Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
350 PM EDT Tuesday Mar 11 2014
a vigorously deepening late winter storm system will impact the
area on Wednesday...followed by very cold and blustery conditions
for Wednesday night into Thursday. Temperatures will then
rebound...but remain slightly below normal through the weekend.
Near term /until 6 am Wednesday morning/...
today/S mild temperatures will carry into tonight as warm air in
place wll be reinforced by a very mild day today will be followed
by increasing SW/S flow ahead of an approaching very potent storm
system. Temperatures will dip down near freezing along the PA/New York
border...and remain in the 40s across the southern half of County Warning Area.
Moisture aloft will continue to thicken up tonight. Sub-tropical
high centered east of the Bahamas will supply the good srly flow
and real Gomex moisture to a strong system currently dropping southeast
from the High Plains into MO. The sub-1000mb low will deepen even
further as it rolls eastward along the weak boundary over the Ohio
Valley and northern Middle-Atlantic States. The low is prognosticated by all models
to cross the southern tier of PA Wednesday - at 12z it should be entering far
southwestern PA...and will deepen to a 980mb low by the time it scoots
east of kabe Wednesday evening.
Light precipitation will initially slide into the northwest tonight
/around 06z/...with 850mb temperatures above zero it should fall as
mainly rain...though some wet snowflakes may be mixed in. First
wave of moderate precipitation should be approaching County Warning Area western edge by
Short term /6 am Wednesday morning through Wednesday night/...
sub-1000mb low will continue to deepen as it rolls eastward along
weak boundary over the Ohio Valley and northern Middle-Atlantic States. The
low is prognosticated by all models to cross the southern tier of PA Wednesday - at
12z it should be entering far southwestern PA...and will deepen to a 980mb
low by the time it scoots east of kabe Wednesday evening. Very strong
and near- textbook kissing jet couplet will enhance the lift and
frontogenesis as it moves through the state. The warm air to the
south /highs should slip into the 60s in the lower susq/ and the
already- anomalously warm temperatures will keep the precipitation rain over all
but the far northern tier through at least middle afternoon Wednesday. Even the
far northern tier will probably have trouble accumulating early on what
does fall as snow...due to the middle- March sun and marginal temperature
profile. But eventually precipitation intensity will win out. Light east
wind could keep temperatures near freezing in the northern mts Wednesday
morning...so isolated pockets of freezing rain may exist in the
northern tier Wednesday...especially for a brief period as colder air quickly dives
southward. As the low deepens and passes to the east...the winds
will go northerly and increase quite rapidly. Sustained speeds in
the 20s and gusts near 40 miles per hour are expected as strong cold air advection drops
temperatures into the 20s in the north very quickly Wednesday afternoon...into central
sections between 21-00z and by 03z in the southeast.
Quantitative precipitation forecast in the 0.75-1.25 inch range across much of the north is most
likely going to be mostly rain...but the strong cold advection and
coupled jet in the afternoon will bring mesoscale snow band/S and
temperatures will then be conducive to allow accumulation. Thus...the
accumulations could reach 6 inches or more along the northern tier by
late Wednesday night...with colder air spilling further south late
afternoon/early evening producing minor accums in the mountains the cold
winds will help mins into the lowest single digits in the north. This
will also lead to low wind chills. Have transitioned winter
weather watch over to a warning for northwest counties with an advisory
for the remainder of northern tier extending down across the
Main threat in the south as low tracks across PA will be potential
for convection. Storm Prediction Center places southern PA in slight risk...and with
strong dynamics associated with this system...mentioned threat in
severe weather potential statement.
On the back end of the storm...quite cold air /as cold as -20c at
850mb/ gets driven into the region on a strong gusty northwest wind later
Wednesday night into Thursday...with by far the coldest day of the week in
store for Thursday. Wind chills should reach near advisory
criteria over the northern mountains and Laurel Highlands...range from 0 to
-10f over the Central Ridge/valley region and dip to around zero
in the lower susq valley.
Long term /Thursday through Tuesday/...
after the storm...quite cold air...around -20c at 850mb...gets
driven into the region on a strong gusty northwest wind later Wednesday night
into Thursday...with by far the coldest day of the week in store
Thursday. Wind chills should reach near advisory criteria over the
northern mountains and Laurel Highlands...range from 0 to -10f over the
Central Ridge/valley region and dip to around zero in the lower
The well-below normal cold will be short-lived though...as temperatures
rebound decently Friday into Sat...bouncing back to near seasonal
normals. However this winter's defining feature...the persistent
West Coast ridge...is again expected to re-establish itself
heading into next week. This will allow for cooler air to filter
back into the region in persistent northwest flow over PA...keeping temperatures
near or slightly below normal and preventing any kind of
significant warm up.
Aviation /20z Tuesday through Sunday/...
widespread VFR conditions across central PA today with light west/SW
winds. Middle/high clouds will thicken late this afternoon and this
evening ahead of an approaching vigorous storm system.
Restrictions arrive overnight as light rain /and poss snow north/
begin to move in around 06z in the northwest...and heavier area of precipitation
arrives starting around 12z Wednesday. Bulk of heavier precipitation
will be between Wednesday morning and midnight Wednesday night.
Widespread adverse conditions on Wednesday...with rain across much of
the area...snow across the far north...and some risk of strong
thunderstorms near the Maryland border. By afternoon...strong wind fields will
bring increasing northerly flow...llws...and gusty winds up to 40
miles per hour. These continue through the first half of Thursday as very cold air
stampedes into PA. With strong storm dynamics...concern exists for
a burst of heavy wet convective snow /and poss thunder/ near the
center of the low Wednesday/Wednesday night.
Wednesday...widespread MVFR-IFR restrictions in rain and snow. Strong
north/northwest winds developing. Low level wind shear.
Thursday...strong/gusty north/northwest winds...gradually diminishing in the
Fri-sun...no sig weather expected.
with warmer temperatures and midweek rainfall...expect moderate
rises on rivers and streams mainly for the southern half of the
County Warning Area. Still enough ice in spots to bring ice jams...though
significant decay has occurred at many locations. Any ice jams
will be isolated in nature. All persons should monitor water
levels closely for the rest of the week.
Winter Storm Warning from 8 am Wednesday to 8 am EDT Thursday
Winter Weather Advisory from 8 am Wednesday to 8 am EDT
Thursday for paz006-010-011-037.
Winter Weather Advisory from 3 PM Wednesday to 8 am EDT
Thursday for paz017-024-033.