Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
543 am EDT Wednesday may 27 2015
high pressure at the surface and aloft will remain anchored just off
the East Coast through the end of this week. A cold front will
likely push across the region Saturday night or Sunday...then
stall just south of the state early next week.
Near term /until 6 PM this evening/...
regional radar loop at 09z shows a dwindling band of showers entering
western PA in associated with approaching shortwave over the Great Lakes.
Expect the weakening trend to continue early this morning...as
blyr continues to cool/stabilize. Latest hrrr/NAM indicate scattered
showers will work into the Allegheny plateau between 09z-12z...then
the central mountains between 12z-15z.
Of greatest concern today will be the expected regeneration of
thunderstorms and rain along front as it enter the susq valley this afternoon during peak
heating. Gefs/sref mean convective available potential energy peak around 1200 j/kg across the southeast
counties this afternoon. This moderate instability...combined with 6km
wind fields around 40kts could support isolated severe weather during the afternoon
hours across the eastern counties. Storm Prediction Center slight risk area runs
roughly east of kipt and khgr.
In general...this will not be the type of rain needed to break US
out of the recent dry spell. Consall model blended quantitative precipitation forecast suggests average
rainfall will range from spotty amts of just a few hundredths over
the central mountains...to around a quarter inch across the lower susq
valley. Higher res...convection allowing models indicate local amts
around an inch from thunderstorms and rain this afternoon across the southeast counties.
Mcldy skies will hold temperatures down a bit...but consall still
suggests high temperatures between the u70s-l80s...several degree above normal
for late may.
Short term /6 PM this evening through 6 PM Thursday/...
southerly ll jet and associated plume of highest precipitable waters /instability will
shift east of the region by this evening. Thus...expect a dry
night for most of central PA. A weak cold front pushing into northwest PA
could support an isolated rain showers late tonight over the central/northern
The weak cold front will be the focus for an possible isolated
rain showers/thunderstorms and rain across southern PA on Thursday. Otherwise...expect fair
and less humid conds...as northwest flow in wake of front advects a lower
precipitable water air mass into PA. Under mostly sunny skies...ens mean 800 mb temperatures
are supportive of maximum temperatures from the u70s northwest mountains...to the M/u80s
across the lower susq valley.
Long term /Thursday night through Tuesday/...
after a brief respite from the humidity Thursday/Thursday night...medium range
guidance signals a return to summerlike weather Friday/Saturday...with
00z gefs showing anomalous 500mb heights and surface pressure off the East
Coast. Developing southerly flow will draw an increasingly
humid/unstable air mass into the area Friday...which may support
scattered diurnally-driven PM convection. However...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.
Aviation /09z Wednesday through Sunday/...
a Summer-time pattern will persist through the week.
Radar continues to be quiet across central PA at 04z...though some
convection beginning to edge eastward across the Ohio/PA border into
west PA. Majority of County Warning Area will remain dry overnight...but some showers
may slip into far western counties from kbfd-kjst after 10z. VFR
conditions have been the rule so far /except at kipt where rain
fell late Tuesday afternoon/ but as sunrise approaches and moist low
level flow picks up a bit...expect MVFR ceilings/visibility to develop over
much of County Warning Area.
Sref model guidance suggests /and even NAM MOS hints/ that the
lower ceilings may linger into late morning from kipt-kmdt before a
return to VFR...middle morning elsewhere. Chances for
showers/isolated thunderstorms peak across western half of County Warning Area between
12-18z...and slide eastward after 16z.
Wednesday...patchy a.M. MVFR fog/br. Scattered showers/tstms.
Thu-Fri...patchy a.M. MVFR fog/br. Isolated p.M. Thunderstorms.
Sat...patchy a.M. MVFR fog/br. Scattered-numerous p.M thunderstorms west/cold frontal passage.
Sun...MVFR ceilings poss northwest. Otherwise mainly VFR in scattered showers.