Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
1022 PM CDT Sat Aug 29 2015
Updated aviation portion for 06z taf issuance
issued at 957 PM CDT Sat Aug 29 2015
Fog...dense in a few locations...was gradually developing this
evening. MVFR clouds which blanketed much of the area today and
early evening over east central and central Wisconsin continues
to very gradually erode. The locally dense fog has developed over
areas which cleared out the last few hours. Already issued a Special Weather Statement
for the fog to handle any evening activities and will may need to
consider a dense fog advisory for the overnight hours if the dense
fog becomes more widespread in the next few hours.
Short term...tonight and Sunday
issued at 258 PM CDT Sat Aug 29 2015
The main forecast issues to be on clouds trends and fog potential
tonight/Sunday morning. If the clouds hold tough...this would inhibit
dense fog formation. If clouds thin this evening...this could lead
to dense fog developing over a large part of NE WI and the
possibility of headlines.
The 19z msas surface analysis indicated a very weak area of low pressure
over east-central MO with an inverted trough extended northeastward into eastern WI.
Weak hi pressure stretched from the Central Plains northeastward into central WI.
Vsbl satellite imagery showed plenty of clouds generally south of a
line from eau-imt with some clearing across parts of northern and western
WI. The radar mosaic was quiet...other than some showers over northern Illinois
and northern Indiana.
The inverted surface trough and middle-level shortwave trough will exit the
region this evening...leaving the weak area of hi pressure over WI for
the remainder of the night. Light winds...combined with lingering
low-level moisture...will allow for fog to develop especially where
the heavier rains occurred last night (cntrl/E-cntrl wi). The
problem for dense fog is the stubborn stratus deck which would
prevent visibilities from dropping too far. Satellite does show some thinning
of the clouds late this afternoon...therefore have continued with
the areas of fog across the forecast area...but raise to widespread
fog across central/E-cntrl WI. Not confident enough on how low visibilities
will be able to attain with the current stratus deck in place.
Thus...no headlines forthcoming as of now for inland areas.
However...webcams are already showing some pretty good fog over
the nearshore waters of Lake Michigan...so have issued a marine dense
fog advisory. Min temperatures to range from the lower to middle 50s north-central WI...
middle 50s to around 60 degrees central/E-cntrl WI.
The fog will burn off Sunday morning...leaving a mostly sunny
afternoon across the region with the weak area of hi pressure just off
to our east and upper level ridging building toward WI. As long as
the fog/stratus do not hang around longer than expected...maximum
temperatures on Sunday should rise into the lower 70s near Lake Michigan...but
upper 70s to lower 80s elsewhere which is above normal for late Aug.
Long term...Sunday night through Saturday
issued at 258 PM CDT Sat Aug 29 2015
Warm temperatures with only small precipitation chances expected through
Wisconsin will remain under the influence of a strong upper level
ridge through the period. This ridge may flatten a little midweek
before reamplifying later in the week. Confidence is high in
dry conditions from Sunday night through Monday night...but a
weakening front may bring a slight chance of thunderstorms to NC WI Tuesday
afternoon. Small precipitation chances (20-30) will continue through the
extended forecast...due to a continued feed of Gulf moisture into the
region...daytime instability...and periodic weak short-wave
energy topping the upper ridge. Medium range models now show
the next significant cold front stalling out in the northern
plains next weekend...due to the blocking influences of the
central U.S. Upper ridge.
Above normal temperatures and humid conditions are a good bet
through the entire period...with persistent south flow...and
800 mb temperatures +18 to +20 c. The moist flow may produce areas of marine
fog on Lake Michigan.
Aviation...for 06z taf issuance
issued at 1022 PM CDT Sat Aug 29 2015
An area of MVFR ceilings continue to slowly drift
southward over parts of central and east central Wisconsin late
this evening. Areas of MVFR visibilities due to fog along with pockets of
LIFR visibilities due to fog has been developing over areas just north
of this area of MVFR ceilings. Across northern Wisconsin...VFR
conditions were noted. Still expect areas of MVFR visibilities due to
fog and patchy IFR/LIFR visibilities due ot fog to develop overnight and
persist Sunday morning. High pressure ridge building into the area
on Sunday will eventually improve conditions to VFR conditions by
late morning or early afternoon.