Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 131139
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
639 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 12Z TAFS through 12Z Saturday morning)
Issued at 639 AM CDT Fri Oct 13 2017

Through 13.14z some patchy IFR to MVFR ceilings will effect the
TAF sites.

A band of strong frontogenetic forcing will move southeast into
the TAF sites this afternoon and then move east of them this
afternoon.  This band will produce showers at KRST between 13.17z
and 13.23z and at KLSE between 13.21z and 14.02z. These showers
will be falling out an 8 to 12K deck of clouds.

&&

.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...Boyne
HYDROLOGY...Wetenkamp



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