Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 221733

Area Forecast Discussion
National Weather Service La Crosse WI
1233 PM CDT MON AUG 22 2016

.SHORT TERM...(Today and tonight)
Issued at 308 AM CDT Mon Aug 22 2016

Main forecast concerns for today are on breezy southerly winds
and the slight possibility of a sprinkle or rain shower mainly
over west central into northern Wisconsin.

After some very patchy fog this morning in river valleys, plan on
mostly to partly sunny skies. There will be scattered cumulus
clouds at times. Keeping an eye on weak moisture transport at
850 mb, just brushing western and northern sections of the
forecast areas this afternoon which could produce some sprinkles
or perhaps isolated showers. The better support for this appears
to stay west and north so have left the forecast dry, but will
have to continue to monitor this. Surface high pressure exits the
region today as a trough develops over the plains. This will
tighten the pressure gradient over the region resulting in south
winds of 10 to 20 mph. A few winds gusts of 25 to 30 mph are
possible, especially across the open areas of southeast Minnesota
and northeast Iowa.

.LONG TERM...(Tuesday through Sunday)
Issued at 308 AM CDT Mon Aug 22 2016

A quiet and slightly warmer day is in store for the region on
Tuesday with with highs in the the lower 80s. The focus then quickly
turns to showers and thunderstorms for late Tuesday night into
Wednesday morning. There is the potential for heavy rain during
this timeframe but forecast models are keeping this threat closer
to the interstate 80 corridor across Iowa. Strong 850 mb moisture
transport noted across Iowa late Tuesday night along with warm
cloud depth increasing to 4 KM, and precipitable water values of
of 1.7 to 2 inches. These ingredients will create a favorable
environment for heavy rain. However, its difficult to nail down a
focus for repeated rounds of storms which would lean toward flash
flooding potential. At this time anticipating thunderstorms
capable of producing heavy rain. If the storms would happen to
focus along a boundary, repeating over the same areas, this could
lead to a flooding concern. Thinking this potential would mainly
be across central Iowa, but could shift further north. Will have
to keep a close eye on it. The main threats from any storms
Tuesday night into Wednesday would be heavy rain. Cannot rule out
some storms with gusty winds too with 0-3 km shear increasing to
30 to 40 kts. However, the shear values may have some slight
convective contamination and the low level shear may be a little
weaker, favoring mainly a heavy rain threat. A cold front then
sweeps through Wednesday afternoon with high pressure building in
for Wednesday night.

The next concern turns to valley fog potential for Thursday night
into Friday morning as high pressure slides overhead. After a quiet
day on Friday, the high exits Friday night as a trough deepens over
the central CONUS. The trough then pushes into the Upper Mississippi
River Valley Saturday into Sunday, leading to an active weather
pattern and a wet weekend. We may see several rounds of showers and
thunderstorms during this timeframe. Will maintain a model consensus
blend during this timeframe but if trends continue precipitation
chances will need to be increased.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1233 PM CDT Mon Aug 22 2016

Main taf concern is the potential for low level wind shear at
both RST/LSE taf sites tonight and winds this afternoon/evening.
Latest water vapor satellite imagery shows weak impulse over
eastern Minnesota and western Wisconsin. This is producing
altocumulus clouds over the area per visible satellite imagery.
Latest 17z surface analysis indicates high pressure over the Ohio
River valley. On the backside of the surface high...pressure
gradient has tighten and winds aloft have mixed down. This has
produced sustained southerly winds of 15 knots and gust of 20 to
25 knots. Expect southerly sustained winds around 15 knots with
gust 20 to 25 knots this afternoon into the early evening. As
winds decouple tonight combined with stronger winds aloft...this will
produce low level wind shear after 07z Tuesday at both RST/LSE taf


.ARX Watches/Warnings/Advisories...


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