Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 222345
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
645 PM CDT SUN MAY 22 2016

.SHORT TERM...(This evening through Monday)
Issued at 350 PM CDT Sun May 22 2016

At 3 PM, a 1019 MB high pressure system kept skies mainly sunny
across Wisconsin. Meanwhile the skies in southeast Minnesota and
northeast Iowa ranged from clear to partly sunny. Temperatures
ranged from the upper 70s to mid-80s. Relative humidity values
ranged from 15 to 25 percent.

For tonight and Monday morning, a 500 mb PV anomaly will move
northeast across western and northern Minnesota. This will keep
the synoptic forcing and moisture transport well to our west and
north. As a result, went with a dry forecast.

On Monday afternoon, a weakening short wave trough will approach
the area from western and northern Minnesota. Besides weakening,
this trough will be entering a drier air mass. Like the past
couple of days, soundings continue to suggest that the surface dew
points are too high. As a result, lowered the dew points by 3 to
6F. This will lower the afternoon relative humidity values to
around 30 percent in western Wisconsin and in the 35 to 45 percent
range across southeast Minnesota and northeast Iowa.

Besides lowering the relative humidities, it will also lower the
CAPES on Monday afternoon. As a result, prefer the GFS CAPES (up
to 1000 J/kg) over the NAM CAPES which are in the 2000 to
2500 J/kg range. The latest HRRR really weakens the CAPES as it
moves into the forecast area. This makes a lot of sense.

Like the past couple of days, both the 0-3 km and 0-6 km shear
remain generally less than 20 knots. As a result, not anticipating
any organized severe weather. However with plenty of dry air below
the cloud base, there will be gusty winds and a small potential
for a dry microburst (this would fit well with the SPC marginal
risk on Day 2). With the soundings showing very skinny CAPE
profile, not seeing much a signal for large hail.

.LONG TERM...(Monday night through Sunday)
Issued at 350 PM CDT Sun May 22 2016

On Monday night, a weak front will move as far south of Interstate
94. Both the GFS and NAM are starting to trend more toward the
ECWMF and they show that the best synoptic lift and moisture
transport will be to our north and west. As a result, confined the
60 to 70 percent precipitation chances north of Interstate 90.
With the CAPES continuing to range from 500 to 1000 J/kg during
the evening and less than 500 J/kg overnight and 0-3 km and
0-6 km shear less than 20 knots, no severe weather is
anticipated.

From Tuesday through Wednesday, the front will remain somewhere
near Interstates 90 and 94. However there is rather limited
moisture convergence along this front. As a result, any showers
and storms that do develop will be highly dependent upon how much
CAPE can build up during the day. The shear remains rather weak on
Tuesday, so not anticipating any organized severe weather.
Meanwhile on Wednesday, the 0-6 km shear climbs above 40 knots in
the NAM, but the GFS only has it 0-6 km shear up to 25 knots. So
there are still questions on the shear.  As a result, the confidence
on any severe weather remains on the low side.

Beyond this time period, there has been very little run to run
continuity, so just stayed with the model consensus.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 645 PM CDT Sun May 22 2016

VFR conditions will continue at KRST/KLSE through the period.
Mostly clear skies this evening will give way to mid-high level
clouds overnight into Monday morning as thunderstorms across the
Dakotas move east and weaken. Some of this activity may hold
together long enough in shower form to impact KRST Monday morning,
so will continue VCSH mention. Additional shower and thunderstorm
development is possible Monday afternoon, mainly impacting areas
west of the Mississippi River, but timing and coverage uncertainty
precludes mention in the KRST TAF at this time. KLSE will remain
dry through 24.00Z.

South winds at the surface will continue overnight from 6 to 12
kts. However, added a wind shear component at KRST overnight as
winds in the 1500 to 2000 ft agl layer increase to between 40 and
45 kts. Deep mixing and a strengthening surface pressure gradient
on Monday will result in frequent gusts into the mid 20 kt range,
possible higher at KRST.

&&

.ARX Watches/Warnings/Advisories...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...BOYNE
LONG TERM...BOYNE
AVIATION...ROGERS



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