Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
320 am CDT sun may 24 2015
Forecast discussion for routine morning forecast issuance
Short term...today...tonight...and Monday
issued at 320 am CDT sun may 24 2015
A low pressure system will continue to develop across the Central
Plains today as thickening clouds continue to stream in from the
south. The area of rain across northern Missouri and southern Iowa
will steadily advect northward today coincident with a middle level
shortwave and Theta-E advection. As was the case with previous
model runs the rain appears to hold off until the afternoon hours.
However unlike previous model runs the later arrival of the rain
will not lead to higher than expected temperatures as the
thickening clouds block much of the incoming solar radiation with
highs ranging from around 70 to the lower 70s away from Lake
Michigan. The chance for thunder today does not appear all that
great as instability is very limited. Close inspection of upstream
lightning trends also shows this scenario does not appear very
likely as lightning with this area of precipitation has been
mostly confined to eastern Oklahoma. However given the dynamics
thunder cannot be completely ruled out so will leave a token
chance in the forecast.
This area of rain will continue tracking north tonight as the
surface low ejects out of the plains and tracks towards Iowa. As
it does it will lift a warm front into Wisconsin with rain focused
mainly in the northern portion of the state as strong isentropic
lift provides more than adequate forcing. The lift and Gulf
moisture in place will bring the threat for heavy rain during the
overnight hours as well as a continued threat for thunder.
The low itself lifts north through Wisconsin on Memorial
Day...bringing a dry slot through the southeastern portion of the
County Warning Area during the afternoon hours. As the low lifts north we will be
well in the warm sector...with increased instability as convective available potential energy soar
to around 1 j/g with decent directional shear in the low levels.
If some partial clearing can be had in the dry slot on Memorial
Day instability could be enhanced...raising the chances for strong
thunderstorms and maybe even a few severe storms. Current day 2
outlook has the area in a marginal risk for severe weather which
appears warranted given the Reliance on getting some sunshine to
increase instability. With the area expected to be in the warm
sector Memorial Day will continue with higher than MOS
temperatures during the afternoon hours across the area.
Long term...Monday night through Saturday
issued at 320 am CDT sun may 24 2015
Looks like a rather warm and wet period of weather during this
part of the forecast...though forecast confidence remains low.
Monday night precipitation chances are questionable as a surface
low departs to the northeast and another approaches from the
south. Tried to remain close to the previous forecast and also
blend with surrounding grids...so chance probability of precipitation prevail across most
of the area.
The 00z NAM and 00z GFS were both slower than the 00z European model (ecmwf) with
the next batch of showers and storms approaching from the south so
went the slower Route and only have slight chances in the north
and chance probability of precipitation in the south on Tuesday.
Chance probability of precipitation spread across most of the area for Tuesday night as
the surface low and upper trough move through the region. Kept
some slight chances for showers on Wednesday...but have a dry
forecast for Wednesday night due to surface and upper level
ridging. As another system approaches the area from the west...it
looks like a chance for showers and thunderstorms across parts of
central and north central Wisconsin on Thursday...with slight
chances farther to the east. Chances for showers and storms spread
across the area Thursday night and continue through Friday night
before a large surface high brings drier air...and probability of precipitation fall into
the slight chance category on Saturday.
Aviation...for 06z taf issuance
issued at 1050 PM CDT Sat may 23 2015
VFR conditions should prevail through Sunday morning...with
mainly middle-level clouds and only isolated sprinkles anticipated.
An increasing surge of warm and moist air should lead to shower
development during the middle afternoon on Sunday...with a steady
rain spreading north across the forecast area during the late
afternoon and evening. Instability appears to be too weak to
mention thunderstorms in the tafs at this time. MVFR ceilings will develop in
the steadier showers over parts of central and east central
Wisconsin later in the afternoon...with IFR conditions likely
during the evening. Have added some low level wind shear at most of the taf
sites later in the evening.