Area Forecast Discussion

FXUS63 KARX 180802
Area Forecast Discussion
National Weather Service La Crosse WI
202 AM CST Mon Dec 18 2017
.SHORT TERM...(Today through Tuesday Night)
Issued at 202 AM CST Mon Dec 18 2017
Main concern in the near term will be timing of dissipation of 
fog/low clouds. Current water vapor imagery shows a distinct mid-
level trough moving east out of the Dakotas into MN. Attendant 
surface trough washes out somewhat as it pushes into the area today 
but surface pressure gradient tightens, which in turn increases 
boundary layer/surface winds out of the southwest. This is expected 
to scour/clean out the fog/low clouds across the area from west to 
east. Meanwhile, will likely see some cirrus/altocumulus above this 
dissipating lower cloud in advance of a cold front dropping through 
ND/northern MN by late in the afternoon. Otherwise, partial sun and 
neutral to weak warm air advection should push temperatures today 
into the middle 30s to middle 40s. 
Cold front makes passage across the area tonight with main 
forcing/saturation for light snow chances remaining just north of 
our area. Will keep us dry for now.  
Tuesday looks like a mostly sunny/breezy day, with west winds 
generally in the 15 to 25 mph range. Plan on highs in the 30s to 
lower 40s.
.LONG TERM...(Wednesday through Sunday)
Issued at 202 AM CST Mon Dec 18 2017
Attention is on likelihood of accumulating snow from Wednesday 
afternoon through Friday. 18/00z models seem to be coming into 
better consensus (for now) on idea of a warm air advective band of 
snow mainly north of I-90 Wednesday afternoon into Thursday where 
potentially several inches of snow could fall, generally along/north 
of I-90. There could also be some precipitation type issues farther 
south with warm nose of air poking in. Then for Thursday night into 
Friday, potential is there for a long duration deformation snow 
moving through the area as surface low tracks across northern 
IL/southeast WI. With this track, heaviest snow band looks to set up 
from southeast MN into central WI. However, there is still a lot of 
uncertainty on snow amounts. Also, this is early in the game and the 
track of the low could shift some. Bottom line, accumulating snow 
looks likely and will likely impact travel. Advice is to keep up 
with latest forecasts and details.
Much colder air filters into the area through the weekend with highs 
Saturday in the teens to lower 20s, and single digits to teens for 
Sunday. There will also be another shot for some light snow Saturday 
night into Sunday as a trough of low pressure rotates through.
.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1100 PM CST Sun Dec 17 2017
Cigs: snow melt, lingering moisture and a light wind field will work 
to keep low cigs locked in at the TAF sites into Mon morning - 
mostly LIFR/IFR. Once winds start to pick up from the southwest Mon 
morning as responsible shortwave trough exits east, cigs should 
rise/scatter out.  00z NAM quicker with exit of the low cigs 
compared to previous run, more like the GFS/RAP now - and will 
continue to trend forecast this way (exiting between 15-18z).
WX/vsby: a lot of ifr/mvfr br out there right now (per sfc obs) and 
meso models suggest this will continue into Monday morning. How low 
it goes is uncertain, along with how much/if it will "bounce around" 
(KRST already fluctuating). Won't get too aggressive at the moment 
- monitor and adjust if necessary. Fog should clear as winds 
pick up Monday morning.
Winds: light southwest tonight, increasing for Monday. Some 
gustiness possible. In addition, Bufkit soundings (esp in the NAM) 
showing the potential for LLWS Mon evening. RAP/GFS less on the 
winds. Will hold off adding to the forecast, but something to watch.