Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
225 PM EDT Sat Jul 30 2016
a plume of deep moisture on the west side of the subtropical ridge
will produce showers and thunderstorms over the region into early
Sunday. A weak trough will push the deep moisture to our east
Sunday. Behind this system it will slowly dry out. A ridge
building to our west early next week will work its way eastward
producing some hot weather later in the week. This surge of warm
air appears to be just ahead of what could be a real cold front
and a real break from the warm weather we have had for the past
Near term /until midnight tonight/...
radar shows several areas of rainfall over the region. An
east-west band along the weak frontal boundary is over the
northern tier counties. Some locally heavy rainfall in this
boundary with 1-3 inches as it drifts slowly to the northeast this
There is a band moving across central regions which is producing
1-2 inches based on sta and mrms data. To the east some scattered
showers area ahead of this and another area of rain is to our west
The air mass is very moist with 1-2sd above normal precipitable water values and
dew points in the east are in the 70s. Cores of heavy rain are
possible. Along the northern tier counties dew points are still in
the low to mid 60s.
The hrrr implies these 3 features move slow east (northern band
drifts northeast). The hrrrv1 and v2 imply that the stuff in
central PA might develop into moderate to severe convection as it
moves into southeastern areas. Some runs now show linear and
possibly bowing segments this afternoon from Franklin County east.
Areas under these bands could see moderate to heavy rainfall and
embedded thunderstorms of course. Put moderate rain shower and thunder with
heavy rain in the grids 17 to 03z.
Short term /midnight through 6 PM Sunday/...
the NCEP hrrrv2 appears to get 80 percent of the rain out of our
area by about 0500 UTC. Rain should taper off west to east this
evening and tonight with most of the steady rain to our east a few
hours either side of midnight.
The larger scale models still have moisture lingering and a slow
drying trend. Thus they still produce afternoon convection and
nearly all have some quantitative precipitation forecast. Kept pops lower than the model blends as
they have a significant wet bias. But heating Sunday will likely
produce at least a chance of showers and thunderstorms.
Long term /Sunday night through Friday/...
short-waves sweeps to the coast but broad upper level trough
lingering across PA. The main trough axis lies through central PA
by 12z Monday and slowly progresses east through the day. With
the trough and cyclonic flow aloft scattered showers/isolated
thunderstorms are possible with best chances over the eastern
counties in the afternoon. High pressure builds in Monday night
and everything begins drying out. For Tuesday into Wednesday a sharp
upper level ridge is to our west over the Great Lake region with
the trough now off the coast, dry northwest flow and surface high
pressure across the region.
Short-wave weakens the ridge into Thursday. European model (ecmwf) takes this south
across Ohio into Virginia leaving PA dry. GFS is weaker and further
north with some convection over the PA mountains which it moves
east across PA through Thursday night. Stayed closer to the European model (ecmwf)
solution with no pops at this point. Both models agree on a more
rigorous cold front dropping southeast toward PA on Friday. This
will help surge the temperatures and humidity up ahead of it over
central PA Friday. Right now the timing is such that late day
convective storms will feed off the days heat and humidity and
roll through late in the day into the overnight. Models bring the
cold front southeast across PA overnight and then stall it near
the Mason-Dixon line for Saturday.
Aviation /18z Saturday through Thursday/...
showers and thunderstorms are slowly moving across central
Pennsylvania and there is a weaker line of showers near the New
York border. Showers and thunderstorms will lower ceilings and
visibilities to IFR at times. Some of the storms in southern PA
will have heavy rainfall at times with them.
There could be some winds shear near the storms and the outflow
from the storms.
Overnight the rain and shower activity diminish. Rapidly in the
00 to 03 UTC range. But the moisture air with recent rainfall
favors fog and patch dense fog in valleys. Lots of IFR after
Fog Burns to haze early Sunday mainly VFR and MVFR by mid-morning.
Could be showers/thunderstorms in the afternoon Sunday. Far fewer
Outlook... sun- Monday...morning fog restrictions, then scattered
showers and isolated thunder. Tuesday- Wednesday...mainly VFR, but with
morning fog restrictions.