Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
206 PM EST sun Feb 1 2015
low pressure will move up the Ohio Valley tonight...and cross the
state on Monday. This will produce widespread wintry precipitation
across the area into Monday morning. A period of freezing rain is
likely across the southern and central sections of the state
overnight. Another shot of Arctic air will follow for Monday
afternoon into Tuesday...with low wind chills Tuesday morning. A
cold front moving through Wednesday will be accompanied by some
light snow...mainly in the northwestern half of the state.
Near term /until 9 PM this evening/...
pretty solid band of warm air advection snow is pushing through western PA but not
much behind it. Mesoscale models have been playing that break up for a
little while...and it looks like it is coming to fruition. This
will yield a 3-4 hour break in the snow for most places. While it
has been snowing all day out the window...it still really has not
started sticking to anything. This appears to be the case almost
everywhere in the County Warning Area judging by web cams. But the higher elevs of
The Laurels should be getting white any time now. Will just work
the probability of precipitation around to try to show that Little Break...but it is such
a small-scale feature that it may just end up washing out in the
bigger picture. Temperatures dancing around 32f in the central cos but
well into the m30s in the southeast. Precipitation there will be very light
until much later/this evening. So...p-type will be difficult to
pin down. Certainly if it decides to snow heavily...it will be
snow for that time...but will likely be a mix when light in the
S/se. Temperatures move little all evening...but will probably cool just
a little with wet bulbing. Dewpoints already rising some locally.
Short term /9 PM this evening through 6 PM Monday/...
the best period of snow continues to look like it will be between
00-09z with the worst of it across the northern half of the area. The
warm air aloft looks to make in-roads all the way to I-80 by
sunrise Monday. Thus...the icing potential is still there. So
while the snow amounts - especially if you only measure in the
morning - will be lower than previously advertised in the southern half
of the area...there is still some /weak/ justification for holding
onto the warning along the rte 22 corridor...for now.
The quantitative precipitation forecast is a mixed-bag of signals right now. GFS and Euro are
holding onto 0.80 or more in the northern half of the area...with only
real snow there. The NAM and the sref mean totals there are only
about 0.50. Will continue with the party line of 8-10 for a storm
total...but reworked the numbers down barely an inch on the whole
so the terrible dark blue of 10-14 does not hit people in the
face. Again...just half an inch to an inch of a downward move on
the snow. This is due to the relatively high uncertainty at this
range. Still looks like a solid warning any way you slice it up
for our entire northern half. Some pretty wicked sf rates will be had
overnight and very early Monday in the north and perhaps as far S
as State College and Sunbury but most likely - the heaviest snow
will be just to the north of those two cities.
Precipitation cuts off pretty quickly after 12z/14z in the central cos.
The east may see precipitation linger into the middle morning as the cold
air moves in and temperatures drop. After what may only be a brief
break...the northwest winds will upslope into the alleghenies and
laurels. Cold air advection will create numerous shsn over the western high terrain
and flurries elsewhere. There may even be some decent shsn as the
precipitation ends in the southeastern third of the area. Yet another reason to
not monkey with the warnings/advisories just yet. It could be a messy
commute for groundhog morning. Winds will get strong and rather
gusty - especially on the hill tops and in the southeastern third/downslope areas
closest to the deepening low moving off the coast.
Long term /Monday night through Sunday/...
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 /19z Sunday through Friday/...
deteriorating flying conds expected this afternoon and evening...as low
pressure approaches from the Midwest...spreading snow and lowering
ceilings across central PA. At 17z...IFR conds already noted across
western PA. Upstream radar returns and latest hrrr output suggests
IFR conds will develop at kaoo/kunv/kipt between 19z-21z. Across the
southeast counties...latest model data suggests a band of light
snow/visible reductions could come through between 22z-01z at kmdt/klns.
However...confidence in IFR conds will increase markedly at
kmdt/klns between 03z-06z...as heaviest snow arrives.
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. Marginal low level wind shear remains
a possibility late tonight across southern PA...as core of strong
winds aloft slides across the area. However...latest model
soundings suggest most places will remain just blw criteria.
Marked improvement is expected between 15z-18z Monday...as low pressure
passes east of the area...and drier northwest flow develops. Focus will
shift toward strong gusty winds Monday PM. Gusts to around 40kts are
possible Monday afternoon and evening...as strengthening storm system
passes east of PA.
Monday...am rain/snow and low ceilings. PM gusty northwest winds.
Tuesday...no sig weather expected.
Wednesday...am light snow possible northwest mountains
Thursday...am light snow possible.
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-