Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1043 am EST sun Feb 1 2015
low pressure will cross the central Mississippi River valley
today and move into the Ohio Valley tonight...and cross the state
on Monday. This will produce widespread wintry precipitation
across the area this afternoon into Monday. A period of freezing
rain is likely across the south and central sections tonight.
Another shot of Arctic air will follow for Monday afternoon into
Near term /until 6 PM this evening/...
only some really patchy and light snow is falling over the western
half of the area. But some more-intense bands moving over pbz/S
area and into The Laurels at this time. These should make some
accumulationin the west/central cos by middle- afternoon...but the
sun is managing to make a bright spot in the clouds over State
College right now. It is still snowing with visibility lt 4sm.
But...anything more than a few tenths of snow accumulate are unlikely
before middle afternoon. Mesoscale models hint at a break after a few bands of
snow slide SW-NE through the area this afternoon...then the snow moves
back in and intensifies from SW-NE this evening. All this is
pretty much unchanged.
With that said...
With each passing model cycle it looks like we will get less snow
on the whole...whether due to lower quantitative precipitation forecast due to only a couple of
heavier bands and perhaps only one 3-6 hour period of heavy snow -
or due to more rain/mix occurring in the southern half of the
area. However...it has barely started snowing. Lets at least let
it start to play out. Will not make any tweaks to snow or ice
accums or changes to headlines at this point. But the later
updates today may just follow this milder/drier trend if the
newer GFS and ec look similarly mild and less wet.
Short term /6 PM this evening through 6 PM Monday/...
low pressure moves up the Ohio River tonight. By Monday morning
it should be over kpit...and roll over the southern half of the
local area. Main quantitative precipitation forecast falls in the 03z to 09z timeframe for many...
and this six hour period will be critical for snow accums over the
central mountains...just north of the changeover zone. Faster/
greater mixing will decrease snow amounts substantially. For now
have nudged the mixing zone north and decreased snow amounts south
of Interstate 80 into the 4-6" range. As a result...greater freezing rain
potential exists with this solution than previous thinking.
While the farther north/warmer solution will cut down the snow
amounts in the central zones...warning criteria snowfall is
expected north of Interstate 80. Advisory and sub advisory snow
amounts are expected across the southern third of central PA...
but the chance for icing is enough to warrant at least an advisory
Surface low rapidly tracks east of the area by midday Monday...with
colder air pouring back into the commonwealth on the backside of
the low. Expect little if any additional snow accumulation by Monday
afternoon across the north. Precipitation will have shut off across
central and southern areas by midday. Sharply colder air is poised
to overspread central PA again on Monday night.
Long term /Monday night through Saturday/...
main impacts from winter storm will have moved away from region by
Monday night...but Arctic air pushing in will bring a very cold
night with lows bottoming out in the single digits south and below
zero north. Though stronger winds in the evening will be gradually
diminishing overnight...enough of a breeze will remain to drop
wind chill values below zero for all...with northern mountains and
Laurel Highlands likely needing a Wind Chill Advisory /-15f/ Monday
night into early Tuesday. This could add to storm-related
impacts...including potential for patchy black ice.
High pressure will bring cold but generally quiet weather into
midweek. A weak system moves through Wednesday that may bring light
accums to the northwest half /before the system deepens more rapidly over
New England/...which will be followed by a shot of more Arctic air
as cold high pressure builds in for Thursday into Friday - including a
return of below zero wind chills.
Temperatures moderate a bit...but remain below normal...on Sat. Another
low pressure area may impact the region on Sunday...but at this
time it looks to be on the weaker side.
Aviation /16z Sunday through Thursday/...
deteriorating flying conds expected this afternoon and evening...as low
pressure approaches from the Midwest...spreading snow and lowering
ceilings across central PA. At 15z...IFR conds already noted across
western PA. Upstream radar returns and latest hrrr output suggests
IFR conds will develop at kaoo/kunv around 16z and at kipt around
18z. Across the southeast counties...some minor visible reductions
appear likely this afternoon in light snow. However...IFR conds will likely
hold off at kmdt/klns until late this evening.
Warmer air working into the state will change snow to either rain
or freezing rain across the southern half of the state late tonight.
However....widespread IFR to LIFR conds expected everywhere in
continuing precipitation and low ceilings resulting from moist southeast flow
ascending the higher terrain of central PA. Low level wind shear remains a
possibility late tonight across the S/southeast as low level jet rotates
Marked improvement is expected between 15z-18z Monday...as low pressure
passes east of the area...and drier northwest flow develops.
Monday...reduced conds early...gradually improving as the storm
moves away from the area. Low level wind shear poss Monday aft/night.
Tuesday...no sig weather.
Wednesday...MVFR in shsn northwest...VFR southeast.
Thursday...no sig weather.
Winter Storm Warning until 1 PM EST Monday for paz004>006-
Winter Weather Advisory until 8 am EST Monday for paz033>036-
Winter Storm Warning until 8 am EST Monday for paz024>028-056-