Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kpbz 230530 
afdpbz

Area forecast discussion
National Weather Service Pittsburgh PA
130 am EDT Fri Jun 23 2017

Synopsis...
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 today/...
rain showers associated with an upper-level shortwave are
entering our southern zones as of 1am. These light to moderate
showers will slide north-northeast this morning following the
shortwave, bolstered by mid-level speed convergence and upper-
level divergence. Despite any evidence of embedded
thunderstorms, rain rates may increase with this activity in the
pre-dawn hours as it lifts northward. This is due to an
increasing 850mb jet that will continue to feed moisture into
this already moisture-laden atmosphere. This will pre-
condition much of the Flash Flood Watch area with around a half
an inch of rain, before the heavier rain chances arrive later
today. The already hard hit areas of Armstrong and Indiana
counties will also see this rain before daybreak. Flash flood
warnings continue for these locations.

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.

&&

Short term /tonight through Saturday night/...
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/...
highlights:
- 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 /05z Friday through Tuesday/...
most ports begin the 06z taf period with VFR conditions, but
these should deteriorate rather quickly. An upper-level
shortwave trough will spread light to moderate rain north-
northeast in the pre-dawn hours, lowering ceilings to low MVFR
and perhaps IFR. Keeping most ports in low MVFR through
daybreak, with gradual lifting through the afternoon.

Restrictions will likely continue through Friday as the
remnants of Tropical Storm Cindy merge with an approaching cold
front. Showers, thunderstorms, and low ceilings will be common
Friday afternoon through the evening.

Wind will remain west-southwest through the period, with gusts expected
Friday afternoon.

Outlook...
widespread restrictions are likely through Saturday morning with
the passage of a cold front.

&&

Hydrology...
a Flash Flood Watch has been issued for areas along and south
of Interstate 70. Allegheny and Westmoreland counties are also
included because of lower guidance in the urban areas, as well
as Armstrong and Indiana County because of flash flooding that
already occurred Thursday afternoon. 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
anomaly.

&&

Pbz watches/warnings/advisories...
Maryland...Flash Flood Watch through late tonight for mdz001.
Ohio...Flash Flood Watch through late tonight for ohz057>059-068-069.
PA...Flash Flood Watch through late tonight for paz021>023-029-031-
073>076.
WV...Flash Flood Watch through late tonight for wvz002>004-012-021-

National Weather Service Glossary of Abbreviations