Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Green Bay WI
1058 PM CDT Monday Mar 30 2015

Updated aviation portion for 06z taf issuance

issued at 302 PM CDT Monday Mar 30 2015

Some light mixed precipitation tonight...then showers and possibly
some thunderstorms Wednesday night into Thursday.

Progressive and energetic band of westerlies will continue across
much of the Continental U.S. And southern Canada throughout the period. The
amplitude of the large scale pattern will remain limited for most if
not all of the forecast period. That will result in weather primarily being
controlled the synoptic systems migrating across the Continental U.S....with
considerable daily temperature variations due to the passage of
each system. Overall...readings will probably end up averaging a
little above normal for the period. There will be enough opportunities
and sufficient available moisture to result in near normal precipitation for
the period.

Short term...tonight and Tuesday
issued at 302 PM CDT Monday Mar 30 2015

Main forecast concern will be the upper level disturbance moving
through tonight.

Afternoon surface analysis showed a weak area of low pressure
moving into western Minnesota. This system will push into
northeast Wisconsin tonight as it couples with an upper level
shortwave and jetstreak...bringing with is the chance for
precipitation. Models have trended south with the track of the low
and precipitation...mainly moving along an 850mb baroclinic zone.
Comparing current 850mb temperatures...precipitation trends over
the past 6 hours...and surface low positions to model solutions for
18z Monday...seems liked the nam12 and GFS were handling the
development of this system the best. Leaned towards a blend of
these solutions for the overnight forecast. This lowered
precipitation chances in the north and northeast corner. This
matched up well forcing coming through as the shortwave swings
southeast through the state. Looks like the best chance for
precipitation will be in central WI towards he Fox Valley and
the central Lakeshore around 06z tonight as the best forcing and
moisture moves through. After 06z...moved precipitation area to the
northeast and diminished chances towards daybreak.

While precipitation should start off as rain across the County Warning Area...a
change over is expected in the far north and northeast. Kept close
to previous forecast with precipitation transition. While model guidance
had trended warmer at the surface...midlevels were cooler on all
the models with added evaporational cooling. A mixture of rain and
snow...then a change to all snow will start in the far northeast
around 03z tonight...and gradual work its way southwest through
the night. Areas north of a Wausau to Green Bay line should remain
all rain through at least 09z Tuesday before mixing with snow
Tuesday morning. Not much accumulation is expected...with around
an inch possible to the north.

Precipitation should come to an end in most location through
Tuesday morning. Light precipitation is still possible in northern
Wisconsin as another weak impulse moves through the mean upper
level flow. Models are having an issue resolving this feature and
therefore do not agree on precipitation chances. Lowered chances a
bit in the afternoon as any forcing that moves through should be
quick hitting and short lived.

Long term...Tuesday night through Monday
issued at 302 PM CDT Monday Mar 30 2015

The main weather maker will be the cyclone and associated frontal
systems crossing the region mid-week. Models have trended a little
slower with the arrival of the precipitation with the system compared to adjusted the forecast accordingly. With the precipitation band now
arriving late in the night...some of the models suggest it may be
dissipating as it crosses the region. That would be more typical of a
system later in the warm season...when forcing is typically
weaker. Forcing from the shortwave still looks pretty carried
likely probability of precipitation across the region...though did not place them in the east
until Thursday morning. The Storm Prediction Center day 3 convective outlook issued
early this morning carried a marginal risk of severe into far western
WI...and general thunder across the area. Middle-level lapse rates
prognosticated to be fairly held on to mention of thunder
despite the later arrival of the main precipitation band.

Temperatures taken from blend of top performing guidance products...with
some extra weight on the European model (ecmwf)/European model (ecmwf) MOS and their related bias-
corrected products.

The remainder of the forecast is dominated by smaller/weaker
shortwaves embedded in the fairly low-amplitude large scale flow. As
such...timing and placement was quite different among the models.
Given the pattern...stuck with the Standard extended forecast
initialization grids based on a broad blend of guidance products.

Aviation...for 06z taf issuance
issued at 1057 PM CDT Monday Mar 30 2015

As a weak area of low pressure exits the region...light
rain will end over northeast Wisconsin around or shortly after
midnight. Thereafter...guidance was quite pessimistic in regards to
low ceilings behind the system...but upstream observation do not support
widespread MVFR or lower ceilings developing. So backed off the lower
ceilings after midnight. Another disturbance will arrive Tuesday
afternoon over northern Wisconsin which could create spotty
showers. Coverage is too low to insert into the tafs though. That
disturbance will exit Tuesday evening...leaving clearing skies for
the rest of the night.


Grb watches/warnings/advisories...


short term.....Allen
long term......skowronski

National Weather Service Glossary of Abbreviations