Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 160838

Area Forecast Discussion
National Weather Service La Crosse WI
338 AM CDT Tue Aug 16 2022

.DISCUSSION...(Today through Monday)
Issued at 337 AM CDT Tue Aug 16 2022

Key Messages:

 - River valley fog this morning

 - Precipitation chances Thursday through Saturday

 - Cooler end to the week


Another night, another round of fog for the forecast area.
Widespread dense fog is not expected, but travelers could encounter
stretches with rapid changes in visibility during the morning
commute. Most of the dense fog is confined to the river valleys
where light winds and low dew point depressions should support dense
fog through mid morning. Quiet conditions follow for the remainder
of the day with sunnier skies.


The main forecast concern for the next seven days is the return of
higher precipitation chances Thursday through Saturday.
Deterministic models continue to show a shortwave trough ejecting
from south-central Canada into the Northern Plains before evolving
into a closed upper low that propagates east over the Upper
Mississippi Valley this weekend. Details in the placement and timing
of this system will ultimately drive the timing of our precipitation
chances, but individual ensemble members still show a spread of
solutions. The NBM has the first push of higher PoPs Thursday
afternoon-night and another push of higher precip chances Saturday
afternoon. Convective parameters do not currently support organized
severe weather during this stretch.


Uncertainty remains for how low temperatures will fall as the upper
low approaches this weekend as well. GEFS members show a spread from
the mid 60s to low 80s on Saturday in Rochester, while ECMWF
ensemble members show more agreement with highs in the upper 60s
to mid 70s. Regardless, a cooler weekend with below average
temperatures looks probable.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1110 PM CDT Mon Aug 15 2022

Satellite indicates clearing occurring across the area with just
patches of mid-high cloud expected overnight. Dewpoint depressions
are quite low for 04Z and with calm winds across the area,  and a
more aggressive fog forecast has been issued for KRST/KLSE via an
evening amendment. Confidence has grown over the past hours on
fog, and LIFR fog at KLSE is likely as all the signals are coming
in at 03z: calm wind, T-Td spread of 3F, and light wind layer near
4kft. Valley webcam is showing increasing haze in the Miss River
Valley over La Crosse which adds more confidence to the forecast
for KLSE LIFR fog. Believe the potential is growing at KRST for
LIFR fog as well, but confidence is a shade lower, so have not
gone into LIFR category in TAF yet.




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