Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 192110
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
310 PM CST Sun Feb 19 2017

.SHORT TERM...(This evening through Monday night)
Issued at 310 PM CST Sun Feb 19 2017

Light return flow has set up ahead of developing low pressure across
the high plains. 19.12Z model solutions have remained quite
consistent in lifting the low northeastward into Canada as an
elongated upper shortwave trough moves across the Upper Midwest on
Monday, dragging a surface boundary through the region Monday
evening. Strengthening low-level warm/moist advection will help
keep temps very mild tonight in the 40s over much of the area. As
for precip, if anything, models have maybe trended a bit quicker
with the system, with showers moving from west to east across the
region Monday into Monday evening within the warm advection regime
ahead of the upper wave/surface boundary. Weak instability up to
a few hundred J/kg of MUCAPE combined with an unseasonably moist
prefrontal air mass being transported northward could lead to
isolated storms. Forecast surface dew points in the 50s and
precipitable water values over an inch are certainly very
impressive for February. Areal averaged rainfall amounts generally
in the 0.25 to 0.75 inch range are expected, but given the high
atmospheric moisture content and potential for pockets of
convection, locally higher amounts are possible. The rainfall
falling on frozen/saturated ground, combined with melting of the
remaining snow, will lead to run off into rivers/streams, which
will result in rises and potential flood concerns. See the
hydrology section below for more details. Near record highs in the
50s to low 60s are expected Monday, but the effects of cloud
cover/rain could put a damper on temp rises.

.LONG TERM...(Tuesday through Sunday)
Issued at 310 PM CST Sun Feb 19 2017

The upper flow becomes zonal Tuesday/Wednesday and with no cold air
sinking southward behind the early week system, high temps likely
will remain 20-30 degrees above average through Wednesday in the 50s
and 60s, near record territory. Current forecasts may still be on
the conservative side for high temps.

An upper shortwave trough passing through the flow on Wednesday will
drag a cold front through late Wednesday, with cooler temps for
Thursday. Otherwise, though, the importance of this front is to
set up a low-level baroclinic zone somewhere nearby ahead of a
stronger upper level trough that will eject out of the Rockies
late this week bringing a potential winter storm to the region.

For the late week storm, details are far from certain at this
point, but it does look like winter will make a comeback as the
aforementioned upper trough moves into the plains and a surface
cyclone lifts northeastward along the low-level baroclinic zone.
The 19.12Z GFS/ECMWF are in decent agreement in tracking the upper
wave from the central high plains Thursday evening to eastern WI
by Friday evening, although there are some difference with the
placement of the surface low (ECMWF a bit farther north). The
placement of the low will impact where the deformation zone and
heaviest precip end up as well as precip types. It still looks
like more of a rain/snow event vs the wintry mix events we`ve seen
several of this winter. Boundary layer temps thus will be key in
determining precip type. Model solutions indicate plenty of
available moisture with the system and strong dynamics with a well
defined mid-level baroclinic zone aiding in strong frontogenesis
in the deformation zone and also potential upper jet coupling. In
addition to the precip, strong winds may be a concern with a
pretty tight gradient on the backside of the low. It`s too early
to get into any specifics, but after an early taste of spring,
wintry weather will make a return late this week including the
potential for significant snow somewhere across the Upper Midwest,
and this potential winter storm will need to be watched
carefully. Temps will return to near seasonal averages for next
weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1130 AM CST Sun Feb 19 2017

Quiet conditions to persist through the evening as the high
pressure over Illinois will still be the dominant feature.
However, as this continues to pull away and the system currently
in the lee of the Rockies approaches, the low level jet is
expected to develop this evening and produce a period low level
wind shear at both airports. The wind shear should dissipate late
tonight as the speeds aloft start to decrease as the storm system
gets closer to the area. The forcing from this system will produce
widespread rain that will start to move into Monday morning. As it
spreads in, expect conditions to go down to MVFR with IFR ceilings
possible shortly after the rain starts. The rain should move into
KRST by mid morning. At KLSE, the rain should move in right
around 20.18Z, so for now, have only shown the ceilings starting
to come down ahead of the rain.

&&

.HYDROLOGY...
Issued at 310 PM CST Sun Feb 19 2017

There are several factors that could contribute to river rises over
the next several days: 1) Forecast QPF of 0.25 to 0.75 inches
on Monday. 2) Well above normal temperatures will continue to
melt what snow there is left. Snow pack has already eroded
considerably across most of the area. 3) Ground may be frozen,
leading to more efficient runoff (though shallow unfrozen layer
near the surface is likely given the warm surface air
temperatures). 4) Soils may still be saturated from above average
precipitation over past several months, also leading to more
efficient runoff. 5) Additional QPF likely later this week.
Locations along the Trempealeau, Black, Kickapoo, Wisconsin, and
Yellow Rivers in Wisconsin will be most prone to rises. A few
locations could potentially experience some minor flooding,
especially along rivers whose sources are in northern and central
Wisconsin where there is a greater amount of snow to melt. Those
with interests along streams rivers and streams should closely
monitor river forecasts throughout the week.

&&

.CLIMATE...
Issued at 310 PM CST Sun Feb 19 2017

As of 3 pm today, La Crosse has reached 63 degrees, setting a new
daily record (59/1930). The official daily max will be available
later this afternoon.

High temperatures will be near record territory through Wednesday
at La Crosse and Rochester. Lows will also be near record high
minimums at times through mid-week.

Below are the records for La Crosse and Rochester through
Wednesday February 22nd:

                          Record Highs
                          ------------

             La Crosse                     Rochester
            -----------                   -----------

Sun (19th)    59/1930        Sun (19th)     59/1930
Mon (20th)    61/1930        Mon (20th)     60/1930
Tue (21st)    64/1930        Tue (21st)     60/1930
Wed (22nd)    62/1984        Wed (22nd)     59/1930

                         Record High Lows
                         ----------------

Mon (20th)    41/1930        Mon (20th) 34/1954
Tue (21st)    48/1930        Tue (21st) 39/1930
Wed (22nd)    39/1930        Wed (22nd) 42/1930

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...JM
LONG TERM...JM
AVIATION...04
HYDROLOGY...Hollan
CLIMATE...JM


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