Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 260140
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
840 PM EST Sat Feb 25 2017

.UPDATE...
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
convergence.

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...(Sunday night through Saturday)
Issued at 348 PM EST SAT FEB 25 2017

The active weather will continue next week with multiple chances for
precipitation across the area and in the traditional lake effect
snow belts. Temperatures will be variable next week with a few
bouts of cold air and warm air advection moving through the area.

Sunday night as shortwave energy lifts east across the northern
Great Lakes, expect area-wide snow to come to an end. Behind the
shortwave, a transient area of colder 850mb flow will allow LES to
linger in the west wind snow belts, primarily across the Keweenaw
before diminishing Monday morning. On Monday zonal flow will
transition to southwest flow aloft as troughing digs across the
Intermountain West, 850mb flow will back to the southwest and allow
for warm air advection to return to the area. This will temperatures
to warm back up into the 30s across the area on Monday.

Ahead of the main upper-level trough, a shortwave is progged to lift
across the area as a mid-level baroclinic zone develops along the
leading edge of warm air advection from the south and cold air
advection sliding south across the northern Plains. Resulting height
falls at the surface will allow for an inverted trough to develop
across the in area, in fact the NAM even hints towards a weak area
of low pressure developing across western portions of Upper Michigan
during the day on Tuesday. The enhanced low-level convergence
coupled with mesoscale and synoptic forcing will result in the
development of snow across western portions of the area on Tuesday.
Tuesday afternoon through the overnight hours in to Wednesday,
expect precipitation to move east into central and eastern portions
of the area as well. With much of the area in the transition zone
between warm air to the south and colder air to the north, thermal
profiles suggest much of the area will have low SLRs. Therefore,
snow that does fall will likely have wet and heavy characteristics.
The big question will be how far north the nose of warm air will get
to cause precipitation to transition over to rain. The NAM is the
most robust, with the 850mb zero degree isotherm spreading north
across much of south central and eastern Upper Michigan; whereas,
the remainder of the medium range models have the zero degree
isotherm clipping the area. Therefore, confidence is not high in
regards to precipitation type Tuesday into Wednesday. Tuesday night
into Wednesday, expect the snow to linger, especially across the
higher terrain near Lake Superior where low-level upslope flow will
develop behind the inverted surface trough.

On Wednesday as the main upper-level trough lifts out across the
central CONUS, a lee cyclone will lift northeast across the Middle
Mississippi Valley up into the lower Great Lakes region. The current
model trends over the past 24 hours with this system are to slow the
system down and take a bit more southern track, but there is still
quite a bit of uncertainty with this system. At this time the
majority of the system precipitation looks like it will remain south
of the area. The GFS would favor wrap around precipitation from this
system to impact south central and eastern portions of the area;
whereas, the ECMWF favors a much drier solution as it takes the
system further southeast of the area. However, colder 850mb air will
filter south across the area as we remain on the north side of the
main system. With the 850mb flow progged to lift across lower
Michigan, this would allow northeast flow to develop across the area
during the day on Wednesday. Even though 850mb temperatures do not
look impressive, it will be cold enough to support the development
of light upslope/lake effect snow in the northeast wind snow belts.
Wednesday night into Thursday as the main axis of the upper-level
trough begins to move overhead, 850mb flow will back from the
northeast to the north with colder temperatures pushing across the
area. This change in wind direction will likely disrupt the ongoing
LES at the time, but will allow for lingering LES in the north wind
snow belts into the morning hours on Thursday. Then on Thursday the
deep upper-level trough will encompass much of central and eastern
portions of the CONUS, with a few upstream shortwaves in resulting
northwest flow across the northern Plains. With 850mb flow becoming
northwesterly and much colder on Thursday, expect LES to develop in
the northwest wind snow belts and linger through the end of the
week. Late on Thursday, as one of the above mentioned upstream
shortwaves digs south across the area, expect the snow to not only
impact the northwest wind snow belts, but a good portion of the
area. Behind this shortwave, 850mb temperatures are progged to drop
to around -20 to -25C, this coupled with remaining northwest flow
will allow LES to continue in the northwest wind snow belts through
the first half of Friday. During the afternoon on Friday, LES will
transition to the west wind snow belts as flow backs ahead of upper-
level ridging sliding across the central CONUS.

There is some disagreement amongst the GFS and ECMWF in regards to
this weekend, so confidence is not high in how precipitation chances
will play out as a clipper system approaches from the northwest.
&&

.AVIATION..

Expect VFR conditions this evng at all the TAF sites under a passing
sfc hi pres rdg/dry airmass. Gusty winds early in the period at CMX
and SAW wl diminish this evng with the arrival of the rdg axis.
During the ngt, an aprchg lo pres trof wl bring some -shsn to IWD
and CMX along with MVFR conditions. The shsn wl continue at both
these locations thru much of the day on Sun and perhaps reduce vsbys
into the IFR range at times, especially at CMX where the llvl wly
wind component wl upslope. While the shsn wl also impact SAW in the
aftn, conditions no worse than MVFR wl occur there.
&&

.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.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Warning until 10 PM EST this evening for LSZ266-267.

Lake Michigan...
None.
&&

$$

UPDATE...KC
SHORT TERM...07
LONG TERM...Ritzman
AVIATION...KC
MARINE...07


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