Scientific Forecaster Discussion
Area forecast discussion
National Weather Service La Crosse WI
749 am CDT Sat Jul 26 2014
issued at 748 am CDT Sat Jul 26 2014
The 26.06z deterministic and mesoscale models continue to suggest that
there will be strong 900 to 500 mb frontogenetic forcing mainly
south of Interstate 90 today. VAD wind profilers show a 30 to 45
knot convergence into the 700 mb front across southwest Minnesota.
Overall the hrrr and a couple /members 2 and 3/ of the 26.06z hop
WRF show that the precipitation currently over eastern South
Dakota and southwest Minnesota will continue to spread east into
the areas mainly south of Interstate 90. Due to this...raised the
chances of showers up significantly. There will be even enough
instability aloft for isolated thunderstorms.
Short term...(today and tonight)
issued at 320 am CDT Sat Jul 26 2014
Latest water vapor satellite imagery indicating upper level closed
low over southern Saskatchewan and west to east zonal flow over
the northern plains. Weak shortwave trough over central and
eastern South Dakota embedded in west to east zonal flow is
producing showers and isolated thunderstorms over central South
Dakota per mosaic radar.
Main forecast concerns are precipitation chances today into tonight.
The 26.00z GFS/NAM are in good agreement in moving weak impulse over
central South Dakota into the southern part of the forecast area.
The 26.00z GFS/NAM are indicating isentropic lift at 315k surface
and produce light quantitative precipitation forecast across parts of northeast Iowa and southwest
Wisconsin. The latest 26.05z hrrr is indicating the rain showers/thunderstorms and rain over
central South Dakota to weaken and possibly produce light showers or
sprinkles over the southern part of the forecast area. BUFKIT
soundings show quite a bit of dry airmass below 700mb over the
southern forecast area. However...with the lift associated with the
weak impulse...this may produce an isolate rain showers/thunderstorms and rain across southern
forecast area this morning into the early afternoon hours. Have
introduce a small chance of precipitation over northeast Iowa and
parts of southwest Wisconsin.
Upper level closed low over southern Saskatchewan moves south
into the Great Lakes region tonight. The 26.00z GFS/NAM suggest
increasing forcing/lift after 06z over northern parts of the
forecast area and indicate elevated cape associated with upper
level closed low. Will continue trend of precipitation chances
across the northern parts of the forecast area.
Long term...(sunday through friday)
issued at 320 am CDT Sat Jul 26 2014
Sunday...the 26.00z GFS/NAM continue to show decent 500-300mb pv
advection and deep qg forcing associated with the closed upper level
low over much of the northern and eastern part of the forecast
area. Confidence is increasing this area will see showers and
possibly an isolated thunderstorm.
The 26.00z GFS/Gem/ECMWF are in good agreement digging upper level
trough over the eastern United States Sunday night into Friday. The
main difference between the models is timing the very weak impulses
embedded in the northerly flow aloft into the Great Lakes region.
The models continue to produce light quantitative precipitation forecast over parts of the
forecast area mainly from Wednesday into Friday. However...with
very weak moisture convergence and very weak impulses embedded in
northerly flow. Confidence in precipitation chances is low through
Temperatures Sunday night into Friday will be unseasonably cool
through middle of the week and moderate to near normal by end of the
Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 655 am CDT Sat Jul 26 2014
Areas of dense fog at krst will become MVFR by 26... VFR
by 26.17z. The ceilings will likely be LIFR through
26... become MVFR by 26... then VFR. Meanwhile
at klse the MVFR ceiling will become VFR by 26.16z. One thing that
will have to be watched this morning is the showers and scattered
thunderstorms across southwest Minnesota. With most of the models
showing strong 900 to 500 mb frontogenesis...there is the
potential that this precipitation could move into krst after
26.15z and klse after 26.16z. This precipitation could then linger
For the remainder of the period...VFR visibilities and ceilings