Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 222348
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
548 PM CST Sun Jan 22 2017

.SHORT TERM...(Tonight through Wednesday)
Issued at 310 PM CST Sun Jan 22 2017

High Impact Weather Potential: A return to wintry conditions appears
in the works toward Tuesday and Wednesday, with accumulating
snowfall likely for many areas. The potential exists for warning
criteria snow of 6 inches or more, especially near/west of the
Mississippi River.

Quite mild spring weather we`ve been having lately, eh? All good
things must of course eventually end (it is only late January
after all), and that end will come later Tuesday into Wednesday
with our next shot of wintry precipitation. Prior to that time,
the focus remains on this pesky stratus and fog we`ve been stuck
with for several days now. Visibility have improved markedly
areawide this afternoon, save for ridge top locations which remain
stuck in the muck. Confidence in more widespread fog overnight is
much lower than recent nights, thanks mainly to a better gradient
as weak ridging builds to our south. No doubt there will likely be
some patchy dense fog in spots (ridge tops and more into
Wisconsin where the gradient is a bit more baggy) but don`t
envision another widespread advisory event, with SREF progs
strongly agreeing. Clouds not likely to break through tonight,
but there is a small chance we could bust through the thin stratus
in a few lucky spots on Monday as transient shortwave ridging
arrives. Fingers crossed.

Bigger story by far is the Tuesday-Wednesday timeframe with regard
to wintry precipitation. Quite the upper trough off the West Coast
at the moment, and some of that energy has been progged for days now
to lift from southern California through the Central Plains by
Tuesday, attempting to close off as it does so. Just how fast and
how much that upper wave closes off will have a big impact on our
sensible weather locally, but the overall trend from recent days of
a robust closed wave tracking through the region remains intact.
Starting to get a better model consensus of the track as well,
though the GFS does remain slightly stronger/northern and faster
while the ECMWF has been steadfast for 72 hours. GEM is just a big-
time southern/weaker outlier, so have discounted it for now.

Consensus track of the 850-700mb and surface low just to the
south of the region strongly favors the best
frontogenetic/deformation forcing laying out somewhere either side
of the I-90 corridor, with enough cold air entering the picture
for this to be a mostly wet snow event. That said, a slightly
farther north scenario a la the GFS and many of its 12Z ensembles
would suggest some boundary layer issues at lower elevations for a
time Tuesday afternoon and evening, with hints of a 1.5kft melting
depth at LSE and locations farther south. That`s going to be a
nearer term issue once we get a better consensus on track, but for
now a general 3-7" snowfall appears likely for many areas, with
steady snow tapering to snow showers on Wednesday as lingering
wraparound moisture/cyclonic flow prevails behind the upper wave.
May be tough to get actual warning criteria snow in 12 hours but
expected wet nature of the snow should have a pretty big impact.
For now, have coordinated a Winter Storm Watch for much of
northeast Iowa into southeast Minnesota (where snow begins first
on Tuesday), but it may need to be extended eastward overnight.

.LONG TERM...(Wednesday Night through Sunday)
Issued at 310 PM CST Sun Jan 22 2017

Still looking like an extended period of overall northwest flow
aloft through late week end next weekend as heights build
considerably over the western CONUS with time, eventually perhaps
pulling some more seasonably colder air our way toward Saturday or
Sunday. Various weak ripples in said flow should serve to keep
things rather cloudy with high temps a little closer to reality for
late January but overnight lows holding well above normal.
Additionally, bouts of deeper moisture and some shallow instability
each day should bring chances for some flurries or even snow showers
at times, with even a risk for some light additional accumulation
(less than an inch) later Thursday into early Friday as a better
defined shortwave trough slides through the area.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 548 PM CST Sun Jan 22 2017

As has been the case for the past several days, IFR/LIFR ceilings
will persist at both KLSE/KRST through at least Monday morning,
possibly lifting to near 1000 ft agl by late in the period.
However, dense fog this evening and overnight likely to be more
patchy in coverage, so will keep visibility restrictions at 1SM
or more at this time. That said, updates still possible to drop
visibility below 1SM, especially late tonight into Monday morning.
Light northwest winds will persist, generally being 8 kts or less.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for MNZ079-086>088-094>096.

IA...Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for IAZ008>011-018-019.

&&

$$

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


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