Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 120309

Area Forecast Discussion
National Weather Service La Crosse WI
1009 PM CDT Fri Aug 11 2017

.SHORT TERM...(This evening through Saturday)
Issued at 311 PM CDT Fri Aug 11 2017

At 3 PM, a surface low was located over northern Lake Huron. Cold
air associated with its upper level low was producing a scattered
to broken 4-5K deck diurnal clouds across the Upper Mississippi
River Valley. There were even a few showers north of the Twin
Cities. Meanwhile further west, there was a surface high extended
from eastern North Dakota into northwest Iowa.

The 11.12z models are in good agreement that with the loss of
diurnal heating that these clouds will quickly go away and we will
be left with primarily clear skies overnight. A pressure gradient
between the departing low pressure area and the high to the west
will provide enough winds that most areas will not see any valley
fog. The only exceptions may be in the sheltered river valleys of
the Mississippi tributaries and in the lower Kickapoo and
Wisconsin River valleys. The combination of dry air and light
winds will allow the bog areas of central Wisconsin to cool into
the mid and upper 40s and into the lower and mid 50s elsewhere.

On Saturday, high pressure will build across the region. Skies
will be mainly sunny with high temperatures ranging from the mid
70s to lower 80s. The warmest temperatures will be found in the
Mississippi River Valley.

.LONG TERM...(Saturday night through Friday)
Issued at 311 PM CDT Fri Aug 11 2017

On Saturday night, high pressure will be centered over the Upper
Mississippi River Valley. While much of the night will be clear,
some mid and high clouds will be moving into the area toward
sunrise. These clouds will be ahead of an approaching short wave
trough moving out of the Northern Plains. These clouds may act as
a hindrance for the development of valley fog. For now, decided
not to add any valley fog to the forecast grids.

From Sunday into Monday morning, a short wave trough will move
east southeast through the region. There will be limited
instability ahead of this wave (surface-based CAPES only up to
1000 J/kg), so only anticipating isolated to scattered showers at
this time.

A ridge of high pressure will build across the area on Monday
night and Tuesday. This ridge will provide dry weather through
Tuesday night.

From Wednesday into Friday, the models continue struggle with the
timing of a short wave move through the region. As a result just
kept rain chances in the 20 to 40 percent range.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 1009 PM CDT Fri Aug 11 2017

High pressure continues to build into the area will result in VFR
conditions the next 24 hours. Could still see a touch of fog in
the low lying areas and some river valleys through sunrise,
though stronger northerly winds just off the surface should keep
any fog or stratus out of the LSE terminal. Winds will remain from
the north under 10 knots.

Looking just ahead, the setup for some fog later Saturday night
into Sunday morning for LSE looks much better as high pressure
drifts overhead, but any fog would occur after the end of the
current TAF period.




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