Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
529 PM CDT Monday Sep 22 2014
Updated aviation portion for 00z taf issuance
Short term...tonight and Tuesday
issued at 219 PM CDT Monday Sep 22 2014
Quiet stretch of weather expected for Great Lakes region. High
pressure will slowly drift east tonight...and will continue to
influence our weather on Tuesday. Thus...very little change to the
previous forecast was necessary.
Warm air advection around the top of an upper level ridge will
result in warming 850mb temperatures through the night. Therefore...even
with clear skies and light winds...lows will not be nearly as cool
tonight as last night. Added some splotchy fog to the north and
central as some moisture lingers in this area and winds should be
light to calm.
Tuesday will be a beautiful day. The center of surface high pressure
will sit to our south...and upper level ridging will hold over the
region. Mostly sunny skies are expected across the state.
Temperatures will be warmer than normal Tuesday as 850mb temperatures
between 11 to 12 degrees will result in highs in the 70s...with
cooler readings near the lake and Bay.
Long term...Tuesday night through Monday
issued at 219 PM CDT Monday Sep 22 2014
Models are in general agreement with the mean flow becoming more
amplified across the Continental U.S....while a fast zonal flow to exist
across central and eastern Canada. Biggest forecast headache to be during
the middle-week period as a weakening shortwave trough approaches the western
Great Lakes. Can this weak system generate any precipitation into NE wi? If
not...a dry stretch of weather on tap as a broad upper ridge to
encompass the eastern half of the Continental U.S.. there are some concerns
regarding the eventual movement of the western Continental U.S. Upper trough early
next week...but latest indications show this trough remaining well
to our west through Monday. Temperatures will be above normal through the extended
period with readings around 10 degrees above normal.
The shortwave trough to stretch from the upper MS valley S-SW to the Southern
Plains Tuesday night...sandwiched between an upper ridge over The Rockies
and an upper ridge over the eastern third of the Continental U.S.. there could be
some increase in hi clouds into central WI late tonight night...but
expect most of the night to be mostly clear across the forecast area.
Under these mostly clear skies with light winds...we may again see
patchy fog develop after midngt. Min temperatures to range from the middle
40s north...upper 40s to around 50 degrees south.
This shortwave trough edges eastward on Wednesday and will be approaching extreme
western sections of the Great Lakes by late in the day. A modest
increase in moisture...coupled with shortwave energy within the trough
itself...may be able to develop isolated showers just to our west.
Have kept any probability of precipitation out of the forecast for now...but may need to
increase clouds a bit...especially over north-central WI. Maximum temperatures to
range from the middle to upper 60s Lakeside...lower 70s central/E-cntrl WI.
Some doubt has crept into the forecast for Wednesday night as some of the models
have changed course with respect to the movement of the shortwave
trough. Initially...the models showed this trough being sheared with its
northern part lifting NE into Canada and being absorbed by the
westerlies. Meanwhile...the southern part of this trough reverses course
with a S-SW drift. Now...the majority of the models bring the shortwave
trough into the western Great Lakes before starting to dissipate. The
new solution would bring more clouds into the forecast area and
perhaps bring a spotty shower or two into central WI Wednesday night. Have
added a minimal pop for central WI...but kept eastern WI dry. Min temperatures
to be uniform with most locations in the upper 40s to lower 50s. The
remains of the shortwave trough does finally weaken enough by Thursday to keep
the vast majority of the region dry. A stray shower or a few
sprinkles cannot be completely ruled out...but feel any precipitation would
be too light/isolated to mention in the forecast. Amount of cloud cover
will be tricky and could have an impact on temperatures. Have maintained
readings reaching the lower 70s with cooler temperatures near Lake Michigan.
A major shift in the mean flow to be underway by Friday as a deep upper
trough hits the West Coast and upper ridge builds across the central
Continental U.S.. surface hi pressure to our east and the upper ridge overhead should
bring plenty of sunshine to NE WI with temperatures gradually warming.
Look for maximum temperatures on Friday to be in the lower to middle 70s with enough of
an onshore component to the wind to keep Lakeshore areas in the
upper 60s. The upcoming weekend looks dry and warm with the upper trough
headed toward The Rockies and the broad upper ridge to encompass the
eastern half of the Continental U.S.. maximum temperatures for both Sat and Sunday should
easily reach the lower to middle 70s (upr 60s lakeside) with a few of
the warmer sites making a run at 80 degrees.
Forecast gets more sketchy headed into Monday as the models begin to
disagree with the movement of the upper ridge. Some of the models wrap
the trough into a closed upper low over the northern hi plains...while
other models weaken the trough and rotate it into the plains. For
now...this difference will not impact NE WI weather on Monday so have
gone with another dry day with temperatures about 5 degrees cooler than the
Aviation...for 00z taf issuance
issued at 522 PM CDT Monday Sep 22 2014
Cumulus clouds have dissipated over the area...and clear skies
are expected to continue overnight. A ridge of high pressure will
set up over the Wisconsin River Valley (nc/c wi) late tonight...
causing winds to become light and variable at the western taf
sites. Areas of fog are possible over NC/c WI...with patchy fog
possible farther east. Will have visibilities dropping to IFR at
cwa/auw...and IFR/LIFR at rhi...late tonight into early Tuesday.
VFR conditions will return by middle-morning on Tuesday...with a few
afternoon cumulus (bases 4-5k ft)...and light S-SW winds.