Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 281748
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1248 PM CDT THU JUL 28 2016

.UPDATE...
Issued at 1248 PM CDT Thu Jul 28 2016

Low pressure continues to very slowly pivot across the area, with
most of the CWA firmly in the "cool" sector now but far southern
sections down toward Grant County still just barely on the warm
side. Continue to watch convection bubbling down that way and for
areas mainly east of the Mississippi, in the vicinity of an
inverted trough axis. With broad but weak ascent in the presence
of a moist airmass (with some SBCAPE pushing 1000 J/kg across
southern areas), don`t see why our current setup will change much
heading into the afternoon hours, with a few more showers/periods
of some drizzle rotating across areas along/north of I-90 while
southern spots east of the Miss River continue to see periods of
showers and a few storms.

Still a little concerned about non supercell tornado threat
across Grant county where NST values are pegged around 3 right
along the trough axis, but the best risk for that looks to be into
northern IL where low level lapse rates continue to steepen
considerably. One other thing to watch with any convection
through the afternoon will be the heavy rain risk with storm
motion only around 5 knots and PWAT values around 1.5 inches,
though thankfully any really heavy totals should remain fairly
isolated.

&&

.SHORT TERM...(Today and tonight)
Issued at 400 AM CDT Thu Jul 28 2016

At 3 AM, a weak surface low was located near La Crosse WI. A weak
warm front extended east of this low across central Wisconsin.
Showers and isolated thunderstorms were located across western
Wisconsin north of Interstate 90.

For today, a slow moving upper level low and inverted trough will
move south across the Upper Mississippi River Valley. The
surface-based CAPES along and south of Interstate 90 corridor are
forecast to climb into the 1000 to 2500 J/kg range this afternoon.
The highest values are located across southwest Wisconsin. This
makes sense, because this area has the highest probability of
seeing some sunshine today. Due to these surface-based CAPES and
weak cyclonic lift, scattered showers and thunderstorms will
develop across the area. The strongest low level convergence looks
to be a across the southern half of Wisconsin, so there is some
concern that the precipitation chances may be too high west of the
Mississippi River. This is likely the reason why many of the meso
models are currently not showing many showers and storms in those
areas today.

While 0-3 km and 0-6 km shear continue to remain very weak today,
there is a concern for the potential non-supercell tornadoes this
afternoon and evening along a nearly stationary west to east
boundary across southern Wisconsin. This boundary will be likely
located near or south of Interstate 90. Along this boundary, the
NAM and RAP show that the 0-2 km lapse rates will be around 8C/km,
the 0-3 km CAPES will be in the 200 to 250 J/kg range, and there
will be moderate surface relative vorticity. Due to this, the
non-supercell tornado parameter climbs to around 1. A similar
boundary did produce a tornado near Chetek (Barron County) in
central Wisconsin on Wednesday evening.

For tonight, the inverted trough and upper level low will move
slowly south into the Mid Mississippi River Valley. In addition,
the surface-based CAPES will fall below 1000 J/kg. As this occurs,
the areal coverage of the showers and thunderstorms south of
Interstate 90 will decrease.

.LONG TERM...(Friday through Wednesday)
Issued at 400 AM CDT Thu Jul 28 2016

From Friday into Saturday, the inverted trough will extend from
northern Iowa east into the Ohio River Valley. Surface-based CAPES
during both afternoons will climb into the 1500 to 2500 J/kg
range and there will some weak ascent below 875 mb. Due to this,
kept a 20 to 30 percent chance of showers and thunderstorms across
southwest Wisconsin and parts of northeast Iowa.

From Tuesday into Wednesday, both the 28.00z GFS and ECMWF are now
in agreement that a short wave trough will move through the
region. This trough will push through the area and keep the very
warm 925 and 850 mb temperatures well to the south of the forecast
area. As a result, the high temperatures on both of those days
will likely remain in the lower and mid 80s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1248 PM CDT Thu Jul 28 2016

Widespread low clouds and periods of showers will continue through
the afternoon at both RST and LSE as slow moving low pressure
meanders through the region. Conditions will likely very slowly
lift toward MVFR levels, but with periods of IFR through 22Z. As
the low departs this evening and tonight, there should be an
influx of drier air from the northeast, allowing for ceilings to
slowly return to VFR levels, though that may take some time around
RST.

&&

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

$$

UPDATE...Lawrence
SHORT TERM...BOYNE
LONG TERM...BOYNE
AVIATION...Lawrence



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