Area Forecast Discussion
Issued by NWS La Crosse, WI

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761
FXUS63 KARX 282342
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
542 PM CST Tue Feb 28 2017

.SHORT TERM...(Tonight through Thursday Night)
Issued at 257 PM CST Tue Feb 28 2017

High Impact Weather Potential: Main focus is on the increasing
potential for some accumulating snowfall late tonight into
Wednesday, particularly focused near and east of the Mississippi
River where a few inches of accumulation are likely. Other focus
is on evening convective chances, though the greatest risk appears
to be south/east of the local area.

Quite an active stretch of weather into midweek! Midday analysis
places a lead shortwave working through northern Minnesota
(responsible for some snow up that way), with a stronger upper
trough working east out of the central/southern Rockies. A surface
warm front continues to bow northward into southern Wisconsin as of
18Z, tied to an elongated surface low across eastern Iowa, while a
cold front sits just upstream to our north. Quite the airmass change
across the region given the setup, with temps into the 50s/60s south
of the warm front but only in the teens/20s across northern
Minnesota, and of course, in typical fashion for this winter, our
local CWA is sitting right in between.

From a radar perspective, one batch of earlier convection (complete
with some small hail and even weak circulation aloft given pretty
good elevated shear) has worked off to the north, with much of the
area sitting in "no man`s land" currently with classic a "north
of the warm front" hodge podge of drizzle, low clouds, and fog.
However, we are awaiting convection firing off just to the south
and east in an increasingly unstable airmass near/south, and in
advance of stronger forcing ahead of the approaching stronger
upper wave and within the axis of stronger moisture transport
(PWATs an impressive 1"+ once again). Given surface-based
instability pushing 1000+ J/kg in the presence of modest low level
and deep layer shear, do have some concern about the potential
for severe convection along the warm front (and especially farther
to the south/east), maybe just clipping southern Grant County but
more likely into southeastern Wisconsin and especially northern
Illinois.

Focus then shifts to the wintry component later tonight through
Wednesday (welcome to March!) as the upper wave shifts through the
region. Uptick in mid level deformation forcing in combination with
deeper layer TROWAL development as the system deepens should prove
sufficient to drive additional precipitation development across much
of the area later tonight through Wednesday, heaviest east of the
Mississippi River Wednesday morning where the deeper moisture gets
wrapped back westward. All the while, increasingly colder air
bleeding in from the north/crashing thickness values should change
precip type over to snow as the warm boundary layer and residual
warmer layer aloft is gradually erased. Given the setup, still
envision the potential for a quick 2-4" of snow accumulating
mainly across western and central Wisconsin Wednesday morning
before forcing wanes through the afternoon, though some trends of
late would suggest the potential for even a little more than that
as ratios ratchet upward with heavier QPF progged toward central
Wisconsin squarely in the TROWAL feature. All told, the potential
does exist for advisory-level snows over our eastern areas, and
per coordination with MKX/GRB, have issued a Winter Weather
Advisory for Juneau and Adams Counties for now. That headline may
need to be massaged westward at some point pending the evolution
of forecast snow. Much lower amounts in the 1 to maybe 2 inch
range appear likely into southeast Minnesota...lesser amounts into
northeast Iowa.

We`re not quite done yet, with another series of weaker "clipper"
waves slated to arrive Wednesday night through Thursday evening.
Trends over the past 24 hours have continued to suggest the greatest
risk for snow occurring on Thursday with an uptick in 850-700mb
frontogenetical forcing pretty much bisecting the CWA in combination
with deeper cold air in place (meaning higher snow ratios). Could be
looking at a pesky light accumulation during this timeframe, but
looking like mainly an inch or less at this time. Temps through
Thursday definitely trend strongly back toward below normal.

.LONG TERM...(Friday through Tuesday)
Issued at 257 PM CST Tue Feb 28 2017

Ready for milder weather? It arrives through the weekend as upper
heights build over much of the central CONUS while southerly flow
also strengthens. The end result should be temps responding back
through the 40s and 50s (coldest initially over existing snow pack),
and honestly wouldn`t be shocked if some spots make a run at 60
degrees toward Sunday. Could also see similar warmth into Monday but
with increasing hints of better moisture advecting back north
through the region, resulting in increasing rain chances as stronger
low pressure takes shape over the upper Midwest. The specifics of
that system remain somewhat lower confidence, though the trend for
stronger low pressure nearby has been there for several days now.
Pending timing and evolution of that system, Tuesday may end up
being cooler and windy, but again plenty remains to be worked out
during this time range.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 542 PM CST Tue Feb 28 2017

IFR to LIFR conditions are expected through much of the TAF
period. Low stratus and fog are expected this evening with
ceilings falling to around 300 ft at KRST and to around 800 ft
KLSE. The visibility may fall to 1/2 mile or less at times at
KRST in fog this evening. A rain/snow mix is expected at the TAF
sites after midnight, switching over to all snow during the late
night and early morning hours. Once the snow sets in, plan on
visibilities falling to around 1 SM in snow. The switch over to
snow looks to happen after 9Z. Look for winds to switch to the
northwest by midday Wednesday with snow tapering off during the
early afternoon hours. Conditions should then improve to MVFR
Wednesday afternoon with ceilings lifting to 1000 to 1500 ft.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 6 AM to 6 PM CST Wednesday for
     WIZ043-044.

MN...None.
IA...None.
&&

$$

SHORT TERM...Lawrence
LONG TERM...Lawrence
AVIATION...Wetenkamp



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