Scientific Forecaster Discussion
Area forecast discussion
National Weather Service La Crosse WI
307 am CDT Tuesday Apr 28 2015
Short term...(today and tonight)
issued at 307 am CDT Tuesday Apr 28 2015
Latest water vapor satellite imagery shows upper level low over
northeast United States...shortwave ridge over Wisconsin/Iowa and
shortwave trough over the northern plains. Latest 08z surface
analysis indicates surface front extending from southern Ontario
into northern Nebraska in association with shortwave trough over the
northern plains. Mosaic radar shows light rain showers or sprinkles
over northwest Minnesota in association with low level convergence
along and behind surface front.
The latest 28.00z GFS/NAM/ECMWF are in good agreement moving and
weakening shortwave trough/surface front across the Great Lakes
region today into tonight. Due to dry air aloft over forecast area
and lift/low level convergence weakening with the shortwave
trough/surface front expect the precipitation over northwest
Minnesota to weaken and diminish. Will continue with dry forecast
across the forecast area today into tonight.
Long term...(wednesday through monday)
issued at 307 am CDT Tuesday Apr 28 2015
The 28.00z GFS/NAM/ECMWF indicating upper level closed low/trough
tracking south into the Great Lakes region Wednesday into
Wednesday night. The models show slight differences in strength
and placement with the upper level closed low/trough.
However...the 28.00z GFS/NAM BUFKIT soundings suggest steep lapse
rates of 8 to 10 degrees celsius per kilometer up to 700 mb by
21z Wednesday. Combined with weak low level moisture convergence
..daytime heating and 500-300mb potential vorticity
advection...this will allow for the possibility of showers over
central Wisconsin Wednesday afternoon into Wednesday evening. The
28.00z NAM/GFS indicate 100-200 j/kg 0-6km most unstable cape
over this area Wednesday afternoon. A thunderstorm or two will be
possible Wednesday afternoon into the early evening hours. Have
introduced small precipitation chances and isolated thunderstorms
based on this Wednesday afternoon into Wednesday evening.
Surface ridge builds into the area Thursday into Thursday night.
Subsidence under surface ridge will provide dry weather across the
Main forecast concerns Friday into Monday are precipitation chances
through the period. The 28.00z GFS/ECMWF/Gem are in good agreement
in developing west to east zonal flow across the northern tier
states through the period. Differences are indicated between the
models on timing and placement of shortwave troughs/surface features
across the upper Midwest and Great Lakes region. The first impulse
affects the forecast area Friday. The 28.00z GFS/European model (ecmwf) shows surface
moisture convergence and 850mb moisture transport along the surface
front in association with the impulse. Will continue with mention of
small precipitation chances across much of the forecast area. The
28.00z GFS/European model (ecmwf) indicate a stronger shortwave trough/surface low
pushing into the upper Midwest and Great Lakes region Saturday night
into Monday. The 28.00z GFS/European model (ecmwf) show differences in timing and
placement of shortwave trough/surface features...however models
suggest decent moisture convergence and lift in association with
shortwave trough/surface feature. Confidence is increasing that
precipitation will occur over much of the forecast area between
Saturday night into Monday.
With decent southerly flow into forecast area. This will allow
for warmer air to advect into the Great Lakes region out ahead of
surface low/shortwave trough this weekend. Temperatures across
forecast area should warm into the 70s this weekend.
Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1145 PM CDT Monday Apr 27 2015
High pressure will provide clear skies through Tuesday morning.
Middle and high clouds will increase across the area during the early
afternoon as a weakening cold front moves toward the area.
Ceilings will lower into the 4 to 6k range during the late
afternoon and evening...and then persist through the remainder of
the evening. Winds will remain out of the north and northwest at
10 knots or less through the period.