Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 201707
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1207 PM CDT Fri Oct 20 2017

.SHORT TERM...(Today through Sunday)
Issued at 330 AM CDT Fri Oct 20 2017

Great end to the work week...stormy (severe?) start to the weekend.

1) Warmth: 850 mb temps +15 C today with NAEFS anomalies around +2.
Highs in the mid to upper 70s should result, with a few locations
flirting with 80. Gusty southerly winds will also play a part in the
mild end to the work week. Get out and enjoy the warmth while you
can - cooler, more seasonable air returns Sunday.

2) Storms: The models have been consistent with tracking a 500 mb
trough from the west coast eastward...sliding it across the
upper/mid mississippi river valley sat night/sun morning. A cold
front leads the trough into the region, centered north-south across
the local forecast area Sat night. Decent low level moisture return
for late Oct ahead of the front, pushed along by a 40-45 kt 850 mb
jet.

Some instability to play with, around 500-1000 J/kg of MUCAPE along
and ahead of the cold front. Bufkit CAPE profiles are long and
skinny though, not supportive of strong updrafts. Shear is strong,
albeit mostly along and west of the front. About 40 kts 0-3 km and
50 kts 0-6 km. There is enough instability/shear overlap though that
there will be a strong, potentially severe risk Sat evening. Strong
to damaging winds would be the main threat.

.LONG TERM...(Monday thru Thursday)
Issued at 330 AM CDT Fri Oct 20 2017

A return to reality - at least for temperatures - as the models move
from the ridging/mild pattern of the current week to more
troughing/northwest flow a loft for next week. So, say goodbye to
the 70s and hello to more seasonable 50s.

The GFS and EC drop a 500 mb tough southwest out of Canada and
through the region Mon/Tue with another trough taking a similar path
for Thu/Fri. Both bringing cold air, but moisture looks meager at
this time - which will be a limiting factor for shower chances. That
said, plenty of upper level energy and low/mid level cold air that
there should be at least small chances for showers. Will let the
consensus solution detail that.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1207 PM CDT Fri Oct 20 2017

The first concern with the forecast is with low level wind shear
for much of the overnight hours. As the mean long wave trough
swings out of the Rockies tonight, the low level jet will increase
ahead of this with the 20.12Z NAM soundings showing speeds up to
50 knots possible in this. Will continue with the trend of
including the wind shear for both sites starting right about at
sunset and then diminishing late tonight before sunrise as the low
level jet starts to weaken. The other concern is with the shower
potential Saturday morning. The NAM shows a lead short wave trough
coming out ahead of the main trough and moving from central Iowa
into northern Wisconsin. This is expected to interact with the
remains of the low level jet/moisture transport to pop some
elevated showers. This idea is supported by several of the hi-res
meso-scale models and will include a VCSH at KRST. Expecting this
activity to stay west of KLSE so will stay with a dry forecast
there.

&&

.FIRE WEATHER...(Today)
Issued at 330 AM CDT Fri Oct 20 2017

Drying crops/fuel with natural maturity and progression of fall
raises some concern for heightened fire weather conditions today.
Gusty south winds 15 to 20 mph gusting 25-30 mph will be seen for
many locations by this afternoon along with minimum relative
humidities values in the 30-40 percent range.

&&

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

$$

SHORT TERM.....Rieck
LONG TERM......Rieck
AVIATION...04
FIRE WEATHER...DAS



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