Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 212013

Area Forecast Discussion
National Weather Service La Crosse WI
313 PM CDT Sun May 21 2017

.SHORT TERM...(This evening through Monday)
Issued at 313 PM CDT Sun May 21 2017

Main impactful weather concerns in the short term are on
thunderstorm chances Monday afternoon and evening with potential
for a few stronger storms.

Light rain and areas of drizzle will gradually lift north tonight,
but a secondary shortwave rotating around an upper low will move
through this evening into the overnight. This wave will generate a
few light showers across areas north of Interstate 90.

The main forecast concern will be on Monday as a frontal boundary
and upper level trough dive into the region. Afternoon surface based
CAPE values look to climb into the 500-700 J/kg range. 0-6 km bulk
shear values are expected to be in the 15 to 30 kt range with 0-6 km
bulk shear values of 35 to 40 kts by the time the storms form.
However, the strongest shear appears to be exiting the area as the
CAPE builds from the late afternoon into the evening. So what is
initially potential supercell shear early in the day weakens to
the point where storms will likely struggle to organize. Freezing
levels are fairly low at around 7 kft. So, the main severe weather
threat will mostly likely be some large hail (up to quarter
size?) and possibly some gusty winds given a dry sub-cloud
layer/inverted v type of soundings. The main area of concern in
along and south of the Interstate 90 corridor.

.LONG TERM...(Monday night through Sunday)
Issued at 313 PM CDT Sun May 21 2017

Low pressure will slowly slide south across the region late Monday
night through Tuesday night with continued chances for showers. Weak
CAPE attempts to build over the area Tuesday afternoon so we may
see some isolated thunderstorms. We stay in weak cyclonic flow
aloft going into Wednesday with continued chances for rain
showers. We will finally see a break in the rain chances on
Thursday as ridging moves across the Upper Mississippi River
Valley. Then another trough pushes through the region late
Thursday night into Friday. This feature looks to bring showers
and perhaps some thunderstorms to the region. Temperatures take a
slight trend upward for the weekend with highs climbing into the
70s at many locations. Another trough could bring showers and
thunderstorms to the region but details are far from certain
since forecast models are showing considerable differences.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1243 PM CDT Sun May 21 2017

An upper level low, currently located between Duluth and the Twin
Cities, will slowly transition north northeast toward Lake
Superior. This low will continue to produce MVFR ceilings and
isolated showers for the TAF sites through this evening. Skies
will become scattered between 22.09z and 22.12z and remain that
way through much of Monday morning.

Steep 950 to 900 mb lapse rates will produce wind gusts of 15 to
30 knots through 22.02z.


Issued at 313 PM CDT Sun May 21 2017

Heavy rains over the past week have resulted in flooding on many
area rivers. River Flood Warnings continue for the Mississippi
River at Wabasha, the Trempealeau River at Dodge, the Black River
at Galesville, and the Yellow River at Necedah. Monitor the
latest river forecasts closely this week as additional flooding is
possible along portions of the Mississippi River.




SHORT TERM...Wetenkamp
LONG TERM...Wetenkamp
HYDROLOGY...Wetenkamp is the U.S. government's official web portal to all federal, state and local government web resources and services.