Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 170814

Area Forecast Discussion
National Weather Service La Crosse WI
314 AM CDT Tue Oct 17 2017

.SHORT TERM...(Today through Tonight)
Issued at 313 AM CDT Tue Oct 17 2017

At 3 AM, the infrared satellite imagery showed deck of mid and
high clouds south of the Interstate 90 corridor. These clouds are
associated with a short wave trough located over northeast
Nebraska and northwest Iowa. The 17.00z models are in good
agreement that this system will move southeast away from area this
morning. As a result, these clouds will be moving out of the area
toward sunrise.

Further to the north, water vapor imagery showed a short wave
trough over northern Wisconsin. This system was producing a
scattered to broken deck of cirrus across the northern half of
Minnesota and northwest Wisconsin. These clouds will move through
the much of the area this morning. The only model that had these
clouds were the experimental HRRR, but it seemed to be too high
with its cloud percentages so tempered them back some with a
blend with the National Data Blend.

The combination of sunny skies this afternoon and 925 mb
temperatures about 3C warmer than Monday will result in warmer
temperatures this afternoon. Mixing down the temperatures from
925 mb yielded high temperatures in the upper 60s north of
Interstate 94 and in the lower 70s elsewhere. This seems realistic
since the MOS temperatures were too cool on MOnday.

.LONG TERM...(Wednesday through Tuesday)
Issued at 313 AM CDT Tue Oct 17 2017

From Wednesday into Wednesday night, a rather vigorous short wave
trough will move from Saskatchewan to Hudson Bay. With the
moisture transport and forcing remaining well to our north, not
anticipating any rain from this system. However, it will drag a
Canadian cold front through our area during the afternoon and
evening. Southwest wind ahead of this front will result in high
temperatures in the upper 60s north of Interstate 94 and in the
lower and mid-70s elsewhere.

On Thursday, the 925 mb temperatures will cool by 3 to 5C during
the morning and then there will be some recovery during the
afternoon. Due to these slightly cooler temperatures aloft, the
high temperatures will be slightly cooler than they were on
Wednesday. High temperatures on Thursday will be in the mid-60s
north of Interstate 94 and near 70 elsewhere.

On Thursday night, an upper level ridge will build across the
region. This ridge will then move east of the area on Friday.
Southwest winds in the wake of this high will bring warm air aloft
back into the region. In addition, a strong gradient aloft will
aid in mechanical mixing and this will help this air to mix to the
surface. The models differ somewhat on how deep we will
ultimately mix. They vary anywhere from 900 to 825 mb. For now,
took a compromise and went with 875 mb. This results in high
temperatures in the mid to upper 70s. If we happen to mix even
deeper, we could see some high temperatures in the 80s.

On Saturday afternoon and evening, a long wave trough and surface
cold front will move east through the region. The 17.00z GFS and
ECMWF have dramatically increased the 0-3 km shear into the 25 to
35 knot range ahead of this front. In addition, they have most
unstable CAPES up to 750 mb. However, there is no cap, so there
is concern that the showers and storms ahead of this front could
significantly lower the instability ahead of the front.

From Sunday night into Monday, another short wave trough will move
through the region. The GEM is the fastest with this system and it
has it moving through on Sunday night. Meanwhile, the ECMWF is
the slowest and it moves through the region on Monday afternoon.
The GFS was a good compromise between these two. This system will
bring a quick shot of rain to the area.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1140 PM CDT Mon Oct 16 2017

The core of the strongest low level winds should be over the area
at this time. This core of stronger winds will be shifting to the
east and away from the area through the overnight as the weak
trough aloft moves across the Upper Midwest. This will allow the
low level wind shear to end at both airports before sunrise. After
that, VFR conditions expected through Tuesday evening with little
to no cloud cover and south to southwest winds of 10 knots or




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