Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
611 am EDT Sat Apr 25 2015
high pressure ridging into Pennsylvania from the north will help
to maintain dry...cold conditions early today...as a thickening
layer of middle level clouds spreads across the commonwealth. Low
pressure moving from the middle Mississippi to the Carolina coast
will bring the risk of light rain across southern Pennsylvania
later today into Sunday...with the possibility of some wet snow
mixing in across the highest elevations of the Laurel Highlands. A
persistent upper level trough over the northeastern United States
will favor unseasonably cool temperatures through the end of this
month. Heading into the first few days of may another sharp trough
will form over the eastern U.S. With a likelihood of blustery
conditions with well below normal temperatures.
Near term /until 6 PM this evening/...
thickening Alto cumulus and altostratus deck will advance east and
blanket most or all of our forecast area by 12z.
Favorable conditions for radiational cooling of the Earth/S
surface occurred for much of the night across the eastern half of
our County Warning Area and allowed temperatures to tumble...but fall a few degree f shy of
record lows at kmdt and kipt. Record lows of 30f and 26f for this
date at kmdt and kipt are probably safe...but it should be close.
A freeze warning remains in effect through 13z today for the
counties across the southeast...where growing season has begun.
Latest mesoscale observation show temperatures in the upper 20s to lower 30s in the
Rural Valley of the scent and southeast counties...while the larger metropolitan
areas and hilltop ob sites should stay generally between 33 and
35f. This may be the coldest morning until the fall...but early
may may hold a surprise or two based on latest medium range
guidance which shows another deep trough forming over the eastern U.S.
Late in the upcoming week. More on that in the long term section
Initial arm of middle level warm air advection light rain /ahead of a weakening
shortwave trough/ was spreading southeast across northestern Ohio and far southwestern
Penn. Enhanced reflectivities in vicinity of kpit and kcle dual pol radar
sites indicate the low melting layer of only 1000-2000 feet above ground level. This
stratiform precipitation area should continue to dissipate gradually as
it encounters the slightly drier air and NE edge of stronger deep
layer subsidence beneath strong confluent flow aloft. Mentioned a
slight chance for rain/snow showers across The Laurels early
High res model data appears to be dissipating the precipitation shield
quicker than what we/re seeing on the regional radar mosaic loop
at this time. Wouldn't be surprised to see a light coating of snow/pl
across The Laurels this morning. Elsewhere...skies will be mostly
cloudy to cloudy with a few sprinkles /or early morning flurries/
falling in the corridor between rt22 and Interstate 80.
As a nearly east/west belt of -2 to -3 sigma 850 mb east-
northeasterly winds slides across far southern Penn late today
and tonight...rain should become steadier and even fall moderately
heavy for brief periods. Elevations at or above 2400 mean sea level could see some
wet snow mixed in as 850 mb temperatures teeter on 0c.
High temperatures this afternoon will vary from near 50f across the
Laurel Highlands and northern mountains...to between 55 and 60 elsewhere
across central and southern Penn. These forecast maximum temperatures could bust
slightly by being a few to several degree f too high this afternoon.
Short term /6 PM this evening through 6 PM Sunday/...
weakening shortwave and associated anomalous easterly 925-850 mb
flow /approaching from the miss valley/ will likely spread a
shield of steadier /mainly light/ rain into the SW counties toward
evening. Models continue to show a sharp moisture gradient across
southern/central PA tonight.
Will carry Cat probability of precipitation across Somerset Colorado this morning...but carry
no mention of rain from I-80 northward. Only a few sref and gefs
ensemble members bring measurable rain as far north as kunv.
Probability of precipitation decrease from northwest to southeast late tonight/early Sunday...as lg
scale forcing wanes behind the departing shortwave.
However...models indicate lingering fgen forcing/deep layer moisture
along the S tier through sun am...so occasional light rain may linger through
16z Sun Down there.
Long term /Sunday night through Friday/...
wave sliding west-east through the middle Atlantic region along a frontal
boundary will keep mention of primarily light rain in the forecast
heading into Sunday for southern portions of County Warning Area...with precipitation
shield already receding toward the southeast by 12z sun...and exiting
the region by late morning. Consensus of medium range models supports
fair and cool weather for remainder of Sunday...as weak surface ridging
builds southward across PA.
Early next week a shot of cool unsettled weather arrives as a back
door cold front is nudged southward across PA from an upper low
over new eng. Cool temperatures aloft associated with upper low will likely
lead to a good deal of daytime cloudiness and scattered rain showers /esp over
the mountains/ Monday and Tuesday.
By midweek...this low finally lifts out for good. But digging
trough from upper Midwest will extend into the southeast U.S. By
late week...combined with a southern stream shortwave lifting out
of the S plains toward the East Coast will bring possibility of a
developing storm sliding northeastward off the eastern Seaboard.
Track/strength still quite uncertain...but at this time looks like
we/ll be between that low pressure area and a high over Ohio
Valley...likely keeping clouds and scattered showers around as temperatures
cool back down a bit.
Aviation /10z Saturday through Wednesday/...
09z update...lowered ceilings at jst based on radar/observation trends which
show a band of precipitation extending from pit to 2g9. Dry air in the
lower atmosphere seems to be keeping returns aloft for now over the far
SW airspace but will continue to monitor and issue amend if necessary. If
precipitation can reach the ground at jst it would most likely fall as snow
early this morning.
Low pressure tracking south of PA will bring clouds to most of the
area but the bulk of the precipitation will stay south of the region. Expect
flgt cats to remain VFR in the northern airspace. Jst and aoo have the
highest risk for a period of light rain and MVFR ceilings from late this
afternoon through early tonight.
A large upper level low over New England will dominate the
regional weather pattern early next week with several small scale
disturbances rotating around the western periphery of the
circulation center. The models seem to agree that one of these
disturbances will bring a period of showers to the airspace on
Monday. The north-northwest flow should favor the greatest risk of MVFR ceilings
over the northern and western airspace in zob sector.
Tuesday...improving conditions west to east.
Wednesday...generally VFR early with chance of PM showers.
freeze warning until 9 am EDT this morning for paz026>028-035-