Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 221142
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
642 AM 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 12Z TAFS through 12Z Friday morning)
Issued at 642 AM CDT Thu Jun 22 2017

Lower confidence forecast this TAF issuance with instability
around and multiple waves of storms expected. A cold front will
move into the instability today and bring a wind shift and also
periods of storms. Confidence is low on the timing of the storms
but high that storms will be periodic through the day.

Storms could very easily bring vsbys down to IFR depending on the
strength.

The front will move south through the area and bring clearing
overnight.

Amendments are likely given the complexity of the forecast today
and this evening.

&&

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

$$

SHORT TERM...JM
LONG TERM...JM
AVIATION...Baumgardt



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