Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 200822

Area Forecast Discussion
National Weather Service La Crosse WI
322 AM CDT Sat May 20 2017

.SHORT TERM...(Today through Sunday Night)
Issued at 322 AM CDT Sat May 20 2017

20.08Z water vapor loop shows a strong closed low near the CO/NE
border. At the surface, low pressure is located over northeast KS
with a warm front draped across northern MO into central IL. As
the trough aloft lifts northeastward through the day, the surface
low is forecast to move into western IA by 00Z tonight and then
across east-central MN/west-central WI overnight. This will result
in a broad band of showers/isolated thunderstorms coincident with
strong mid-level warm air advection and isentropic lift moving
from south to north through this afternoon. Behind this band of
showers, models are consistent in showing a dry slot across the
forecast area. That said, could see some additional convective
development in the drier airmass given strong potential vorticity
advection aloft and MUCAPE values up to 500 J/kg. Although there
is strong deep layer shear during this time, limited instability
should preclude severe convection. Of greater concern will be
rainfall amounts through tonight with PWATs briefly climbing to
around 1.25 inches, resulting in rainfall amounts from 0.75 to
1.25 inches. See hydro section below for possible impacts. Besides
the rain, today will be cloudy and cool with breezy easterly
winds. Afternoon highs will top out in the 50s.

Tonight through Sunday night will see some lingering showers,
especially for areas north of I-90 as the surface low moves into
the Upper Great Lakes region. Cloudy and cool conditions will
persist on Sunday with highs once again in the 50s. Winds will
still be breezy, but from the west-southwest on the backside of
the departing low.

.LONG TERM...(Monday through Friday)
Issued at 322 AM CDT Sat May 20 2017

The next round of showers and thunderstorms move in late Monday
and Monday night as a Canadian short-wave merges with the broader
trough over Ontario and rotates across the Upper Midwest. While
0-6 km MUCAPE increases to between 500 and 1500 J/kg by 00Z
Tuesday, forcing aloft and shear are strongest south of the
forecast area, such that severe convection is not expected at this
time. Shower and thunderstorms chances continue into Tuesday with
a few more weak short-waves rotating through the region. Once
again, shear/instability profiles do not support severe convection.
Temperatures will warm briefly Monday into the 60s before crashing
back down into the 50s for Tuesday.

Wednesday and Thursday look dry with short-wave riding aloft and
high pressure at the surface. Should finally see more sunshine and
with 925 hPa temperatures rising to between +10 and +14 Celsius,
should see afternoon highs in the 60s both days. While the timing/
strength of the next Pacific trough differs between the GFS/ECMWF
for the end of the week, it appears Friday should also be mostly
dry and warmer with highs rising back above 70 degrees for many


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1110 PM CDT Fri May 19 2017

Cigs: clouds will continue to thicken/lower overnight as an upper
level trough/sfc low approaches from the southwest. Expecting a drop
into mvfr/ifr between 12-15z...likely holding there through Sat
night and the better part of Sunday.

WX/Vsby: showers move back into the area around 12z Sat, with the
bulk lifting north of the taf sites by 21z. Could see some
convection develop along the system`s cold front/dry slot by late
afternoon/early evening. Maybe some thunder chances with this,
otherwise the thunder threat looks minimal. There will be vsby
restrictions with the rain, generally mvfr but a period of ifr
possible (more likely krst).

Winds: easterly in direction with some increase toward 12z Sat as
the sfc low approaches - and then a decrease in speeds as the low
moves through. Some hints of LLWS potential overnight/early Sat
morning - moreso for KLSE. Not confident enough to include at this


Issued at 322 AM 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 at Castle Rock Dam
as runoff from the very heavy rain earlier this week continues
to move through the river system.

Another round of rain and isolated storms will move through the
area late today and tonight. Additional rainfall amounts will
range from around 0.75 to 1.25 inches across the region. These
rains will result in further rises on area rivers and streams.|




LONG TERM...Rogers
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