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Area forecast discussion 
National Weather Service Green Bay WI
612 am CDT Tuesday Oct 21 2014

Updated aviation portion for 12z taf issuance

Short Wednesday
issued at 315 am CDT Tuesday Oct 21 2014

The latest RUC analysis and satellite/radar imagery show high
pressure centered over Ontario and a surface ridge axis running
southwest over the northern Mississippi Valley and Central Plains.
East of the ridge axis...north to north northeast flow continues
over the western Great Lakes. The combo of unstable conditions over
Lake Superior and thermal troughing are contributing to widespread
strato-cumulus across the northeast half of Wisconsin. Area observation are
still reporting spotty sprinkles. Further north...drier air is
working southward over Lake Superior. Looking upstream...a strong
upper level ridge exits over the central of the continent which is
leading to clear and quiet conditions. Forecast concerns include
clouds trends today followed by temperatures.

Today...not an easy cloud forecast today. High pressure will be
build southward out of Ontario...but 925mb thermal troughing and
north to north-northeast flow continue off Lake Superior. With lowering
inversion heights and unstable conditions over Lake Superior...think
clouds will continue to hang around over north-c and most of eastern
Wisconsin through the middle-morning hours. But with daytime
heating...mixing should tap into the very dry air above the
inversion which should lead to rapid clearing early this afternoon.
The exception will likely be the Lakeshore where north-northeast winds will keep
lake clouds around through late afternoon. Highs in the upper 40s
to lower 50s.

Tonight...Canadian high pressure will be building southward into the
central Great Lakes. This incoming airmass will be very dry...with
precipitable waters under a quarter of an inch. With clear skies and light
winds...should have nearly ideal radiative cooling conditions.
Dropped low temperatures below the coldest guidance. Lows in the
lower 20s will be possible across north-c Wisconsin. Mainly middle 20s to
low 30s everywhere else.

Wednesday...high pressure will remain over the region. A frontal
boundary will move into the northern Mississippi Valley in the
afternoon but will be too far west for any impact on our sensible
weather. So should see another day of plenty of sunshine. Low
inversion heights will prevent much mixing. So expect seasonable
temperatures in the lower 50s.

Long term...Wednesday night through Monday
issued at 315 am CDT Tuesday Oct 21 2014

Upper ridge over Wisconsin and Illinois gets dampened
and pushed to the east as an upper trough drops towards Wisconsin
from central Canada Wednesday night through Thursday night. An
associated surface front approaches late Wednesday night and then
moves slowly east across the area Thursday while a wave moves to
the north along the front. The models are in relatively good
agreement with the arrival of the showers but there are
differences in how quickly it exits. Most places should get some
shower activity Thursday and Thursday evening but amounts look to
be modest and around a quarter to half inch. After that upper flow
becomes northwest with dry weather expected through at least
Sunday. Rising upper heights should bring above normal
temperatures starting on Friday.

Aviation...for 12z taf issuance
issued at 612 am CDT Tuesday Oct 21 2014

Very dry air surging southward over Lake Superior will help the
broken to overcast strato-cumulus to gradually break up later this
morning into early this afternoon. Onshore flow off Lake Michigan
will likely keep at least scattered coverage through the afternoon along
the shoreline. Then Canadian high pressure will bring clear skies
and light winds tonight through much of Wednesday.

Grb watches/warnings/advisories...


Short term.....Mpc
long term......rdm

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