Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 242201

Area Forecast Discussion
National Weather Service La Crosse WI
500 PM CDT Mon Oct 24 2016

.SHORT TERM...(This evening through Tuesday night)
Issued at 306 PM CDT Mon Oct 24 2016

Main forecast concerns are on timing the arrival of rain Tuesday
afternoon into Tuesday evening along with location of heaviest
rainfall from Tuesday night into Wednesday morning.

High pressure slides east of the region tonight into Tuesday morning
as a shortwave trough moves across the northern plains and heads
toward the Upper Mississippi River Valley. Clouds will be on the
increase tonight through Tuesday as the wave approaches. Rain
will develop across the forecast area from west to east late
Tuesday afternoon into Tuesday evening as Isentropic Lift
increases on the 290-310 K surfaces. There is some weak MUCAPE
noted mainly along and south of interstate 90 with values of
100-200 J/KG. So, will keep low chances for thunderstorms confined
to portions of northeast Iowa and far southwest Wisconsin. A
surface low deepens along the baroclinic zoned situation across
the forecast area leading to increasing southeasterly winds
Tuesday night into Wednesday. The winds could be rather gusty
during the evening and overnight with gusts to around 35 mph
possible. The real limiting factor on winds not being stronger are
the lack of steep lapse rates near the surface and unfavorable
time of day to mix down the strongest winds above 1 kft.

Much of the local area will see rainfall amounts of 1 to 2
inches. With only weak CAPE, precipitable water values around 1
inch, and a this being a fairly progressive system, we should not
see any flooding issues. Also, the past 30 days have been on the
drier side for areas along and south of Interstate 94, with 30 day
means running at 25 to 50 percent. Also, with the exception of
northern Clark and Taylor Counties, much of the area has seen
little or no rain over the past 7 days.

.LONG TERM...(Tuesday night through Monday)
Issued at 306 PM CDT Mon Oct 24 2016

Rain will continue across much of the area at least through midday
Wednesday then it should start to taper off. A trailing inverted
trough will likely maintain some low clouds and possibly light
rain or drizzle. NAM forecast soundings look ideal for this, with
saturation from near the surface through nearly 8 kft. This layer
really doesn`t dry out until late Wednesday evening into early
Thursday morning. Quiet weather then returns on Thursday as weak
high pressure slides through.

The GFS and ECMWF remain consistent for this period with the general
pattern of shortwaves moving through a ridge over the Plains and
seasonable temperatures. These two models have also come into a
bit better agreement on the timing of the first wave, progging
some precipitation for the area on Friday with the heaviest
remaining north. Even with this better agreement, it is difficult
to have much higher than 20 or 30 POPs since the ECMWF only
recently came to this solution and both models` QPF is on the
lighter/spottier side. Models then diverge on timing and intensity
of the subsequent shortwaves with the 24.12Z ECMWF bringing
precipitation through the area again Saturday afternoon into
Sunday and the 24.12Z GFS keeping the area dry through Monday.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 500 PM CDT Mon Oct 24 2016

Wing of warm air advection slated to push northward across the
region Tue morning. Should result in a mid level deck of
clouds...but with appreciable dry air sub 750 mb (per Bufkit
soundings)...not anticipating much of a rain threat into the
afternoon. By the evening, a sfc low/upper level shortwave starts to
approach, along with the nose of the low level jet. The lower levels
will saturate and rain is likely. A rumble or two of thunder can`t
be ruled out, but not a high enough threat to include in the TAFs.
The overnight period looks particularly wet, with accompanying
reductions in vsby/cigs - ifr/mvfr conditions expected. Winds will
also be on increase thanks to a tightening pressure gradient.




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