Area forecast discussion
National Weather Service State College PA
247 am EDT Friday may 24 2013
Synopsis...
a cold front will push across central Pennsylvania and the
Susquehanna valley early today. An upper low will traverse the
region during the day today providing unseasonably cool...showery
and quite breezy conditions. Canadian high pressure will build over
Pennsylvania and bring drier weather on Saturday which should last
through rest of the Memorial Day weekend. Temperatures will trend
colder over the next few days...before moderating through the early
to middle part of next week.
&&
Near term /until 8 am this morning/...
strong...surface cold front extended from The Finger lakes region of New
York...south-southwest to the Laurel Highlands. Temperatures were in the u50s to l60s
ahead of the front...across roughly the southeast half of Penn at 06z...and
sliding through the 50s across much of the Allegheny plateau. Temperatures
have dipped into the lower to middle 40s across extreme northwestern Penn...and
the mean 925-850 0c wet bulb line is along the North Shore of Lake
Erie.
Scattered rain showers will be drifting east or northeast across the
entire County Warning Area through the middle morning hours as the cfront /and strong
diff positive vorticity advection in its wake/ moves over the region.
900-850mb wet bulb temperatures will fall to -1 to -2c across the northern and
western mountains of Penn beginning in the 09-12z period...and remain there
through 16z before moderating a tad this afternoon.
05z GFS lamp guidance and 00z NAM indicates the potential for some
wet snow to be mixed in with the showers across mainly elevation at or above
1800 feet mean sea level across The Laurels and northwest mountains during the middle to late
morning.
Only expecting a few hundredths /to perhaps one tenth of an inch of
additional rainfall in a few locations/ through the middle morning.
Temperatures will dip into the upper 30s for several hours during the late
morning and midday hours across the northern and western mountains before
rebounding a bit this afternoon. The Mercury will slowly fall to the
upper 40s and lower 50s across the central mountains temperatures currently in
the lower 60s across the susq valley...will slowly fall into early
this afternoon...reaching the lower to middle 50s...then stay steady
for the rest of the day.
&&
Short term /8 am this morning through 6 PM Saturday/...
showers will gradually diminish by this afternoon in the west...but
will be likely for most of the day across the eastern half of the County Warning Area
as the upper low cuts off and propagates eastward. Cool air behind
the surface cold front will make for a very unpleasant day. Kept highest
probability of precipitation across the north central mountains in anticipation of orographic
enhancement along The Spine of the Appalachians. The arrival of much
drier air wrapping into the west side of developing cut off may shut
off any showers early in the day across Warren Colorado.
Well channeled northwest flow and a tightening surface pressure
gradient will result in a blustery day for late may. Northwest winds
should gust between 25-30kts during the afternoon. Temperatures in the 40s and
50s...combined with these gusty winds...will likely result in
apparent temperatures in the 30s during the afternoon across the
alleghenies...and 40s elsewhere. Brrr...
&&
Long term /Saturday night through Thursday/...
main concern Friday night will be the potential of frost/freeze
headlines across the Allegheny plateau. Aforementioned pressure
gradient appears likely to keep the winds up Friday night...so
widespread frost seems unlikely. Hard to believe there will be a
widespread freeze this late in the season without a calm wind...so
have leaned on the warm side of MOS /closer to ec MOS/ and kept
temperatures just above freezing for most of the West Mountains Friday night.
Model trend continues to slow eastward progression of upper
low...so have kept mention of rain showers in the forecast through Friday night
across the eastern zones...and tapered them off later across the
central counties.
Eastern PA will remain on western periphery of upper low Sat/Sat
night. So...have increased the cloud forecast a bit over the eastern
counties and can/T completely rule out a stray rain showers over Sullivan
or Schuylkill Colorado. Elsewhere...confidence in a mostly sunny Saturday is
fairly high...as all model data pulls low precipitable water air southward across
central/western PA on Sat. However...despite strong may
sunshine...model 800 mb temperatures well blw normal should cap readings in the
l/M 60s across much of the area...with highs in the u50s likely
across the high terrain. Deep mixing should draw some gusty winds
to the surface again on Saturday. 800mb wind fields suggest much of
the area will see gusts between 25-30kts by afternoon.
Bulk of medium range guidance continues to indicate a high degree of
confidence in dry weather holding through Memorial Day...along with a
gradual warming trend...as upper low over new eng slowly lifts away
from the area. The models have slowed the progression of the
exiting low...so with northwest flow and colder air over the region with
light winds...there remains a chance for frost over the northwest mountains
Sunday night/Monday morning. The rest of the regions will be in
the low 40s.
By the middle of next week...a building upper level ridge is
advertised by the medium range guidance over the miss valley. Across
the east...surface high will pass off the coast...resulting in a
warmer SW flow. Some model diffs with respect to how fast the low
level moisture returns. However...have gradually introduced a chance of
diurnal convection in the Tuesday/Wednesday time frame.
&&
Aviation /06z Friday through Tuesday/...
an unseasonably strong/deep upper-level trough will rotate eastward
from the lower Great Lakes/Ohio Valley through the middle-Atlantic and northeast
states over the next 48-72 hours. A cold and blustery north-northwest flow
will accompany widespread stratus/stratocu with MVFR and IFR conds
continuing through the first part of today. Peak wind gusts this
afternoon will top-out in the 25-35kt range...with the highest gusts
forecast at MDT/lns. Given the anomalous pattern...guidance may be too
quick with improving ceilings although shallow mixing and dry air
advection should lift bases out of IFR range. VFR/MVFR ceilings late
today will eventually give way to a prolonged period of VFR flying
over the Holiday weekend...as Canadian high pressure drifts southeastward
from the Great Lakes.
Outlook...
Sat-sun...VFR. Gusty northwest winds.
Monday...VFR. No sig weather expected.
Tuesday...scattered PM thunderstorm impacts possible.
&&
Ctp watches/warnings/advisories...
none.
&&
$$
Synopsis...dangelo/Lambert
near term...dangelo/Lambert
short term...devoir/Lambert
long term...Fitzgerald/ceru
aviation...steinbugl
