Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 220815
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
315 AM CDT Mon May 22 2017

.SHORT TERM...(Today through Wednesday night)
Issued at 315 AM CDT Mon May 22 2017

The main forecast concern today centers around convective potential
later this afternoon/evening and strength of storms. Large scale
forcing will be weak this afternoon, while the stronger height
falls/forcing arrive later tonight. At the surface, a weak
surface frontal boundary will approach late today. However,
moisture return will be weak ahead of the system, limiting
instability. As a result expect only around 500 to maybe 1000 J/kg
of MUCAPE this afternoon in a skinny profile with 35-40 kts of
0-6 km bulk shear. Coverage/placement of storms is somewhat in
question given the limited moisture, but at this time the highest
chances still appear to be near/south of I-90 late this afternoon
into the evening where low-level moisture and instability is a
bit higher. Very cool mid-level temps/steep mid- level lapse rates
would suggest hail to be the primary threat for any storms that
occur through early evening, with some potential for gusty winds
with a dry subcloud layer. Storms should be on the decline during
the evening as instability wanes.

The upper low will settle slowly southeastward Tuesday into
Wednesday with cool and cloudy conditions continuing. Under cyclonic
flow aloft and very cool 500 mb temps, scattered showers and maybe
an isolated rumble of thunder will continue Tuesday and Tuesday
night before gradually diminishing on Wednesday as surface high
pressure begins to nose into region from the north. Highs on
Tuesday/Wednesday likely will be limited to the 50s to low 60s
underneath the widespread cloud cover.

.LONG TERM...(Thursday through Sunday)
Issued at 315 AM CDT Mon May 22 2017

The upper trough finally will move east on Thursday as shortwave
ridging brings a brief break from rain chances. However, the ridging
will be short-lived as an upper trough over the northern Rockies
into northern plains sets up a more west to southwest flow pattern
over the area late week into the weekend. Precip chances may
increase as early as Friday as Thursday night/Friday as shortwave
energy comes out of the plains. Confidence remains low for next
weekend with evolution of the upper trough and placement of embedded
shortwaves. Temps late this coming week should be within a few
degrees of seasonal averages.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1100 PM CDT Sun May 21 2017

Cigs: blanket of low clouds exiting east at late evening, and should
clear KLSE before 06z. Expect VFR with generally sct skies for the
rest of the overnight through Mon morning. Clouds will be on the
increase for the afternoon though, and could eventually drop back
into MVFR territory Monday night as ripples in the upper level flow
spin across the region.

WX/Vsby: scattered light showers will persist well north tonight
with no impact to the TAF sites. SHRA/TS could move back across the
region by late Mon afternoon as upper level shortwave troughs track
east across the region. The threat increases Monday evening. How far
north the shra/ts threat extends is not certain through, with some
variability in the models. Going to cover the chances with VCSH for
now, and will refine forecast for the rain/storm potential as
confidence increases.

Wind: westerly though the period, hovering near 10 kts - some
lightening for Mon evening.

&&

.HYDROLOGY...
Issued at 315 AM CDT Mon May 22 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. A few other sites along
the Mississippi may also approach minor flood stage over the next
several days as water from area tributaries contributes to rises
on the Mississippi.

&&

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

$$

SHORT TERM...JM
LONG TERM...JM
AVIATION...Rieck
HYDROLOGY...JM


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