Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 221725
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1225 PM CDT Thu Jun 22 2017

.SHORT TERM...(Today and tonight)
Issued at 315 AM CDT Thu Jun 22 2017

Still quite a challenging forecast over the next 24 hours with
regard to convective potential. Early this morning a surface
trough/cold front was situated from western Minnesota westward
back into South Dakota, while a warm front was lifting northward
across the area. Elevated convection has developed in the mid-
level warm advection/frontogenetical zone across northern Iowa
through southern Minnesota into western Wisconsin. This activity
is expected to advance eastward early this morning. The storms formed
above the inversion in a region of 1000-2000 J/kg MUCAPE and
30-50 kts of effective shear. With the elevated nature of these
storms, a bit of hail and locally heavy rainfall are the primary
concerns.

Heading into today, there may be some decrease in convective
activity for a time this morning. However, high-res models really
have struggled with this environment over the past several hours.
With forcing tied to the mid-level warm advection/isentropic lift
continuing through the morning, really cannot rule out storms
just about anywhere this morning. Model guidance generally
supports showers/storms continuing to develop within the sloping
mid-level frontal zone across South Dakota this morning moving
eastward into the are later this morning and into the afternoon,
especially near and north of Interstate 90. However, some
intensification/redevelopment of storms should occur southwestward
along the surface front during the afternoon with MLCAPEs near
1000-2000 J/kg and deep layer shear of 30-45 kts to work with as
inhibition weakens. The morning precipitation certainly has the
potential to influence this afternoon`s convective potential,
including placement of boundaries and degree of destabilization.
While the shear profiles would support supercell storms early on,
would expect a trend toward a linear orientation of storms fairly
quickly given the strong frontogenetic forcing. The main threats
should be hail and winds, with locally heavy rainfall possible if
storms train over the same areas. Otherwise, showers/storms should
diminish from north to south tonight as the front slides south.
Warm temps in the 80s are expected ahead of the front across
northeast Iowa into southwest Wisconsin, with highs in the 70s to
near 80 farther north.

.LONG TERM...(Friday through Wednesday)
Issued at 315 AM CDT Thu Jun 22 2017

Cooler air will filter across the region behind a cold front on
Friday with breezy northwest winds, but with mainly dry conditions.
A longwave trough then will deepen across the Great Lakes this
weekend into Monday. This will result in cool high temps in the mid
60s to low 70s with spotty chances for showers/thunder as shortwave
troughs rotate through the flow. Overall, expect precip to remain
isolated to scattered at best, with highest chances during the
afternoon hours during peak heating.

The flow will begin to flatten on Tuesday and Wednesday. Surface
high pressure building across the region early in the week will
begin to shift east by Tuesday, allowing warmer, more seasonable air
to lift back north Tuesday and Wednesday with the potential for
showers/storms increasing towards mid-week as low pressure develops
to the west across the plains.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1225 PM CDT Thu Jun 22 2017

Sct SHRA/TSRA to continue across the area thru the early/mid
afternoon hours, which makes trends in the tafs a bit difficult thru
21-22z. General VFR conditions expected, but short periods of MFVR
can be expected if a SHRA or TSRA would move across one of the taf
sites.

Stronger signal for an approaching/passing cold front to trigger a
broad band of SHRA/TSRA later this afternoon and evening as it
passes, mainly 23-03z at KRST and 00-04z at KLSE. Carried VFR with
SHRA this period and tempo MVFR/IFR in TSRA/CB as the band of
convection would sink south across the area.

Once this band moves south of the taf sites, improving/good VFR
expected for the overnight hours tonight and Fri as drier Canadian
high pressure builds in. N to NW winds 5-10kts later tonight
expected to limit any late night/early morning BR/FG, so left that
out of the tafs. Tighter gradient/mostly sunny skies/deeper diurnal
mixing on Fri to result in NW winds 10-15kt G20-25kt by late in the
morning and for Fri afternoon.

&&

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

$$

SHORT TERM...JM
LONG TERM....JM
AVIATION.....RRS


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