Area Forecast Discussion
Issued by NWS La Crosse, WI

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903
FXUS63 KARX 271729
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1229 PM CDT WED JUL 27 2016

.SHORT TERM...(Today and tonight)
Issued at 400 AM CDT Wed Jul 27 2016

At 3 AM, a 1016 mb surface high was centered over northern
Illinois. This high kept skies mostly clear to partly cloudy skies
across central and southwest Wisconsin. This has allowed a stratus
deck to develop over the Mississippi channel, but it is not as
thick as it was at this time on Tuesday morning. As a result, not
anticipating too much valley fog.

Meanwhile further to the north, there is a warm front located
across northern Wisconsin and central Minnesota. There is
scattered convection located along this boundary. With weak shear
and most unstable CAPES of 500 to 750 J/kg, these storms have not
been severe.

Overall, the NSSL and HRRR CR models seem to be handling the
showers and thunderstorms along this front the best, so trended
the forecast toward them. For this morning, it looks like the
precipitation will stay mainly north of Wisconsin 29. As a short
wave trough, currently over the eastern Dakotas, moves into the
area this afternoon and evening, a cold front will sag southward
across the area. With 0-1 km CAPES of 1-2K, expect showers and
storms to spread across the area. The highest rain chances will be
located along and north of Interstate 90. With weak shear, not
expecting any organized severe weather. One uncertainty for today
is whether there will be a bit more sunshine across central and
southwest Wisconsin this morning. If this does indeed occurs, the
temperatures may end up being a few degrees warmer than it is
currently forecast to be.

During the overnight, the weak 925 and 850 mb moisture transport
shifts east of the area. As this occurs, the coverage of the
precipitation will become less and less.

.LONG TERM...(Thursday through Tuesday)
Issued at 400 AM CDT Wed Jul 27 2016

From Thursday into Friday morning, a short wave trough will move
slowly southeast through the area. Like the previous days, the
27.00z models continue to show very little 925 or 850 mb moisture
convergence. In addition, the warm cloud depths are 3500 km or
less and precipitable water values are generally less than 1.5
inches. Due to this, not anticipating any heavy rain threat. In
addition with 0-1 km CAPES of 500 to 1500 J/kg and weak shear, the
threat for organized severe weather looks to be very low.

For Tuesday, there continues to be considerable differences with
the amplitude of an upper level ridge across the Upper Mississippi
River Valley. Over the past 3 to 4 days, the GFS has been
consistently showing more amplification of the 500 mb ridge. As a
result, it has been showing very warm 925 mb (28-30C) and 850 mb
(24-28C) temperatures. This would result in high temperatures in
the lower to mid 90s. Meanwhile the ECMWF has been keeping this
ridge much further south with zonal flow across the Upper
Mississippi River Valley. As a result, the 925 mb and 850 mb (both
levels ranging from 20 to 24C) temperatures are much cooler. This
results in our high temperatures ranging from the lower to mid
80s. With neither of these models budging, opted to stay with the
model consensus.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday morning)
Issued at 1229 PM CDT Wed Jul 27 2016

Low pressure, a couple of fronts and a couple of disturbances aloft
will move toward and across the area this afternoon into Thu
morning.  As these features approach, sct SHRA/TSRA expected to move
into the TAF sites late this afternoon into much of this evening.
Finer details of timing/coverage of TSRA thru this evening remain
unclear, and left thunder mention as VCTS at both KRST/KLSE for now.
By later tonight and for Thu morning, deeper layered convergence
sets up over the fcst area as a sfc-700mb low/trough drifts slowly
across MN/WI. this convergence/lift and a rather moist airmass looks
to result in numerous SHRA and BR, along with MVFR cigs/vsbys,
around the TAF sites for most of the second half of this TAF period.
Some IFR cigs/vsbys in BR/SHRA likely a couple hours either side of
sunrise Thu and added a tempo period for this in the 09-13z time-
frame. Conditions to slowly improve Thu afternoon as the low/trough
move east of the area and cooler/drier high pressure starts to build
in.

&&

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

$$

SHORT TERM...Boyne
LONG TERM....BOYNE
AVIATION.....RRS



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