Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 040525
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1125 PM CST Sun Dec 3 2017

.SHORT TERM...(Tonight through Monday)
Issued at 255 PM CST Sun Dec 3 2017

At 2 PM, a 998 mb surface low was located over northeast Wyoming.
Mid and high clouds ahead of this system were located across the
Upper Mississippi River Valley.  These clouds were
holding down the temperatures some.

For tonight, the 925 and 850 mb moisture transport will increase
across the area.  As this occurs, showers will develop across the
area between 04.04z and 04.06z.  These showers will then continue
through Monday morning.  There are even some hints in the soundings
that there will be enough elevated instability for an isolated
thunderstorm.  After a brief drop in temperatures early this
evening, strong warm air advection will allow temperatures to rise
through the night.  By sunrise, temperatures will be in the mid and
upper 40s north of Interstate 94 and in the lower and mid 50s
elsewhere.

On Monday afternoon, the models are coming to a consensus that a dry
slot will move into the area.  The GFS and experimental HRRR even
suggests that we could see some clearing.  Temperatures will quickly
climb to around 60 south of Interstate 94.  These temperatures will
be warm enough that a few records may be tied or broken.  This near
record or record warmth will be short lived as strong cold air
advection moves in during the late afternoon.  With winds gusts
climbing up to 40 mph in southeast Minnesota and northeast Iowa, we
will be issuing a Wind Advisory.  These strong winds will then
continue into Monday night.

Unlike yesterday, the soundings look less favorable for
thunderstorms on Monday afternoon.  This is due to strong capping
that develops above 850 mb.  Due to this, lowered the thunderstorm
chances from scattered to isolated.

.LONG TERM...(Monday Night through Sunday)
Issued at 255 PM CST Sun Dec 3 2017

High Impact Weather Potential: Watching winds Monday night with
gusts of 40-50 mph quite likely. Will need a Wind Advisory for parts
of the area (maybe all areas?), with a lower end chance that a few
gusts could approach 55 mph in some spots.

So, what month is this again? (checks calendar). Yep, that`s what I
thought. It IS December. Guess it`s time to start forecasting cold
weather again.

Hope everyone has enjoyed the recent mild stretch as things come to
a crashing end Monday evening and night. As well advertised for
about a week now, the ongoing strong east Asian/Pacific jet that has
flooded the Lower 48 with mild conditions is in the process of
breaking down into a more typical Aleutians trough/western north
American ridge, while ridging also builds across Greenland with
time. That pattern looks to become rather stable for the next 1-2
weeks, opening the gates for much colder/more typical wintertime
chill to spill into the Great Lakes and points farther south and
east.

The whole change begins Monday night with a rapidly deepening
surface cyclone tracking over western Lake Superior, with a strong
cold front exiting the area no later than 03Z. Impressive cold
advection through the night will quickly steepen low level lapse
rates as winds in the mixed layer ramp up into the 40-50 knot range
coincident with a strong isallobaric response. Per forecast
soundings, looking like a pretty good wind event for a few hours
across the area (after Monday afternoon`s possible gusty conditions)
with surface gusts of 40-50 mph likely, perhaps even briefly higher
in a few open spots or ridge tops. Looking like a solid Wind
Advisory event for areas west of the Mississippi River and have
issued said advisory for those areas, including a period tomorrow
afternoon where we could really mix out if skies clear for a time.
Areas farther east into Wisconsin are a little more tricky as we may
not see true advisory criteria for many locations (save for the
ridge tops) so prefer to hold off at this point.

Not looking like we`ll have to deal with much in the way of "wrap-
around" deformation-driven snow as forcing across the local area
quickly departs after 00Z. However, we will likely deal with
periodic flurries or some very light snow at times through Tuesday
night as persistent low/mid level cyclonic flow remains and a
stratus deck working back across the area increasingly bisects the
dendritic growth zone, though winds will gradually subside with time
despite remaining on the breezy side.

From midweek and beyond, all eyes will be on harder-to-time
shortwaves dipping southward into the longwave trough axis centered
roughly over the central Great Lakes, though there are persistent
signals for the past 24 hours that a stronger wave will drop through
the region sometime Thursday night or Friday with perhaps a little
accumulating snowfall for some areas. Plenty of time to watch that
system over the next few days as well as chances for occasional
flurries, with the overall larger theme simply being a return to
much colder temperatures for the foreseeable future.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1125 PM CST Sun Dec 3 2017

Multiple challenges persist over the next 24 hours at both TAF
airfields as a strong low pressure system moves across the
region. These include timing of lower ceilings/rain and timing/
magnitude of low-level wind shear.

VFR ceilings for most of last evening will eventually give way to
MVFR/IFR cloud bases overnight as low-levels saturate. With these
lower clouds will come a chance for rain and some reductions in
visibility to around 5 SM. Could even see a few thunderstorms,
especially at KLSE, but not enough confidence to add at this time.
A dry slot will then move into the area Monday afternoon,
bringing an end to the rain and higher cloud bases. While VFR
conditions should continue through the rest of the period at KLSE,
a return to MVFR ceilings is likely at KRST as a deformation
precipitation band passes to the north and west.

Southerly winds will be strong through Monday afternoon with
frequent gusts between 20 and 30 kts. Winds then shift quickly to
the west Monday evening as a cold front passes through the area.
Gusts behind the front are likely to increase to between 30 and 40
kts, possibly higher at KRST. For tonight, still expecting low-
level wind shear issues with 45 to 50 kts in the 1500 to 2000 ft
agl layer, but these concerns will wane Monday morning as surface
winds increase.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Wind Advisory from 3 PM Monday to midnight CST Monday night for
     MNZ079-086>088-094>096.

IA...Wind Advisory from 3 PM Monday to midnight CST Monday night for
     IAZ008>011-018-019-029-030.

&&

$$

SHORT TERM...Boyne
LONG TERM...Lawrence
AVIATION...Rogers



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