Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
202 am EDT Tuesday may 26 2015
high pressure off the East Coast will keep a warm and increasingly
humid airflow in place for much of the upcoming week. A strong
cold front will push across the state Saturday afternoon or
night...ushering in cooler and less humid conditions for the
remainder of the weekend.
Near term /until 6 am this morning/...
deep southerly flow on western periphery of East Coast ridge is
transporting Gulf of mex moisture northward into western early
this morning. Sat-derived precipitable waters near 1.7 inches across
northern/western PA at 06z. Regional radar at 06z showing scattered rain showers
developing in this moist air mass in advance of a middle level vorticity maximum
lifting NE out of southern Ohio. Based on radar trends and latest
hrrr output...will carry chance of rain showers across roughly the northwest half
of the County Warning Area early this morning. For areas south and east of
kjst/kunv/kipt...the pre-dawn hours should remain dry.
Have tweaked overnight mins a bit based on mcldy skies expected
across the northwest counties. Lows in the l/m60s expected for the entire
Short term /6 am this morning through 6 PM Wednesday/...
precipitable waters continue to rise through the short term and will get above
1.75 inches by Tuesday afternoon. The deep southwesterly flow will
transport remnant mesoscale convective vortex/S and clusters of showers/scattered thunderstorms and rain from the
very active Southern Plains states and lower miss valley convection.
These weak and difficult to capture features will trigger
some rain showers/thunderstorms and rain as they cross the area. Models have a tough time
capturing/timing the impacts of such weak shortwaves during the
overnight and morning hours...while forecasts of peak instability
during the afternoon hours provide much greater confidence in at
least scattered rain showers/thunderstorms and rain between 17z-01z.
Storm Prediction Center continues to paint a marginal risk up and over the western half to
two-thirds of the County Warning Area for day 2 - Tuesday afternoon and Tuesday night.
Will mention this in the severe weather potential statement.
Mean sref convective available potential energy top out between 1500-2000 j/kg 18-23z
Tuesday...and 0-3km shear is weak-MDT with a generally linear
profile. A few marginally severe multi-cell thunderstorms and rain are possible
Tuesday afternoon/evening across the County Warning Area.
Maximum temperatures may actually be a degree or two cooler on Tuesday with more
clouds than we had during the day today /Monday/.
High chance probability of precipitation will be painted Tuesday with a widespread 40-50 percent
over most of the area. Will keep them lower in the southeast - where they
will be farther from the forcing and under warmer temperatures aloft and
more suppressive influence from the nearby upper ridge axis .
Long term /Wednesday night through Monday/...
the middle to long range models continue to show agreement in
position and movement of the upper level ridge. The low will
continue to dig into the Great Lakes region...and a line of
showers and thunderstorms should form out ahead of the approaching
cold front. Expect moist southeasterly flow to continue Wednesday
into Thursday. Precipitation chances should increase Wednesday and
The models begin to diverge throughout the latter half of the
week and into next weekend. There should be a boundary that could
persist across the New York border...which could bring daily
chances for rain through the weekend. The models continue to trend
cooler temperatures and have adjusted maximum and min temperatures as
such...but expect temperatures to remain above normal through the work
Aviation /06z Tuesday through Saturday/...
isolated shower activity has shifted into western New York with no impact to
bfd. VFR should continue at most sites over the next 24 hours.
Highest confidence in brief 1-3hr period of 3-6sm visibility
restrictions in br/haze is at MDT/lns around daybreak Tuesday.
Given relatively low probability/expected coverage...decided not
to explicitly mention thunderstorms in terminals at this time. Later
issuances should introduce a thunderstorms in the vicinity from group with either the 06 or
A Summer-time pattern will persist through the week with replay of
patchy morning fog giving way to VFR and afternoon isolated-scattered thunderstorms. A
more defined thunderstorm risk should arrive by next weekend as a cold
front presses southeastward from the Great Lakes.
Tue-Fri...patchy a.M. MVFR fog/br. Isolated-scattered p.M. Thunderstorms.
Sat-sun...patchy a.M. MVFR fog/br. Scattered-numerous p.M thunderstorms west/cold