Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1220 PM EDT sun Jul 13 2014
a strong upper level trough will drop into the upper Great Lakes
by Monday. A pair of surface cold fronts associated with this
trough will push southeast and bring several rounds of showers and
thunderstorms to the region over the next 36 hours. Cooler and
drier air will move into the commonwealth for the middle to late week
Near term /until 6 PM this evening/...
the nose of stronger 35 to 40 kts southwesterly low level winds and 2 inch precipitable water
air /associated with a warm front/ will slide across northwestern Penn
through this afternoon. This axis of higher wind and moisture
will shift a bit further south and east late this afternoon.
Pockets of moderately high surface based instability will develop and
combine with the anomalous 850-700 mb winds to bring the threat of
scattered strong to severe thunderstorms and rain this afternoon and early this
Convective available potential energy this afternoon could top 1500 joules. Storm Prediction Center has almost the entire
area in the slight risk area today into tonight. NAM 0-1 km ehi
values peak between 2-3 m2/s2 across the ncent mountains 17-20z...then
shift to the middle susq valley and adjacent areas of ecent Penn
20-22z. These will be the areas of greatest concern for a few
supercells...and perhaps 1 or 2 brief tornadoes. Otherwise...mini
Bow echoes with localized damaging microbursts will be the most
probable type of severe weather this afternoon and early this
evening. More scattered...multi-cell /or perhaps a brief
supercell/ thunderstorms and rain is anticipated across the southeast half of the County Warning Area.
Rainfall could be heavy across the northern tier...but the fast
35-45kt east-northeast movement of the cells will make it difficult for any
one or two bursts of rain to cause flooding. However...
multiple/repeated storms are likely in the northwestern half of
the area through the near term...and this may cause local
poor drainage and small stream flooding. Ffg/S continue to be
rather high and serious problems/flash flooding is not anticipated
at this time. Locally heavy rain near Lebanon and Lancaster has
lowered flood guidance there...but the storms will be more-
scattered around that particular area today.
The thickness/persistence of the cloud cover today will be the
trick to where temperatures go. Due to the clouds and anticipated
convection/rain - will hang with continuity and add about 10f to
the current temperatures in the northwest and about 15f to the current temperatures in
the southeast for maxes today.
Short term /6 PM this evening through 6 PM Monday/...
convergence will concentrate from jst-unv-ipt this evening...and
only sink slowly to the south. But this first shot of cooler air
from the northwest is not enough to displace the warm air and high
moisture so additional storms are expected overnight.
Redevelopment is almost surely in the cards for Monday as clouds
thin briefly and July sun stirs up the boundary layer over most
of the area. Slight risk outlook from Storm Prediction Center is held to just the S/southeast
third of the area Monday. However...feel that strong storms are
possible a little farther to the north with low-level ambient
moisture still high and overall moisture high with precipitable waters between
1.5 and 2 inches. Will hold the catg probability of precipitation to the southeast...but go
likely probability of precipitation over much of the rest of the area on Monday.
Long term /Monday night through Sunday/...
the GFS and NAM guidance is much quicker to push the front
through...with the European model (ecmwf) deepening the upper level trough...though
the latest run has opened up the closed low. The ec develops a
coherent surface low over the middle MS valley and moves it to our west/north on
Tuesday as it deepens to near 1003mb.
High amplitude ridge/trough pattern develops across the much of
North America beginning late in the weekend...and continues
through the first half of next week.
The brunt of the greatest 850-700 mb temperature anomalies and
associated below normal 500 mb heights will be aimed at the lower
Ohio Valley and middle miss valley Tuesday and Wednesday...with our
region residing on the active/eastern side of this slow moving
As additional energy is driven south-southeast into the back side of the high
amplitude Midwest trough...prolonged high precipitable water air /and lift
beneath the right entrance region of an upper jet/ may linger
across the southeastern zones with scattered...mainly afternoon thunderstorms and rain
The pattern over the northern Continental U.S. And southern Canada appears to Delaware-
amplify later next week as the eastern U.S. Trough begins to shear
out to the NE.
The driest period of the long term will be Thursday and
Friday...though some isolated convection still cant be ruled out
either of those two days.
Temperatures start out at or above normal preceding the cfropa next Sunday...and
perhaps Monday across the southeast zones...then cool to at least 4-6f
below normal for daytime highs Tuesday through Thursday. Temperatures
will likely rebound to near normal late next week.
Aviation /16z Sunday through Thursday/...
an approaching front will bring the chance of thunderstorms and rain impacts to the
mainly the northwest mountains of Penn /then central counties/ today.
Most numerous rain showers/isoltd thunderstorms and rain at this time located were located mainly
to the east of the rt 219 corridor from kbfd and kfig...to kjst
and moving quickly to the east. This convection will spread southeastward
throughout the afternoon hours today...but sites will remain
mainly VFR through the bulk of the taf period. Brief reductions in
visibility and ceilings are possible again tomorrow afternoon in
this afternoon and evening...brief thunderstorm impacts possible.
Sun night-Monday night...numerous showers/thunderstorms and rain with mainly brief
periods of IFR to MVFR.
Tues-Wed...thunderstorm impacts possible...mainly in the
Thursday...no sig weather expected.