Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 101737
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1137 AM CST Sun Dec 10 2017

.SHORT TERM...(Today through Tuesday)
Issued at 322 AM CST Sun Dec 10 2017

High Impact Weather Potential: Another batch of accumulating
snowfall likely across parts of the area later tonight into part of
Monday. Could also be looking at some mixed precipitation in some
areas, particularly near and west of the Mississippi River. Travel
impacts very much possible for the Monday morning commute.

Another day...another challenging "clipper" wave crossing the area.
Not much to discuss for today, save for some increasing lower clouds
from the north, so let`s skip ahead to a shortwave just coming
onshore over British Colombia as I`m typing this, with that feature
expected to amplify rather quickly over the western CONUS ridge and
pretty much drop directly across the local area later tonight into
Monday morning. As discussed yesterday, forcing is rather robust
with this feature with a solid axis of 35-50 knots of deep layer
isentropic upglide (warm advection) working a cross the area, but
with said warm advection also adding a layer of complexity to
precipitation type as we try to introduce a 1-2C warm nose for areas
near and west of the Mississippi River.

Similar to yesterday, my personal confidence in a band of
accumulating snowfall near and east of the Mississippi River is
pretty high, and given the strength of the warm advection, can`t
rule out some pretty hefty snowfall rates for a few hours, though to
be honest, the exact placement of the heaviest snow band is still
somewhat in question (a county or two displacement could make a big
difference here). Current thinking still paints a band of 1 to maybe
2 inches near and east of the Mississippi River where we should hang
onto a sub-freezing column for much of the event, but farther west
there are questions about saturation initially as well as a pretty
good signal we may deal with some sleet or even brief freezing rain
pending just how robust the warm nose ends up being. Similarly,
can`t totally rule out some convective elements working into western
areas late tonight with an axis of 7.5-8C/km 700-500mb lapse rates,
coincident with the strongest deep layer Q-vector convergence axis
squarely pegging the local area. Should said convection occur, that
throws the whole precip type forecast out the window with forecast
soundings indicating we may at times eradicate the warm nose to
force more of a snow or all sleet setup. All told, suspicion is that
system has a few tricks up its sleeve and has a high potential to
impact the Monday morning commute with some slick travel as well as
perhaps a narrow axis of heavier snowfall, which could potentially
warrant an advisory if we can narrow down the heaviest snow or mixed
precip potential.

Departure of the wave will shut down much of the precip quickly by
noon or so Monday, with our next round of robust cold advection
kicking into gear Monday evening and night. Could be some flurries
within any lingering stratus Monday night as the cloud layer bisects
the dendritic growth zone, but not really worried about that at this
point. Bigger story is a cold day on the way for Tuesday, with highs
only in the teens and lower 20s and breezy conditions pushing wind
chill readings near 0 for much of the day.

.LONG TERM...(Tuesday Night through Saturday)
Issued at 322 AM CST Sun Dec 10 2017

Active weather pattern set to continue through the weekend, but with
continued hints we may see a very brief respite from the coldest
weather at some point by late week or through the weekend itself.
Next feature of interest will be an incoming shortwave Wednesday
with another round of snow very much possible across much of the
area, though again with questions about the exact placement of the
better snow band. Several additional weaker waves crossing the
region Thursday into Friday may deliver some snow showers at times,
but not looking like anything too impactful at this time. Larger
story may end up being a nice respite in the coldest weather by next
weekend, with some hints showing up that some spots could push 40
degrees by either Saturday or Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1137 AM CST Sun Dec 10 2017

Area currently enshrouded in MVFR stratocumulus in broad cyclonic
flow. Bout of impactful weather expected tonight into Monday as a
low pressure system drops southeast out of Canada into the region.
Light snow expected to break out at KRST around 05z and KLSE by
07z. Expected MVFR cloud to continue through the period with the
exception of occasonal IFR (mainly 06-08z time frame for KRST and
08-10z at KLSE). Expect reductions in visibility in the snow as
well down to 1sm in the snow during same time periods. Right now,
thinking total snow amounts will be around an inch.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Lawrence
LONG TERM...Lawrence
AVIATION...DAS



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