Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
343 PM EDT Tuesday Jun 2 2015
an upper-level low will nearly stall over the Ohio and Tennessee
valleys through Thursday...with rainfall chances mainly south and
east of Pittsburgh. Temperatures will rise to more seasonable
levels as the week progresses.
Near term /until 6 am Wednesday morning/...
cloud shield is slowly starting to break up across far northern PA
as NE wind funnels in drier air. Its still a tough call how far
partial clearing gets this afternoon. Latest hrrr has it reaching
the I-80 vicinity. This agrees well with the ongoing forecast.
Farther south...soundings illustrate deeper moisture and dewpoints
staying within a few degrees of their current readings...so mostly
cloudy/cloudy works. With the overcast sky...temperatures will be 15 to
20 degrees below normal...however most locations should see at
least 60f. The record low high for Pittsburgh is 51 and we are
already at 57 which means its safe for another year.
As for measurable precipitation...baroclinic zone remains draped
along The Spine of Appalachians...and weak pockets of DCVA riding
northeast coupled with a saturated column yield isolated showers
for the afternoon over the mountains of northern WV and western Maryland.
Short term /6 am Wednesday morning through Friday/...
not much change to the forecast weather pattern. Closed upper low
is still expected to cross the Tennessee Valley and slowly trudge
eastward...before weakening and crossing the Carolina coast on
Friday. NAM/GFS try to move the low center a little quicker than
previous runs...but the European model (ecmwf) and ensembles continue to be a
little slower...which is preferable in this stagnant pattern.
Still expect most rain shower activity Wednesday/Wednesday night
to lie south and east of pit...especially close to the ridges...as
easterly flow keeps most moisture locked up there. This is also
the area that will be more subject to midlevel ripples rotating
around the upper low. Did reduce probability of precipitation on Wednesday and continued
to keep thunder out of the forecast...as the transition to a more
southerly flow component looks delayed as compared to yesterday.
On Thursday and Friday...BUFKIT profiles show a more favorable
environment for diurnal convection areawide as return flow sets up
on back of departing surface high to our north. Given the lack of
a coherent trigger...will keep probability of precipitation in the scattered/chance
category west of the ridges. Weak upsloping will continue in the
higher elevations...with a damming look to the low level wind/temperature
Fewer clouds and the return of southerly flow will point to a
warming trend...with above normal temperatures expected by the end
of the week.
Long term /Friday night through Tuesday/...
model and ensemble guidance continue to favor the passage of a
northwesterly cold front on Saturday...which should finally bring
a drier period with ample sunshine behind it. However...the
improved conditions will likely be short-lived as the consensus
favors cyclonic flow re-establishing itself over the County Warning Area by early
next week...meaning a southerly drop of the jet axis and a better
chance the storm track would favor wet conditions again by early
Aviation /19z Tuesday through Sunday/...
MVFR conditions continue south of a line from kyng to near
kbfd...with dry air north of this line aiding in slow southward
erosion of the overcast deck. This line is expected to meander
southward only a bit before wind direction turns to the east and
reinforces the stagnant low-level airmass.
There is lesser confidence in the overnight forecast as guidance
is not consistent in showing resuming MVFR-IFR ceiling and reduced
visibility. Given the stagnant airmass and veering wind...this
forecast was trended slightly more pessimistic at many sites.
As east-southeasterly wind increases Wednesday morning...cloud height of any
overnight stratus/stratocu should increase accordingly to high
MVFR levels. In short...most terminals /with the exception of
kfkl/ are likely to have a prolonged period of MVFR conditions or
worse tonight into Wednesday morning.
Outlook.../Tuesday through Saturday/...
conditional restrictions are expected into late week as upper
trough remains entrenched over the eastern U.S.