Scientific Forecaster Discussion
fxus63 kgrb 240353
Area forecast discussion
National Weather Service Green Bay WI
1053 PM CDT Fri Aug 23 2019
Updated aviation portion for 06z taf issuance
Short term...tonight and Saturday
issued at 229 PM CDT Fri Aug 23 2019
Quiet weather is anticipated in the short-term, with only cloud
trends, temperatures and nighttime fog potential to consider.
Canadian high pressure was ridged over northeast WI this
afternoon, with scattered diurmal cumulus covering much of the
forecast area. Temperatures were cool, ranging from the middle
60s to lower 70s.
The Canadian high will drift slowly eastward through Saturday. At
the same time, an upper level ridge will build into the region.
The combination of these features, along with very dry air in
place, will lead to quiet conditions. The main concern with this
setup will be patchy fog over northern WI late tonight into early
Saturday. Otherwise, expect diurnal cumulus to dissipate early
this evening, then reform during the late morning and afternoon
Cool temperatures will persist into Saturday. Lows tonight will
range from the upper 30s in the cold spots of north central WI to
the 40s and lower 50s elsewhere. Highs on Saturday may be a degree
or two warmer than today, with most locations getting into the
upper 60s to middle 70s.
Long term...Saturday night through Friday
issued at 229 PM CDT Fri Aug 23 2019
Models continue to show a strengthening upper trough that will dig
southeast into the Great Lakes early next week. Eventually, this
trough to expand and cover much of the northern tier of states as
a closed upper low develops over northwest Ontario/Hudson Bay. The
resultant broad, cyclonic flow aloft to keep an unsettled weather
pattern for northeast WI through mid-week. Canadian high pressure
is forecast to build into WI later Wednesday into Thursday before
the passage of a cold front on Friday brings rain chances back
into the forecast. Temperatures should be a bit below normal this
weekend, rise to around normal Monday-Wednesday, then fall below
normal again Thursday-Friday.
Northeast WI to remain on the western periphery of the broad area
of high pressure centered over southeast Canada/northeast Continental U.S.
Saturday night. Another night of clear skies and light winds can
be expected with min temperatures in the middle to upper 40s
north, lower to middle 50s south. The high pressure finally begins
to lose its influence on our weather on Sunday as a prevailing
southeast wind begins to pull more moisture north into the region.
Still expect dry conditions through the day, but we may see more
cumulus clouds compared to Saturday. Temperatures to remain below
normal with most locations in the lower to middle 70s.
Clouds will be on the increase Sunday night ahead of the
strengthening upper trough moving into the northern plains. If
saturation can be achieved, there could already be a few showers
to reach central WI after midnight. Min temperatures to be in the
lower to middle 50s north, middle 50s to around 60 degrees south.
The upper trough is forecast to reach the upper MS valley on
Monday with a series of mid-level shortwaves moving within the
trough. Models are now showing a better signal that one such
shortwave will lift northeast into the region and help to set off
showers/slight chance of thunderstorms by Monday afternoon.
Instability still looks weak, but there may be enough shear to
provide for a locally strong storm. Precipitable water values of around 1.5" may
also provide for locally heavy rainfall. Max temperatures for
Monday to be in the lower 70s north-central WI/near lake mi,
middle to upper 70s elsewhere.
Showers/isolated thunderstorms to continue into at least Monday
evening as the upper trough (and its associated cold front) drive
eastward into the western Great Lakes. As the stronger lift and
forcing push east overnight, anticipate the precipitation to
become more scattered in nature. Still cannot rule our a few
showers/rumble of thunder on Tuesday as northeast WI to be under a
broad, cyclonic flow aloft. Max temperatures for Tuesday to be in
the upper 60s to lower 70s north-central WI, lower to middle 70s
Other than a few showers that could linger into the evening hours,
the vast majority of Tuesday night should be dry as daytime
heating wanes. Wednesday could be a replay of tuesday's weather as
the region remains under the influence of the broad upper trough.
Once again, any precipitation would be spotty with many dry hours
in between. Max temperatures to reach the middle to upper 60s
north-central, lower to middle 70s for everyone else.
There remains questions in the forecast for late next week as
the models have timing issues with regards to the passage of the
next cold front. The Gem advertises a frontal passage as early as
Wednesday night, while the GFS/European model (ecmwf) suggest a late Thursday
night/Friday passage. Have leaned the forecast toward the latter
model solution, thus allowing high pressure passing to our south
to keep Wednesday night through most of Thursday night dry. Chance
of showers/possible thunderstorms to then accompany the cold
front for late Thursday night into Friday. Gulf moisture may be
limited, thus any rainfall should not be heavy. Max temperatures
for both Thursday and Friday to be slightly below normal with
readings from the middle to upper 60s north/near lake mi, upper
60s to lower 70s south.
Aviation...for 06z taf issuance
issued at 1052 PM CDT Fri Aug 23 2019
Mostly clear skies and VFR conditions should rule over many of the
taf sites during the period. The main exception will be some
patchy MVFR/IFR fog across northern Wisconsin later tonight into
Saturday morning. Diurnal cumulus clouds are again expected to
develop during the morning and into the afternoon on Saturday,
then dissipate after sunset.
Winds will be light from the northeast to east, so patches of
lake-enhanced low clouds cannot be ruled out near Lake Michigan
late tonight into early Saturday. Confidence is not high enough to
include at mtw or grb at this time.