Area Forecast Discussion
Issued by NWS La Crosse, WI

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350
FXUS63 KARX 211743
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1243 PM CDT Sun May 21 2017

.SHORT TERM...(Today through Monday Night)
Issued at 242 AM CDT Sun May 21 2017

08Z water vapor loop shows a closed low along the SD/MN border
with its surface reflection just slightly farther east across
south-central MN. This nearly stacked low with its surface
occluded front will slowly lift northward today, reaching the
Canadian border by 00Z tonight. A line of showers with an isolated
rumble of thunder or two early this morning across north-central
WI will continue northward and move out of the forecast area by
10Z. In its wake, expect scattered showers today and tonight for
areas mainly along and north of I-90 as wrap-around moisture moves
across the region. Mostly cloudy skies will continue with a
breezy westerly wind, gusting at times to 25 mph. Unseasonably
cool temperatures will persist, topping out in the lower to mid
50s this afternoon.

Low-level warm air advection overnight will usher in a slightly
more moderate air mass for Monday with 925 hPa temperatures
ranging from +12 to +15 Celsius. This will result in afternoon
highs from the lower 60s across the northwest to the lower 70s
across the southeast. While Monday morning will be mostly dry with
some sunshine, expect cloud cover and shower/thunderstorm chances
to increase in the afternoon/evening ahead of southeastward
advancing cold front. Despite surface dewpoints in the mid to
upper 40s, cold temperatures aloft and modest mid-level lapse
rates will allow for some instability with MUCAPE values between
500 and 1000 J/kg. Deep layer shear is marginal, but could see
some stronger thunderstorms in the late afternoon/evening for
areas south of Interstate 90 coincident with the SPC Day 2
marginal risk area across IA. Small hail and gusty winds are the
primary threats.

.LONG TERM...(Tuesday through Saturday)
Issued at 242 AM CDT Sun May 21 2017

The cold front pushes east of the forecast area on Tuesday, but
with a 500 hPa closed short-wave overhead, cold/cyclonic flow
aloft could result in additional scattered afternoon showers/
isolated thunderstorms. Weak instability/shear profiles preclude
any severe convection. Temperatures in the wake of Monday`s
frontal passage will be cooler, ranging from the upper 50s to
lower 60s.

Short-wave ridging aloft and high pressure at the surface will
result in a drier period for Wednesday/Thursday. Winds will be
light with temperatures generally in the 60s, although some spots
may rise above 70 degrees by Thursday. Southwest flow aloft
returns on Friday into the weekend as the ridge axis moves into
the lower Great Lakes region. Good agreement between the GFS/ECMWF
with another short-wave lifting across the forecast area on
Friday, bringing another chance of showers/storms. Timing/strength
of short-waves thereafter are not well resolved, resulting in
lower forecast confidence.

&&

.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.


&&

.HYDROLOGY...
Issued at 242 AM CDT Sun May 21 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 Tuesday, an upper level low will result in periodic rain
showers and perhaps a few thunderstorms. The heaviest rain will
be south of Interstate 90 late Monday and Monday night. During
this time frame, rainfall amounts will be up to a half inch.

&&

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

$$

SHORT TERM...Rogers
LONG TERM...Rogers
AVIATION...Boyne
HYDROLOGY...Rogers



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