Area forecast discussion
National Weather Service State College PA
214 am EDT Thursday may 23 2013
Synopsis...
an amplifying upper-level trough and its associated cold fronts
will cross the northern Middle-Atlantic States over the next 48
hours. Canadian high pressure will build southeast from the Great
Lakes through the Memorial Day weekend. The overall pattern will
be unsettled through Friday with improving conditions expected
during the weekend. Temperatures will trend colder over the next
few days...before likely moderating through the early to middle
part of next week.
&&
Near term /until 8 am this morning/...
regional radar loop shows lingering convection across the eastern
half of the state has largely dissipated...as blyr cools/stabilizes.
However...lg scale forcing ahead of shortwave over the Ohio Valley
is supporting a broken line of shra/tsra...which is just entering
western PA at 05z. This middle level feature is prognosticated by model data to
weaken as it lifts into PA between 06z-12z...so for the overnight expect
the best chance of a rain showers/thunderstorms and rain to be over the West Mountains between 06z-09z.
Plenty of middle level cloudiness ahead of aforementioned shortwave
should reduce the chance of radiational fog...despite wet ground and
light winds. Cloud cover and plenty of low level moisture should
result in cooling of only a few degree for the rest of the night with
min temperatures in the l/M 60s.
&&
Short term /8 am this morning through 6 PM Friday/...
area remains in Storm Prediction Center see text outlook Thursday. Generally weak
instability is prognosticated in the pre-frontal warm sector...and will
be dependent on the extent of any prefrontal warming/partial
clearing. Moderate shear present which could promote a few
stronger storms ahead of the front Thursday afternoon...especially
east.
Continued eastward progression of the expansive eastern Continental U.S. Trough is
expected this period...however it may be at slower pace as some
model data is trending slower/sharper by the end of the period.
The attendant cold front will traverse the area during the afternoon
and evening before exiting the eastern part of the County Warning Area around
midnight.
A lighter...deformation precipitation axis is prognosticated to set up over the
area Thursday night into Friday as a shortwave embedded in the larger-
scale trough digs from the Great Lakes toward WV. There are some notable
model diffs heading into day 3 surrounding the depth and speed of
the 500 mb trough crossing the middle-Atlantic region. More on this in the
long term section.
&&
Long term /Friday night through Wednesday/...
expect plenty of clouds and light rain in the deformation zone on
Friday...with temperatures falling back to 55-65f. A bit of a range due
to the model variability and have gone with the Mode and trended
toward the European model (ecmwf) solution as it would linger light rain over the area
/esp in the east/ into Saturday...but did not fully buy-into this
given how strong it was with the closed 500 mb low compared to the
other global guidance. Canadian high pressure extending southward from
Nunavut into the upper Midwest will shift eastward across the Great Lakes
and eventually take up residence over the northeast by Memorial
Day. Ens data continues to show negative thermal/moisture anoms
supporting an unseasonably cool and dry weekend with the potential
for frost in the northern and western mountains Sat/sun am. The growing season
is underway in this area /as of may 20th/ and therefore will
continue to mention frost in severe weather potential statement. Elsewhere low temperatures will be
chilly by late-may standards...but not quite cold enough for
frost.
Q-stnry/warm frontal zone initially centered from Iowa-WV should
slowly return northward through the Ohio Valley early next week. GFS/ec diffs
in the pattern evolution continue into the end of the medium range
particularly upstream. In general...there should be a gradual
early-middle week warming trend with heights rising as the upper trough
continues to move away from the northeast.
&&
Aviation /06z Thursday through Monday/...
5/23/06z...
lg scale forcing associated with approaching upper-level trough and
surface cold front impinging on Reservoir of above normal moisture
over the region will result in numerous showers today. Some strong to
locally severe thunderstorms are also possible across the eastern 1/3 of the airspace.
Expect mainly VFR conds with occasional MVFR restrictions. Highest
confidence in MVFR near-term is over the eastern terminals with the
development of low ceilings/fog during the 08-15z timeframe. Most of
the precipitation through 12z should be across the western terminals in zob sector.
The upper trough will amplify as it digs across Virginia on Friday and may
even cut-off as it reaches the Delaware-Maryland-Virginia/southern middle-Atlantic coast. This
will result in a cool stratiform -ra with a breezy north-northwest wind. There
is some uncertainty with how fast this system will exit the area.
However the worst flying conds should be on Friday with gradual
improvement into the weekend...as Canadian high builds southeast from the
Great Lakes.
Outlook...
Friday...low ceilings with area of light rain. Gusty north-northwest winds.
Sat-Mon...becoming VFR. No sig weather expected.
&&
Ctp watches/warnings/advisories...
none.
&&
$$
Synopsis...steinbugl
near term...Fitzgerald
short term...devoir/steinbugl
long term...ceru
aviation...steinbugl
