Synopsis:
- Temperatures in the 80s today again
- Longwave trough axis over GL
- Shortwave trough exiting OV into PA
- Storms this evening, slight chance of severe weather
Satellite:
Today we continue to see large upper level low over the GL
Water vapor shows increased moisture (green shading) moving its way through PA.
Current Analysis:
Large upper level low seen again in Canada. Purple line is the shortwave trough and the green parallelogram is where the stronger thunderstorms are expected to develop.
850 mb winds and RH
relative humidity values along with mid-level southwest wind will aid in thunderstorm activity. As we saw in the water vapor loop above, the atmosphere is starting to get some moisture.
Discussion:
The National Weather Service in Mt. Holly has issued a slight risk of severe weather for today. This generally reflects weak nature of the 500 mb shortwave that will be attempting to induce the thunderstorm activity.
There will be some CAPE (available energy – 1st image) and lapse rates (rate at which temperature decreases with height – 2nd image). CAPE is used a hypothetical energy tap for thunderstorms to use. The lapse rates add to faster upward motion in the atmosphere should there be a trigger to cause the upward motion and thus create further instability and thunderstorm activity.
End result is between 3PM and 6 PM there will be line of storms pushing through the area. Local rainfall rates could cause flash flooding. The severe weather aspect is related to the flash flooding and possibly gusty winds. Both hail and tornado threat a minimal.
Philadelphia Weather Authority 