Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Green Bay WI
512 am CDT Thursday Oct 30 2014

Updated to add short term portion for morning forecast issuance

Synopsis...
issued at 506 am CDT Thursday Oct 30 2014

A brief taste of wintry weather late tonight through Saturday...then
a return to much quieter late-autumn conditions.

Strong amplification of the large scale pattern underway. Amplitude
should peak early in the weekend...with deep troughs near the West
Coast and over the eastern Continental U.S....sandwiching and a sharp full-
latitude ridge over the plains. The pattern will remain
progressive. That will keep the high amplitude short-lived...with
the western trough expected to reach the area early next week.

A significant shot of cold air will affect the area for the end
of the work week and start of the weekend...then temperatures will
rebound back close to or maybe even a little above seasonal
normals next week. The main opportunities for precipitation will be with strong
shortwave digging across the region and into the amplifying eastern noam
lngwv trough early in the period...and again next week when the
large-scale western trough arrives. Given the limited moisture...precipitation
amnts are likely to end up at or below normal for the period. The
exception could be the Lake-Superior snowbelt.
&&

Short term...today...tonight...and Friday
issued at 506 am CDT Thursday Oct 30 2014

Lots of forecast details to work out this morning. Intense northern
stream shortwave will dig south-southeastward into the eastern Continental U.S. Upper trough. Rapidly
building anticyclone supported by the shortwave ridging behind the
upper system will drive cold Canadian air rapidly southward into the area.
Given the source region of the air mass in northern Canada and it/S
rapid transport south...it will still be very chilly when it
arrives. The colder temperatures combined with windy conditions will
probably make it/S arrival even more noticable.

Will just hit the highlights...

Rain showers with the upper system will change to snow as the colder air arrives
in the north this evening. Northerly flow off Lake Superior will result in
some lake-effect. There is likely to be a period of time during
the evening when the synoptic forcing overlaps the lake-
effect...and the most vigorouos shsn are expected then. Shsn will
continue the rest of the night and into Friday morning...but will be
fighting large-scale subsidence by that point. Given it/S the
first event of the season and there will be some wind...conditions
seemed worthy of an advisory...so one was posted.

Northerly flow over the Bay and lake will promote deep mixing...into
50 knots winds around 850 mb. Posted a Wind Advisory for the door.
Current forecast conditions for the Fox Valley eastward to the Lakeshore
would also support a Wind Advisory. But confidence in hitting
advisory criteria is a little lower in this area /00z European model (ecmwf)
backed off a bit on winds/ so stuck with mention in the severe weather potential statement and
an Special Weather Statement. This will allow the day shift the maximum flexibility to
adjust the forecast after reviewing the latest data.

Long term...Friday night through Wednesday
issued at 324 am CDT Thursday Oct 30 2014

Temperatures should gradually rebound to near normal by early next
week as 500mb ridge builds across the eastern United States. Main
issues for this package will be Friday night with cloud cover and
potential precipitation chances near the Bay and lake...and then
again early next week with timing of the arrival and departure of
a slow moving cold front.

For Friday night...high pressure was expected to build into central
and western Wisconsin...bringing clear skies and the coldest
temperatures of the season. This still holds true across our west...
but latest GFS/WRF models indicated 850/925mb winds turning northeast
late Friday night into Saturday morning. If this scenario does come
true...will need to add more clouds and the possibility of rain/snow
showers due to the fact the Bay and lake are still relatively warm.
Could be long fetch down the Bay for the possibility of Bay effect
rain/snow showers. The winds and clouds off the Bay and lake could
play havoc on low temperatures Friday night. Since this scenario
by the WRF/GFS is a change from previous forecasts and the European model (ecmwf)
is more northerly with the low level winds...will add more clouds
to the forecast and bump up minimum temperatures and hold off on
adding precipitation chances. If models continue with low level
winds turning to the northeast...day shift can add precipitation
to the Friday night/Saturday morning periods.

The next chance for rain (some snow north late at night/early
morning) is from Monday through Tuesday morning. The weak cold front
will approach Wisconsin on Monday...then across the region Monday
night and Tuesday. Another clipper system will approach the area from
the northwest on Wednesday. Have left Wednesday dry for the moment...
but it is possible that precipitation chances will need to be added
to the forecast with this system.
&&

Aviation...for 12z taf issuance
issued at 506 am CDT Thursday Oct 30 2014

MVFR ceilings still hanging tough across the north. Those will eventually
shift off to the NE this morning. Middle and high clouds will have
overspread the area by then...but those are much less of a concern
for aviation interests. The most sig aviation concerns the next 24
hours will be snow across the north late tonight into Friday morning...and strong
winds across the area late tonight and Friday.
&&

Grb watches/warnings/advisories...
Wind Advisory from midnight tonight to 4 PM CDT Friday for
wiz022.

Lake effect Snow Advisory from 9 PM this evening to 11 am CDT
Friday for wiz005.
&&

$$

Synopsis.......skowronski
short term.....Skowronski
long term......eckberg
aviation.......skowronski

National Weather Service Glossary of Abbreviations