Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 211720

Area Forecast Discussion
National Weather Service La Crosse WI
1219 PM CDT Wed Sep 21 2016

.SHORT TERM...(Today and tonight)
Issued at 400 AM CDT Wed Sep 21 2016

For early this morning, the combination of moderate to strong
isentropic lift and 850 mb moisture transport will result in the
continual development of showers and storms along the Mississippi
River. With precipitable water values climbing to around 1.7
inches and warm cloud layer depths of 3.5 to 4 km, these storms
will capable of producing very heavy rain. In addition with steep
mid-level lapse rates will have to watch for an isolated threat
for damaging winds and large hail. As the morning progresses, the
moisture transport will slowly slide east and any additional
development will likely occur along the western periphery of the
cold pool across southwest and central Wisconsin.

For early this afternoon, it looks like an 850 to 700 mb cap
will limit the convection across much of southeast Minnesota,
northeast Iowa, and near the Mississippi River in western
Wisconsin. Meanwhile additional thunderstorm development looks likely
along the warm front across north-central and southwest
Wisconsin. The CAM models look to be handling this well, so
trended the forecast toward them, so some better timing could be
included into the forecast.

For late this afternoon into tonight, another short wave trough
will move through the area. As the ascent increases ahead of this
short wave, the 850 to 700 mb cap will gradually erode across
central and southwest Minnesota. With the 0-1 km mixed layer
CAPES between 2.5 and 3.5K J/kg ahead of this front, storms will
quickly develop ahead of this wave. It looks initially that there
will be the potential for supercells to develop. The main threat
with these storms will be large hail and isolated tornadoes. This
convection will then evolve into a line which will be capable of
producing damaging winds. Due to this, the Storm Prediction Center
has southern Minnesota, west-central and southwest Wisconsin, and
northern Iowa under a slight risk of severe storms.

The combination of moisture from Gulf of Mexico and Hurricane
Paine will result in the precipitable water values climbing to
around 2 inches. This is near records for this time of year. In
addition the warm cloud depths will be in the 3.5 to 4 km range.
This will result in rather efficient rain-producing showers and
storms. Additional rainfall amounts will be in the 1 to 4 inch
range. This could result in some flash flooding.  A few location may
see a 2-day rainfall total in the excess of 7 inches by Thursday

.LONG TERM...(Thursday through Tuesday)
Issued at 400 AM CDT Wed Sep 21 2016

On Thursday, the moisture transport starts to shift east of the
area. As this occurs, the better forcing will be moving away from
us and the showers and storms will become more scattered. With
precipitable water values still in the 1.5 to 2 inch range and
warm cloud depths of 3.5 to 4 km, the storms will be capable of
producing some heavy rain.

On Friday and Friday night, the warm front will move north across
the area. As this occurs, the chances of rain will be on the

The next round of heavy rain looks to be on Saturday night and
Sunday as a cold front moves east through the area. This front
looks to be progressive, so the threat for additional flooding
looks minimal.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1219 PM CDT Wed Sep 21 2016

General VFR conditions expected although a lot will depend on
convection with heavier storms producing IFR to MVFR at times. Very
scattered nature to storms, at least initially, will make it
difficult to time, but this evening storms expected to form larger
mesoscale convective system that would bring a more prolonged period
of intense rains and hence, limitied visibilties and ceilings. Hard
to pin-point exact timing for that trend, but will look for
opportunities where convection is more likely at TAF sites.


.HYDROLOGY...Today through Thursday
Issued at 400 AM CDT Wed Sep 21 2016

It continues to look like there will be a potential for a serious
flooding situation from today through Thursday. The first round of
this morning is mainly preconditioning the soils which will make
it easier for flash flooding to occur with the second round of
very heavy rain which is expected to move into the area from late
this afternoon into tonight. It looks like there will be a
potential for another 1 to 4 inches of rain with this round.

Localized rainfall amounts from Tuesday night through Thursday may
be in the excess of 7 inches.

Stay weather aware and be ready to move to higher ground! Several
rivers could go into flood. Minor to major river flooding is


WI...Flash Flood Watch through Thursday evening for WIZ017-029-

MN...Flash Flood Watch through Thursday evening for MNZ079-086>088-

IA...Flash Flood Watch through Thursday evening for IAZ008>011-018-



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