Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 131646
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1145 AM CDT Fri Oct 13 2017

.SHORT TERM...(Today and tonight)
Issued at 318 AM CDT Fri Oct 13 2017

At 3 AM, a cold front extended from the Minnesota Arrowhead to
Lincoln NE.  Little weather was associated with this surface front.
However, in the wake of this front, there is strong 800 to 500 mb
frontogenesis located over eastern South Dakota.  This forcing is
producing light rain across northeast South Dakota. Meanwhile,
further to the south, a warm front was located over southern Iowa.

For today, the frontogenetic forcing over South Dakota will move
southeast into southeast Minnesota and north central Wisconsin late
this morning and early afternoon and then move southeast into the
Interstate 90 corridor by mid to late afternoon.  Meanwhile, further
south, the warm front will move north across Iowa and spread showers
into northeast Iowa and southwest Wisconsin.  With most unstable
CAPES climbing up to 250 J/kg, there may be some isolated
thunderstorms.

For tonight, the frontogenesis near Interstate 90 will move east
into east central Wisconsin. As this occurs, the rain will move out
for areas along and north of the Interstate 90 corridor. Meanwhile,
as the 850 mb moisture transport veers southeast of the area, the
chances of showers and isolated thunderstorms will gradually shift
to our southeast.

.LONG TERM...(Saturday through Thursday)
Issued at 318 AM CDT Fri Oct 13 2017

Main impactful weather concerns in the long term:

1) Potential for thunderstorms with locally heavy rainfall Saturday
into Saturday evening.

2) Strong westerly winds late Saturday night into Sunday.

3) Colder temperatures Sunday night with the possibility for
widespread frost and the potential for below freezing temperatures
in cold favored locations of central Wisconsin.

Low pressure will lift through the Upper Mississippi River Valley
Saturday into Saturday evening. As this low moves in a warm frontal
boundary, mainly elevated, edges into northeast Iowa and southern
Wisconsin. Precipitable water values climb into the 1.5 to 1.8 range
across portions of northeast Iowa into southwest Wisconsin.
Meanwhile, warm cloud depth increases to around 3500 ft.  This will
set the stage for possible locally heavy rainfall which could lead
to ponding of water and river rises. The latest ECMWF is keeping the
bulk of the heavy rainfall south and east of the local area, so will
have to keep a close eye on this trend. If the warm sector, warm
front, edge further north we may see a threat for a couple of severe
storms. At this time it appears the warm sector and supportive CAPE
stay just south and east of the area, mainly across northern
Illinois and southeast Wisconsin.

The heaviest rain should then taper off as the low deepens and heads
for Northern Lake Michigan Saturday night or possibly eastern Lake
Superior. Look for strong west to northwest winds of 15 to 25 mph
with gusts of 30 to 40 mph to develop after midnight and continue
through around sunrise. The strongest winds will be across the open
areas of southeast Minnesota, northeast Iowa, and the ridge tops of
western Wisconsin.

Much cooler air then moves into the region Sunday into Sunday night
as 850 mb temperatures fall into the +1 to -2 C range. Low
temperatures Sunday night are expected to fall into the 30s with
some 20s possible in cold favored spots. This could be the first
widespread frost for many locations. If trends continue a frost
advisory may be needed for much of the area with the potential for a
freeze warning across central into northern Wisconsin.

A gradual warming trend is then expected for next week with mainly
dry weather. We could see a few dry cold fronts move through along
with the potential for breezy southerly winds. If we see a few days
of drying weather we could see an increase in the potential for
crop/field fires on Wednesday and maybe again on Friday. Minimum
Relative humidity values don`t appear particularly low at this point
with afternoon readings expected to be in the 40s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1145 AM CDT Fri Oct 13 2017

Cigs: mvfr cigs look to clear KLSE by approx 18z with mostly mid
level cigs ~10 kft through the rest of today into Sat morning.
Increasing low level moisture ahead of an approaching low pressure
system from the south should drop the TAF sites back into MVFR
before 18z Sat.

Wx/vsby: frontogenetic band -shra related to an upper level trough
will bring on/off showers to KRST/KLSE through the afternoon -
lingering into early evening. Generally not expecting any vsby
restrictions - although could drop briefly in any heavier shower.

Showers return late Sat morning, more likely for the afternoon/night
time hours. Thunder chances look to hold south of the TAF sites for
now. Could see some mvfr vsby restrictions for sat night.

Winds: should become more northeast/east by Sat morning and
increase. As the low passes overnight Sat, the pressure gradient
increases. Going to get strong/gusty and swing back to the
northwest.

&&

.HYDROLOGY...Saturday Into Saturday Night
Issued at 318 AM CDT Fri Oct 13 2017

Locally heavy rainfall is possible Saturday into Saturday night
when 1 to 1.4 inches of rain could fall across portions of
northeast Iowa into far southwest Wisconsin. This rainfall will
likely result in within bank rises on area rivers. At this time it
appears the heaviest rain will fall over northern Illinois into
southeast Wisconsin. If this axis of heavier rain shifts further
northwest, we could see some localized flooding concerns.

&&

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

$$

SHORT TERM...Boyne
LONG TERM...Wetenkamp
AVIATION...Rieck
HYDROLOGY...Wetenkamp



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