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Area forecast discussion 
National Weather Service La Crosse WI
540 am CDT Thursday Jul 24 2014

Short term...(today and tonight)
issued at 237 am CDT Thursday Jul 24 2014

Main concern for this forecast remains thunderstorm complex expected
tonight and early Friday...which could be biggest impact of any
weather through next week.

A quiet morning on tap with large area of high pressure over western
Great Lakes. Still monitoring fog development but will likely be
limited to favored valleys in Wisconsin given dew point depression
early this morning and recent stretch of dry weather.

Ended up raising temperatures for today based on trends from high pressure begins to shift east. Should be just as
warm if not a few degrees warmer most locations.

As upper low over Washington state moves into and past Canadian
rockies today...low level response will be strongest over northern
plains initially. This area of warm air advection and relatively
strong low level moisture transport will then migrate east overnight
and could increase as low level jet strengthens leading to storm
complex which should be centered on area come daybreak Friday

Deterministic outcome of 24/00z guidance fairly consistent with
timing now although axis of possible mesoscale convective system still a bit uncertain.
Prefer blend of NAM/European model (ecmwf) that drives brunt of complex across
southern Minnesota...far northeast Iowa...and into southwest
Wisconsin mainly between 25/08z and 25/15z. 0-3km MUCAPE values get
as high as 1200 to 2000 j/kg tonight but values drop and shift south
towards Friday morning likely leading to weakening storms as they
pass through. Best shear remains in 0-3km layer so besides some
heavy rain...could see some gusty winds with any stronger
elevated storms with drier low levels.

Long term...(friday through thursday)
issued at 237 am CDT Thursday Jul 24 2014

With ongoing mesoscale convective system...some question on how long complex will linger
Friday morning. Best low level forcing gradually shifts east during
the day but storms could certainly linger until afternoon in parts
of the area.

Medium range guidance has discrepancies after this initial mesoscale convective system based
on whether short wave energy ejects out of developing westerly flow
as upper low begins to drop into northern U.S. Some hints of
redevelopment along boundary Friday night but confidence is low with
some models keeping things dry.

Should be between any features on Saturday with drying west wind but
as upper low moves across western Great Lakes Sunday...additional
showers certainly possible.

As large upper low establishes over Hudson Bay...colder...below
normal regime sets up for much of next week. Northwest flow with
little in the way of waves to resolve so could see dry weather and
highs mainly in the 70s. Sporadic model guidance to include rain
chances has been thrown out for drier solutions.


Aviation...(for the 12z tafs through 12z Friday morning)
issued at 540 am CDT Thursday Jul 24 2014

Most everything was setup for dense fog in the valley at klse...but
T/dew point spread appears to have been too large to overcome. Lack of
longer night also a factor - with less radiational cooling. Could
still be some fog/stratus on the main body of the river...but
doesn/T appear it will spread across the Airport. Of course...will
monitor visual cues and observation...and will updated forecast if

Storm complex will develop across the northern plains this
evening...dropping southeast across the local area overnight. A few
-shra/ts could develop out ahead of this main mass of precipitation. Heavy
rain will accompany some of the storms...along with higher wind
gusts. Mostly expecting VFR conditions through 12z. That said...a
short period of MVFR/IFR ceilings/visibility with stronger storms will be
possible. For now...with use -shra/-tsra to cover more probable
times...mostly in the 09-14z Friday time frame. Later forecasts can
provide some refinement as needed.


Arx watches/warnings/advisories...


Short term...Shea
long term....Shea

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