NWS-La Crosse Forecast Discussion


						FXUS63 KARX 282041

Area Forecast Discussion
National Weather Service La Crosse WI
240 PM CST Sun Nov 28 2021

.SHORT TERM...(Tonight through Monday)
Issued at 240 PM CST Sun Nov 28 2021

Bits of upper level shortwave energy slated to top ridge and drop
across northern MN-northern/eastern WI later tonight/Sunday. Decent
QG convergence with the feature, mostly confined from the MN
arrowhead through northern WI btwn 18z Mon-00z Sun. Meanwhile, a
warm front current entering the western Dakotas, will march east
bringing a north-south swath of low level warming/isentropic upglide
with it. This warming increasing over western WI between 12-18z Sun,
quickly shifting east in the afternoon. This thermodynamic lift will
be the main lifting mechanism for the local forecast area.

Saturation continues to be a concern. To the north, models paint
more/deeper RH. To the south, Bufkit soundings and RH fields show a
drier picture, with lift/pcpn production having to go into
saturation initially. How quickly this occurs combined with movement
of the system across the area presents challenges in snowfall
potential. As it sits, most likely areas for snow will lie to the
north (I-94 and north/eastward) where the additional upper level
forcing will work on deeper saturation. In the south, chances should
increase from west to east with increasing thermodynamics and better
chances to saturate near sfc layer. Amounts still look minimal and
generally confined northeast of I-94.

While snow will be the main pcpn type, the low level warming could
result in partial melting/full before pcpn shifts east. Trends in
RAP/NAM suggest enough warming that a wintry mix would be more
likely on the southern flanks of the pcpn band (south of I-94). Not
much QPF anticipated with this potential wintry mix, so impacts look
minimal/if any at this time.

.LONG TERM...(Tuesday through Sunday)
Issued at 240 PM CST Sun Nov 28 2021

Upper level flow continues to lean toward a mostly northwest look
through the new week.

Bits of shortwave energy progged to spin across the region on/off
for the work week, bringing light pcpn chances here and there. The
GFS and EC continue to show some differences in placement/strength,
but generally favor keep the main sensible/impactful weather mostly
north of the local forecast area.

The weekend could be more interesting with the potential for a storm
system to shift out of western Canada, driving across the Upper
Mississippi River Valley Sat night/Sun. Snow and rain could
accompany the shortwave, with the potential for several inches on
the northside of its associated sfc low. Latest EC and GFS would
keep this snow band to the north with some potential for rain/mix
along/ahead of accompanying cold front. Many of EC ensemble members
shift this band even farther north, as does the bulk of the GEFS
members. WPC cluster analysis generally favors ridge building to the
west (to varying degrees) with northwest flow/troughing across the
region. Bulk of the EC lies here. Meanwhile, a portion of the GFS
suggests that the strong upper level ridging would build across the
region - a milder/dry solution. Looking at the GEFS members bears
this out with a large grouping of dry solutions...although the ones
that are wet produce a decent amount of QPF. Will lean the forecast
toward the more favored outcome for now (brings the shortwave in),
although the details/outcome remains very murky. It has a chance to
be an impact storm for some - whether that includes part of the
local area remains very much in question.

As for temps, still looking like a seasonable to mild end to nov-
start to dec. Highs could reach/exceed 50 for some Wed/Thu. Trends
then favoring cooling come the weekend.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1120 AM CST Sun Nov 28 2021

Mid and high level clouds will increase with gradually lowering VFR
ceilings tonight. Although the higher probabilities of precip will
remain north and east of KLSE/KRST late tonight, very light
(freezing?) showers/sleet/flurries are possible for a time after
midnight through early morning. Given the low confidence in precip
occurrence and ptype, will include only VCSH. NW winds will become
S/SE ahead of a front that will move through late Monday morning or
early afternoon.




LONG TERM....Rieck