Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1018 PM EDT Friday may 22 2015
A large area of high pressure will bring US the coldest night
we are likely so see until October. A gradual warming trend is
forecast to begin over the weekend...with warm and humid
conditions in store with a chance of a shower or thunderstorm each
afternoon during the Tuesday through Friday period.
Near term /until 6 am Saturday morning/...
Winds are dropping off over the northwest and the temperatures are already down
in the lower 40s. Previous reasoning looks good with the wind
dropping off in most areas allowing for a late Spring frost/freeze
under nearly prime radiational cooling conditions.
Lows will drop to the 33 to 36 range over the Central Ridge-
valley areas. A hard freeze is expected across much of the
northern mountains where temperatures will bottom out in the middle to upper
20s in many locations. Wouldn't be surprised to see a few coop
observers and mesoscale ob sites come in around 20f across portions of
McKean...Elk and Potter counties.
The Laurel Highlands will teeter around the 32f mark at sunrise
Saturday...but most of the population there should see lows of
33 or 34f with frost almost a certainty.
These cold temperatures will approach or drop below record lows in many
locations. The most likely area to just escape a record low by
1-3 degree would be the lower susq valley...where a light northwest breeze
could persist until well after midnight. Lows there will be in
the u30s to lower 40s. Some rural cold spots could see patchy
frost with a Sat morning min of 35 or 36 degree.
Short term /6 am Saturday morning through Saturday night/...
high pressure over the commonwealth Sat morning will drift southeast to
the Delaware-Maryland-Virginia coast by Sat evening. Very low precipitable water air of only
around 0.25 inch and large scale subsidence will lead to abundant
sunshine with light wind.
Maximum temperatures in the middle 60s north...to around 70f in the south will
still be a few to several degree f below normal.
Some thin high clouds will drift in from the west late Sat night
with a light southwest wind. Temperatures will be quite cool again Sat
night with lows in the middle 30s to lower 40s. A few places in northern
Penn could see a patchy light frost toward daybreak Sunday...but
nothing close to what/S in store for early Saturday.
Long term /Sunday through Friday/...
after a cool start...Sunday Marks the beginning of a robust warm-
up that will continue through next week. All guidance signals this
warming trend...with high confidence in above normal temperatures
by Memorial Day as anomalous 500mb ridge builds over the eastern
Some differences on placement of a warm frontal zone lifting northward
from the Southern Plains/lower MS valley which will have impacts on precipitation
risk early next week...though best daily probability of precipitation will be over the northwest.
Dewpoints on Sunday will be still in the 40s. Hard to see much
chance of any showers. Better chance of showers north of PA...in
area of better warm advection.
Dewpoints will be mainly in the 50s the first part of next week
for most of the area. Southeast PA will likely see dewpoints in the
60 to 65 degree range...but not really that high for late may.
At the same time...500 mb heights come up...as the upper level
Warm front also forecast to lift well north of the area on Tuesday.
Thus based on these factors and other factors...did lower
probability of precipitation some...and edge temperatures up a degree or so.
Overall...not looking at temperatures or dewpoints as high
as recent events. Thus a nice Holiday weekend in store for the
area...and not a bad period of late Spring weather next
week...enjoy the Holiday weekend.
Aviation /02z Saturday through Wednesday/...
gusty west-northwest winds 20-30kts will gradually weaken through 03z with light
and variable winds expected late tonight through Saturday as high
pressure builds across the airspace. Widespread VFR conditions
will continue through Sunday as high pressure shift off the middle Atlantic
Mon-Wed...VFR with isolated/low risk of thunderstorm impacts.
freeze warning until 8 am EDT Saturday for paz004>006-010>012-
Frost advisory until 8 am EDT Saturday for paz019-024>028-033-
near term...la corte