Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
830 PM EDT Monday Sep 1 2014
scattered showers and storms will diminish in coverage going into
the evening...with humid and somewhat unstable conditions
continuing through early Tuesday. A cold front will advance across
the area Tuesday...bringing widespread showers and storms.
Near term /through Tuesday/...
with 830pm update...cut probability of precipitation through the rest of the overnight
hours with coverage having significantly decreased in the last
hour or two. Upstream precipitation coverage is also on the
wane...and high resolution models do not show much more developing
overnight. Line of convection well north of the forecast area will
not have an impact. Only minor changes to other portions of the
forecast. Previous discussion follows.
The real focus by tonight looks to be turning to the daytime on
Tuesday...when the middle-level system approaches from the Great
Lakes along with the associated cold front. Model solutions seem
to be keying in on a late morning/early afternoon arrival into
northwest portions of the area...with a middle-afternoon Crossing of
the Pittsburgh area...and a late afternoon/early evening exit of
the County Warning Area for the frontal boundary. Instability along the front
while likely continuing to be rather deep...should also be rather
unimpressive owing in large part to a lack of insolation ahead of
the front through the early portions of the day. This should limit
additional destabilization. Additionally...owing to the fact that
the middle-level wave largely shears off to our north...0-6 km bulk
shear values really only run up toward 35 kts of weakly veered
flow as the boundary impinges upon the area. Again with this
variable...those values do not exactly make this forecaster
particularly jumpy. Furthermore...with shear values that high and
a fairly quick moving wave passage...while the cells that do move
through are likely to be heavy rain producers...prolonged heavy
rainfall in any particular location as well as training of echoes
seems unlikely. This should minimize the risk of flash flooding as
well. It is Worth noting that Storm Prediction Center has placed the area in a slight
risk for tomorrow...however owing to less than stellar instability
values...moderate shear...a lack of insolation...forcing that
focuses height falls largely to the north of the area along with
the highest shear values...it seems like this slight risk is a
less confident slight risk than normal. Fries
Short term /Tuesday night through Thursday night/...
cold front exits east Tuesday night quickly as the upper level flow
GOES zonal. High pressure quickly builds at the surface Wednesday with
skies generally clearing through Thursday. Temperatures will remain at or
above average both days as the surface high shifts east allowing for
warm...albeit weak...southerly flow. High pressure will keep
threat of rain out of the forecast during the latter part of the
Long term /Friday through Monday/...
high pressure will remain along the East Coast through Friday...
allowing conditions to remain dry. Cold front will bring showers
and storms for the beginning of the weekend...with cooler drier
air for the end of the long term.
Aviation /01z Tuesday through Saturday/...
isolated showers will dissipate through 02z with end of daytime
heating. Expect MVFR fog at most locations in low level moisture
with kfkl and kduj having IFR stratus before daybreak. For Tuesday
cold front will move into the region with showers and thunderstorms
becoming more numerous west to east late morning to early
afternoon. For now will go with MVFR thunder at times in tafs as
this will need to be refined in later issuance. A weak westerly wind
shift will work into the region late day.
Outlook.../Tuesday night through Saturday/...
a chance of showers/storms will linger into Tuesday night...with
restrictions possible Wednesday morning in fog/stratus.
Restrictions are then possible Friday/Saturday with another cold