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Area forecast discussion 
National Weather Service La Crosse WI
306 PM CDT sun Apr 20 2014

Short term...(this evening through Tuesday night)
issued at 121 PM CDT sun Apr 20 2014

The main forecast problem is with the rain chances through

Surface analysis this afternoon indicates the stationary front
extends from western Iowa into southern Wisconsin and is over the
very southern parts of the forecast area. Local and regional
radars shows the most concentrated area of rain north of the front
from northeast Iowa into western Wisconsin with more scattered
activity back into the north central Iowa.

Given the movement of the current activity...expect that most of
this will have moved east of the forecast area by 00z. How much
additional activity will form along the front is rather uncertain.
The forcing does not look to be all that strong with the area
split between the northern stream system moving across southern
Canada and a short wave trough getting ejected out of the system
over the Southern Plains. The indications are that this wave
coming out of the southwest will track across southeast Iowa into
northern Illinois. The best pv advection in the 500-300 mb layer
will be with the Canadian system with some very weak pv advection
across Missouri and Illinois with the southwest wave. Weak to at
times moderate frontogenesis will be in place north of the front
in the 1000-700 mb layer tonight and then shifting southeast
across the area Monday morning as the front moves out with the
short wave trough. Isentropic up Glide of 3 to 5 ubar/S will occur
into and over the front on the 300k surface into Monday morning.
The moisture transport on this level is not very strong and is
parallel to the boundary and not into it. With the weak forcing
along the boundary...confidence on how much additional activity is
going to develop overnight is not very high. Have continued the
trends from the previous forecast of showing the highest chances
along and north of the boundary with a band of 50 to 70 percent
chances. Will also continue to mention some thunder for most of
the area...except northeast of Interstate 94 where it looks like
there will be little to no cape in place. The rain chances will
persist through Monday morning before diminishing through the
afternoon as the front moves away from the region.

High pressure will then build over the area for Monday night and
persist into Tuesday night. Quiet weather with some slightly
cooler air with overnight lows dropping into the 30s with some 20s

Long term...(wednesday through sunday)
issued at 121 PM CDT sun Apr 20 2014

An extended period of wet weather looks to be possible starting
Wednesday and persisting through Friday with additional chances
then for the upcoming weekend. The upper level ridge will get
pushed east of the region as an upper level low comes across the
northern rockies. A lead short wave trough is expected to come out
of the upper level low and ride up the backside of the departing
ridge. This will help generate the first rain chances as low
pressure should develop over the High Plains with strong warm
advection over the region ahead of this surface low and short wave
trough. The next short wave trough rounding the upper level low is
forecast to become very strong and cause a new upper level low to
form over the upper Midwest as the first upper level low weakens
and dissipates. This new upper level low will then move slowly
from the upper Midwest across the Great Lakes keeping the
precipitation chances going. Differences then between the 20.12z
European model (ecmwf) and GFS on how strong the subsequent ridging will be with
the European model (ecmwf) weaker allowing more short wave energy to move over the
region for the precipitation chances next weekend.
Unfortunately...temperatures look to be cool enough Friday and
Saturday night for the possibility of a rain/snow mix or light


Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 306 PM CDT sun Apr 20 2014

Cold front lies across southern Minnesota into western Wisconsin
with first round of showers moving through. This complex will push
east of krst early this afternoon...and klse by middle afternoon.
Subsidence in its wake will briefly scatter clouds out and end
precipitation threat. With additional daytime heating...and lingering
boundary in wont take too much to reignite shower
activity by late this afternoon. Even more so...another shortwave
trough approaches from the southwest...reinforcing moisture
transport and lift. Expecting highest coverage of showers from
early this evening through the overnight hours. Soundings do show
some elevated threat for thunder continues but
not enough confidence to include in tafs at this point. Showers
and isolated thunderstorms look to continue through 10z or so...then
begin to push east. Light winds and lingering low level moisture
suggests patchy fog/br at krst and possibly klse...and have
reduced visbys down to low end MVFR...but could see 1-2sm at times
through middle morning before northwest winds help to mix out the low
levels and bring VFR conditions back to the terminals.


issued at 306 PM CDT sun Apr 20 2014

Flooding along the lower reaches of the Mississippi River will
continue through the first part of the week as runoff from
upstream snow melt and recent rain runoff moves downstream.
Rainfall overnight into Monday is not anticipated to be enough to
produce any additional flooding concerns.

Arx watches/warnings/advisories...


Short term...04
long term...04