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Area forecast discussion 
National Weather Service La Crosse WI
1202 PM CDT Friday may 29 2015

Short term...(today through tonight)
issued at 255 am CDT Friday may 29 2015

Area of light showers expected to become a little more widespread as
it advances northeast across the region early this morning - mostly
driven by low level warm air advection and a weak ripple in the
upper level flow. Low level jet/moisture transport focused into Lake
Superior while little/if any instability indicated over the forecast
area. Still...mesoscale models all point to an expansion of the showers
as they advance northeast...hinting at some thunder potential too.

To the west...a line of convection is ongoing...associated with an
approaching cold front. While the boundary isn/T overly impressive
in terms of a saggy pressure obviously has enough
frontogenetic forcing to pop showers/storms. The front will move in
this afternoon...dropping southeast overnight. NAM builds about 1 k
j/kg of SBCAPE ahead of the boundary...with the GFS more robust at
nearly twice that. Some question on how much instability will be
realized as morning convection exits and debris clouds linger. If
several hours of sun do result in GFS-esque like values...BUFKIT
soundings show a rather skinny profile to cape...not supportive of
deep/strong updrafts. In addition...wind shear is relatively
meager...mostly Post the front...and in the 0-3 km layer.
Overall...not a favorable scenario for severe weather. Can/T rule
out a few stronger storms...with small hail and enhanced wind
gusts...but unless stronger instability develops and overlaps with
the marginal shear more...the severe risk is low.

Long term...(saturday through thursday)
issued at 255 am CDT Friday may 29 2015

The GFS and European model (ecmwf) favor dry conditions for the weekend and most of
next week. Both build broad upper level ridging by the early part of
next week...amplifying it as a West Coast trough deepens. This
amplification would serve to shuffle most bits of energy ejected out
of the trough west/north of the local forecast area. That said -
both models suggest a bit of upper level energy could spin across
the region Sun night. The problem for this ripple is the amount of
moisture to work with...which is minimal via relative humidity fields/BUFKIT
soundings. Also...a surface high is slated to be just east of the local
area. With all this mind...will keep most of the forecast area dry
through Wednesday...holding onto small chances across the far
north...closest to any forcing. Consensus solution gives small probability of precipitation
for much of the region on Thursday/Thursday night. Don/T see a lot of support
per the 00z runs of the GFS/ec...but will hold with this forecast
for the moment. Caveat to the expected dry conditions...if the
ridge isn/T quite as strong as prognosticated...rain chances will creep
into western/northern parts of the forecast area.

With the passage of the cold front air returns for the
weekend. 850 mb temperatures prognosticated to drop from around 14 c this 4 c by 00z sun. Naefs 850 mb temperature Standard anomalies
are only 0 to -1 Sat/ its not an anomalously cold
airmass...but will keep US a several degrees below the late may
normals. With the building ridge for the new work week expect temperatures
to rebound for the start of June...with some 80s looking likely.


Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1202 PM CDT Friday may 29 2015

Scattered showers continue across the region and may see a general
increase in activity through the afternoon as the cape slowly
increases. Not expecting the activity to become more widespread
until the cold front across Minnesota advances into the area. For
krst...the 29.15z hrrr suggests this will not occur until almost
00z while the 29.12z hi-res arw is a couple of hours faster. Given
that the current activity is starting to increase just a bit
faster than the hrrr would suggest...will lead toward the slightly
quicker arw and show a chance of storms between 22z and 24z. As
the activity then shifts east...the storms should be possible at
klse between 00z and 02z. Once the front moves through...the
storms will end with just some lingering light rain showers for a
couple of hours. Ceilings should remain VFR ahead of the
front...except for MVFR in any storms that develop. Once the front
GOES through...ceilings should then come down to MVFR for the rest
of the night into Saturday morning. Decent low level lapse rates
look to develop behind the front at krst to produce some gusts to
around 20 knots overnight.


Arx watches/warnings/advisories...


Short term...rieck
long term....rieck

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