Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 210248

Area Forecast Discussion
National Weather Service La Crosse WI
945 PM CDT Sat May 20 2017

.SHORT TERM...(This evening through Sunday)
Issued at 316 PM CDT Sat May 20 2017

At 3 PM, dry slot was approaching the Interstate 90 corridor. This
dry slot will provide some dry time for late this afternoon and
early evening...then as the upper level low and occluded front
moves through the area another band of rain will move through the
region. With most unstable CAPES climbing up to 500 J/kg, there
will be enough instability for isolated thunderstorms during the
mid to late evening. The RAP soundings suggest that there may be
brief window (1 to 2 hours) where there may be enough instability
and 1-6 km shear for the potential of some hail. If this occurred,
it would be in northeast Iowa and southwest Wisconsin.

Warm air advection will allow temperatures to continue to rise
this evening. As a result, our high temperatures for today will
likely not occur until then.

On Sunday, the closed low will move into northern Minnesota and
northern Wisconsin. The cyclonic flow associated with low will
keep skies cloudy across the region and there will be isolated to
scattered showers mainly north of Interstate 90.

.LONG TERM...(Sunday night through Saturday)
Issued at 316 PM CDT Sat May 20 2017

From Sunday night into Wednesday, an upper level low will slowly
transition southeast across the Upper Mississippi River Valley.
This low will produce periodic showers. There will be enough
instability on Monday and Monday evening (CAPES up to 1250 J/kg
south of Interstate 90) and Tuesday afternoon and evening (CAPES
up to 500 J/kg) for isolated to scattered thunderstorms to
develop. With limited shear, not anticipating any severe weather
with these storms. The heaviest rain will be south of Interstate 90
from Monday night into Tuesday. During this time frame, the
rainfall amounts will be up to a half inch.

From Wednesday night into Friday, a 500 mb ridge will provide dry
weather and near-normal temperatures.

On Friday night and Saturday, a short wave trough will be moving
northeast out of the southern Plains. Most unstable CAPES will
climb into the 1500 to 2500 J/kg range. However the shear remains
weak, so not anticipating and severe weather.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 945 PM CDT Sat May 20 2017

Cigs: blanket of ifr/mvfr cigs holding across the region, and likely
will stay that way into Sunday night. The sfc low responsible for
the low clouds will gradually exit northward into southern Canada
after 12z Mon-and not expecting a lot of improvement until it does.
Expect some minor diurnal "bump up" Sun afternoon, with a better
shot for clearing after 06z Mon.

WX/Vsby: cold front associated with the low pressure system sliding
northeast across the local area this evening. Forcing along the
boundary should be enough to pop a few scattered showers, with some
potential for thunder (better to the southeast of the TAF sites).
Most of this shifts northeast after 06z.

Had some reductions in vsbys from areas of drizzle earlier in the
evening - most of which has shifted north with the isentropic lift.
Some ifr/mvfr br still found north of the low/sfc front though - and
could impact the TAF sites for a few hours post 06z. Will monitor
and make adjustments as needed.

Wind: east southeast will swing to the south then southwest by Sun
afternoon as the low pulls away. Could be some gustiness to the
southwest of the low.


Issued at 316 PM CDT Sat May 20 2017

River Flood Warnings continue along the Mississippi River at
Wabasha, the Trempealeau River at Dodge, the Black River at
Galesville, the Yellow River at Necedah, and along the Wisconsin
River at Castle Rock Dam as runoff from the very heavy rain
earlier this week continues to move through the river system.

Through Wednesday, an upper level low will provide periodic rain.
The heaviest rain will be south of Interstate 90 from Monday
night into Tuesday. During this time frame, the rainfall amounts
will be up to a half inch.




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