Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 260448

Area Forecast Discussion
National Weather Service La Crosse WI
1148 PM CDT Tue Oct 25 2016

.SHORT TERM...(This evening through Wednesday)
Issued at 324 PM CDT Tue Oct 25 2016

Main impactful weather concerns are on 1 to 2 inches of rainfall
from tonight through Wednesday morning with locally higher amounts
possible. This could lead to localized ponding of water in poor
drainage areas.  River rises are possible with some locations along
the Trempealeau and Kickapoo Rivers rising to action stage and may
edge toward minor flood stage later this week.

A shortwave trough continues to slide east across the Central
Plains this afternoon heading toward the Upper Mississippi River
Valley. Weak frontogenesis in the 800-500 mb layer continues to
drive some light rain showers across portions of northeast Iowa,
southeast Minnesota, and extreme southwest Wisconsin. The
frontogenesis band will continue to meander to the northeast
producing light rain and we should start to see a increase in rain
along it later this evening. Heavier rain will move into the area
mainly after midnight as strong isentropic lift and moisture
transport focus into he area. The strongest lift moves through in
the 6Z to 15Z period on Wednesday and this is when we will see the
heaviest rainfall. Given the recent stretch of drier weather,
widespread flooding issues shouldn`t be a concern. However, with
precipitable water values running in the 1.0 to 1.25 inch range
and strong forcing moving through we may see some moderate to
heavy rain at times. MUCAPE is rather weak with values increasing
to around 200 J/KG when lifting a parcel from 825 mb. The strong
synoptic forcing will be enough to overcome the lower CAPE values
to produce isolated to scattered thunderstorms mainly along and
south of Interstate 90. Will have to keep a close eye on urban
areas where a quick inch of rainfall or repeated rounds of
moderate rain could lead to some minor flooding. Also, southeast
winds will increase across the region tonight as low pressure
deepens and moves through the area. Winds gusts of 30 to 35 mph
are possible and we may see some gusts approach 40 mph along ridge
tops and open areas if deeper mixing occurs.

Rain lingers through at least midday Wednesday across much of the
area, especially for locations along and east of the Mississippi
River. Plenty of lift and deep enough saturation to produce light
rain or drizzle at times along the inverted trough on Wednesday.
Have increased precipitation chances for the afternoon hours. The
rain will then finally exit by late Wednesday afternoon into the
early evening hours.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 324 PM CDT Tue Oct 25 2016

High pressure builds in for Wednesday night into Thursday. If
skies clear we may see some fog development early Thursday
morning. Current thinking is that cloud cover will hold across
much of the area limiting fog potential. The next timeframe we are
watching closely is Friday for strong southwest winds, warming
temperatures, and possibly some lower relative humidity values. A
tight pressure gradient sets up cross the area producing strong
southwest winds on Friday. Depending on how deeply we mix, we may
see winds approach advisory levels. Also, we could see some fire
weather concerns if we see these stronger winds and lower relative
humidity values. Forecast models do bring some moisture return on
Friday with dew point values climbing into the lower 50s. This may
not happen, given how dry the airmass in place over the local area
will be. Have increased high temperatures 1-2 degrees on Friday
along with increasing winds and wind gusts. We may see gusts
approach or exceed 45 mph at times in open areas west of the
Mississippi River.

The next system to keep an eye on is a trough swinging through
Saturday into Sunday with the potential for light rain. There is an
increasing model consensus that we may see some rain showers by
Saturday afternoon into Saturday night.  The ECWMF, GFS, and
Canadian all favor this.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1148 PM CDT Tue Oct 25 2016

The showers have increased in coverage this evening as expected
and are now affecting both airports. This is occurring ahead of
the short wave trough over eastern South Dakota and Nebraska and
surface low between KSUX and KOMA. These two features will
continue to move east tonight into Wednesday to keep the showers
and some storms going into Wednesday morning. Ceilings starting to
come down to IFR in the Interstate 35 corridor and expect these
will expand overnight as the low levels continue to saturate from
the rain. The visibility will also come down to MVFR/IFR in the
showers. The heavier rains should move past both airports by the
middle of the morning but some light rains could linger into the
afternoon with an inverted surface trough on the north side of the
surface low. Forecast sounding from the 26.00Z NAM suggest the low
levels will remain saturated into Wednesday evening which should
keep the IFR ceilings in place.


.HYDROLOGY...Tonight through Wednesday
Issued at 324 PM CDT Tue Oct 25 2016

Heavy rainfall is possible late tonight into Wednesday morning
which may lead to river rises and possible minor flooding in urban
areas. 1 to 2 inches of rain are expected and there is the
potential for locally higher amounts up to 3 inches. Be alert for
ponding of water in low spots/poor drainage areas. River rises are
also expected and depending on where the heaviest rain falls,
minor flooding cannot be ruled out. Latest forecasts along the
Trempealeau River and Kickapoo River indicate that river levels
may climb to above action stage.




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