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Area forecast discussion 
National Weather Service La Crosse WI
704 am CDT Wednesday Jul 30 2014

Short term...(today and tonight)
issued at 308 am CDT Wednesday Jul 30 2014

Main forecast concerns are precipitation chances today.

Latest water vapor satellite shows several shortwave troughs
rotating around the closed upper level low over southern Hudson
Bay. Latest mosaic radar indicates shower/thunderstorm activity
from late evening have dissipated over the area early this
morning. This is due to loss of heating and lift associated with
impulse moving southeast of forecast area.

The forecast area will remain under the influence of the closed
upper level low over southern Hudson Bay today into tonight.
Confidence is not as high as yesterday with development of showers
and isolated the latest 30.00z GFS/NAM and rap
show weaker instability and a slightly stronger cap atmosphere
over the forecast area per BUFKIT soundings. However...the
GFS/NAM/rap continue to show weak shortwave energy to move across
the eastern parts of the forecast area. This will provide enough
lift during the peak heating of the day to warrant a small chance
of precipitation...albeit 20 to 30 percent...over the forecast
area mainly this afternoon into early this evening.

Long term...(thursday through tuesday)
issued at 308 am CDT Wednesday Jul 30 2014

With several shortwave troughs wrapping around the upper level
closed low into the Great Lakes region. Diurnal convection looks
possible again Thursday and will carry small chances of
precipitation over the forecast area.

Stronger shortwave energy moves over the area Friday...with the
30.00z GFS/NAM showing steepening lapse rates and cape ranging from
a few hundred to around 1000 j/kg across forecast area per BUFKIT
soundings. Plus...the 30.00z GFS/NAM indicate pv advection to add in
vertical motion in association with shortwave energy. Confidence is
increasing that scattered showers and thunderstorms will develop
over the forecast area during the afternoon hours and continue into
the early evening hours. Have increase precipitation chances
across the forecast area.

Main forecast concerns Saturday into Tuesday are precipitation
chances Sunday into Tuesday. The latest 30.00z GFS/ECMWF/Gem are
indicating shortwave ridging building into the northern plains and
Great Lakes region Saturday. Then...a shortwave trough/surface
front breaks down ridge and pushes into the upper Midwest and
Great Lakes region Sunday through early next week. The 30.00z
GFS/ECMWF/Gem differ significantly on placement and timing of the
surface front/shortwave models show surface front
remaining nearly stationary over the upper Midwest and Great Lakes
region. This will have impacts on where precipitation sets up over
forecast area through this period. The 30.00z GFS/Gem/ECMWF
indicate decent moisture transport/convergence in association with
shortwave trough/surface front. With significant differences
between the models on placement and timing...confidence is low on
where precipitation will occur over forecast area.


Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 703 am CDT Wednesday Jul 30 2014

Through 30... dense fog across north central and central
Wisconsin...and in the Wisconsin and La Crosse river valleys will
dissipate. Northwest winds kept the dense fog from impacting klse.
However will have to watch the IFR deck moving southwest through
Jackson County.

Another short wave trough will bring another round of scattered
showers and storms as it moves south through the area this
afternoon and evening. While the coverage does not look as much as
yesterday...kept a vicinity shower and both taf sites. Ceilings
will be around 5k feet.

After 31... the NAM and GFS suggests that the short wave
currently over northern Ontario will produce a broken deck of 5k
clouds and maybe some showers. Meanwhile the other deterministic
models keep the area dry. Will just stay dry for now.


Arx watches/warnings/advisories...


Short term...dtj
long term...dtj

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