Scientific Forecaster Discussion
fxus61 kpbz 221903 cca
Area forecast discussion...corrected
National Weather Service Pittsburgh PA
303 PM EDT Thu Jun 22 2017
downpours are possible through Friday night with a tropical
airmass in place. A cold front sweeping through early Saturday
will return comfortable humidity levels by the weekend.
Near term /through tonight/...
showers and storms will continue to ride east - southeast south
of the warm front that is draped across northern Pennsylvania.
The best instability resides farther south toward the I-70
corridor, however it will take an outflow boundary to trigger
any convection due to the lack of synoptic triggers in this
region. Any storm will be capable of producing downpours with
the amount of low level moisture.
The focus shifts to the southwest as a wave brings showers and
scattered storms through after midnight. The overall speed of
the system will keep the heavy rain threat to a minimum, however
a quick inch of rain is possible given what happened this
morning over parts of Greene County. Confidence is high enough
to go categorical pops after midnight area wide.
Short term /Friday through Saturday night/...
..downpours possible through Friday evening with left overs from
Tropical Storm Cindy...
For information regarding the threat of high water, please
reference the hydrology discussion located near the bottom of
The remnants of Cindy pass Friday afternoon and evening. This
will bring a widespread area of showers and storms to the region
especially south of I-70. There should be not a lot of
precipitation around during the morning and early afternoon
hours, however with the approach of a the cold front during the
afternoon hours this will trigger storms and interact with
moisture associated with Cindy.
The cold front crosses during the overnight hours Friday night
so come daylight Saturday any measurable quantitative precipitation forecast should be east of
the mountains. Clearing will rapidly take place before 15z then
a cu field will develop during the afternoon hours. Humidity
levels will be noticeable lower as dewpoints drop into the 50s
some 20f lower than today.
Benign weather Saturday night with moisture arriving from the
northwest ahead of the next upper disturbance.
Long term /Sunday through Thursday/...
- cooler weather
- no signs of a high water threat
Full latitude trough will bring a period of below normal
temperatures to the region. Afternoon high temperatures will be
running nearly ten degrees below their normal benchmarks Sunday
- Tuesday. With the trough axis overhead, scattered showers and
perhaps a thunderstorm are possible through mid week, but with
low level moisture lacking due to the placement of high
pressure southeast of the western Great Lakes. A transitory
high pressure takes over at weeks end bringing temperatures
back to their normal location and returning dry weather.
Aviation /18z Thursday through Tuesday/...
scattered MVFR cigs will prevail under increasing moist low
levels through the afternoon. Increasing instability and
moderate levels of shear will support scattered showers and
storms, mainly north along a frontal boundary, with potential
impacts to kfkl and kduj. A few storms may produce strong gusts
but will not make any mention of these conditions unless
Otherwise, more notable weather and terminal impacts arrive
overnight as moisture associated with remnants of tropical Cindy
approach and interact with a sagging cold front. Will trend all
sites to MVFR, but some guidance suggests lower by midday
Friday. Heavy rain will likely lead to brief IFR restrictions at
any terminal but again, will not put this in at this time.
Wind will remain WSW through the period, with gusts this
afternoon with plenty of mixing and again Fri afternoon.
widespread restrictions are likely through Saturday morning with
the passage of a cold front.
a Flash Flood Watch has been issued for areas along and south
of Interstate 70. A piece of energy crosses tonight and will
bring upwards of an inch of rain as it passes. With flash flood
guidance in the 3 hour time frame over 1.5 inches outside urban
areas /Allegheny and western Westmoreland/. The current thinking
is as long as we do not get too much rain this afternoon in one
location we should be able to hold the rain overnight. The main
concern would be quantitative precipitation forecast Friday afternoon and evening.
Meteorologically values all point to high water issues with
precipitable waters over two inches, warm cloud depths above 13kft, and a
strong low level jet. Gefs M-climate values are near or at
record levels for precipitable waters on return interval, and climate
Maryland...Flash Flood Watch from late tonight through late Friday night
Ohio...Flash Flood Watch from late tonight through late Friday night
PA...Flash Flood Watch from late tonight through late Friday night
WV...Flash Flood Watch from late tonight through late Friday night