Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 220815

Area Forecast Discussion
National Weather Service La Crosse WI
315 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

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 06Z TAFS through 06Z Thursday night)
Issued at 1130 PM CDT Wed Jun 21 2017

Cigs: mid/high level clouds across taf sites, and should hold into
thu morning.

Cold front slated to drop across the region late Thu morning. Should
see lowing cloud deck with the boundary, and maybe a dip into mvfr
especially along and post of the front. Likely see a clearing out of
any low cigs by the overnight.

WX/vsby: first, convection firing off over northwest IA, making
progress eastward. Region of low level convergence and favorable
instability mostly responsible for the shra/ts, but also a hint of
ripple in the upper level flow lending a hand. Unclear whether these
storms will hold together as they move east. Radar trends currently
showing a decaying trend, but the influence of the upper level
shortwave could keep them going - and a potential impact for KRST.
For the moment, going to keep KRST dry, but will monitor closely.

A couple other focuses for shra/ts threat for KRST and KLSE. First
is a cold front slipping across the area late Thu morning/afternoon.
Meso models now developing convection a bit earlier than some
previous runs, and have an increased threat between 15-18z, which
likely continues into the early afternoon. Could see a few hour
break before the next focus - upper level shortwave and elevated
frontogenetic region - brings another band of shra/ts across the
area. Without a lot of confidence in timing and placement of the
main bands, keeping with vcts and won`t get too cute with timing.
Anticipate updates with tempo groups providing more clarity. There
will be vsby reductions with the showers/storms - all capable of
heavy rain.

Winds:  some LLWS concerns for the overnight, mostly through 10z, as
the low level jet pushes overhead. Sfc direction will stay generally
southerly until the passage of the cold front late Thu
morning/afternoon - going northwest to north.




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