Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 300737

Area Forecast Discussion
National Weather Service La Crosse WI
237 AM CDT SAT JUL 30 2016

.SHORT TERM...(Today through Monday)
Issued at 237 AM CDT Sat Jul 30 2016

Water vapor satellite early this morning indicates a weak short
wave trough was over North Dakota. The 30.00Z models all bring
this wave southeast and across the region today. As this wave
moves in, it should only be able to produce some very weak pv
advection in the 500-300 mb layer this afternoon. The surface
trough that was over the area Friday is still over northeast Iowa
and is not expected to move much, if at all, today. The 30.00Z
GFS suggests there could be some very weak frontogenesis in the
1000-850 mb layer near the trough and this combined with the weak
forcing from the short wave trough could be enough to generate a
few afternoon showers. These showers should quickly die off in the
evening as the low level surface ridge builds in from the
northeast for tonight. This ridge looks to remain over the area
Sunday for a dry day.

The models are all in good agreement that this low level ridge
will remain over the area Sunday night. Upper level heights are
expected to rise with short wave ridging ahead of a short wave
trough coming across the Dakotas. The higher heights and slower
timing of the short wave trough should keep any rain west of the
area so have removed the rain chances that were over the southwest
part of the forecast area. This short wave trough then looks to
move into the region Monday with the GFS showing some weak to at
times moderate pv advection in the 500-300 mb layer. The low level
ridge still looks to be rather slow to retreat which will keep
some drier air over the eastern sections of the forecast area.
There does not look to be a surface boundary coming in with the
short wave trough to help focus any convection development. There
does not really look to be a concentrated region of low level
moisture convergence. The GFS shows the best axis of moisture
transport over the Missouri River Valley into the western Ontario
but does bring the convergent eastern edge of this into the
western sections of the area Monday afternoon. This, combined with
the forcing from the short wave trough, may be enough to generate
some scattered showers and storms from about the Mississippi River
back to the west.

.LONG TERM...(Monday night through Friday)
Issued at 237 AM CDT Sat Jul 30 2016

The short wave trough will continue to advance east across the
area Monday night with the GFS showing the moisture transport
becoming focused on the area at times. A warm front looks to take
shape across Iowa with some frontogenesis developing in the
1000-700 mb layer. The warm air advection ahead of the short wave
trough kicks in as well to help produce 2 to 4 ubar/s of up glide
on the 305K isentropic surface. This looks to be the best chance
for rain and will have up to a 50 percent chance across a good
share of the area. This system will move past the area Tuesday
with the upper level ridge expected to build back in. However, the
ridge is not all that amplified so that short wave troughs coming
out of the western long wave trough that ride up and over the
ridge will be close enough to possibly bring some more showers and
storms from Tuesday night through Thursday. The upper level ridge
then looks to move east of the area allowing a stronger short wave
trough to come in for Thursday night.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1145 PM CDT Fri Jul 29 2016

Low confidence forecast overnight. Cloud cover has dissipated more
than expected, especially for areas mainly east of the MS River.
While forecast consensus is to build clouds back across much of
the region overnight, latest satellite trends would suggest less
cloud cover. If this clearing trend continues, an adequately deep
light wind layer and ample low level moisture lends itself to
valley fog impacting KLSE. If fog develops, visibility could
rapidly drop below 1SM between 30.10Z and 30.13Z. However, given
low confidence, will only add BCFG SCT003 at this time and
closely monitor observations.

At KRST, higher confidence that cloud cover will hold tough
through the night, resulting in only some MVFR visibility
restrictions. Beyond 31.13Z and through the rest of the period,
expect VFR conditions at both TAF airfields with periods of VFR
cloud cover and light east-northeast wind.


.ARX Watches/Warnings/Advisories...


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