Area Forecast Discussion
Issued by NWS La Crosse, WI

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550
FXUS63 KARX 192338
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
638 PM CDT TUE JUL 19 2016

.SHORT TERM...(Tonight through Wednesday)
Issued at 250 PM CDT Tue Jul 19 2016

Juicy airmass across the region tonight/wed...heating up for
thu/fri. Airmass ideal for heavy rain production - and more on that
and the potential for flash flooding in the hydrology section
(below) - but where storm initiation will be, and where the
kickers/forcing mechanisms will move, is not clear. Detailing where
the higher rain chances thus is problematic.

One of the problems...maybe the biggest...is there doesn/t seem to
be a strong focus for storm initiation. Some weak frontogenetic
forcing, but not a standout warm front. Weak ripples in the upper
level flow, but not a sharper/strong trough. 60 kt 300 mb jet streak
right entrance region, but not a stronger/more curved jet. Models
trending nose of LLJ into north central MN - shifting into
northern/eastern WI, not pointing into the local forecast area.

A lot of little things, but not something stronger that improves
confidence on where the main focus for initiation and movement of the
storms would be.

Going to follow the LLJ for more likely initiation region, then
track that with the low level warm air advection/thermal gradient,
for movement of higher rain chances. This would start things up over
central MN, with a roughly north-south running band gradually
developing southward, shifting into western WI overnight. Trends
would continue to push the higher pcpn chances eastward. Weak
shortwave trough topping the upper level should help out Wed
morning/afternoon convection in WI. Convection already firing with
this feature across ND.

.LONG TERM...(Thursday through Tuesday)
Issued at 250 PM CDT Tue Jul 19 2016

Hot and humid air still slated to move in for Thursday and Friday,
making for steamy and dangerous heat. 925 mb temps still progged to
climb into the upper 20s (especially southern 1/2) with NAEFS 850 mb
temp anomalies from 2 to 2.5 (highest Thu). Low to mid 90s still
look on tap, without much relief thu night as lows only bottom out
in the mid 70s. Friday may be a bit cooler than previously expected
with some hints in the models that the cool front could move through
a bit earlier. This could impact headlines between warning/advisory.
Thu still looking like the hot day with heat warnings likely for
most areas. Advisories more likely for the bulk of the forecast area
Friday. Don/t have to make this decision today though. Adv may be
needed for a few hours Wed to the west.

Some model/s suggesting small rain chances for the thu-fri
period...riding weak upper level shortwaves across the ridge. Low
level cap pretty hefty though, per bufkit soundings. Will keep this
period dry for the moment, keeping those rain chances north/east of
the local area.

A little relief from the temps for the upcoming weekend...but still
above the seasonable normals. Sat still looks rather steamy with
highs in the upper 80s coupled with dewpoints near 70. Better
chances for showers/storms during the weekend...with perturbations
rippling along the upper level flow through the ridge, along with a
cold front expected to slide across the region sat night/early sun.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 638 PM CDT Tue Jul 19 2016

A quiet evening and first half of the overnight with storms well
off to the south of the TAF sites. The big question late tonight
remains just how widespread any additional showers and storms will
become for KRST/KLSE. Per our latest thinking, still believe there
is a window between roughly 08Z and 14Z when stronger moisture
transport points into our local area, with a return to increasing
elevated instability perhaps fueling at the least scattered
convection working across the terminal sites. Any storms that do
develop will be slow moving and will produce locally very heavy
rainfall, and there is a small possibility for brief IFR
conditions in said heavy downpours. Increasing warmth aloft
working in from the west should gradually push any storms east of
the TAF sites by mid morning, leaving not much to speak of for the
afternoon as heat and humidity start to really build northward.
Winds do look to become more gusty from the south, with some gusts
perhaps approaching 25 knots possible later in the afternoon.

&&

.HYDROLOGY...
Issued at 230 PM CDT Tue Jul 19 2016

Water laden atmosphere will provide ample fuel for heavy rains
across the region tonight through Wednesday morning. PWs around 2
inches...NAEFS PW anomalies around +2...and warm cloud depth in
excess of 4 km...1-2" per hour rainfall rates with stronger storms
would be possible. Totals of 2 to 3" are possible for some
locations...with locally 4" if storms would train across the same
areas.

All said, it/s still not entirely clear where the greater storm
chances will lie. Forcing mechanisms (shortwaves/fronts) aren/t
robust, and despite a steady stream of low level moisture transport,
the nose of the LLJ seems more focused into central MN rather than
over the local area. Recent meso models trending toward a greater
storms/heavy rain threat from around the Mississippi River to points
east. Much of Southeast MN/northeast IA could be on the western
fringes.

Will let the Flash Flood Watch stand as is for now...with confidence
not high enough to start pealing counties out of the watch...or
adding.

&&

.ARX Watches/Warnings/Advisories...
WI...Flash Flood Watch through Wednesday morning for WIZ032-033-041-
     053>055-061.

     Excessive Heat Watch from Thursday morning through Friday
     evening for WIZ017-029-032>034-041>044-053>055-061.

MN...Flash Flood Watch through Wednesday morning for MNZ079-086>088-
     094>096.

     Excessive Heat Watch from Thursday morning through Friday
     evening for MNZ079-086>088-094>096.

IA...Flash Flood Watch through Wednesday morning for IAZ008>011-018-
     019-029-030.

     Excessive Heat Watch from Thursday morning through Friday
     evening for IAZ008>011-018-019-029-030.

&&

$$

SHORT TERM...RIECK
LONG TERM....RIECK
AVIATION...Lawrence
HYDROLOGY....RIECK



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