Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 041743
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1143 AM CST Sun Dec 4 2016

.SHORT TERM...(Today)
Issued at 251 AM CST Sun Dec 4 2016

Active period of weather! Current nearly neutral tilt upper trough
continues to work east through the Central Plains early this
morning, with a notable shortwave on the southern flank across
Kansas at 06Z quickly lifting through the area this morning. Plenty
of warm advection ascent in advance of that upper wave working its
magic with top down saturation well underway and mainly light snow
spreading north across the area. Quick regional radar check
continues to show plenty of moisture just upstream, with healthy
0.25 to 0.40 inch amounts the past 6 hours across eastern KS. It`s
that axis of deeper moisture/precip that is expected to get lifted
through the region roughly 12-18Z this morning, all while the upper
wave tries to take on a negative tilt, further helping enhance lift.

Based on the current setup, am a little concerned that snowfall
amounts could over-perform mainly along/east of the Mississippi, and
perhaps even a little farther west. Forecast RAOBS continue to peg
pretty good lift through a 100-ish mb deep dendritic layer, though
warmth below that may help offset ratios to some degree. Still, with
good forcing and moisture into the area (PWAT values a respectable
0.5 inches), do get the feeling a period of more intense snow may
result this morning for many areas. Based on that idea and near term
guidance trends, have upped snowfall amounts for most spots, with a
solid 2-5" from west to east across the CWA, highest over far
northeast IA into southwest WI. Current advisory area looks pretty
good, and does include some impact component as opposed to straight
criteria-based numbers, but will really have to watch some
southern/eastern spots as it`s not totally impossible we could push
warning criteria if we can manage slightly higher ratios. Snow
should taper from west to east into the afternoon/early evening,
with even a hint of clearing possible far western spots by 00Z.
Based on a slight slower easter progression of precip, have nudged
highs down a solid 3 degrees or so for today.

.LONG TERM...(Tonight through Saturday)
Issued at 251 AM CST Sun Dec 4 2016

The 04.00z GFS/NAM/ECMWF are in decent agreement in digging upper
level trough over the Northern Rocky Mountains and building
shortwave ridge over the Great Lakes/Upper Midwest Region tonight/Monday.
The 04.00z deterministic models indicate slightly warmer air
advecting into the region with 925mb temperatures warming to 0 to
plus 2 degrees celsius. With fresh snow cover and the
deterministic models suggesting mid level cloud deck over the
forecast area during the day in advance of the upper level
trough...feel high temperatures will mainly be in the 30s for much
of the forecast area Monday.

Upper level trough digs into the Northern Plains States Monday night
into Tuesday and tracks cold front across the forecast area. The
04.00z GFS/NAM show weak forcing/vertical motion along the
front...with the better lift/forcing north and south of forecast
area. Precipitation amounts along the front will be light...less
than five hundredths of an inch. Will continue with small
precipitation chances across parts of the forecast area Monday night
into Tuesday. Behind the cold front...cooler airmass filters into
the forecast area Tuesday. High temperatures (upper 20s to middle
30s) will occur early Tuesday morning and temperatures are expected
to slowly fall into the teens to middle 20s Tuesday afternoon.

Main forecast concerns Wednesday through Saturday are precipitation
chances and temperatures through period. The 04.00z GFS/GEM/ECMWF
are in much better agreement in digging upper level trough over the
central and eastern United States through Friday. The biggest
difference between the deterministic models is timing of impulses
embedded in the upper level trough into the Great Lakes Region
through Friday. With weak lift in association with a piece of energy
rotating around upper level trough and cooler airmass in
place...parts of the forecast area may see some light snow or
flurries mainly Thursday/Thursday night. Small chances of light
snow are warranted during this time frame. Upper level trough
over the eastern United States weakens Friday and the 04.00z
GFS/ECMWF/GEM dig another trough over the lee-side of the Rocky
Mountains Friday night into Saturday. Differences on strength of
the upper level trough occur between the models...however the
04.00z models suggest decent lift/moisture with the upper level
trough and spread snow across much of the forecast area Saturday.
Temperatures through the period will be cooler...as the 04.00z
GFS/GEM/ECMWF show 925mb temperatures in the minus 10 to minus 15
degrees celsius range. This will result in high temperatures in
the teens to 20s across the forecast area through the period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1137 AM CST Sun Dec 4 2016

The back edge of the snow has just past KRST and it will move east
of KLSE between 04.19z and 04.20z. Additional snow amounts at KLSE
will be up to a half inch. In the wake of this snow, MVFR
visibilities will continue through much of the afternoon, and
ceilings will be in the IFR to MVFR range. Both the ceilings and
visibilities will gradually become VFR tonight and remain that way
into Monday morning. If we decouple tonight, we may have to watch
for the potential for some fog for late tonight and Monday
morning.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until noon CST today for WIZ032.

     Winter Weather Advisory until 3 PM CST this afternoon for WIZ017-
     029-033-034-041>044-053>055-061.

MN...Winter Weather Advisory until noon CST today for MNZ088-095-096.

IA...Winter Weather Advisory until noon CST today for IAZ009-010-018-
     019-029.

     Winter Weather Advisory until 3 PM CST this afternoon for IAZ011-
     030.

&&

$$

SHORT TERM...Lawrence
LONG TERM...DTJ
AVIATION...Boyne


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