Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
556 PM CDT Monday Aug 31 2015
Updated aviation portion for 00z taf issuance
Short term...tonight and Tuesday
issued at 215 PM CDT Monday Aug 31 2015
Not much has changed over the past 24 hours with a warm/moist air
mass overhead...light winds and nocturnal development of stratus
and fog that has taken longer than anticipated in dissipating the
next day. This is the continual conundrum headed into late tonight/
Tuesday morning with more stratus and fog expected. Another concern will
be the small chance of seeing precipitation reach north-central Tuesday afternoon.
The 19z msas surface analysis showed weak hi pressure over eastern sections of
the Great Lakes and a weak cold front that stretched from extreme western
Ontario S-SW into the Central Plains. Vsbl satellite imagery indicated
the last of the stubborn stratus over central WI breaking up...only
to be replaced by fair weather cumulus in the heating of the day.
Both the surface hi and upper ridge axis to be situated over the eastern Continental U.S.
Tonight...while a weak surface low to be located over eastern South Dakota along the
cold front. This would keep a prevailing SW flow aloft aimed at WI with
Gulf moisture continuing to be fed northward into the Great Lakes.
Boundary layer winds in the 15-20 knots range above the nocturnal
inversion should prevent widespread stratus/dense fog from
developing...however still anticipate low clouds/areas of fog to
redevelop later tonight. Marine dense fog to persist due to cool
nearshore lake temperatures and warm/moist air mass overhead. Min temperatures
to generally range from the lower 60s (cool locations) to the upper
60s (typical warmer locations).
Once the morning clouds/fog dissipates Tuesday morning...a very warm
and humid day is expected over NE WI as 800 mb temperatures climb to around
+20c. The only fly in the ointment would be the approach of the
weak cold front that is forecast to reach northwest WI Tuesday afternoon. There will
also be a little extra lift provided by the right entrance region
of the upper jet and sufficient instability with convective available potential energy approaching
1500 j/kg. Despite the weak nature of the cold front...prefer to keep a
minimal pop over north-central WI Tuesday afternoon. Maximum temperatures to range from
around 80 near Lake Michigan...lower to middle 80s north and middle 80s to
around 90 degrees south.
Long term...Tuesday night through Monday
issued at 215 PM CDT Monday Aug 31 2015
Warm and humid conditions expected through the week.
A strong upper level ridge and continued south flow at the surface
will lead to an extended period of warm and humid weather...along
with periodic nighttime fog/stratus and dense marine fog. Precipitation
should be spotty and light until the sun/Monday time frame...when
a stronger cold front moves through the region. Timing is still
suspect with this feature. Until then...will just carry small
probability of precipitation across northern WI Wednesday/Wednesday night...as a weak short wave trough tops
the ridge. Will also leave the small probability of precipitation from the model blend
for the extended period...though confidence in the details is
low...and much of the period may end up dry.
Temperatures will be above to much above normal...though any
extensive nighttime stratus or fog may hold temperatures back on at
least a few of the days.
Aviation...for 00z taf issuance
issued at 556 PM CDT Monday Aug 31 2015
VFR conditions expected for most of the evening hours. Visible Sat
imagery continues to show a band of high level smoke will be
passing over tonight. With the lingering moist surface boundary
consisting of surface dewpoints in the 60s...areas of IFR/MVFR of
ceilings/visibilities will again develop overnight. Increasing southwest
gradient should aid with a faster dissipation Tuesday morning for
a return to VFR conditions. The fog over Lake Michigan may linger
near the mtw Airport until southwest winds become the prevailing