Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1043 am EDT Monday Jul 14 2014
a strong upper level trough will drop across the upper Great
Lakes today and slide across southern Ontario and Quebec into the
midweek period. A weak front will focus showers and thunderstorms
with heavy rain over southern and eastern Pennsylvania today. A
second and more definitive cold front will push slowly across the
commonwealth Tuesday. Cooler and drier air will move into the
commonwealth for the middle to late week period.
Near term /through tonight/...
soupy air sitting over much of the area...with thickening/layered
cloud cover spreading quickly NE ahead of a well defined upper jet
maximum and weak surface wave heading NE up the Ohio River valley.
A distinct relative min in precipitable water /only around 0.75 of an inch/ was
noted across far northern Penn this morning...while nearly 2 inch precipitable water
air was nosing into southwestern Penn...just to the south of a washed out
frontal boundary that triggered Sunday/S showers and thunderstorms and rain.
While the cloudy sky this morning will not allow much heating...the
very moist llvls will allow convective available potential energy only in the 500-1000j/kg range
for much of the area...a brief break this morning could allow US
to realize the higher-end values. The forcing arriving for middle-day
will generate widespread showers and storms. The hodographs for
the southeastern third/half of the County Warning Area are a little curved and some
spinning storms are possible. However...think that the main threat
today will be heavy rain along and to the S/east of a jst/unv/ipt
line. See Hydro section for more information.
Temperatures should stay a little cooler today than Sunday due to more
cloud cover and the precipitation. It will be very humid.
The real front is currently draped just north of Lake Erie and back
toward Chicago. It starts to nudge into the state later today and
the lake breeze may also help initiate some showers/storms in the
northwest. Coverage there will be lower than in the southeast. Most of the
strong southeastern storms will be pushing off to the east before 7
PM...but they may linger through 9-10 PM. Scattered rain showers are then
possible through the night due to the humid air and possibility of
many minor boundaries left under neutral to negative forcing. Will
dip probability of precipitation tonight to 30 percent on the whole.
Short term /Tuesday/...
models seem to be agreeable on the major upper feature of note on
Tuesday. The upper trough does cut off and make a dip to 555dam
and is centered over Saginaw Bay by middle-day Tuesday.
Now...depending on which flavor of model guidance you wish to
Sample...the main/real cold front at 18z Tuesday will be somewhere
from western PA to over our eastern counties. Thus...confidence
in the re-development of showers/storms during the day is
low...except over the east. Therefore...will hold the line with
likely probability of precipitation for the entire daytime...especially in the east. The storms
should push to the east of the County Warning Area around sunset Tuesday. See Hydro
section for more. After a mild...muggy start to the day...maxes
will be even cooler than today. Places in the northern mts may not get
out of the 60s.
Long term /Tuesday night through Sunday/...
the pattern over the northern Continental U.S. And southern Canada appears to Delaware-
amplify by middle week the eastern U.S. Trough begins to shear out to
the NE and dry air advects in behind the front.
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. During this timeframe...the cold front
should bring in cool to at least 4-6f below normal daytime highs
Tuesday through Thursday. Temperatures will likely rebound to near normal
late this week.
A weak ridge will shift eastward into Saturday...where all long
term guidance shows a weak negatively tilted low should allow for
a shift to southwesterly flow...which could spark some scattered
showers and storms Saturday afternoon.
Aviation /14z Monday through Friday/...
thickening cloud cover will spread northwest above the stubborn areas of
lowered ceilings and visibilities present across the County Warning Area at this time.
Look for an increasing trend in showers and thunderstorms and rain through this
afternoon with frequent MVFR ceilings and visibilities across the southeast half of
Penn and occasional/brief IFR conditions in the heavier rain showers/thunderstorms and rain this
afternoon and evening.
Kbfd will be mainly VFR through early tonight...though some brief
MVFR conditions are possible.
More lowered ceilings and areas of fog expected for late tonight and
early Tuesday after today/S expected widespread rain...and
partial clearing with light wind and lingering high surface dewpoints
Tuesday...thunderstorm impacts possible.
Wed-Fri...no sig weather expected.
prognosticated mbe vectors today in the southeastern half of the area are fairly
short as the lljet associated with the old complex slides in
from the west-southwest. These 35-40kt winds slow down considerably to the
north of the Turnpike...and lift is anticipated to be maximized in
a corridor from cbe-hgr-MDT-Abe. Multiple/training cells could
produce very heavy rain with precipitable waters near 2 inches. Some of this
area has received two shots of heavy rain over the past couple of
days...and the ground is very wet. The most-recent heavy rain has
not yet been accounted for in the latest flash flood guidance...so
the current guidance values of 2.5 to 3 inches in an hour over
the southeast are most likely too high. Thus...have issued a Flash Flood
Watch for the southeastern third of the region for today/this evening.
The main forcing moves to the east of the region this
evening...leaving a lull in the heavy precipitation tonight and early
Tuesday. Additional storms are expected on Tuesday...but the
coverage and intensity may not be quite as high as today.
Thus...have limited the watch to just today. If conditions
warrant...the watch may be extended into late Tuesday or an
additional/second watch may be necessary for Tuesday.
Flash Flood Watch until 10 PM EDT this evening for paz036-