Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 010600

Area Forecast Discussion
National Weather Service La Crosse WI
1200 AM CST Thu Dec 1 2016

.SHORT TERM...(This evening through Thursday)
Issued at 329 PM CST Wed Nov 30 2016

At 3 PM, a low pressure area was centered over west-central
Wisconsin. With cyclonic flow aloft and surface to 850 mb lapse
rates greater than 8 C/km, numerous rain and snow showers have
developed across the Upper Mississippi River Valley. With the loss
of diurnal heating, the surface to 850 mb lapse rates will
gradually decrease into the 6-7 C/km range. As this occurs, the
areal coverage of these showers will decrease. Any snow amounts
from late this afternoon into tonight will be mainly confined to
southeast Minnesota, northeast Iowa, and the higher terrain in
western Wisconsin. Snow amounts in these areas will range from a
trace to a half inch.

With extensive cloudiness and neutral temperature advection at
both the surface and aloft tonight, did not deviate much from the
low temperatures that occurred this morning.

For Thursday, the surface and upper level low will slowly move
east northeast across central Wisconsin during the morning and
upper Michigan during the afternoon. With the steepest surface to
850 mb lapse rates being off to our east, not anticipating as
widespread rain and snow showers...thus...precipitation chances
are less than 30 percent.

.LONG TERM...(Thursday night through Wednesday)
Issued at 329 PM CST Wed Nov 30 2016

From late Saturday night into Sunday evening, a short wave trough
will move east through the region. Soundings show that the
precipitation will be initially start as snow and then transition
to rain or a mix of rain and snow as the boundary layer warms on
Sunday.  Little is any snow accumulation is anticipated.

From Tuesday afternoon through Wednesday, both the 30.12z GFS and
ECMWF have shifted this low further west with its surface low
track. This allows the strong warm air advection ahead of this
system to move into the region. With 925 mb temperatures climbing
up to 6C across much of the area, any precipitation that falls
with this system will likely be mainly rain. With that said, the
30.12z ECMWF has a 6 standard deviation with their high
temperatures (ranging from a low of 17F to a high of 43F). Some of
this difference is a result to differing timing on the speed of
this system. Meanwhile, the GFS only has a spread of 3 standard
deviations. With high standard deviations showing up in the
temperatures, the uncertainty on any forecast during this time
frame is far from certain.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1159 PM CST Wed Nov 30 2016

The trough of low pressure continues to work east across the area
this evening but the precipitation with it has been slowly
dissipating as the main short wave trough moves off to the east of
the region. This trend will continue overnight and with the
remaining precipitation not amounting to anything more than
sprinkles, do not plan to include this in either forecast.
Ceilings are primarily IFR except for the valley locations where
they are MVFR. Again, little if any change expected until Thursday
morning when some weak diurnal heating should allow these to
slowly rise. Even with increasing heights, KRST could end up
sitting right around 1000 feet for much of the afternoon and




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