Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 141751

Area Forecast Discussion
National Weather Service La Crosse WI
1251 PM CDT Mon Aug 14 2017

.SHORT TERM...(Today through Tuesday)
Issued at 252 AM CDT Mon Aug 14 2017

A relatively slow moving upper trough will swing across the area
today into tonight. An organized area of mainly showers that has
been working across southern MN and northern IA has continued to
weaken as it progresses eastward into a more stable environment.
However, this area of showers will continue to move eastward into
the morning hours with forcing from the upper wave and some 850 mb
moisture transport nosing into the area. Ahead of the cold front
MLCAPEs of around 500-750 J/kg may build this afternoon,
especially over northeast Iowa into southwest Wisconsin. Isolated
to scattered diurnal showers/storms are possible then through the
afternoon into the early evening, but any storms will remain non-
severe given the limited instability. Weak high pressure beneath
transient mid-level ridging should result in a mainly dry weather
later tonight and Tuesday. However, there is concern that low
stratus or fog may develop tonight. NAM soundings are quite
supportive of this, with the SREF also indicating high fog/stratus
probabilities as well. If this occurs, a good chunk of Tuesday could
end on the cloudy side with weak mixing north of the surface
boundary to the south of the area.

.LONG TERM...(Tuesday night through Sunday)
Issued at 252 AM CDT Mon Aug 14 2017

Another upper level trough will begin ejecting across the central
plains by Tuesday night. Strong moisture transport will occur ahead
of the associated frontal cyclone with precipitable water values to
1.75+ inches over the area. The 14.00Z ECMWF has trended slower and
stronger with upper wave, more similar to the GFS. Broad forcing
associated with upper wave and low-level warm advection and
isentropic upglide will lead to increasing chances for showers and
storms Wednesday and Wednesday night, with shower chances possibly
lingering into Thursday if the system continues to trend towards the
stronger/slower side. Deep layer shear profiles are expected to be
on the weak side, with maybe 30 kts of 0-6 km shear. Widespread
clouds may also hinder destabilization and the potential for
stronger storms. However, locally heavy rainfall still appears to be
the main threat, with warm cloud depths extending to above 4 km and
precipitable water standard anomalies of +2. Still a little early to
have a high degree of confidence on the details of the system, but
it certainly looks to be the best chance for widespread
showers/storms over the coming week, with some potential for heavier

Behind this system, a general west to northwest flow pattern looks
to set up into late week. Overall, temps should remain fairly
seasonable heading into next weekend. Poor agreement and continuity
with timing and degree of amplification of embedded upper waves
exists among models late this week, so confidence in rain chances is
low at this time.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1250 PM CDT Mon Aug 14 2017

Cyclonic flow aloft will keep mostly cloudy skies across the
region through Tuesday morning. MVFR/IFR ceiling will continue
west of the Mississippi River and then spread into western
Wisconsin overnight. These clouds will keep visibilities VFR
through the time period.




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