Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 202357

Area Forecast Discussion
National Weather Service La Crosse WI
639 PM CDT WED 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 00Z TAFS through 00Z Thursday evening)
Issued at 639 PM CDT Wed Jul 20 2016

Looking like a hot/humid period of weather upcoming for the TAF
sites, but with some very small (and very low confidence) chances
for showers and storms somewhere nearby. Persistent MVFR cloud
deck around KRST is starting to dissipate, but may briefly pass
back over that site and perhaps even KLSE into late evening as
the low level flow slowly shifts more southwesterly.

Otherwise, we will be closely monitoring upstream convection over
the Dakotas. If (that`s a big `if`) storms can get a little more
organized up that way tonight, it`s not totally out of the
question they could work southeastward and toward the area by
around sunrise, though honestly it appears the better chance will
reside north of KLSE/KRST. Looking like not much for the day on
Thursday itself, with a weak cold front approaching toward 00Z and
maybe spreading in additional shower/storm chances. Too early to
introduce any mention given the low probability but something to
watch as any storms will have quite a bit of instability with
which to work (AKA - they could be on the stronger side).


.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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