Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
748 am EDT Friday Aug 22 2014
unsettled weather will continue through the early part of the weekend
with occasional showers and thunderstorms. Warm and dry weather is
expected early next week.
Near term /through tonight/...
650 am update...mesoscale convective system leftovers have all but dissipated across the
southeast counties. Light showers remain behind. Watching next
complex over Indiana/western Ohio but still think the bulk of this
will remain to our south as well.
County Warning Area is missing the bulk of the impact from mesoscale convective system leftovers rolling
toward the Appalachians across southern Ohio into West Virginia.
Some outflow-generated activity has generated a broken line of
showers in eastern Ohio however. Have this rolling across the
southern County Warning Area with likely probability of precipitation for a few hours. Earlier Lake Erie
storms have degenerated into a few showers sinking towards the fkl
While likely probability of precipitation look appropriate for most of the area...still
think the heaviest rainfall stays off to the south during the day.
Persistent frontal boundary will start to get nudged southward with
time...as the building ridge to the west induces more northerly flow
over our area. Richer moisture in the form of 2+ precipitable water remains
mainly from southeast Ohio into WV...where thickness/corfidi vector
patterns support continued propagation of showers/storms. Much of
our southern counties are relatively drier as well. Latest HPC
excessive rainfall outlook follows this thinking...keeping the
threat just off to the south. Will therefore hold off on a Flood
Watch but will maintain severe weather potential statement mention of possible isolated problems.
Cannot rule out a strong to marginally severe thunderstorm as
well...but organization of these will remain limited.
Loss of heating as well as slow southward movement of front will
allow coverage to wane later this evening and overnight. Expecting
isolated rain showers at best around 12z. Lingering clouds may hinder much
in the way of dense fog development.
Did not make major changes to temperatures...which were in line with
Short term /Saturday through Sunday night/...
guidance continues to aggressively build high pressure at the surface
Sat in the wake of the upper trough being pushed out to sea. This
continues the trend towards an overall drier forecast for the latter
part of the weekend. As for Sat...enough low to middle level moisture
resides through central PA during the morning as a weak 500 mb trough
approaches. Expecting this to activate some convection during the
afternoon hours...but overall coverage and intensity should remain
limited. Any convection that does form will quickly dissipate after
sunset with the loss of daytime heating.
Trimming back probability of precipitation and sky cover sun as surface high builds in over New
England and the upper ridge axis approaches from the west.
Subsidence will work to keep any convection sun at Bay. Temperatures will
remain at or a few degrees above normal...but with drier air in
place...dewpoint temperatures relax a little on sun making it a
little less muggy.
Long term /Monday through Thursday/...
mostly dry conditions expected for the extended period as heights
build under high pressure through midweek. The well advertised upper
ridge will settle into the Ohio Valley early next week deflecting weak
disturbances well to the north. By Wednesday the ridge breaks down as a
broad trough digs into the plains bringing a sweeping cold front
through the western Great Lakes Thursday. Will continue to carry chance probability of precipitation
along the projected front day 7 as there is a considerable amount of
agreement on timing and structure of this system.
Aviation /12z Friday through Tuesday/...
wdpsrd MVFR to IFR conds will continue this morning in fog/St. Experimental a gradual
improvement to VFR by Erly afternoon...though a crossing disturbance will
bring scattered to numerous showers and a few thunderstorms. With cloud cover limiting
instability...mentioned thunderstorms in the vicinity only for sites S of pit where better
instability is prognosticated...with vcsh elsewhere though a thunderstorm can/T be ruled
out. After precipitation decreases as the disturbance exits tonight...experimental IFR fog to
Outlook.../Saturday through Tuesday/...
rstrns are possible Sat in isolated-scattered thunderstorms. Otherwise...rstrns are possible in
Erly morning br.