Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
554 am CDT Friday Aug 28 2015
Updated aviation portion for 12z taf issuance
Short term...today...tonight...and Saturday
issued at 324 am CDT Friday Aug 28 2015
A low pressure system...analyzed early this morning over southern
Nebraska...will continue tracking slowly east through Iowa
today...then through northern Illinois and southern Wisconsin
late tonight and Saturday. The main issue with this system is the
precipitation shield associated with this low pressure system.
Despite a steady progression east of this shield over southern
Minnesota...it had steadily eroded as it heads into drier air in
place across the east...as evidenced by the 00z kdtx radiosonde observation. 00z nwp
models have tracked further south and slower with this system...in
fact there is very little evidence that the rain will make it into
the County Warning Area before the afternoon hours. All models...save for the
GFS...bring the area of rain through the southern County Warning Area this
afternoon and tonight...before exiting the region during the day
on Saturday. However to complicate matters a cold front over
southern Canada is expected to sag south over the northern Great
Lakes during this period...possibly bringing in a one two punch
across the south and north. Given the southern solution of the GFS
it is not surprising this model allows the front to sag south and
affect the north...while the other models in their more northern
solution keep this system across the north. Given the general
model trends and consensus will side with the majority of the
models and bring rain through the southern County Warning Area later than
previously forecast and adjust probability of precipitation accordingly.
The main benefit from a slower progression of the low are high
temperatures today as a later arrival of rain should mean
temperatures across central Wisconsin should rise into at least
the upper 60s if not around 70. Further north and east highs
should generally be in the lower 70s away from the Lakeshore.
Abundant cloud cover tonight will keep lows relatively warm from
about 55 to 60 degrees. Without a push of real cold air behind the
departing low highs on Saturday should manage to get into the
lower 70s away from the Lakeshore where a later departure of the
rain will keep highs around 70 degrees.
Long term...Saturday night through Thursday
issued at 324 am CDT Friday Aug 28 2015
The latest ensemble guidance indicates that a stable pattern will be
in place across North America next week...and will consist of an
upper trough over the West Coast and sub-tropical ridging east of
the Mississippi River. This ridge will provide a prolonged period
of above normal temperatures and dry conditions. The operational
models are in good agreement with the large-scale...but have some
finer detail differences popping up by the middle of next week. A
general GFS/European model (ecmwf) blend will suffice.
Saturday night through Sunday night...clouds will be gradually
departing eastern Wisconsin Saturday night as high pressure moves
into the region. The light winds and clear skies will promote fog
formation late...possibly more dense where the heaviest rains fall
from the day before. Once the fog Burns off...should have mostly
clear and seasonable weather Sunday and Sunday night. No
significant changes to temperatures.
Rest of the forecast...light southerly flow kicks in on Monday which
should give temperatures a boost into the 80s. Could see a weak
disturbance drift into the region during the Wednesday/Thursday time
period...but confidence is rather low in this occurring.
Temperatures will gradually warm through the week...and may approach
90 by Thursday and Friday.
Aviation...for 12z taf issuance
issued at 554 am CDT Friday Aug 28 2015
Timing and location of incoming rain showers are the main concern
with this taf issuance. 00z models have come in much slower than
previous runs...with rain eroding as it heads into drier air.
Therefore will delay rain again with the 12z tafs...focusing more
on this afternoon and tonight rather than this morning.