Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 191648

Area Forecast Discussion
National Weather Service La Crosse WI
1148 AM CDT Mon Sep 19 2016

Issued at 1000 AM CDT Mon Sep 19 2016

Appears forecast is on track this afternoon. Expecting strong to
severe storms to fire along the cold front mainly along and south
of a line from Oelwein IA to Viroqua WI after 3 pm. Appears, per
the latest Convective Allowing Models (CAMS), that the cold front
and storms will push southeast out of the area around 8 pm. Given
forecasted severe parameters, still looks like there will be a
damaging wind and large hail threat. An isolated tornado cannot be
ruled out.


.SHORT TERM...(Today and tonight)
Issued at 403 AM CDT Mon Sep 19 2016

For this morning and early this afternoon, moderate to strong 600
to 700 mb frontogenesis will be found across central Minnesota
and northern Wisconsin. This will result in the showers that are
currently over northern South Dakota to move east across these
areas. Due to this, increased the rain chances up to 50 percent
north of Interstate 94 and this may not be high enough yet.

Between 19.21Z and 20.02z, the models continue to show that the
0-1 km mixed-layer CAPE will climb into the 1 to 2K range across
eastern Iowa, southern Wisconsin, and northern Illinois. This will
be located ahead of a cold front that will be moving southeast
through the region. A few of the models even suggest that a
surface low could potentially develop across central Iowa and
this could increase the shear across the region and even result in
the western end of this front to briefly become a warm front. The
0-6 km shear will be favorable for supercell development with
large hail and damaging winds being the primary threats. In
addition with the 0-1 km bulk shear increasing to around 25 knots,
there will also be the potential for a brief tornado.

.LONG TERM...(Tuesday through Sunday)
Issued at 403 AM CDT Mon Sep 19 2016

From Tuesday night into early Wednesday morning, the 19.00z
models continue to show that a front will be stalled near the
Interstate 90 corridor. As a short wave trough approaches the area
on Tuesday night from the Central Plains, moderate to strong 925
and 850 mb moisture transport will increase across the area. This
moisture will be from the Gulf of Mexico. This will result in the
precipitable water values increasing to around 1.7 inches along
and north of the Interstate 90 corridor. This is 2 to 3 standard
deviations above normal. Due to this, flooding is a concern.

In addition to this, the 0-1 km mixed-layer CAPES south of this
front will be in the 1 to 2K range and the 0-6 km shear will be
favorable for the potential of elevated supercells north of this
front. These storms will have the potential to produce large hail
initially, and then these storms could potentially evolve in an
east or southeast moving mesoscale convective complex near the
Minnesota and Iowa border. The SPC marginal risk for this area
definitely looks warranted.

From Wednesday afternoon through Thursday, the remnants from
Hurricane Paine will move northeast through the area. As this
system approaches, the 925 and 850 mb moisture transport will
once again increase across the forecast area. Precipitable water
values will be in the 1.75 to 2 inch range. This will be near
record values for this time of year. This along with warm cloud
layer depths in the 3.5 to 4 km range will result in highly
efficient rain producers which will likely produce additional
flooding across the area. With the models continue to fluctuate,
the exact area is still a bit uncertain. Due to this uncertainty
held off issuing a Flood/Flash Flood Watch at this time.

South of the front, the 0-1 km mixed-layer CAPES will likely
climb into the 2 to 3K range. While the CAPES will be higher than
Tuesday night, the deep shear is less. However the 0-3 km shear
will be favorable for the potential of damaging winds along one or
more line segments.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1148 AM CDT Mon Sep 19 2016

Watching a cold front sliding south through the area early this
afternoon. Scattered showers and storms expected to fire along this
front...but will likely be south of the KRST/KLSE taf sites by 18z
issuance. This leaves VFR conditions for both sites rest of this
afternoon into tonight. Then for the overnight hours, will have to
watch for fog/stratus development early Tuesday morning which could
impact the Mississippi River Valley/KLSE. Previous 12z taf
issuance carried a sct003 for KLSE after 10z which appears to be
reasonable for now.


.HYDROLOGY...Tuesday night into Thursday
Issued at 403 AM CDT Mon Sep 19 2016

Things continue to come together for a heavy rain threat from
Tuesday night into Thursday. Rainfall totals during this time
frame look to be in the 2 to 4 inch range with locally heavier
amounts possible. Currently the best chance for this heavy rain is
along and north of the Interstate 90 corridor. However with the
models continuing to fluctuate the location of this heavy rain
axis, confidence on the exact area is still uncertain. Due to
this, held off issuing a Flash Flood/Flood Watch for now.




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