Area forecast discussion
National Weather Service State College PA
237 PM EDT Thursday may 23 2013
Synopsis...
a cold front will cross commonwealth tonight and early Friday.
An upper low will traverse the region on Friday...providing cool
and showery conditions. Canadian high pressure will build over
Pennsylvania from the Great Lakes and bring improving and drier
weather through the Memorial Day weekend. Temperatures will trend
colder over the next few days...before likely moderating through
the early to middle part of next week.
&&
Near term /through tonight/...
shallow convection in progress across much of the County Warning Area as surface
heating has been meager thus far. Surface temperatures ~15f cooler than 24
hours ago and speed shear is also 15 kts less overall...
accounting for lesser organization and updraft intensity thus far.
Still...upstream clearing is evident in latest visible imagery over
the Laurel Highlands and may aid in destablization for the south
central mountains and lower susq late afternoon and evening.
BUFKIT cross sections only indicate tapping of 15 to 25 kts at
15-20k feet.
Are will continue to be monitored for convective development but
at this time things are looking rather marginal...with brief heavy
rain and pea sized hail the main threats. Some training occurring
over the lower susq River Valley is producing a minor flood threat
over Lancaster County...and may need to be vigilant for additional
developments in the slightly higher shear environment across my
southeast this afternoon and evening...as a plume of above normal
precipitable water along with decent blyr convergence/upper level
divergence are supportive of localized amts approaching 2 inches.
Cooler...more stable air will begin to work into the area later
tonight in the wake of the cold front. Deformation axis pivots
across central and northern PA early Friday morning...continuing
unsettled conditions. Only expecting a few tens of an inch from
this additional rainfall.
&&
Short term /Friday/...
a good chance of rain showers continues Friday as upper low cuts off
and propogates eastward. Cool air behind the surface cold front will
mamke 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
50s...combined with these gusty winds...will likely result in
apparent temperatures in the 40s during the afternoon across the alleghenies.
Brrr...
&&
Long term /Friday 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 has been 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.
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 /19z Thursday through Tuesday/...
numerous showers and thunderstorms this afternoon and evening. Some strong to locally severe
thunderstorms are possible across the eastern 1/3 of the airspace...mainly in
zny sector. Expect mainly VFR conds with occasional MVFR restrictions.
The upper trough will amplify as short wave digs across Virginia on Friday and
may even form a cut-off/closed low. This will result in a low
ceilings and -ra with a breezy north-northwest wind. There is some uncertainty
with how fast this system will exit the area heading into the
weekend. However the worst flying conds should be on Friday with
gradual improvement as Canadian high pressure builds southeastward from the
Great Lakes.
Outlook...
Friday...low ceilings with area of light rain. Gusty north-northwest winds.
Sat-Mon...VFR. No sig weather expected.
&&
Ctp watches/warnings/advisories...
none.
&&
$$
Synopsis...devoir
near term...devoir
short term...devoir
long term...Fitzgerald
aviation...devoir/steinbugl
