Scientific Forecaster Discussion
fxus63 kgrb 231940
Area forecast discussion
National Weather Service Green Bay WI
240 PM CDT Tue may 23 2017
Forecast discussion for routine afternoon forecast issuance
Short term...tonight and Wednesday
issued at 240 PM CDT Tue may 23 2017
The latest rap analysis and satellite/radar imagery show surface low
pressure centered near The Dells, and associated warm front
extending east across east-central WI. Instability has developed
south of the warm front, leading to thunderstorms developing along
and just north of the boundary. Some of these storms may make it
into areas from Waushara to Manitowoc this afternoon, but
convergence does weaken by early this evening, so think the threat
of storms will end by this time. Looking elsewhere, deeper moisture
is wrapping around the upper circulation across eastern WI, which
should keep the chance of showers highest over eastern parts of the
state for the afternoon. As additional showers move north from
northern Illinois, precip trends are the main forecast concern.
Tonight...center of the upper low will drift south across Iowa and
Missouri, but the upper level trough axis will extend north across
Wisconsin through the night. As the low moves south, think precip
chances will come to an end over north-central WI by late evening.
Eastern WI will not be as lucky, as deeper moisture will rotate
around the trough and across eastern WI from about mid-evening
through the overnight hours. Some of these showers will likely
rotate into central WI as well, but coverage should not be as high
as further east. With ample cloud cover, lows will range from the
low 40s north to upper 40s south.
Wednesday...the upper low will continue to move to the southeast
across the mid-Mississippi Valley. Meanwhile, corridor of deeper
moisture will continue to impact eastern WI into at least early
afternoon with occasional showers, before diminishing. Have
increased precip potential in this area considerably. Otherwise,
skies will remain mostly cloudy and breezy with a stiff northeast
wind. Cool temps rising into the upper 50s to lower 60s.
Long term...Wednesday night through Tuesday
issued at 240 PM CDT Tue may 23 2017
Expecting dry weather for the beginning of the period, then
uncertain precipitation chances for the Memorial Day weekend.
Near normal temperatures are anticipated through the period.
A weak ridge of high pressure at the surface and aloft should
bring mainly dry conditions late Wednesday night through
Thursday evening, though an isolated diurnal shower cannot
be ruled out Thursday afternoon. Weak warm air advection will bring a small
chance of showers back to the forecast area late Thursday night
Models offer widely varying solutions for the Memorial Day
weekend. Saturday is looking like the driest and warmest day
of the weekend, with only a weak cold front moving through the
region. The GFS drops an upper low into the western Great Lakes
on Sunday and Monday, and also brings a swath of a rain to the
southeast part of the forecast area as low pressure lifts through
the Lake Michigan region Saturday night into Sunday. Meanwhile,
the European model (ecmwf) keeps the main upper low to our north, with a series of
short-waves and frontal passages bringing the best precipitation
chances to northern WI. Given the poor run to run consistency of
the GFS, would lean toward the European model (ecmwf) for now. However, overall
confidence in the precipitation chances over the Holiday weekend
Aviation...for 18z taf issuance
issued at 1126 am CDT Tue may 23 2017
An upper level low pressure system will generate scattered showers
through the taf period, most numerous over eastern Wisconsin.
Ceilings will fall tonight with IFR cigs after midnight.
Improvement of cigs will be slow on Wednesday morning, but should gradually
become MVFR towards mid to late morning. Northeast winds will
become gusty tonight and remain breezy for much of Wednesday.