Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
339 PM CDT Thursday Jul 31 2014
Forecast discussion for routine afternoon forecast issuance
Short term...tonight and Friday
issued at 337 PM CDT Thursday Jul 31 2014
Precipitation trends are the main forecast concerns through
The air mass across the forecast area quickly destabilized this
morning once the fog dissipated. Cumulus formed in the unstable
air...some of which developed into scattered showers and isolated
thunderstorms across central and east central Wisconsin this
afternoon. Shower/storm development was aided by some upper level
support that was visible in water vapor imagery. Mesoanalysis
indicated MUCAPE values in excess of 1000j/kg in the area where
the showers and storms developed. Surface observations showed
surface dew points in the upper 50s and lower 60s across the
southern part of the forecast area...to middle 40s to lower 50s
in the north. A wind shift was also evident from between mnm and
sue...southwest to between osh and y50. Did not hear of any hail
as of 20z...though wbz height is lower than it was on Tuesday when
there was plenty of hail.
Expect showers and storms to gradually die off during the evening.
The surface pressure gradient is forecast to remain weak enough
for some fog to develop again overnight...with lowest visibilities likely
to be in north central Wisconsin. Also expect areas of fog over
Lake Michigan to persist due to high dew point air and Cold Lake
Expect the atmosphere to destabilize early Friday. The unstable
air mass and a more significant short wave moving across Wisconsin
will result in showers and thunderstorms developing by midday.
BUFKIT time sections from the 12z model runs shows higher convective available potential energy
on Friday than today. Storm Prediction Center had a 5 percent chance for severe across
the area on day 2...so likely and low end chance probability of precipitation prevail for
Used best performing guidance mixed with the previous forecast for
temperatures tonight and Friday.
Long term...Friday night through Thursday
issued at 337 PM CDT Thursday Jul 31 2014
Northwest flow will continue early in the period...before becoming
more zonal by the end of the period. Temperatures should run at or
slightly above normal.
Showers and thunderstorms will linger into Friday evening...
especially across central into east central Wisconsin. Otherwise...
dry conditions expected late Friday night and Saturday morning.
Enough instability to add a small chance of showers and storms
across the far south Saturday afternoon.
Next system will approach from the northwest Saturday night...but
should affect the area on Sunday. Some questions still remain on
frontal position and how quick precipitation arrive late Sunday
night into Monday morning...and how far south convection will make
across our area Sunday.
Next week turns interesting as European model (ecmwf) model depicts several
complexes on thunderstorms moving across our central and southern
counties Monday through Wednesday. Since models have a hard time
handling convection/outflow boundaries...was thinking precipitation
trends will shift southward due to outflow boundaries shoving the
front further south. High temperatures each day will be dependent
on cloud cover and convection trends.
Aviation...for 18z taf issuance
issued at 114 PM CDT Thursday Jul 31 2014
Dense fog dissipated and cumulus developed across the area this
morning. Lapse rates from the surface to 3km were already very
steep at midday...convective available potential energy were greater than 1000j/kg across central
Wisconsin...and around 500j/kg from sue to rhi. Expect storms to
develop with instability and short wave energy moving through the
state. Showers began to develop early this afternoon...so have
included vcsh at taf sites. Have introduced thunderstorms in the vicinity a little later in
the afternoon and would not be surprised if the storms had some hail
since wbz heights were less than 9kft. Stuck with convection
ending with loss of daytime heating...but was unsure about this as some
showers persisted until after midnight last night. Relatively
light winds and decreasing clouds will allow for fog development
during the night...but kept MVFR visibilities at taf sites...except for
rhi where there will probably be some IFR visibilities at times.