Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
408 am EDT sun Jul 13 2014
a series of cold front will bring showers and storms to the area
through early Tuesday.
Near term /until 6 PM this evening/...
atmosphere will quickly destabilize this morning...as moisture
levels increase due to the a strong south-southwesterly flow.
Model soundings are showing a low level inversion holding until
around 14 or 15z which will cap the lower levels of the
atmosphere. As the afternoon approaches...a shortwave trough will
swing through followed quickly by a weak cold front. The best time
for strong to severe development looks to be with the passage of
this surface boundary. Strong line of low level moisture convergence
and forcing will develop ahead of the front. Atmosphere will be
plenty buoyant with surface convective available potential energy of 2000-2500 j/kg and shear
values will be 35 to 45 kts...strong enough to promote organized
development. In addition to the instability...precipitable water values of up to
2 inches will provide the threat for heavy downpours. There will
be limiting factors however...temperatures aloft are very warm and with
the cloud cover ahead of the front...we may find it difficult to
reach convective temperatures. The slight risk in place looks reasonable.
As front drags southeastward this afternoon it will lose much of
its punch as the moisture convergence and forcing dissipates.
Atmosphere will stabilize as the evening approaches and the line
of shortwaves will move into northern West Virginia.
The overall setup points to a line of convection developing right
along the front and weakening as it moves southward.
Short term /6 PM this evening through Tuesday/...
convection will weaken overnight and the threat for heavy
rain should decrease as well. The front will be difficult to find
later tonight...but it does appear that is will stall over the
southern half of the forecast area. Models are hinting at a second complex
developing as dawn approaches Monday morning along the stalled
boundary. This currently gives ME pause as the main upper level
support will be well to the south by this time and the real
unstable and moist air will also be shoved southward. Its possible
that an mesoscale convective system could develop over the lower Ohio Valley and then
spread eastward along the boundary. If this second complex
develops...high water may become a concern.
Monday's forecast still remains muddled as focus early will be on
the stalled front over the south and then shift to the passage of
a secondary front from the northwest Monday night. Still some
timing issues with the passage of the second front and how much
additional activity will develop ahead of it. Will need to leave
in at least high chance probability of precipitation into early Tuesday.
Front will finally clear early Tuesday as a strong shortwave
trough moves into the upper Ohio Valley. Showers Tuesday morning should
be confined to the east...before exiting by the afternoon.
Long term /Tuesday night through Saturday/...
drier and much cooler air will settle in Tuesday night. Broad
Canadian high will keep the area dry and comfortable through the
remainder of the long term.
Aviation /08z Sunday through Thursday/...
VFR conds expd through tonight with increasing ac/CI. An advancing shortwave will
cross the area sun with showers and thunderstorms expd to develop through the
day...with sites from pit S not expg cnvctn until middle to lt afternoon. Will
maintain a thunderstorms in the vicinity or thunderstorm mention in the tafs for the most likely
time of cnvctn.
Outlook.../Sunday night through Thursday/...
occasional rstrns will be possible until the passage of a Monday night-Tuesday cold front.