Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 261747

Area Forecast Discussion
National Weather Service La Crosse WI
1247 PM CDT Wed Jul 26 2017

.SHORT TERM...(Today and tonight)
Issued at 333 AM CDT Wed Jul 26 2017

At 3 AM, an area of showers and storms was located across central
and north-central Wisconsin. This precipitation was associated
with strong 925 and 850 mb moisture transport ahead of a northern
stream short wave. This slides off to the east early this morning.

Meanwhile, another area of showers and storms extended from
south-central Nebraska northeast into central Wisconsin. As the
low level jet veers early this morning expect these showers and
storms to move into our area. While there is 2 to 3K elevated CAPE
from north-central Wisconsin southeast into southeast Minnesota
and northeast Iowa, the shear is not that impressive. With
precipitable water value of 1.5 to 2 inches and warm cloud layer
depths around 4 km, these showers and storms will be highly
efficient rain producers.

The 26.00z models are in fairly good agreement that the low level
jet will wane across our area later this morning and then refocus
across western Iowa. As a result, expect that the areal coverage
to diminish across the Upper Mississippi River during the mid to
late morning.

A mesoscale convective vorticity will move out of Nebraska and
then moves east across Iowa this afternoon and tonight. Ahead of
this system, there will be strong 850 mb moisture transport and
this will result in a rapid increase of showers and storms along
the frontal boundary. While there is good agreement that this will
occur. There are still some questions on how far north will this
system will track. The RAP, NAM, ARW, and NMM have their showers
and storms much further north than the HRRR. With precipitable
water values of 2 to 2.5 inches, there will be the potential of
very heavy rain. In addition, they will repeatedly moving across
the same areas, so flash flooding will be a distinct possibility
along this boundary. At this time, thinking this will remain south
of the Upper Mississippi River Valley. However, may have to watch
northeast Iowa and maybe southwest Wisconsin if this system
happens to come out further north.

.LONG TERM...(Thursday through Tuesday)
Issued at 333 AM CDT Wed Jul 26 2017

On Thursday afternoon and evening, a short wave trough will move
southeast across northern and eastern Wisconsin. While there are
steep lapse rates (8-8.5 C/km), soundings show a warm layer
between 700 and 500 mb and this may cap off any convection from
even developing. As a result, only have a slight chance of showers
in north-central and central Wisconsin.

From Friday into Sunday, high pressure will be in control of the
area. With relatively dry air, abundant sunshine, and soils drying
out, expect the temperatures in the river valleys to be at or a
few degrees higher than the MOS. Meanwhile at night, the
relatively dry dew points (especially on Saturday morning) will
cause temperatures in central Wisconsin to fall a couple of
degrees cooler than guidance. Overall, a nice time period for any
outdoor activities.

From Sunday night into Tuesday, the extended 26.00z models differ
on when the ridge over the Northern Plains may break down. The GFS
breaks this down much sooner, so scattered showers and storms
move into the area for this time period. Meanwhile, the ECMWF
has its 500 mb ridge further to the east and we remain dry. Due
to these differences, only have a slight chance of showers and
storms in the forecast.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1247 PM CDT Wed Jul 26 2017

Scattered showers will persist across the area through much of the
afternoon. The strongest showers could produce brief MVFR
conditions. Cannot rule out isolated TS, but it is looking more
likely this threat will stay south of the TAF sites. As chances
for showers dissipate early this evening, an MVFR cloud deck is
forecast to develop behind a southward advancing cold front. This
cloud deck should slide off to the south during the overnight
hours. If skies clear earlier tonight, patchy areas of fog could
develop. However, the potential for fog seems to be mitigated by
lower than expected rainfall amounts so far today. VFR conditions
are expected through the remainder of the period.


.HYDROLOGY...through Wednesday night
Issued at 333 AM CDT Wed Jul 26 2017

Flood Warnings continue along the Kickapoo River from Gays Mill to
Steuben. While additional rain is expected across the Upper
Mississippi River Valley through tonight, it continues to look
like the heaviest rain will not impact the Kickapoo River Basin.
As a result, expect to see the river to continue to fall today.




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