Area Forecast Discussion
Issued by NWS La Crosse, WI

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296
FXUS63 KARX 221133
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
633 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 12Z TAFS through 12Z Tuesday morning)
Issued at 633 AM CDT Mon May 22 2017

One batch of showers will move south of TAF airfields this
morning. Then, additional showers and thunderstorms are expected
late this afternoon and evening. Best chance for more widespread
rain/thunder will again be south of KRST/KLSE, with timing and
coverage of convective activity uncertain farther north. Will keep
VCSH idea at both TAF sites, but may eventually need to introduce
-SHRA or even a brief period of thunder sometime after 22.21Z.

VFR ceilings and visibility will be the rule, but reductions to
MVFR possible in heavier showers/isolated thunderstorms. Forecast
guidance does develop more widespread MVFR ceilings late in the
period, but will maintain VFR conditions for now until better
consensus is reached. Light southwest wind this morning will
gradually shift to the northwest later this afternoon/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...Rogers
HYDROLOGY...JM



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