Scientific Forecaster Discussion
Area forecast discussion
National Weather Service La Crosse WI
650 am CDT Wednesday Oct 1 2014
Short term...(today through tonight)
issued at 303 am CDT Wednesday Oct 1 2014
Focus is on rain chances today into tonight.
Water vapor imagery/rap 500mb analysis showing a broad middle-level
trough across the western half of the Continental U.S.. within this long wave
trough...a closed low was moving north out of ND into southern
Saskatchewan while a fairly strong middle-level trough was pushing east
across neb/KS. A band of showers and thunderstorms were out of the
wave...extending north-S from Iowa into eastern KS/OK.
Look for this middle-level wave to lift northeast into the upper
Mississippi River valley region today. Corridor of moderate 850mb
moisture transport and isentropic lift ahead of the wave expected to
drive shower activity across the area. Cannot rule out a few rumbles
of thunder as well. 850mb temperatures climb into the 12-15c range
ahead of the wave. This should translate to high temperatures
ranging from the upper 50s across north central WI...to the 60s
elsewhere across the arx forecast area.
Look for scattered showers and a few thunderstorms to continue into
this evening...but then a tapering trend late in evening/overnight
as the wave pushes off to the east. Otherwise...cloudy conditions
will persist with lows bottoming out in the 50s.
Long term...(thursday through tuesday)
issued at 303 am CDT Wednesday Oct 1 2014
Rainfall...wind...possibly some light snow mix all a concern in the
After somewhat of a break in the action later Wednesday
night...will be watching a stronger middle-level wave driving surface
cyclogenesis Thursday morning over the Southern Plains. Models
deepen this low and take it northeast across the area Thursday night
into Friday. NAM/GFS increases precipitable water values into the 1-
1.5 inch range during the day Thursday into Thursday night as Gulf
moisture is pulled northward into the area. Broad 850mb moisture
transport/isentropic lift ahead of the approaching low Thursday will
drive increasing shower/isolated thunderstorm coverage through the
day. Then as the low pulls across WI Thursday night...increasing 850-
500mb frontogenesis will continue to drive/focus moderate rainfall
across the area. In addition...plan on northwest winds to increase
late Thursday night as the low pulls toward Upper Michigan.
Cold air advection/gusty northwest winds take place Friday behind
the departing/deepening surface low. Middle-level low/pv-advection will
also produce fairly widespread shower activity during the day Friday
as highs top off only in the upper 40s to the middle 50s. So
overall...looks like raw/blustery day will be on tap.
The upper low continues to push across the area Friday night for
lingering shower activity. With lows dropping into the 30s...there
is the possibility of some light snow mixing in with the showers
late in the night/toward Saturday morning. However...it looks like
the bulk of the precipitation will have moved east of the area by the
time thermal profile cools enough.
Saturday looks to be an unseasonably chilly day as highs are
expected to only top off in the middle/upper 40s. Brisk northwest
winds will add to the chill. A few showers will also be possible
east of the Mississippi River.
Cooler northwest flow aloft will dominate through the rest of the
period. A couple embedded shortwave troughs produce periodic shower
chances Sunday into Sunday night and again Monday night into
Tuesday. Look for highs in the 50s on Sunday...moderating perhaps a
couple degrees by Tuesday.
Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 650 am CDT Wednesday Oct 1 2014
Wet period starting today...persisting through Friday...as various
low pressure systems make their way across the region. Expecting a
prolonged period of MVFR/IFR cigs/vsbys...and likely some
An area frontogenetic/warm air advective -shra will move in this
morning gradually shifting east late this afternoon. Could see more
scattered -shra late afternoon-early evening as a cold front and
upper level disturbance approach from the west and southwest. Some
isolated -tsra is possible...but not high enough confidence to add to
the forecast at this time.
Observation and BUFKIT soundings supporting IFR/MVFR ceilings through the
day...with LIFR/IFR tonight. While the anticipation is krst/klse
will stay dry overnight...see the potential for widespread
fog...reducing visibilities to 1/2sm or less. Guidance favoring
this...while sref and mesoscale models also siding with several hours of
sub 1sm visibilities. Going to steer the forecast this way. Might be too
optimistic in timing...could be earlier.