Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 102340
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
640 PM CDT Thu Aug 10 2017

.SHORT TERM...(This evening through Friday)
Issued at 330 PM CDT Thu Aug 10 2017

At 3 PM, a cold front extended from Ontonagon Michigan to Madison
Wisconsin to Kirksville Missouri. The mean-layer CAPES ahead of
this front up to 2500 J/kg. In addition, the 0-6 km shear was
marginal for supercell development. A few supercells have
developed across southern and eastern Wisconsin and northeast Iowa
this afternoon. One produced golf ball size hail in Olin IA
(Jones County).

Additional showers and storms were found north of Interstate 90.
These were associated with a low pressure system over northern
Wisconsin. The 10.12z models are in agreement that these showers
and storms on the southern periphery of this low will gradually
sink south into the Interstate 90 corridor late this afternoon and
then dissipate with the loss of diurnal heating this evening.
With less instability and shear in this area, not expecting any of
these storms to become severe.

On Friday, a trough will move southeast across northern and
eastern Wisconsin. While much of the lift and instability will be
to our northeast, we may get brushed by a few showers during the
morning and early afternoon.

.LONG TERM...(Friday night through Thursday)
Issued at 330 PM CDT Thu Aug 10 2017

On Friday night, the combination of light winds up to 900 mb and
clear skies may result in the development of some patchy valley
fog in the Mississippi River tributaries. In addition, there will
likely be widespread fog in the Wisconsin and lower Kickapoo river
valleys.

On Sunday and Sunday night, a short wave trough will move
east southeast through the Upper Mississippi River Valley. With
the models consistent with timing of this system, the rain chances
were raised a bit more. While increased deep shear ahead of the
mid level low will sufficient enough for super cell storms, the
instability remains weak, so severe weather chances remain low.

In the wake of this system, a ridge of high pressure will build
across the region. This high will provide dry weather from Monday
afternoon through Wednesday morning.

From Wednesday afternoon through Thursday, another short wave
trough will move east through the region. This system has a bit
better instability than it predecessor. However the models have
differing opinions on the shear. The GFS would be supportive of
supercells. Meanwhile the ECMWF has less shear. Due to this, the
confidence for any severe weather during this time frame remains
low.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 640 PM CDT Thu Aug 10 2017

Scattered showers continue to dance in and around RST and LSE at
this late afternoon hour, and that trend should continue through
8-9 pm before activity fades with loss of daytime heating. As that
precipitation ends, cooler air spilling southward should result
in a blossoming area of stratus from central Wisconsin working
south into areas near and east of the Mississippi River overnight,
and in fact we are already seeing signs of said stratus developing
to the north right now. Confidence in how far west lower stratus
ends up is low, and it is plausible that RST may escape with just
a brief period of MVFR conditions. Will need to watch trends after
sunset of course, but LSE looks to be impacted by MVFR ceilings
mainly after 06Z. The good news is that stratus should be scoured
from the north pretty quickly Friday morning as drier air works
into the area, with just some scattered diurnal afternoon cumulus
again expected. Winds will shift northerly overnight, and range
from 10-15 knots for much of Friday.

&&

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

$$

SHORT TERM...Boyne
LONG TERM...Boyne
AVIATION...Lawrence



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