Area Forecast Discussion
Issued by NWS Marquette, MI

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859
FXUS63 KMQT 240021
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
721 PM EST Thu Nov 23 2017

.SHORT TERM...(This evening through Friday)
Issued at 406 PM EST THU NOV 23 2017

WV imagery and RAP analysis indicated a mid/upper level trough over
Quebec and a ridge from the sw CONUS into the nrn plains resulting
in nw flow through the nrn Great Lakes. Upstream, a vigorous
shortwave trough was moving through the Pacific northwest. At the
surface, a ridge from northwest Ontario into Lake Superior was
sliding to the east as a 992mb low moves into srn Saskatchewan. A
warm front extended southward through the cntrl Dakotas. Vis loop
showed mostly clear skies over most of the cwa with some lingering
clouds north from moisture off of Lake Superior.

Tonight, after a period of additional clearing north this evening as
winds back to the southwest, clouds will increase as mid level
WAA/isentropic ascent shifts into Upper Michigan. However, any pcpn
is expected to remain over northern Lake Superior or northern
Ontario.

Friday, Rain chances will increase during the morning as the WAA
regime strengthens further. However, confidence in pcpn chances is
still low given potential of a lingering dry 900-700mb layer, per
fcst soundings. The best chance for widespread pcpn will be during
the afternoon from west to east as the shortwave and cold front
approaches with moderate to strong 700-500mb fgen moving through
the cwa. Since moisture inflow will still be limited, QPF values
only around a tenth of an inch are expected. The WAA will help
push temps into the mid and upper 40s, especially for downslope
locations.

.LONG TERM...(Friday night through Thursday)
Issued at 254 PM EST THU NOV 23 2017

...Varying temps into next week with light lake effect on Sat...

Upper air pattern to start the weekend features broad ridge over
western Conus with downstream troughing over Upper Great Lakes and
eastern Canada. Shortwave moving through in the troughing aloft will
support rain showers late Fri into Fri evening. Lift with shortwave
is not very strong so not expecting anything heavy. Could be a bit
of drizzle once deeper moisture moves out by late Fri evening but
dry sub cloud layer/inverted v look in soundings may just keep it
mainly dry at the sfc. Late Fri night into Sat morning, another
shortwave moving through along with arrival of polar jet will bring
colder airmass across Lk Superior and Upper Michigan. Expect lake
effect to increase as H85 temps fall to -10c which will produce
sufficient over-water instability with water temps of +4C. Soundings
show inversions up to 7kft with temps at inversion top of -13c. Some
question on extent of moisture at top of inversion though as GEM is
drier than the NAM and GFS. NW flow leading to additional moisture
off Lk Superior and daytime heating/instability should allow for
expansion of some snow showers and flurries over most of Upper
Michigan, except far scntrl forecast area vcnty of southern
Menoninee county. Weak cyclonic flow and weak low-level convergence
and dry air moving in with approaching high will keep snow
accumulations on the light side. Main issue will be that whatever
snow is occurring will be blown about since it will be higher SLR
type. Soundings indicate tapping into mixed layer winds of 25-30 kts
with deepest lake convection over east pulling down gusts over 35
kts. Think the main snow/blowing snow/reduced vsby hazard will be
over east where higher coverage of snow showers and strongest winds
are progged.

Any lake effect and winds diminish steadily from west to east Sat
night as subsidence/anticyclonic flow increase as sfc high pressure
briefly builds across from northern Plains to the Upper Great Lakes.
NW winds, H85 temps staying blo -10c and lingering moisture to
H85/4kft will continue to support light lake effect/flurries over
eastern forecast area. Even this lake effect will end after midnight
with lowering inversions and winds backing to WSW after 09z Sun.
Clipper shortwave and weak sfc low slide by north of Lk Superior on
Sun. Looks mostly cloudy, especially north with breezy conditions
possible, but should be no big weather impacts. Temps should stay
cool with low 30s west to upper 30s scntrl and east. Upper ridge
builds across on Mon though 12z GEM is slower with that idea. At
sfc, troughing settles over scntrl Canada to the high Plains. Return
flow ahead of the trough and thermal ridge should result in high
temps warming into the 40s. Now looks like there will be some mid-
high clouds around but even mixing to 900mb would support highs well
into the 40s and even around 50F depending on how much sunshine is
realized.

Blend of latest models and NAEFS/ECMWF ensembles point to lowering
heights and cooler air gradually working back over the region by
middle of next week. Could be some light lake effect for NW flow
areas. Details in how long this cold air persists is uncertain
though. Unlike yesterday there is no sign from main models of any
kind of strong storm system.
&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 717 PM EST THU NOV 23 2017

VFR conditions will give way to MVFR conditions on Fri afternoon
with a lowering of ceilings and areas of rain developing ahead of
an approaching cold front from the west. LLWS is expected to
develop late this evening and continue into Fri morning as a low-
level wind max noses in from the west.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 406 PM EST THU NOV 23 2017

Westerly winds of 15 to 25 knots will back to the south late tonight
into Friday at 20 to 30 knots with gale force gusts to 35 knots
expected. So a gale warning remains in effect from late tonight into
Friday afternoon for most of Lake Superior. On the back side of the
strong low pressure system additional gales of 35 to 40 knots are
possible on colder northwest flow into the area. Winds are expected
to remain in the 20 to 30 knot range through at least mid weak.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Warning from 7 AM Friday to 5 AM EST Saturday for
     LSZ246>251-265>267.

  Gale Warning from 5 AM EST /4 AM CST/ Friday to 1 AM EST
     /midnight CST/ Saturday for LSZ240>245-263-264.

Lake Michigan...
  Gale Warning from 4 AM to 4 PM EST Friday for LMZ221-248-250.

&&

$$

SHORT TERM...JLB
LONG TERM...JLA
AVIATION...Voss
MARINE...JLB



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