Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
926 PM EDT Wednesday Mar 12 2014
An intense late winter storm will continue to move into southern
New England overnight...to be over down-East Maine by Thursday
morning. Temperatures will plummet tonight into early Thursday as
strong and gusty northwest winds in the wake of our departing
storm sweep across the region. The cold blast will be short-lived
with a nice rebound in temperatures on Friday. A series of
Canadian frontal passages over the weekend will send temperatures
back to seasonably cold levels into early next week.
Near term /until 6 am Thursday morning/...
Mesoscale anal shows the deepening surface low moving over northern
New Jersey/southeastern New York toward New England. A large isallobaric pressure rise
couplet of 20mb/6hr is moving into southwestern PA...providing a very
blustery evening. Have decided to expand the Wind Advisory based
on the robust pressure rises and scattered reports of strong wind
gusts from social media. A pressure rise couplet of this magnitude
is generally strong enough to provide warning strength wind
gusts...however at least two factors keeping wind gusts at
relatively modest levels are the wind speeds from 850 through
700mb averaging generally under 50kt...and a respectable amount
of directional shear through that layer lasting well into the
evening. By the time we get favorable alignment of wind directions
through a deep layer...wind speeds are forecast to be only in the
35-45kt range up through 700mb.
Have also dropped all Snow Advisory headlines given the rapid
drying and drop off to just scattered light snow showers behind
the departing storm. Still some rain showers over the far southeast but
temperatures are falling fast there.
The big picture remains largely unchanged with the precipitation
expected to continue to wind down over the area during the evening
hours as the low continues to deepen and race toward the New
England coastal waters.
For the rest of the overnight...the biggest issues will be the
cold and wind. Rare middle-March sub zero readings expected over my
far northern tier...while single digits and teens will be commonplace
further south. Gusty winds will bring wind chill values down to
between 15 and 20 below zero over the high terrain of the west and
north where a Wind Chill Advisory is in effect.
Another concern will be for rapid refreeze of roads and walkways
as temperatures plummet this evening.
Short term /6 am Thursday morning through 6 PM Thursday/...
cold windy start....bundle up on way out in the morning.
Winds should diminish late morning into the middle afternoon hours.
Very windy very cold.
No significant precipitation.
Just a cold wintry day with a shot at some near record low high
temperatures if temperatures do not begin to rise before sunrise
Long term /Thursday night through Wednesday/...
the good news is that the cold blast will be short-lived...with a
rapid moderation occurring on Friday. Temperatures should even level off
or go non-diurnal late Thursday night into the predawn hours Friday morning
especially across the western mountains some of the sheltered valleys in the
eastern part of the County Warning Area may still decouple toward daybreak.
Breezy SW return flow in advance of northern clipper surface low tracking
across the upper Great Lakes/southern Ontario and downsloping effects
should help to boost temperatures into the low/middle 40s north and low/middle
50s south. The models turn the low to the northeast up the St.
Lawrence Valley on day 5/Sat...dragging a trailing/weak cold front
across the northeast and middle-atl states. 12z model guidance indicates
some light shower activity along the cold front...with the highest
probability of precipitation based on consensus blend across northwestern sections between 00-06z Sat
GFS and ec ensembles show a cold upper-level trough remaining a
fixture over eastern Canada and the northestern Continental U.S....with ridging along
the West Coast possibly breaking down into early next week. At
the surface...a modestly strong/1040mb high pushing southeastward from the
upper Midwest/western Great Lakes should direct colder air into the
region behind a reinforcing Canadian frontal passage on Sunday...with temperatures
trending lower on day 5/6.
The key feature of interest will be a surface wave migrating northeastward from
the Texas/la Gulf Coast across the southeast to the Outer Banks by 12z
Monday. The 12z GFS trended in the direction of the 00/12z European model (ecmwf)
which has indicated a deeper and 'more defined' low for the past
four cycles. The 12z UKMET is very close to the European model (ecmwf) and just a
tad weaker. The GFS and especially the gefs are more suppressed vs
their non-NCEP counterparts. Regardless of the solution choice...the
main forecast challenge will initially be the track followed by potnl
rain/snow transition line on northwest periphery of the associated precipitation
shield. Final probability of precipitation were nudged in the direction of the European model (ecmwf)
bringing chance mentions of rain/snow to much of south-central PA
Sun night into Monday.
Aviation /01z Thursday through Monday/...
conditions continue to improve as northwesterly flow has allowed
for snow at all taf sites outside of MDT and lns...where lns still
has lingering rain showers. These will end shortly.
MVFR conditions will give way to VFR conds as the night
progresses. By 03z at lns and MDT. Aoo...ipt and unv will linger
in MVFR through early Thursday morning. However precipitation will
end by middle evening...improving visibilities...but ceilings will continue to
linger until 09z. Reduced ceilings will linger across the western
Highlands /kbfd and kjst/ into Thursday morning. Gusty winds will
pick back up and continue into Thursday.
Quieter weather should return for Friday.
Thursday...gusty north/northwest winds...gradually diminishing in the afternoon.
Friday...no sig weather expected.
Sat...weak cold front could produce scattered -shra/-shsn.
Sun-Mon...low pressure will pass to our south and could brush southern PA
with some precipitation.
with rainfall today...we expect minor to moderate rises on rivers
and streams over the next several days. The most significant
rises are expected on the main Stem susq.
There is still enough ice in spots to lead to ice jams...though
significant decay has occurred at many locations due to the
recently warm weather. Ice jams are possible but not predictable.
Monitor water levels closely for the rest of the week. Some minor
flooding/ponding of water is possible in areas where snow and ice
block drains and slow run off.
Wind Advisory until noon EDT Thursday for paz012-017>019-
Wind Chill Advisory until noon EDT Thursday for paz004>006-
near term...la corte