Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
110 PM EST Thursday Dec 5 2013
A cold front will sag through the area later today and this
evening...becoming stationary just south of Pennsylvania tonight
and Friday. A series of waves will ripple northeast along the
nearly stationary frontal boundary followed by high pressure for
Saturday into Saturday night. A new winter storm will move into
the area Sunday into Monday.
Near term /until 6 PM this evening/...
Rain will continue to race east into the region. Will lower probability of precipitation a
bit over the far north where there appears to be a northern edge
which will skirt my northwestern zones. The mild readings will continue
and this could very well end up being the warmest day we will see
for the rest of this year with highs ranging from the middle 50s
across the northern mountains...to the upper lower 60s across most of
central and southern PA.
Short term /6 PM this evening through Friday night/...
Short range operational models agree in forming a wave along the
cold front and rippling it over my southeastern zones later today and
tonight...allowing the steadiest precipitation to taper off by or shortly
after midnight. There will be a race between the colder air
wanting to filter in from the gr lakes and the rain wanting to
exit off to the east. At this point it looks like there will be a
brief mix or changeover to snow on the back edge of the precipitation
that could bring a coating of snow by morning...mainly to higher
elevations of the N-NW. There are no indications of having enough
quantitative precipitation forecast in the cold air to support much more than nuisance
amounts...but travel could get slippery.
This first round of liquid quantitative precipitation forecast today and early tonight will
likely average 3/4 to 1 inch across much of my County Warning Area...while less
than 1/2 inch should fall in the far southeast.
Another wave is expected to form along the boundary south of PA
Friday with another slug of precipitation for Friday afternoon and
evening. Strong frontogenetic forcing will develop under the
entrance region of a very strong jet streak that will race down
the St Lawrence River valley. The biggest issue with the second
wave will be the amount of wintry weather associated. Colder air
will be returning quickly...especially in the afternoon as the
heaviest precipitation will be occurring. The precipitation types will be
complicated and changing as the event evolves...but at this point
we feel that the far northwest will probably be mainly snow with rain
transitioning through mixed precipitation then ending as snow in a stripe
in between mainly rain which should be over about the southeastern 1/3 or
so of my forecast area.
Thinking is for a general 1-4 inch snowfall over my northwestern zones
with just enough ice mixed in over south-central and Laurel Highland
areas to make for a slippery commute. Have put an advisory up for
the snow-sleet-freezing rain potential lasting into late Friday
Deepening cold air will advect into the state by 12z Sat with
lingering light snow/mixed precipitation tapering off quickly in the
east...and just some flurries elsewhere as the strong cold front
reaches the East Coast.
Long term /Saturday through Thursday/...
high pressure over the upper Midwest Saturday will build east over
the state Saturday night...before becoming centered/retreating to
the New England states by late Sunday.
The active winter pattern develops again by late Sunday into early
next week with another potential significant overrunning mixed
wintry precipitation event slated for sun-Mon. A consensus of medium range
model and ensemble guidance shows low pressure developing over the lower
MS/Tennessee Valley and lifting northward along the west-side of the applchns through
the Ohio Valley/Great Lakes. A surge of above normal precipitable waters will spread northeastward
from the Gomex behind a broad southwesterly flow aloft and overrun a
retreating cold sector airmass associated with a modified Arctic surface
high migrating eastward from the upper Midwest into southern Quebec and northern
New England. The synoptic pattern looks very conducive for a
potential significant freezing/frozen precipitation event as the deep moisture
and and strong warm air advection aloft flows over the top of a shallow sub-fzg
airmass that could be entrenched /via cold air damming/ east of the
alleghenies for a prolonged period of time. Based on the evolving
trends in the guidance...increased probability of precipitation into the high likely range for
days 5-6. Will continue to highlight winter storm potential in the
severe weather potential statement.
In the wake of this system...a very cold northwest flow should grip the
region with well below normal temperatures and possible lake effect
snows over the northwest mountains
Aviation /18z Thursday through Tuesday/...
regional analysis continues to show widespread MVFR/IFR
conditions due to rain and low ceilings...with LIFR over the lower
susq terminals where fog is still locally dense. Improvement will
be painfully slow today...with current flying conditions only
hoping to improve to MVFR at best as rain associated with the
front moves into the region.
MVFR and lower flight categories will continue into Friday as more
rain...snow...and wintry mix overspread the region.
Friday...MVFR in rain southeast. IFR in snow/wintry mix northwest.
Sat...MVFR snow showers in the mountains. VFR in central/eastern
Sun...reductions developing with approaching storm that will bring
a wintry mix spreading south to north into Sun night.
Monday...widespread MVFR/IFR associated with a passing cold front.
Winter Weather Advisory from 1 PM Friday to 5 am EST Saturday
near term...la corte
short term...la corte/steinbugl