM EST SAT JAN 21 2017

A relatively weak pressure gradient over the Upper Great Lakes in
the absence of any strong weather systems will result in winds under
20 kts over Lake Superior most of the time into early next week.
Expect NW winds to increase to 25 kts by middle of next week as
low pressure over the central Plains moves toward eastern Canada.

Upper Michigan...
  Dense Fog Advisory until 1 PM EST /noon CST/ Sunday for

Lake Superior...
Lake Michigan...
  Dense Fog Advisory until 1 PM EST Sunday for LMZ248-250.



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