Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1100 PM EDT Thursday may 28 2015
Summer-like conditions with above normal temperatures will come
to an end by the end of the month as a cold front moves across
central Pennsylvania this weekend. The frontal passage will
likely be accompanied by showers and thunderstorms. The front is
expected to stall near the Mason Dixon line which should favor a
cooler weather pattern to start the month of June.
Near term /until 7 am Friday morning/...
all radar returns staying south of the Maryland border. Lower susq sies
may see light fog in the morning as it should be mainly clear - at
least early - with dewpoints a bit higher than elsewhere in the
County Warning Area. Surface winds may start to veer around to the southeast-S by the end of
the night and be around 10 miles per hour over the high terrain of The
Laurels. Will go with none probability of precipitation. Interesting creeping lower-VFR
clouds just into southern Somerset Colorado now. Will increase cloud/sky
cover for overnight using concept of upslope southeast winds coming from
area which had some showers earlier today and NAM relative humidity profile as a
guide. Most of the moisture is well-aloft though. While the mesoscale
models continue to generate some convection in the far southeast...have to
discount it based on the over- done coverage forecasts they had in for
this afternoon/evening over PA and no surface instability. S/b a
comfortable night for almost all the area.
Short term /7 am Friday morning through 6 PM Friday/...
the aforementioned return southerly flow will draw the
humid/unstable air mass back into the area Friday...supporting
scattered diurnal PM convection. Light winds beneath upper level
ridge should result in northward-drifting pulse type thunderstorms and rain with
little threat of severe weather. Model soundings support maximum temperatures in the
l80s most places...with the greatest departures from average across
Warren Colorado due to downsloping south-southeast flow. Best chance of convection
will be to the west closer to the ring of fire...and over
elevated heat sources Friday afternoon. Highs will range through the
lower to middle 80s from north to south.
Long term /Friday night through Thursday/...
high pressure at the surface and aloft will allow for subsidence once
daytime heating diminishes Friday evening. There is a slight
chance for topographic forcing to allow for a slight chance of
precipitation Friday night into Saturday through the central and
northwestern mountains. The rest of Friday night should be fair and
summerlike with high dewpoints allowing temperatures to fall only into the
Medium range guidance signals a continuation of summerlike weather
into Saturday...with 12z gefs showing anomalous 500mb heights and
surface pressure off the East Coast. However as Saturday continues the high
will be shifted eastward and a large upper level trough will move
a fairly strong boundary through central PA. The models vary in
the timing but there will be a better chance of rain showers/thunderstorms and rain by middle to
late Saturday with approach of a cold front. The larger model
timing diffs have been resolved with model consensus now pushing
cold front through Sun morning.
In wake of the front...a couple days of cloudy...cool and showery
weather appears on tap for central PA with front stalling out south of
PA and a likelihood of overrunning rain/showers. Anomalous
easterly flow/precipitable waters indicated in 12z gefs over central PA between
surface high over new eng and front to the south. In addition to the
moisture...central PA will remain in favorable jet entrance region
sun-Mon..providing the lg scale forcing to support periods of
rain sun-Mon..12z gefs mean quantitative precipitation forecast between sun-Monday ranges from 0.5 to 1
inches. The models have shifted the timing of the moisture pool
shifting it south of the Mason Dixon. This however comes in
conjunction with an influx of colder air as a surface high builds
over eastern Canada.
Have continued to lowered the maximum temperatures through the first half of
next week and lowered probability of precipitation accordingly. Improving conds appear
likely through most of the work week as upper ridge continues to
build and expand northward into PA.
Aviation /03z Friday through Tuesday/...
03z taf update.
No major changes made.
Mainly looking at some high clouds overnight. Most areas should
remain VFR. However...dewpoints higher at lns...thus added some
fog to the forecast from 10z to 13z Friday morning.
Some showers possible far western areas later on Friday...thus
have vcsh in for bfd and jst.
Sat...patchy MVFR fog/ceilings early. Scattered-numerous afternoon thunderstorms west/cold
Sun-Tue...VFR/MVFR conds with scattered showers/tstms.