Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 110841

Area Forecast Discussion
National Weather Service La Crosse WI
241 AM CST Sun Feb 11 2018

.SHORT TERM...(Today through Tuesday)
Issued at 241 AM CST Sun Feb 11 2018

Local and regional radars showing some light snow falling across
Iowa into Illinois and southern Wisconsin. The northern edge of
this snow has snuck into the southern sections of the forecast
area but expecting that this will end/move east of the area
shortly after sunrise. Will continue to monitor radar trends, but
will likely need to continue some snow chances across the
southeast sections through about 14Z or so. After that, subsidence
behind the departing short wave trough will allow skies to clear
out with mostly sunny skies expected for the entire area by the
lunch hour and through the afternoon.

A large area of high pressure will be over the Upper Midwest
tonight and Monday before moving east of the region Monday night.
As the ridge moves away, a weak positive tilted trough with an
embedded short wave trough will approach the region for Tuesday.
The models have been showing this short wave trough for several
runs, but have not been very consistent on placement or strength.
The current runs suggest the wave will bring in some moderate pv
advection in the 500 to 300 mb layer, but not much else for
forcing will be in place. The best isentropic up glide will occur
Tuesday morning with the 11.00Z GFS showing up to 4 ubar/s on the
280K surface. There will be a lot of dry air for this wave and
isentropic up glide to displace so it become questionable if
saturation will be achieved. Right now, the models suggest the
best chance of this occurring could be across central Minnesota
into northern Wisconsin so that any light snow could miss the
forecast area and will not include any snow chances for this

.LONG TERM...(Tuesday night through Saturday)
Issued at 241 AM CST Sun Feb 11 2018

This period looks to start with quasi-zonal flow over the northern
tier of the country with a cut off low off the southern California
coast. Not a lot of agreement between the extended models on the
pattern moving into next week. Both the 11.00Z ECMWF and GFS show
a short wave trough coming onshore over the Pacific Northwest
Tuesday night and Wednesday but are much different on what happens
to this wave. The ECMWF digs it south and uses it to open up the
cut off low and kick it out toward the Midwest Thursday with a
broad, positive tilt trough following behind it for Friday. The
GFS has this short wave trough bypass the cut off low bringing it
across the region Thursday followed by weak northwest flow aloft
into the weekend. These differences lead to a lot of uncertainty
on when and how much precipitation there could be toward the end
of the week. Right now, the ECMWF would bring a surface low out
with the short wave trough with a pretty decent snow event hitting
the southeast parts of the forecast area Thursday. The GFS on the
other hand is essentially dry for the entire week and the start of
next weekend. With all this uncertainty, will only include some
snow chances Thursday afternoon to honor the ECMWF solution.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1140 PM CST Sat Feb 10 2018

Broad band of light snow from southeast NE into southern WI will
remain south of TAF airfields overnight with the primary impact at
KRST/KLSE being ceilings of 10 kft or higher. A return to mostly
clear skies is expected Sunday morning, continuing through the
rest of the period. Winds will be light with a favored west-
southwest direction.




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