Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 120353
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1053 PM CDT Tue Aug 11 2020

.SHORT TERM...(This evening through Wednesday)
Issued at 250 PM CDT Tue Aug 11 2020

Dry conditions will persist for the remainder of today as surface
high pressure resides over the region. Afternoon temperatures up
to the mid 80s are expected today and tomorrow. Overnight low
temperatures dip into the upper 40s for the cranberry bog areas of
Wisconsin, but low temperatures elsewhere across the region are
expected to be in the upper 50s.

Light winds and (mostly) clear skies overnight set up another
favorable environment for patchy fog to develop Wednesday morning.
Mainly expecting the Mississippi River valley tributaries to be
impacted. There is some uncertainty with how widespread the fog
will become. Clouds could spill in from the west this evening from
the current convective system in South Dakota, which will limit
the radiational cooling needed to reduce the dewpoint depression.

An approaching shortwave trough from the west introduces low
precipitation chances late Wednesday morning with the greater values
of moisture transport remaining off to the west. These chances
continue through the afternoon for the northwestern parts of the
area as the shortwave passes through the region and high pressure
slides off to the east. Not expecting much for storm chances as the
greater instability remains off to the west of the region.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 250 PM CDT Tue Aug 11 2020

Wednesday Night through Friday...
This period is characterized by a fairly persistent pattern with
moisture and instability anchored in Minnesota and Iowa...with the
gradient just east of I-35 and into the western forecast area.
With shortwave trough activity and surges of low-level moisture
transport convergence moving through periodically off to the
northwest, almost daily storms will occur to the northwest of the
area...with diminishing chances eastward. It may be difficult for
central and southwest Wisconsin to see any rain. Any storms do
not appear to pose a severe risk and most likely would be in a
diminishing state as they move in.

Friday Night through Saturday Night...
This is a lower confidence period with increasing instability and
at some point a cold frontal passage...most likely Saturday. But
the model guidance has a good deal of spread on the timing and
details right now. The moisture axis should advect into the area
by Friday afternoon with a return of higher dewpoints and
instability. With a stronger signal for longwave evolution to
northwest flow, cold frontal passage and storms look more likely
areawide at some point in this period - probably Saturday - but
forcing and timing will be key to rain/storms/severity.

Sunday through Tuesday...
After cold frontal passage early Saturday night / Sunday, a dry
and below normal temperature period looks on tap through Tuesday.
Northwest flow will dominate with pleasant conditions.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1053 PM CDT Tue Aug 11 2020

The latest guidance through the evening continues to indicate that
fog over the main channel of the Mississippi River impacting KLSE
is not likely. Still expecting clear skies through the night with
a deep light wind layer, but the temp/dew point spread at 03Z was
still 11 degrees and not much recovery is expected in the dew
point overnight. Saturation at the surface does not look like it
will occur and even if it did, there is much drier air just above
the surface to further hinder fog development. Convection moving
across the Dakotas with a short wave trough will continue to move
east but should weaken late tonight/early Wednesday morning west
of the area as it moves out of the main moisture transport axis.
This activity will spread a high VFR ceiling over both sites for
the afternoon into the evening.

&&

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

$$

SHORT TERM...Peters
LONG TERM...Baumgardt
AVIATION...04



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