Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 231936

Area Forecast Discussion
National Weather Service La Crosse WI
235 PM CDT Sun Oct 23 2016

.SHORT TERM...(Tonight and Monday)
Issued at 235 PM CDT Sun Oct 23 2016

Fast moving short wave passing through western Great Lakes this
afternoon with surface low now east of the area and decent surface
pressure rises noted in wake. With winds expected to diminish
somewhat this evening, main issue is extent of cloud cover.

Stratus field not being handled well by short term models, which
persist at keeping bulk of clouds north and dissipate them this
evening. While much of this is likely dirunal driven, will have to
increase sky cover for a time this evening, before some clearing

Ridging expected for Monday which should be another nice fall day.

.LONG TERM...(Monday Night through Sunday)
Issued at 235 PM CDT Sun Oct 23 2016

Monday night through Wednesday

Main focus in this time frame is rain chances, especially Tuesday
night into Wednesday. Models have been shifting a bit north and
south with each run but general idea of widespread rain still
looking favorable.

Short wave in upper flow is subtle initially in 23.12z guidance as
it ejects out of west coast trough, but becomes a bit more
noticeable on Tuesday as it moves into the Central Plains. This
feature generates a low level response in the form of warm air
advection and more importantly moisture return ahead of it that is
directed into Upper Mississippi River valley region by Tuesday
night. Precipitable water values just southwest of area, in source
region, climb into the 1.0 to 1.5" range.

As far as model differences go 23.12z NAM/GFS are nearly identical
while other guidance is a bit leaner on rain amounts. NAM/GFS bring
bulls-eye of forecast precipitation along MN-IA border into western
Wisconsin with a general 1-3". General idea in forecast therefore
has not changed and will keep high rain threats in forecast per
coordination with neighboring forecast offices, especially Tuesday
night and Wednesday. Most unstable layer CAPE values remain south of
the area but given extent of lift with signs that wave could grow
stronger as it approaches, will honor small risk of thunder mixed in
with precipitation mainly south.

Did lower high temperatures for Wednesday given expected cloud
cover, rain, and raw east winds. This is more in agreement with some
of the concensus model data as well.

Wednesday night through Sunday

This storm system and associated precipitation will be exiting to
the east at the beginning of this period. The GFS and ECMWF agree on
the general pattern of seasonable temperatures and a trough off the
west coast sending shortwaves through a ridge over the Plains.
However, no consensus has been reached on when and where
precipitation associated with these shortwaves will occur. The
23.12Z GFS sends a low pressure system along the US/Canada border on
Friday and keeps precipitation to the north with the low and to the
east along the associated cold front. The 23.12Z ECMWF progs a
similar system farther south on Saturday, which would give the
forecast area its next chance of precipitation. Overall, too much
uncertainty to put anything higher than slight chance pops over the
area at any given time.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1219 PM CDT Sun Oct 23 2016

Main concern this TAF period is later this afternoon/evening as the
sfc-mid level trough axis passes and MVFR clouds in the NW flow
behind it spread SE into the area. Distance-speed has these into the
TAF sites around 20z. With deeper mixing thru the afternoon, left
these as a sct025/sct030 layer at KRST/KLSE in the 20-03z time-frame
when the deeper of the 925mb moisture progged to rotate across the
area. Good VFR expected after 03z thru the rest of the TAF period as
Can high pressure builds in. Tighter gradient moves over the area
this afternoon. Deeper diurnal mixing to result in NW winds 10-20kt
G20-30kts across the area, with the stronger winds at the higher
elevation/ridge top locations. Winds to diminish quickly this




LONG TERM....Aegerter
AVIATION.....RRS is the U.S. government's official web portal to all federal, state and local government web resources and services.