Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
515 am CDT Tuesday may 26 2015
Today and tonight...forecast confidence medium.
An outflow boundary is slowly moving eastward into south central WI early
this am. This will likely continue to trigger at least isolated showers
or thunderstorms through the morning. The upper trough currently moving
toward the middle MS River Valley will then swing northward through southern WI
this afternoon with a wave of low pressure to track across eastern Iowa
into c WI by 00z Wednesday. The leading edge of positive vorticity advection and the nose of a
developing southerly low level jet will move into the region from the middle to late
morning hours into the afternoon. Precipitable waters will increase to 1.5 inches
during this time with tall and skinny cape on the forecast soundings.
High probability of precipitation are forecast for the showers/thunderstorms today with heavy
rainfall rates at times. Only chances of precipitation tonight as the system
mainly moves to the north and a weak cool frontal passage occurs. The MLCAPE
today will likely stay below 500 j/kg given the early arrival of
clouds/precipitation as well as poor middle level lapse rates. Thus the severe
tstorm threat is minor despite MDT deep layer and low level shear
Wednesday through Friday...forecast confidence...medium
A shortwave will move through southern Wisconsin Wednesday
morning...departing the forecast area early afternoon. Will
probably see a few showers and storms as the wave moves
through...mainly during the morning hours. A drier airmass will
move in behind the wave...likely bringing decreasing clouds west
to east during the afternoon. Additionally...temperatures aloft will
recover behind the wave to around 18-20c at 925 mb by late
afternoon. This will allow temperatures to climb toward 80 west...with
somewhat cooler temperatures east with the clouds exiting later.
Dry weather is expected Wednesday night and Thursday as shortwave
ridging builds into the area for a short time. Above normal high
temperatures are likely Thursday...though temperatures will be somewhat cooler
near Lake Michigan under persistent southeast winds.
A chance for showers and thunderstorms will return for Thursday
night...as 850-700 mb warm advection increases along with
Showers and storms are likely Friday and Friday night as a
shortwave moves through while a cold front drops southward into
the area. Above normal temperatures are expected to continue.
Saturday through Monday...forecast confidence...low
Models diverge for Saturday through Monday. The GFS keeps a slow
moving upper low and associated surface low close to the forecast
area right through Monday...bringing persistent shower chances.
The European model (ecmwf) and Canadian solutions have high pressure building in
quicker and shoving the low farther south. These models would
result in dry weather from Saturday afternoon through Monday.
Consensus approach to the forecast resulted in some lingering probability of precipitation
right through Monday...though obviously not a lot of confidence in
precipitation chances at this point.
One things that looks a bit more certain in the extended is that
it will turn cooler for Saturday through Monday. Given model
differences though...it is yet to be determined how cool.
Hopefully the forecast trends away from the GFS...which suggests
temperatures struggle in the 40s under an all day rain event Saturday.
Keep your fingers crossed that the high moves in quicker per the
European model (ecmwf) and Canadian.
Aviation/12z tafs/...shower and thunderstorms will occur at times from
later this morning through the afternoon and possibly the evening as
low pressure passes through the region. Areas of 1.0-3.0 kft ceilings
will occur at times as moist air flows into southern WI with visibilities
reductions within precipitation. Westerly flow will bring drier
conditions for Wednesday.
Today/tonight and aviation/marine...gehring
Wednesday through Monday...ddv