Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 201936

Area Forecast Discussion
National Weather Service La Crosse WI
236 PM CDT THU JUL 20 2016

.SHORT TERM...(Tonight through Thursday Night)
Issued at 236 PM CDT Wed Jul 20 2016

Concern through the period continues to be increasing heat and
some storm chances.

GOES Water Vapor satellite imagery/RAP 500mb analysis showing an
expansive ridge of high pressure over the central conus with
monsoonal plume of moisture pushing into the region. Embedded/
nondescript shortwave troughs within this flow sparking occasional
rounds of convection over the region. Once such area of shra/ts was
pushing east out of the area into southeast MN/northern IL. Some
showers also burbling along the MN/IA border. This seems to be
firing ahead of a weaker mid-level trough moving across eastern

Models continue to show increasing 850mb moisture transport through
tonight ahead of low pressure over the Northern Plains. This, and
the possibility of another nondescript mid-level wave in the
aforementioned monsoonal tap, will produce a chance of showers and
storms mainly east of the Mississippi River or on the eastern
periphery of strengthening 850-700mb cap. Otherwise, looks like a
fairly uncomfortable night ahead as lows only dip into the
lower/middle 70s with dew points in the 70s as well.

The heat is on for Thursday as 925mb temperatures surge to around
30C. Some question as to how much ongoing elevated convection will
be going on or amount of convective debris cloud will be overhead.
Current thinking is that surface temperatures will respond to the
warm air advection...topping off in the 90s. This pushes heat
indices into the 100-115 range during the afternoon. As
such...Excessive Heat Warning goes into effect at Noon
Thursday...dropping off at 10 pm for Clark/Taylor counties but
continuing through Friday for the rest of the area as heat/humidity
continues. Please see our latest Excessive Heat Warning products for
latest details.

Otherwise, looks like a frontal boundary drops through Thursday
night. However, NAM Bufkit sounding shows a stout cap in place. Will
carry a 20-30 pop for now based on this. Overnight lows Thursday
night only falling into the lower/middle 70s again.

.LONG TERM...(Friday through Wednesday)
Issued at 236 PM CDT Wed Jul 20 2016

As mentioned above...Excessive Heat Warning continues through Friday
for most of the area with the exception of Clark/Taylor counties in
north central Wisconsin where some cooling takes place. Will have to
watch for a continued chance of thunderstorms mainly south of I-90
in the vicinity of the surface frontal boundary.

Thunderstorm chances return to the area late Friday night, then
becoming likely Saturday into Saturday night as a warm front pushes
into the area ahead of low pressure approaching from the Northern
Plains. Will have to watch for severe threat given ample CAPE and
decent 0-3km Bulk Shear.

There will be a slight chance of storms Sunday, but looks like most
of this should be pushed east with cold front.

High pressure builds in Monday for a brief dry period, but
shower/thunder chances move in again Tuesday night into Wednesday as
both the ECMWF/GFS bring a trough through the region.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1155 AM CDT Wed Jul 20 2016

Generally good VFR expected this period as warm mid level ridging
and mdt sfc pressure gradient build across the fcst area. South
gradient winds around 10kts to keep the boundary layer stirred
thru tonight, and any late night/early morning BR to a minimum.
The warming mid level temps should keep clouds thru the period in
the sct 5k-10k ft range.  However, there are some caveats as a
sfc-850mb trough/front slowly sags south toward the fcst area.
Airmass over the area is quite moist with perhaps a shortwave
ripple or 2 to move thru the rather flat ridging aloft over the
region. Some signals among the models these could be strong enough
to trigger convection that may move into the TAF sites late
tonight into Thu morning. Confidence not high enough to include a
TSRA mention in the TAFs after roughly 09Z at this time.


.ARX Watches/Warnings/Advisories...
WI...Excessive Heat Warning from noon Thursday to 7 PM CDT Friday for

     Excessive Heat Warning from noon to 10 PM CDT Thursday for

MN...Excessive Heat Warning from noon Thursday to 7 PM CDT Friday for

IA...Excessive Heat Warning from noon Thursday to 7 PM CDT Friday for



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