Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 260834
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
334 AM 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 06Z TAFS through 06Z Wednesday night)
Issued at 1110 PM CDT Tue Jul 25 2017

Cigs: high broken clouds expected through the night, with a gradual
lowering as a cold front sags south/southeast toward the TAF sites
Wed morning. Could see a drop into MVFR for a few hours as the
boundary moves through, and have added a mention to KRST. Nothing
out there yet, per sfc obs. Expecting the cigs to improve post the
front in the afternoon, with clearing looking likely for the
evening/overnight.

WX/Vsby: change in the forecast as meso models trending toward an
earlier arrival with the shra/ts threat. Current convection to the
north is associated with an upper level shortwave, while to the west
the low level jet was interacting with a west-east running front.
Models suggesting this activity spreads east as the jet/moisture
transport bends east along the front...then gradually drops
southward through Wed morning, sagging south of the taf sites by
early afternoon. Looks reasonable given ongoing convection, and have
adjusted timing for pcpn chances. Haven`t added in any vsby
restriction yet, but a tempo group may be required when/if timing
can be refined.

With clearing skies tonight and mostly light winds, see some threat
for at least mvfr fog.

Winds: Southerly fetch swinging to the northwest/north Wed afternoon
as that front slips south. Generally then light north Wed night.

LLWS for a few hours post 06z tonight with the low level jet
streaking overhead. Borderline criteria wise, but will continue
mention.

&&

.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.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Boyne
LONG TERM...Boyne
AVIATION.....Rieck
HYDROLOGY...Boyne



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