Area forecast discussion
National Weather Service State College PA
1114 PM EDT Tuesday Jun 18 2013
Synopsis...
the persistent June pattern of a broad through over the middle-
Atlantic and northeast states is forecast to transition and be
replaced by a summertime upper level ridge migrating eastward from
the plains. A slightly cooler and less humid air mass will follow
in the wake of a cold front tonight into Thursday. Increasing heat
and humidity will arrive on schedule with the official start of
astronomical Summer...and last into the upcoming weekend.
&&
Near term /until 6 am Wednesday morning/...
850 mb the boundary sinking southward across the Laurel Highlands
and south central mountains late this evening. Ruc13 has good
handle on boundary location and near term convection...which it
dissipates by 08z for most. Think given the extent of ongoing
activity and trends that keeping probability of precipitation up into the pre dawn hours
near and south of the Turnpike will be prudent as convection has
out lived its previous expectations.
Subsidence and clearing will cover the northern half of central PA
but will be slower to arrive across the south given latest infrared
trends of additional middle layer moisture streaming eastward from
southern Ohio...in addition to debris from dissipating shower
activity overnight. Also...expect some fog in southern valleys as
well since winds do go calm in many locations. Mins will be chilly
up north...middle 40s for most...while central and southern
sections range through the 50s.
&&
Short term /6 am Wednesday morning through 6 PM Wednesday/...
last shortwave to enhance the trough overhead will run over the
region around sunrise...and then The Heights start to rise
steadily. Surface high pressure finally pushes far enough to the south
and into PA to remove most cloud cover and almost every bit of
probability of precipitation. Will just hang onto a slight chance over the highest terrain of
The Laurels/SC mts where enough moisture and elevated heating surfaces
may combine to pop off a rain showers or two. Temperatures will be a degree or two
lower Wednesday than Tuesday.
&&
Long term /Wednesday night through Tuesday/...
upper ridge over Central Plains will build eastward into PA Wednesday
night through Saturday...as 500 mb heights rise to 588dm. Center
of surface high slips southeast across Great Lakes and is located over
central PA on Wednesday night...setting up ideal radiational cooling
conditions. Dewpoints will still be lingering in the 50s across
southern PA...but much lower dewpoints north of I-80 will allow
temperatures to drop well into the 40s.
Starting Thursday...low level S-southwesterly return flow around surface high /drifting
off the East Coast/ will bring a gradual increase in low level moisture
through the end of the work week...with just a slight chance for an afternoon
pop-up/airmass type thunderstorm on Friday. Otherwise...sunny to mostly sunny
conditions will prevail as temperatures climb to seasonal normals on Thursday
and begin a string of above normal days on Friday.
Heat and humidity continue to increase heading into the weekend as
heights peak. Bigger surge of higher dewpoints slides in from the
west as heat continues to build...so a series of very warm and
humid days are in store for Sat into Tuesday...with overnight lows
remaining quite mild as well. With stagnant air and increasing
humidity on back side of surface high...held on to 20-30 probability of precipitation most
afternoons - with highest chances over western higher terrain of
isolated differential heating initiated storms.
Pattern also has a ring-of-fire look to it so will need to watch
for mesoscale convective system activity/ridge rollers sliding down from the northwest...though
latest models not quite as bullish on that. Ec overall producing
more convection than the GFS...but general areas are similar.
&&
Aviation /03z Wednesday through Sunday/...
A weak surface boundary continues to act as a loose focus for
slow moving showers and thunderstorms over the southern 1/3 of the
forecast area. Most sites will remain VFR into the overnight...but
some MVFR conditions are possible from jst eastward as the showers
meander about. Best chance for reduced conditions will be where it
rained this evening.
Any early MVFR over southern areas will improve shortly after sunrise
leading to widespread VFR Wednesday as high pressure builds out of
the gr lakes.
High pressure will control the weather into the weekend.
Outlook...
Thu-Fri...no sig weather expected.
Sat-sun...isolated PM thunderstorms and rain impacts possible.
&&
Ctp watches/warnings/advisories...
none.
&&
$$
Synopsis...steinbugl
near term...dangelo/devoir
short term...dangelo
long term...rxr
aviation...la corte
