Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 260407
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1107 PM CDT MON JUL 25 2016

.SHORT TERM...(This evening through Wednesday night)
Issued at 230 PM CDT Mon Jul 25 2016

The concern during this period is how much shower and storm
activity will be around the area. The forcing during this period
looks to be weak which leads to a rather low confidence forecast.
To reflect this low confidence, limited the rain chances to 50
percent or less.

The upper level flow pattern will start the period flat and zonal
coming off the Pacific and across the northern Rockies. By
Wednesday night, the flow will start to amplify as the upper level
ridge builds north along the West Coast which will allow the flow
over the Upper Midwest to become more northwest. The models have
been consistent in showing this flow pattern to be rather dirty
with several weak short wave troughs in it. With the lack of any
strong short wave troughs, the confidence on where and when any
rain will develop is low. The models have slowed down the arrival
of the first short wave trough with it now approaching the area
late Tuesday afternoon before moving across Tuesday night. Another
weak short wave trough should cross the area Wednesday before the
flow pattern starts to push subsequent waves farther south. The
25.12Z GFS still tries to suggest there could be some periods of
weak to possibly moderate pv advection in the 500-300 mb layer with
the Tuesday afternoon/evening wave and again Wednesday evening.
The 25.12Z NAM however, is much weaker and shows almost no pv
advection occurring with these waves. The weak warm air advection
ahead of these short wave troughs will bring some isentropic up
glide over the area. This looks to stay north of the area through
Tuesday and then could be up to 2 ubar/s on the 305K surface
spreading in Tuesday night. This then looks to be mainly south of
the area Wednesday and Wednesday night according to the NAM while
the GFS still brings some across the area Wednesday. Both models
agree there will not be any low level features in place to help
focus any convective development. Both models do agree that the
surface ridge will still be over the area through Tuesday and that
any showers and storms that develop should stay to the north of
the area, so dropped the small rain chances across the north.
This surface high will be slow to depart Tuesday night which
should help to limit the rain chances to just the northern
sections. These chances should then drift south across the area
Wednesday and Wednesday night as the surface high continues to
move farther away from the region.

.LONG TERM...(Thursday through Monday)
Issued at 230 PM CDT Mon Jul 25 2016

The northwest flow looks remain into the start of the weekend
before the upper level ridge starts to move east. This should
allow heights to start rising Sunday with the upper level ridge
axis building in for Monday. With this pattern, the flow of weak
short wave troughs will likely continue which will keep some rain
chances going into the start of the weekend. Sunday and Monday
then look to be dry as the ridge is over the area both at the
surface and aloft.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1107 PM CDT Mon Jul 25 2016

VFR conditions set to continue at LSE and RST into Tuesday evening
as high pressure gradually works across the area. About the only
real issue will be the potential for some river valley fog around
LSE toward sunrise. Current temp/dew point spreads still a little
high at this hour but are slowly closing as winds through 2kft
remain rather light. If the night was a bit longer, would think
the chances are much higher for some dense fog at LSE proper.
Instead, suspect that there will be some fog nearby in parts of
the Mississippi basin but with only a very low probability for it
to meander toward the airport itself. Otherwise, skies should
remain mainly clear, but with perhaps a touch of mid and/or high
cloud at times into Tuesday afternoon pending the evolution of
convection well to our north and west.

&&

.ARX Watches/Warnings/Advisories...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...04
LONG TERM...04
AVIATION...Lawrence


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