Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 242324

Area Forecast Discussion
National Weather Service La Crosse WI
624 PM CDT FRI JUN 24 2016

.SHORT TERM...(This evening through Saturday Night)
Issued at 253 PM CDT Fri Jun 24 2016

Currently as of 19z...water vapor loop and RAP 500mb height analysis
showed an anomalously deep trough over the Pacific Northwest, with
ridging downstream over the Dakotas and MN. This places the forecast
area in subsidence and high pressure at the surface, yielding mostly
sunny skies for most. The lone exception has been a persistent
stratus deck, the one that plagued the area yesterday, which
encompassed southeast MN in portions of northeast IA this morning.
Sunshine has helped mixed most of it out, though. Much more sun
today combined with 925mb temps near 20C has helped propel
temperatures into the upper 70s to low 80s. Dewpoints have been
slowly on the rise as well with low 60s west of the MS river, with
70s streaming northward out of eastern KS and western MO.

Much of the evening looks quiet as the area remains under the
influence of high pressure. However, as the upper ridge axis crosses
the area after midnight, we see an increase of 850mb moisture
transport aiming towards us, though the best convergence on its nose
is more over northern MN. That latter location appears primed to
have convection going if not an MCS, whereas our moisture transport
may lead to just accas or some isolated shower/storm development.
Kept some 20 percent chances for this warm advection potential. Any
of this convection should keep lifting northeast during the morning
and dissipate as the nocturnal jet mixes out.

For Saturday afternoon, we have two areas of focus. The first is
with a low level moisture surge basically marching north up the MS
river. The GFS, ECMWF, Regional Canadian, 12Z NSSL WRF and 09Z ESRL
HRRR all produce some scattered shower/storm activity. This is aided
by temperatures climbing into the upper 80s to near 90, dewpoints
rising into the low to mid 70s, and a weak shortwave trough coming
through the southwest flow aloft. Have kept some 20-30 percent
chances in for this. The next concern is out west where the
anomalously deep trough marches east into the Dakotas, pushing a
cold front into MN and into the warm and humid airmass. Very good
model agreement for storms to erupt with capping breaking between 20-
21Z from Grand Rapids MN to St. Cloud and Sioux Falls SD. Since the
cold front will still reside west of I-35 at 00Z, it`s going to take
the storms cold pools to help march them eastward. Thus, models have
slowed down the storms approach to now make it look like 6-8 pm when
they move into southeast MN and northeast IA. Expect the storms to
march their way across the forecast area during the evening, pushed
along by the cold front and outflow, perhaps lingering a little bit
after midnight in the east.

On the severe weather side of things, given the increasing dewpoints
and warm temperatures, no problems expected with CAPE or CIN. Now
shear is a different story. For the most part 0-6km shear is weak,
sub 30 kt. However, there are some signs for a 30-40 kt 500mb wind
core to come out of central Nebraska at 18z and cross southeast MN
into northwest WI at 00z. If this comes to pass storms could end up
supercellular for a time with hail and damaging winds a threat. More
likely is a broken line of line segments given 0-3km shear in the 25-
30 kt range. Given this shear and a surge of precipitable water
around 2 inches to aid in heavy rain rates and cold pool, would
think strong to damaging wind would be the main threat for our
forecast area. Inflow notches will also need monitoring for
possible tornado given 0-1km shear climbing into the 25-35 kt
range in the evening. Overall highest shear forecast, and most
coverage of severe weather, expected in northwest WI where SPC day
2 enhanced is depicted.

.LONG TERM...(Sunday through Friday)
Issued at 253 PM CDT Fri Jun 24 2016

Sunday through Monday on tap to be breezy days across the region as
the anomalously deep trough moves into the northern Great Lakes
and northern Ontario. Sunday still looks on the warm side with
925mb temps in the 23-26C range, perhaps about 1C cooler than
Saturday. However, drier air coming in will make it feel much less
humid. Secondary cold front associated with the deep trough slated
to come through Sunday night to usher in much cooler air for
Monday, with highs mainly in the 70s. Despite the cooler air,
still looking at dry conditions with any cyclonic flow showers
expected farther to the northeast in Upper MI.

For the rest of next week, it`s looking very quiet across the area.
The upper level flow features the summer heat ridge retrograding to
the western U.S., setting up a fairly amplified northwest flow
pattern in the eastern U.s.. This means a seasonably cool and dry
air flow out of Canada. Coolest time period looks to be Monday night
where our typical cold spots could hit the mid 40s as Canadian high
pressure builds in. The only feature really of interest is a cold
front dropping into the area Thursday through Friday, which is the
next chance of showers and storms after Saturday night. Still, given
meager moisture in the northwest flow only produced from
evapotranspiration, kept chances around 20 percent.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 624 PM CDT Fri Jun 24 2016

Mostly clear skies this evening will give way to some increasing
mid-level cloud cover overnight at KRST/KLSE. Scattered VFR clouds
will then continue through 00Z Sunday. Light south winds through
the overnight will increase mid-Saturday morning with frequent
gusts into the lower to mid 20 kt range. Looking ahead, a line of
strong to possibly severe thunderstorms will move across the Upper
MS River Valley between 25.00Z and 25.09Z, likely to impact both
TAF airfields. Will provide greater detail with the 25.06Z TAF


.ARX Watches/Warnings/Advisories...


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