Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
256 am EDT Sat Sep 20 2014
after a brief period of clouds and patchy drizzle this
morning...fair weather is expected for the second half of the day.
A frontal system will bring scattered showers to the region on
Sunday. Another large area of high pressure and a blocking upper-
level ridge over central Canada will bring additional fair and
cool weather for most of next week.
Near term /until 6 am this morning/...
clouds continue to expand on schedule and in line with current
forecasts. Expect these clouds to continue to lower and become more
widespread overnight as the long fetch off the Atlantic ascends
the mountains of central PA. While the drizzle/fog may not be
quite as bad as advertised...the ridges will still be shrouded
and misty and care will need to be taken when traveling over the
Short term /6 am this morning through 6 PM Sunday/...
the winds should continue to veer today and help the temperatures
warm and allow the low clouds to break up through the morning and
early afternoon. After the cloudy start...temperatures will rebound
nicely in the afternoon with maxes rising into the 70s for most
places - especially in the valleys of the southeast where there should be less
cloud cover. Will hold the temperatures around 70f along The Spine of the
mountains where the clouds will take longest to break.
Long term /Sunday night through Friday/...
all of the guidance shows a frontal system moving northwest to
southeast across the state overnight Saturday into Sunday evening.
This is most likely the only rain event that should affect the
region of the next 7-12 days as a blocking 500 hpa ridge with over
2 sigma height anomalies should provide a prolonged period of dry
At this time the models and ensembles all imply an increase in
shower activity after midnight northwestern Pennsylvania and
toward sunrise in central areas early morning. The gefs and sref
both imply the 12 hour period for the best rainfall will be
between about 8 am and 8 PM Sunday. The rainfall lingers in the
ensemble pdf until between 8 and 2 am Sunday night into Monday in
the east. The rapidly lowering precipitable water field implies all rain gone in
east after midnight Sunday.
At this time the higher probability of precipitation and higher qpfs should be in the
northern areas. Few members of any efs show much more than 0.25
inches with perhaps 40 percent showing 0.50 inches in the northern
areas. Most qpfs imply a 0.10 to 0.20 inch rainfall event. Kind of
anemic. Did mention thunderstorms as there is a warm surge and
some hints of modest cape in the higher resolution models and efs
perhaps 600 to 800jkg-1. Lower in the gefs. A few thunderstorms
could boost qpfs up a bit if they appear.
High pressure builds in Monday behind the front and sort of Parks
itself over New York and New England with +2 to +3 sigma above
normal mslp anomalies by Wednesday-Thursday. High confidence in
this forecast as the models all show a blocking 500 hpa
anticyclone to the northwest as a massive 500 hpa positive height
anomaly of +2 to +3 sigma develops over central Canada by Thursday
and into Friday.
Our models and efs do well forecasting anticyclones. So I am
high on the fair weather forecast next week.
Only fun issues are how much rain Sunday and how sunny will it get
behind the front Monday. Did not attempt to draw the diurnal fog
and low clouds likely to affect the region once the big high takes
hold. This will be a nearly ideal diurnal fog pattern Wed-Sunday.
Aviation /07z Saturday through Wednesday/...
surface high pressure exiting well east of the New England coast...and
a cold front moving across the upper glakes today will create a
light to moderate southerly breeze of 8-10 kts today with some
gusts into the lower 20 kts range this morning as the axis of a
35-40 knots southerly 850 mb jet shifts east across the region.
Early morning 11-3.9 micron satellite loop shows an extensive
area of MVFR stratus entrenced across the Central Ridge and valley
region of Penn...along with the northern mountains of the state.
Kbfd and jst have recently entered into this MVFR realm as the
low level moisture is pushed northwestward across the Allegheny Front.
Expect the potential for fluctuation between MVFR and VFR near the
rt 219 corridor from kbfd...south to kfig and kjst through
13z...while all other central and eastern Penn taf sites stay stuck
well into the MVFR ceiling range. Periods of MVFR visibilities will all
occur...mainly impacting the susq valley airfields. Patchy light
drizzle is possible through the middle morning hours...primarily on
the upslope...southeast faces of the ridges.
Low level wind shear will be likely over all central Penn and susq valley
airfields early this morning. The base and bulk of this sheared
layer will occur within the upper half of the stratus cloud deck.
Southerly winds in the 1500-2000 feet above ground level layer will be blowing at
30-35 kts through about 13z.
After 13z today conditions will steadily improve and become VFR
in all locations by 15z...with broken strato cumulus based around
4500-5000 feet above ground level. VFR expected to continue for most of the night
followed by areas of MVFR ceilings /and visibilities in light fog/ after 07z
sun...am fog possible eastern PA. Slight chance of PM thunderstorms and rain impacts West Mountains
Monday...am low ceilings poss West Mountains
Tue-Wed...no sig weather expected.
near term...dangelo/la corte