Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 222335

Area Forecast Discussion
National Weather Service La Crosse WI
635 PM CDT Wed Mar 22 2017

Issued at 635 PM CDT Wed Mar 22 2017

Radar looking a bit "menacing" with a band of precip rolling in
from the west, though much if not all of that is not reaching the
ground per both obs and more importantly the environment, with a
tremendous dry wedge intact below 8kft (surface dew points in the
single digits/teens!). Current forecast has this handled well,
with maybe a sprinkle or flurry possible through the evening as
mid level warm advection continues to crank up over our area,
though not expecting anything worse.

Of more impact, have introduced a mention of thunder for later
Thursday afternoon and evening. 18Z guidance continued earlier
trends showing a narrow axis of 500+ J/kg elevated CAPE working
north in tandem with an elevated warm front and modest moisture
transport squarely into our area, especially spots near and north
of I-90. Given the setup, can`t at all rule out a few rumbles,
with maybe even a risk for some smaller hail pending degree of
instability, with freezing levels down below 10kft (down toward
6kft far north) and some shear to work with above 600 mb. Don`t
envision that being a huge deal, but something to watch. Also
slowed down the arrival timing of precip chances through the
morning given the remnant wedge of quite dry air in place, quickly
becoming displaced to the east through the afternoon.


.SHORT TERM...(This evening through Thursday)
Issued at 345 PM CDT Wed Mar 22 2017

At 3 PM, a 1037 mb surface high was centered over central Lake
Michigan. East and southeast winds on the back side of this high
continues to bring very dry air into the Upper Mississippi River
Valley. Dew points ranged from 5 to 15F. Temperatures ranged from
30 to 35F north of Interstate 94 and 35 to 41F across the
remainder of the area. Meanwhile further west, weak to moderate
800 to 600 mb frontogenesis was producing some a light wintry mix
of precipitation from southwest Minnesota southeast into central

The 22.12z models continue to show that an elevated warm front
will move east across southeast Minnesota and northeast Iowa
late tonight and Thursday morning and across western Wisconsin on
Thursday afternoon. The HRRR continues to show that maybe some
elevated showers may develop across western Wisconsin overnight
ahead of this warm front. However with the low levels (sub-cloud
layer) remaining very dry, this precipitation may not make it to
the ground. As a result, kept the forecast dry for the overnight.

During the day Thursday, BUFKIT soundings show that the air mass
will gradually saturate as moisture surges ahead of an approaching
front from the northwest. This will result in the development of
rain across the region. The highest chances will be during the
afternoon. With very dry air still advecting into the area during
the morning, there may be the potential for a light wintry mix at
the onset. However this looks to be brief and should not cause any

.LONG TERM...(Thursday night through Wednesday)
Issued at 345 PM CDT Wed Mar 22 2017

From Thursday night into Sunday, a slow moving upper level low
will move from the Southern Plains into the Ohio River Valley. A
deformation band of rain on the north side of this low will slowly
move south across the forecast area. This deformation band will be
mainly along and north of Interstate 90 from Thursday night into
Friday night, and along and south of Interstate 90 from Friday
night into Sunday. It continues to look like the much of the
instability will remain south of the forecast area. As a result,
kept the mention of thunder out of the forecasts. Rainfall amounts
from this system will likely range from 1 to 1.5 inches. With this
rain spread out of over a long-period of time, only anticipating
in bank rises on area rivers.

With the potential that the southern part of the forecast area
could enter the warm sector of this system on Friday, the
temperatures forecast is rather tricky. The ECMWF ensemble is
showing standard deviations of 4 to 6. For the time being, just
staying close to the ensemble mean. However with that said there
could be potential for a large bust in the temperature forecast
for areas along and south of Interstate 90.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 635 PM CDT Wed Mar 22 2017

Mid level clouds continue to thicken from the west at the moment,
and that trend will continue through the night, with ceilings
ending up in the 5-8kft range by sunrise. There is an outside risk
for a sprinkle or flurry at either RST or LSE through the evening
and night, though with no impact to visibility. A better risk for
some showers, and potentially even a few thunderstorms will come
Thursday afternoon as ceilings ease down toward MVFR levels in
advance of a warm front to the south. Given plenty of uncertainty
about the coverage of any showers, a vicinity mention will do the
trick for now, with winds fairly steady from the southeast and
becoming increasingly gusty for all areas later tonight into
Thursday, with gusts of 25 knots expected at RST and just slightly
lower for LSE.


.HYDROLOGY...(Thursday night through Wednesday)
Issued at 345 PM CDT Wed Mar 22 2017

It continue to look like the area will be in a prolong wet period
from Thursday night into Sunday as a thin ribbon of Gulf of Mexico
moisture is brought northward into the region. Precipitable water
values continue to be 2 to 3 standard deviations above normal.
Rainfall totals will likely be in the 1 to 1.5 inch range. However
with this rain spread out of over a long-period of time, only
anticipating in bank rises on area rivers.




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