Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 222109
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
309 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.

Cnsensus 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 18Z TAFS through 18Z Monday afternoon)
Issued at 1210 PM CST Sun Jan 22 2017

Low clouds/fog will continue to be the main aviation impact for this
TAF cycle. Have begun to see some improvement in visibility late
this morning and this trend should continue into the afternoon,
with additional fog development possible overnight tonight.
Confidence is low regarding visibilities overall. However, expect
ceilings to remain generally IFR/LIFR into tonight.

&&

.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...JM



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