Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
514 am 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 /through tonight/...
hrrr/mesoscale models show the batch of rain showers moving across north-central PA
through about 10z. The surface cold front currently moving across Lake
Erie should traverse the northwest mountains by 12z followed by a push of
drier air...which will end precipitation risk for this area through
The trend looks like it will be to the upside for fog/haze and
low ceilings over the lower sqv early this morning based on recent
observation. Moist blyr with middle 60s dewpoints...narrowing dewpoint
depressions and light/vrb winds should all contribute to low clouds
and fog formation/expansion. Some minor adjustments to sky grids
may be in order before sending final ndfd grids. Once the low level
moisture mixes out by middle morning...this area seems prime for at least
scattered convection later this afternoon given combo of best moisture and
instability ahead of weak southeastward-advancing cold front. The front is
forecast to slow/stall near or just south of the Mason Dixon line
tonight and therefore kept very low probability of precipitation in the far southern tier. A
south-southeasterly low level fetch may spell a larger area of low clouds across
south central PA early Friday morning.
Corridor from jst/aoo to unv and ipt should not see much in the
way of precipitation today with frontal passage expected prior to peak heating.
Increased maximum temperatures ahead of the front based on the latest hrrr
which takes readings up to the upper 80s to near 90f in the lower
sqv. Overnight mins will generally range from the low 50s north to
low-middle 60s south.
Short term /Friday through Friday night/...
developing southerly flow will draw an increasingly humid/unstable
air mass into the area Friday...which should support scattered
diurnal PM convection. Friday night will be warm and muggy with
lows in the 60s.
Long term /Saturday through Wednesday/...
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. A better chance of rain showers/thunderstorms and rain comes late
Saturday with approach of a cold front. Some model timing issues
with how fast cold front pushes through Sat night/Sunday.
However...fairly strong signal from all model data that the first
couple days of June /Mon and Tuesday/ will be cool and perhaps
showery...with front stalling out south of PA and potential of
overrunning rain/showers. Have decreased probability of precipitation Friday night into
Saturday...and increased them due to the streaming of moisture out
ahead of the front Saturday night into Sunday. As the boundary
will stall along the southern half of the state have increased
probability of precipitation accordingly.
Aviation /09z Thursday through Monday/...
28/09z...ceiling at bfd dropped to IFR but should be short-lived as
drier air quickly moves in from the northwest in the next 1-3 hours.
Updated lns which went down 2 hours before forecast IFR onset and cut
out IFR at MDT with MVFR looking like the most likely outcome based
on observation trends. No other significant changes at other sites at this time.
28/06z...-shra at bfd should end by 09z followed by a period of
low ceilings. Upstream/nearby observation suggest IFR to even low IFR ceilings and
have low MVFR forecast. Confidence is marginial given favorably light
south-southwest upslope flow and tight T/dew point spread but will update as
necessary. Other trouble spot(s) will be over the southeast airfields in
zny sector with covering of low clouds and fog expanding through
daybreak. Lns went down quicker than forecast and will need to amend.
MDT will likely see a slower downside trend and confidence in IFR is
slightly lower there (vs. Lns). Ipt will be another wildcard and
recently dropped to 2sm. Visbys at jst/aoo/unv should stay at or above
high MVFR range. Once the low clouds and fog burn off...VFR should
prevail into the afternoon with risk of isolated to widely scattered thunderstorms across
the far southern and especially southeastern terminals ahead southeastward
advancing cold front. Limited covering and relatively Low Point-
probability will preclude mention in tafs at this time. The front should
stall near the Maryland border with a developing south-southeasterly flow perhaps
supporting a broader area of upslow low ceilings into Friday morning.
Friday...patchy MVFR fog/ceilings early. Isolated afternoon thunderstorms.
Sat...patchy MVFR fog/ceilings early. Scattered-numerous afternoon thunderstorms west/cold
Sun-Mon...VFR/MVFR conds with scattered showers/tstms.