Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
347 am EST Sat Jan 31 2015
Arctic air and subzero wind chills will impact central
Pennsylvania for much of the day. A large winter storm will target
the area on Sunday...with the potential increasing for a
widespread heavy snowfall across central and northern sections...
and the combination of snow and mixed precipitation across the
south. Another shot of Arctic air will follow for Monday
afternoon into Tuesday.
Near term /until 6 PM this evening/...
inversion heights falling rapidly early today as high pressure
builds from eastern Kentucky and WV. Wind chills in the -10f to -20f
range are common across western and northern sections...and
advisory runs through 16z.
A mostly sunny and chilly day is in store for most...as the surface
ridge axis expands and overspreads all of PA on up into upstate
New York and southern Quebec. High clouds evident in this mornings
infrared loop over the central and western glaks may stream overhead
this afternoon...but won't diminish bright skies which should help
diminish the nip of the afternoon. Highs from the middle teens to
middle 20s north to south will be about 15 degree below normal on
Short term /6 PM this evening through 6 PM Sunday/...
dirty ridge axis builds eastward from the Ohio Valley tonight and
Sunday...as a vigorous northern stream trough drops across The
Rockies and into the upper plains by midday Sunday. This
confluence is important as it will aid in locking cold air over
the region as the aforementioned trough advects increasingly moist
and mild air towards the region Sunday afternoon and night...
starting as snow for all. Snow should begin from the Allegheny
crest westward by noon before steadily overspreadin the remainder
of central PA during the early to middle afternoon.
Long term /Sunday night through Friday/...
*significant winter weather/snow event possible Sunday-Monday
*bitter cold temperatures and dangerous wind chills possible
Monday night into Tuesday
Latest model simulations and ensembles continue to show very high
potential for heavy snowfall and mixed precipitation (south) to
impact central PA Sunday night through Monday. Latest European model (ecmwf)
solution depicts a Miller-b type surface low evolution...with primary
low tracking to southwest corner of PA by 12z Monday...while
secondary forms over the Delaware-Maryland-Virginia and scoots rapidly out to sea by
Monday afternoon. This will produce a period of moderate to heavy
snowfall across most of central and north central PA...while a
mix and changeover to sleet and freezing rain is likely along and
south of the Turnpike.
A Winter Storm Watch continues in effect for all central PA
counties and is valid from noon EST Sunday through noon EST Monday.
Wpc forecast is weighted heavily in the final gridded snow/ice
accumulations...as before. Confidence is now 80% or greater for 4
inches or more of accumulation in 24 hours by 12z Monday over all but
the southern 1/5 of central PA where mixture is expected. Keeping
recent inconsistencies in mind...do anticipate some changes
regarding numbers and locations of snowfall totals...but with
upper wave over British Columbia now onshore and presumably better initialized
than solutions from 48 hours ago...confidence has markedly
increased for an impactful winter storm to visit the commonwealth
Sunday afternoon through Monday.
A shot of Arctic air is forecast to surge into the area behind the
early week storm with potential for dangerous wind chills Monday
night into Tuesday. This could add to storm-related impacts. High
pressure should bring cold but quiet weather into midweek. Models
and ensembles show a coastal type system sometime next Wednesday-Friday but
it is way too early to speculate on this system.
Aviation /09z Saturday through Wednesday/...
IFR at kjst will continue into the early morning hours as snow
showers and low ceilings persist in the nwrly upslope flow. Upslope
winds also continue to support MVFR ceilings at kbfd and kaoo. VFR
has returned elsewhere and should prevail into tomorrow...though a
stray remaining snow shower could bring some temperature reductions
Gusty winds will continue at most taf locations overnight. Most
have somewhat diminished...but remain between 15-20kts with gusts
as high as 25 to 30kts. Unv is one of the few locations that is
calm winds due to decoupling.
Sun...widespread IFR/MVFR developing associated with a storm
moving toward the region.
Monday...reduced conds early...improving as the storm moves away from
Tue-Wed...no sig weather.
Winter Storm Watch from Sunday afternoon through Monday
morning for paz004>006-010>012-017>019-024>028-033>037-041-042-
Wind Chill Advisory until 11 am EST this morning for