Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 260006
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
706 PM CDT WED MAY 25 2016

.SHORT TERM...(Tonight thru Thursday night)
Issued at 308 PM CDT Wed May 25 2016

Main fcst concerns this period are SHRA/TSRA chances thru the
period, highs Thu.

18Z data analysis had low pressure near the ND/SD/MN, with a warm
front southeast of the low into southeast MN and southern WI. WV
imagery showing several shortwaves rotating northeast across the
Upper Midwest. One of them aiding the lower level forcing/lift/
moisture transport over the warm frontal boundary, with a band of
SHRA/TSRA rotating north across the fcst area early this afternoon.
Temps cool into the 60s with the rain. Outside the rain areas, early
afternoon temps in the mid 70s to mid 80s.

No issues noted with 25.12Z model initializations, though would like
a little tighter overall consensus that what was seen in this
morning`s runs. Solutions quite similar for tonight/Thu as a
stronger shortwave troughing moves across the northern plains and to
north of MN by 00Z Fri and hgts rise over the region behind it. NAM
trends as a outlier tonight swinging a stronger piece of shortwave
energy across southern MN into northwest WI by 12Z Thu. Better
detail agreement for the shortwave ridge axis to move east of the
area Thu night with strengthening southwest flow ahead of the next
wave/low into the central/southern plains. Given the detail
differences early on, short-term fcst confidence is average this
cycle.

In the short term, shortwave energy moving across the area this
afternoon will exit east rather quickly this evening. Any SHRA/TSRA
with these features to exit the fcst area rather quickly this
evening with what should then be a rather quiet, convection-free
period across the fcst area tonight. However, various models
continue some form of weak 850-700MB warm advection/moisture
transport across the fcst area thru tonight into Thu. This moreso
with the NAM and its stronger shortwave across southern MN into
northwest WI overnight. Model soundings showing 500-1500 J/KG of
MUcape remains over the area tonight, with potential of little to no
CIN when lifting 850-800MB parcels. Will continue with a generally
dry fcst behind the departing wave this evening. Cannot rule out
NAM`s solution for later tonight as WV imagery did show a rather
strong shortwave near the Black Hills at 18Z. Will leave the 20-30%
SHRA/TSRA chances after midnight for now. If NAM is more correct
with what would be stronger lift/divergence aloft, a few of any TSRA
later tonight could be strong. Otherwise cape/shear would only
support more general TSRA. Continued a dry fcst Thu morning behind
what would be any passing waves from late tonight.

Cape progged to build over the area Thu afternoon. Any lower level
thermo-dynamic forcing looks to be weak, with area under the right
exit region of a 60-80kt 250-300MB jet max much of the afternoon.
Limited bulk of any SHRA/TSRA chance Thu afternoon to after 21Z and
only 20-30%. Shear remains marginal at best for any severe storms
Thu afternoon. Lack of support aloft and the shortwave ridge axis
overhead not favorable for severe storms either. Shear increases Fri
night as the 850-500MB ridge axis passes. Lower level moisture
transport/theta-e convergence and thermo-dynamic forcing increase
as well. Model soundings showing at least 500-1000 J/KG cape
persisting thru Thu night with at least NAM indicating little to
no CIN when lifting 850-800MB parcels. Limited SHRA/TSRA chances
early Thu evening the continued the trend toward 40-70% later Thu
night as PW values increase back toward the 1.5 inch range. SWODY2
with potential of marginal severe TSRA looks to apply more to Thu
night.

Lastly, with much of Thu looking dry and more of a party cloudy day,
deeper mixing expected. 850MB temps Thu afternoon in the 15C to 18C
range supporting highs in the mid to upper 80s. With dew points in
around 60 to 65F, Thu to feel quite summery. Blend of the numerical
guidance has lows/highs for tonight thru Thu night well trended.

.LONG TERM...(Friday thru Wednesday)
Issued at 308 PM CDT Wed May 25 2016

For Friday thru Saturday night: Main fcst concerns this period are
SHRA/TSRA chances thru the period.

Previous forecaster described it as a noisy pattern to end the week
into the weekend and that still fits. Decent agreement among 25.12Z
models for strong mid level troughing to be over the central/
northern plains Fri, with deep south/southwest flow over the Upper
midwest ahead of it. Models then slowly lift this trough northeast
toward/into the Upper Midwest Fri night thru Sat night. Trend
favors a compromise of the earlier runs on the trough lifting into
the region by Sat night. Fcst confidence in the Fri thru Sat night
period is average this cycle, as plenty of small scale detail
differences to impact sensible weather.

Fri thru Sat night continues to shape up as a period of several
surges of moisture transport/theta-e convergence in deep south/
southwest flow ahead of the trough slowly lifting northeast from the
central plans. Timing details will be everything on the associated
SHRA/TSRA chances with the various rounds of increased lower level
thermo-dynamic forcing expected to lift across the region. These
timing details we don`t know yet, but much of the Thu thru Sat night
expected to be a wet period. Model/ensemble consensus SHRA/TSRA
chances in the 40-60% range across much of the fcst area much of
this period look reasonable at this time. As timing details come
into focus, a couple of these periods likely to end up with higher
rain chances and a couple with lower rain chances. MUcapes of 500-
1500 J/KG progged over the area, at least during the afternoon/
evening hours, with shear mainly on the weaker side and not
supporting organized severe TSRA. However, cannot rule out strong
to isolated severe storms either of the afternoons/evenings. More
clouds much of this period will keep lows on the mild side and
highs similar to those of today. Used a blend of the numerical
guidance highs/lows for Fri thru Sat night.

For Sunday thru Wednesday, days 4 to 7: Main fcst concerns this
period are continued SHRA/TSRA chance thru much of the period.

25.00Z/25.12Z medium range model runs in good agreement for a
stronger shortwave trough to be passing across the region Sun then
shortwave ridging to build across Mon. Models remain in
surprisingly good agreement for another strong shortwave trough
to move into the northern plains Tue and into the Upper Midwest
Wed. Given decent model agreement but sensible weather outcomes
dependent on difficult to predict meso-scale features, fcst
confidence for days 4-7 is average this cycle.

Sfc low thru mid level trough progged to slowly move east of the
region Sun. Continued SHRA/TSRA chances Sun, highest over the
northeast end of the fcst area, reasonable under deeper cyclonic
flow and cooler temps aloft. Mon would trend to be a dry day under a
weak sfc high pressure ridge and the shortwave ridging aloft.
However models showing plenty of lingering moisture over the area
along with returning lower level moisture transport/warm
advection ahead of the next low/troughing developing the plains.
Small consensus SHRA/TSRA chance on Mon okay for now. Lower level
moisture/forcing/lift would then continue increasing over the
region Tue in to Wed, ahead of the next stronger shortwave moving
east across the northern plains. Cannot argue against the
continued consensus SHRA/ TSRA chances out there on days 6/7.
General southwest flow aloft thru the period continues to support
Sun-Wed temps or two above normal. Model/ensemble consensus has
these well trended for now.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 706 PM CDT Wed May 25 2016

Mainly VFR conditions are expected at the TAF sites outside of a
few passing showers and thunderstorms. The main shower and storm
activity looks to move through northeast Iowa and southwest
Wisconsin after midnight tonight into early thursday morning.
Brief MVFR to IFR conditions are possible in any stronger storms.
Another round of storms is possible Thursday evening into Thursday
night.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...WETENKAMP



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