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Area forecast discussion 
National Weather Service Green Bay WI
244 PM CDT Friday Aug 29 2014

Forecast discussion for routine afternoon forecast issuance

Short term...tonight and Saturday
issued at 243 PM CDT Friday Aug 29 2014

The main forecast focus continues to be the heavy rain potential over the
next 24 hours as a moisure-laden atmosphere awaits a trigger.

The 19z msas surface analysis indicated a broad area of weak low pressure
over the upper MS valley. A warm front extended eastward through central WI...
while a cold front stretched SW from central Minnesota to central Nebraska. Much
of NE WI resided in a quiet zone between precipitation to the north
associated with the 800 mb warm front...precipitation to the west associated with
the surface low/cold front and precipitation to the south and east associated with a
shortwave. The lack of precipitation has allowed for some clearing to take
place with some locations soaring into the 80s.

Showers and thunderstorms are still expected to overspread the region this
evening as the weak surface low/associated cold front move into the western
Great Lakes...with a trailing shortwave trough pushing into the upper
MS valley/Midwest. Plenty of low-level moisture in place over NE
WI with dew points in the 60s to around 70 degrees and precipitable water values at
1.5"+. Air mass to also be unstable this evening with convective available potential energy
between 1k and 2k j/kg and lifted indice's around -5...although instability will
weaken a bit upon sunset. Nevertheless...expect to see precipitation expand
in coverage this evening...especially as a jet streak lifts NE
from the Midwest and creates a coupled jet structure with another
jet maximum over central Ontario. In general...anticipate precipitation amounts
to average in the 0.50 to 1" range...but with so much moisture in
the air...would not be surprised to see some totals surpass 1.5"
by daybreak. An esf has already been issued highlighting the
threat for heavy rain and possible flooding of urban areas/near
rivers and streams. Mild night on tap with min temperatures only in the lower
to middle 60s north...middle to upper 60s south.

Showers/thunderstorms to be ongoing into Sat as the cold front drives through the
rest of WI accompanied by the shortwave trough. Even though we lose the
upper jet support...there is still plenty of lift (cdfnt)...forcing
(trof) and moisture available for precipitation to continue through Sat morning
before gradually diminishing from west to east during the
afternoon. Another one-quarter to one-half inch of rainfall is
possible which could aggravate any flooding (if there is any). Maximum
temperatures are expected to range from around 70 degrees north to the upper
70s south.

Long term...Saturday night through Friday
issued at 243 PM CDT Friday Aug 29 2014

Precipitation trends for the end of the Labor Day weekend will be the
main forecast concern for the extended period.

Will maintain small probability of precipitation over far NE WI Saturday a
short wave trough moves through...but weak ridging aloft should bring dry
conditions overnight into Sunday. Patchy fog is anticipated Sat winds decrease and partial clearing occurs. Precipitation should
move into northwest WI late Sunday a low-level jet becomes
focused there...but will continue to hold off probability of precipitation for our wstrn
counties until evg. Warm air advection and partly cloudy skies should allow temperatures
to warm into the upper 70s and lower 80s at most locations.

A short wave trough and upper level jet energy will approach the region
Sunday night...with a 40-50 knots low level jet ramping up ahead of the
advancing cold front. Most of the dynamics will move through late
Sunday night and Monday the highest probability of precipitation (likely) and
quantitative precipitation forecast will be focused during that time frame. Suspect that abundant
cloud cover and widespread shower activity will limit instability
on not expecting any organized severe thunderstorms...
despite the passage of the cold front. Torrential rainfall and
gusty winds may accompany the stronger storms. Have lowered probability of precipitation
on Monday the best short wave energy tracks through the
Lake Superior region...and a dry slot punches into the forecast

Fast zonal flow will set up over the western Great Lakes for the
rest of the week. A weak short wave trough may bring isolated/scattered showers on
Tuesday...but Tuesday night and Wednesday look dry. Models all
suggest that a west-east oriented frontal boundary will set up
across the region for the end of the week...but the position and
movement of the boundary varies from model to model. The presence of
the the return of a moist and unstable air
mass...supports the mention of chance probability of precipitation Thursday into Friday.
Confidence in the overall details is low.

Aviation...for 18z taf issuance
issued at 1235 PM CDT Friday Aug 29 2014

Warm front cutting across central sections of WI this afternoon is
expected to continue moving north and be the primary focus for
additional showers/isolated thunderstorms. Visibilities have been reduced to IFR
conditions north of this fnt...but expect an improvement to at
least MVFR conditions later this afternoon once the fnt clears the
area. Brief clearing behind the warm front over the southern half of WI
should continue with only an isolated thunderstorm expected as the atmosphere has
become unstable. The main action should come tonight as a weak surface
low and upper level trough of low pressure move toward WI. Plenty
of moisture available...thus anticipate a round of showers/thunderstorms to
move through NE WI tonight and when its not raining...fog will be an
issue. Look for both ceilings/visibilities to settle into the IFR category
with localized LIFR conditions in thicker fog. Precipitation chances would
then carry over into Sat as the upper trough moves through the
region. There may be some modest improvement in both the ceilings and
visibilities by afternoon with MVFR conditions anticipated.

issued at 243 PM CDT Friday Aug 29 2014

Have already issued the hydrologic outlook with the concern of
flooding of urban areas/rivers and streams for tonight into Sat.
There is plenty of moisture in the atmosphere for showers/thunderstorms to feed off
of and with possible training of precipitation...rainfall amounts could be
quite impressive by the time the precipitation diminishes late Sat/Sat night.
Most of NE WI will end up with between 1 to 2 inches of rain with
locally higher amounts possible.

Grb watches/warnings/advisories...
beach hazards statement until 10 PM CDT this evening for wiz022-


Short term.....AK
long term......tsk

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