Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 192039

Area Forecast Discussion
National Weather Service La Crosse WI
339 PM CDT Sat May 19 2018

.SHORT TERM...(This evening through Sunday)
Issued at 339 PM CDT Sat May 19 2018

At 3 PM, a weakening low pressure system was located near Slater,
Iowa. Some sunshine ahead of this system has allowed mixed layer
CAPES to climb into the 500 to 1000 J/kg across eastern Iowa,
northwest Illinois, and southwest Wisconsin. This has allowed
showers and scattered thunderstorms to develop across central
Iowa. The meso models are in general agreement that the 0-6 km
effective shear will remain weak, so not anticipating any severe
weather. However, cannot rule out some gusty winds across parts
of northeast Iowa and southwest Wisconsin between 5 PM and 8 PM.

For late tonight and Sunday morning, another weakening trough will
produce showers and isolated storms as it moves northeast Iowa
and southwest and central Wisconsin. With weak shear and limited
CAPES, not anticipating any severe storms.

On Sunday afternoon, the meso models are trending drier across
the area. As a result, the rain chances were lowered some. If this
trend continues, the rain chances may be removed.

.LONG TERM...(Sunday night through Saturday)
Issued at 339 PM CDT Sat May 19 2018

From Sunday night through Monday night, the models continue to
show that a short wave trough will eject out of the Central
Plains and this system then move northeast through the Upper
Mississippi River Valley. With little instability, just went with
scattered showers. The combination of clouds and rain will result
in high temperatures in the lower and mid 60s on Monday.

From Tuesday night through Thursday, the 500 mb ridge will build
north into the region. While there is agreement with this, the
models continue to struggle with the placement of the warm front
during this time frame and this greatly impacts the amount of
instability across the region on Wednesday and Thursday. The GFS
has 2-3K CAPES on Wednesday and Thursday. Meanwhile, the ECMWF
holds these higher CAPES until Thursday. While the CAPES will be
increasing, the shear remains weak, so other than the possibility
on an isolated pulse severe storm no organized severe weather is


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1251 PM CDT Sat May 19 2018

Challenging cloud/ceiling forecast over the next 24 hours. A
nearly stalled frontal boundary extends from near KMDZ to KPRO.
Behind this front is an extensive MVFR cloud deck across east-
central MN into northern WI, although there are large breaks
farther south across north-central IA. General idea is for these
clouds to slowly move south and east, keeping KRST in MVFR
conditions for most of the afternoon/early evening. Cloud bases
are a bit higher at KLSE and should remain above 3000 ft agl.
RST may break back into VFR ceilings later this evening before
forecast guidance hints at clouds lowering again overnight. Less
certain at KLSE, but VFR conditions should be the rule.

Some showers and thunderstorms are possible later this evening
and overnight, but should remain mainly south of TAF airfields, so
will maintain a dry forecast. Light northwest winds into this
early evening will gradually turn to the north-northeast overnight
into Sunday.




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