Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
702 am EDT Sat Jul 12 2014
an approaching cold front will bring showers and thunderstorms to
the area beginning Sunday and continuing into Tuesday.
Near term /until 6 PM this evening/...
no major updates needed so far this morning as the current
forecast aligns well with latest observational trends. Previous
high clouds will cross the area today. They will be
thickest this morning then thin out during the afternoon. High
pressure at the surface will drift eastward and the flow behind
the high will become southwesterly and increase. This will promote
a slow increase in humidity levels.
Short term /6 PM this evening through Monday/...
models are continuing a slowing trend with the next system. First
concern tonight will be the passage of a weakening shortwave
trough. Still some model disagreement on how much affect this
upper level energy will have as it crosses late tonight. Expect
most of the activity to be well to our north and west concentrated
along a frontal boundary over the upper Midwest. Atmosphere
remains stable tonight with the concentration of buoyancy to our
west. Will continue a chance pop forecast for tonight...but think
that we would see mainly showers due to the aforementioned
Front will move through upper Midwest and into western Ohio
Sunday. Another shortwave trough will move eastward ahead of
surface boundary reaching western PA Sunday afternoon. With
southwesterly flow intensifying...atmosphere quickly destabilizes.
A strong area of low level moisture convergence will develop
Sunday afternoon as forcing in the low levels increases. A slight
risk for Sunday looks right on track with lifted indice's of -4 to -6...convective available potential energy
of 1500 to 2000 j/kg and shear values in excess of 30kts. In
addition to the severe threat...heavy rain will be a concern as
the influx of moisture pushes precipitable water numbers close to 2 inches. It
should be noted that cloud cover and the risk for morning showers
may hinder convection as this will keep high temperatures very close to
those needed to initiate convection.
All of the previously mentioned elements move through Sunday
evening...however the trailing cold front gets hung up over the
northern half of my forecast area. This stalled front will continue to
provide showers and storms through Monday. Probability of precipitation will be tricky
Monday...wholly dependent on the location of the stalled boundary.
Long term /Monday night through Friday/...
still seeing some timing issues on the passage of the front Monday
night. Will lean toward the sref/gefs/GFS op here as they are very
similar with frontal passage. This will bring an end to showers
late Monday night. Broad Canadian high will keep area dry and
comfortable through the end of the long term.
Aviation /11z Saturday through Wednesday/...
VFR conditions can be expected for the taf period as surface high pressure slides
across the region...although middle and upper cloudiness will accompany passage
of a weak disturbance.
Outlook.../Sunday through Wednesday/...
restrictions will become likely with the apprch and passage of a cold front
later Sunday and Monday.