Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Pittsburgh PA
1249 am EST Friday Dec 13 2013
a complicated storm system will bring snow and a wintry mix late
Friday night into Saturday night.
Near term /through today/...
made minor changes to overnight period...lowered cloud cover in the
south and adjusted temperatures to latest guidance. Previous forecast
Weak warm advection will begin overnight with a backdoor
cold front lying out across the PA/New York border by Friday morning.
This will bring a few snow showers to the I-80 corridor Friday but
little in the way of accumulation. Temperatures will not fall off
much this evening and may be on the rise toward daybreak. Maximum
temperatures on Friday will be 10 to 15 degrees warmer than Thursday.
Short term /tonight through Sunday/...
another complex storm system for the weekend as low pressure moves
from the Southern Plains to the upper Ohio Valley Friday night
into Saturday. Snow will arrive after midnight Friday night and
quickly overspread the region Saturday. Precipitation looks to
stay all snow north of I-70 much of the day Saturday before mixing
late day as warmer air works north. The rain snow line is still in
doubt but highest snowfall amounts look to be across the north
most likely from Lisbon to Butler and DuBois. South of this region
gradually lower amounts as snow changes to plain rain for
Morgantown Saturday afternoon with a mix into Pittsburgh late day.
Snow in the ridges will mix to freezing rain and sleet Saturday
afternoon and evening as cold air remains trapped.
Snow and rain amounts across the south should be limited by an
upper level dry slot which will enter that region Saturday
As of now no headlines will be issued with snow and or ice amounts
not expected to reach warning levels. Advisories will likely be
issued for the event. Much could still change with this forecast.
By Saturday night a secondary coastal low will be developing off
the East Coast and this will shift deep moisture east along with
significant lift. A light wintry mix across the south and light
snow north will transition to snow showers later Saturday night
and Sunday as cold advection returns behind the East Coast low.
Long term /Sunday night through Thursday/...
the long term period features several fast moving upper level
disturbances crossing the Great Lakes. While confidence in the
southern extent of each of these systems remains low...low chance
probability of precipitation were maintained over the north to take into account any lake
enhanced precipitation. Both models also have a more potent wave cross
midweek bringing yet another Arctic push. Temperatures were
generally kept 10 degrees below normal through the week.
Aviation /06z Friday through Tuesday/...
VFR conditions expected at all ports through the morning. MVFR
stratocu will drift down from Lake Erie this afternoon reach fkl and
Outlook.../Friday night through Tuesday/...
widespread restrictions late Friday night through Sunday in both a
mix of snow/rain as low pressure ejects from the plains towards
the coast. High pressure builds overhead for Monday...with another
chance for snow possible on Tuesday.