Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 231955

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

.SHORT TERM...(Today and tonight)
Issued at 356 AM EST THU NOV 23 2017

No major weather impacts expected through the short-term portion of
the forecast.

Today: A weak shortwave and weak surface trough sliding through
the U.P. this morning will bring some light snow showers or
flurries over the far eastern U.P., mainly east of Munising as
winds become west to west-northwesterly. Otherwise, a surface
ridge over the Mid-Mississippi Valley into the Ohio River Valley
will link up with a weak ridge sliding southeast across Canada.
This will place high pressure across the Upper Great Lakes
throughout the day. This, along with drier air pushing into the
area and warmer air aloft, will bring an end to the precipitation
throughout the day. Cloud cover may linger over the Keweenaw
Peninsula with continued upslope flow off Lake Superior. 850mb
temperatures are progged to steadily warm; however, they should
only warm to around -6C by 00Z/24, again, cool enough for
continued cloud cover, but not cold enough for lake effect
precipitation. Southern and central portions of the U.P. will
likely see the sun sneak out throughout the day, allowing
temperatures to warm into the mid to upper 30s, again, the cooler
areas will be where cloud cover linger through the day, most
notably over the Keweenaw.

Tonight: The surface ridge will shift to the east allowing winds
to become more southerly across the area. At the same time, low
pressure will slide south and eastward into Ontario. This will
allow a weak stationary front to lift north and eastward across
the northern portions of Lake Superior as a warm front. This will
be where the better moisture and forcing/isentropic upglide will
be through the overnight hours. The warmer southerly flow on the
back side of the front and behind the departing surface ridge will
allow temperatures to warm enough, both aloft and at the surface
to keep the precipitation in the form of rain over Lake Superior.
Most of the U.P. is expected to stay dry; however, cloud cover
will steadily increase through the overnight hours. Overnight lows
will be in the upper 20s to low 30s.

.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

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 18Z TAFS through 18Z Friday afternoon)
Issued at 1259 PM EST THU NOV 23 2017

MVFR cigs at KCMX will give way to VFR conditions by late this
afternoon as winds gradually back to the sw. Otherwise expect expect
VFR conditions throughout the forecast period at KIWD and KSAW. LLWS
is expected to develop late this evening into the overnight hours as
a low-level wind max noses in from the west. Expect gradually
lowering cigs Friday morning as a cold front approaches from the
west. However, conditions should remain VFR.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 356 AM EST THU NOV 23 2017

West to west northwest 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. This has led to the issuance of a gale
warning 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 for Friday night into Saturday. Winds are then
expected to remain in the 20 to 30 knot range through at least mid

Upper Michigan...
Lake Superior...
  Gale Warning from 7 AM Friday to 5 AM EST Saturday for

  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.



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