Area Forecast Discussion
Issued by NWS La Crosse, WI

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774
FXUS63 KARX 190412
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1111 PM CDT Sat Aug 18 2018

.SHORT TERM...(This evening through Sunday)
Issued at 313 PM CDT Sat Aug 18 2018

Main forecast concerns in the short term are on dense fog potential
late tonight into early Sunday morning.

Surface high pressure remains in control across the Upper
Mississippi River Valley and western Great Lakes this afternoon.
A few lower clouds were lingering across the area early this
afternoon from this mornings fog and smoke aloft continues over
the region from western wildfires. The smoke is not expected to
reach the surface so the visibility should remain good across the
area. Cannot rule out some patchy smoke over southeast Minnesota
so have kept that going in the forecast. The surface high will
remain in control across the region tonight providing light winds
through a fairly deep layer of the atmosphere, from the surface
through around 6kft. This should set the stage for radiational
fog, especially along and east of the Mississippi River where the
pressure gradient is the weakest. Valley Fog is looking very
likely, and we should see some fog outside of the valley
locations, especially over Wisconsin. Dense fog is a possibility
so we will have to keep a close eye on this with the potential for
a dense fog advisory. Some thin high clouds are expected to edge
in from the west Sunday morning so this could impact the fog
development. The smoke had very little or no impact on the fog
development Friday night into early Saturday morning so thinking
this will once again be the case tonight into Sunday morning. High
clouds will then be on the increase across the region on Sunday
as a trough approaches from the west.

.LONG TERM...(Sunday night through Saturday)
Issued at 313 PM CDT Sat Aug 18 2018

Main forecast concerns in the long term are on widespread rain and
embedded thunderstorms Monday into Monday night, then focus turns to
a windy day across the region on Tuesday.

Low pressure is expected to track across Iowa into northern Illinois
from Monday into Tuesday. This will bring showers and a few
thunderstorms to the local area. With good forecast model
agreement on rainfall across much of the area, have increased
precipitation chances across most of the area from Monday
afternoon into Monday evening. By the time the rain ends,
rainfall amounts are expected to range from around 1/2 inch over
portions of northern Wisconsin to around 1.5 inches over extreme
southwest Wisconsin. Look for a windy day across the region on
Tuesday in the wake of the low. Cooler and quiet weather is then
expected from late in the day on Tuesday through Thursday with
northwest flow aloft and surface high pressure in control. A
potentially more active pattern then looks to setup over the CONUS
for later next week as flow aloft turns zonal. A few systems
could move through the area from Friday through the weekend
bringing chances for showers and thunderstorms.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1111 PM CDT Sat Aug 18 2018

Cigs: weak shortwave ridging a loft and a sfc high will keep skies
generally skc through the better part of Sunday - some haziness from
smoke a loft along with some cu for Sun afternoon. Clouds will be on
the increase later Sunday night ahead of an upper level shortwave.

WX/vsby: main concern here is for river valley fog. Good setup at
KLSE with deep/light wind field, east to southeast at the sfc. T/Td
looking favorable at 03z too - only 5 degrees. Models still sending
some mixed signals, but latest RAP Bufkit soundings getting a bit
more bullish on the fog potential. Confidence growing that 1/4sm is
more likely than not...and will trend that way.

As for KRST, summery airmass could result in some light fuzz
overnight and will hold with a few hour period of mvfr br.

Winds: vrb to east-southeast light winds through the night, mostly
southeast and picking up just a bit for Sunday.

&&

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

$$

SHORT TERM...Wetenkamp
LONG TERM...Wetenkamp
AVIATION...Rieck



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