Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
936 PM EST Friday Nov 28 2014
a warm front crosses tonight bringing snow showers along and north
of Interstate 80. A warm up will allow daytime highs to climb
into the 40s Saturday and 50s Sunday. There will be an abundance
of clouds and possibility of light rain Saturday night into
Near term /through Saturday/...
light snow showers across eastern Ohio will move across the
northern West Virginia Panhandle and western Pennsylvania this
evening...although these showers are not expected to bring much
more than a dusting of accumulation. Slightly heavier snow showers
north of the Pennsylvania Turnpike will generally move through by
midnight...although scattered snow showers could persist
throughout the night. Along the Interstate 80 corridor...snow
accumulations could reach an inch. As southerly flow develops
overnight with passage of a warm front...temperatures should
remain fairly steady into the early morning hours...then slowly
increase towards daybreak.
Broad southerly flow in the lower levels of the atmosphere pump
moisture from the south...thus despite being in the warm sector
overcast or near overcast sky cover is predicted for
Saturday...especially in the afternoon. Any precipitation arrives first
in eastern Ohio by afternoon. BUFKIT soundings do not show any
threat of mixed precipitation from warm air advection aloft...so light rain is
Temperatures were constructed initially from the gridded lamp
tonight then a blend of the existing forecast and adjacent met bias
corrected grids Saturday.
Short term /Saturday night through Monday/...
weather does not change much Saturday night compared to during
the day as broad low level southerly flow continues to back build
all the way to the lower Mississippi River valley. Cross sections
of potential temperature indicates upglide / positive pressure
advection from the surface to 775mb. Specific humidity are
surprisingly modest for this event with values reaching 6gkg-1
Saturday night at 290k. Quantitative precipitation forecast values will not be that great given
lack of any synoptic scale weather feature. Amounts will run on
the order of five hundredths or less...which warrants light rain
attribute in weather grids. Increased probability of precipitation to likely for eastern
Ohio and northwest PA while maintaining chance probability of precipitation elsewhere.
The weak cold front will gradually make it's approach by late
Sunday. While the greatest chance for measurable precipitation
will not come until the fronts passage Sunday night...a strong middle-
level jet should support the development of some showers in advance
of the front. Thus...likely probability of precipitation were carried over Ohio during the
day Sunday...with high chance elsewhere. Out ahead of the
front...strong west-SW flow should allow for temperatures to warm
above seasonal averages.
The models generally agree that the front will be through the
region by Monday afternoon...so the high temperatures for the day
will be realized early.
Long term /Monday night through Friday/...
cool temperatures will only linger for a day before southwesterly
flow returns on Tuesday. Nearly zonal pattern will support for
weak...fast moving storm systems and shower chances through the
end of the long term.
Aviation /03z Saturday through Wednesday/...
prevailing VFR are expected to be interrupted by a period of
restrictions...mainly MVFR...tonight as a fast shortwave interacts with
an advancing warm front. Those restrictions may linger until about
daybreak at fkl and duj with the warm front in vicinity. Otherwise
expect a light surface wind backing from SW to S as these features
Outlook.../Saturday through Wednesday/...
the next chance for widespread restrictions is with the advance and
passage of a cold front during the late Saturday through Monday period.