Mid Atlantic Weather Updates

7/7/12: Severe Weather Update- Squall line or possible derecho approaches Philly Metr

By: weatherenthusiast1, 10:04 PM GMT on July 07, 2012

A severe thunderstom watch has been issued for the counties to the North of Philadelphia. Update: Expire at midnight.

So far, severe weather in the area has been minimal, but a line of thunderstorms is moving towards the region and is intensifying.

At 6:00PM, the line extends from west of Reading to Allentown. By around 7:00PM, the line should reach northern Montgomery County. By 7:30-8, the line should reach Philadelphia.

The main dangers are high wind and small hail. No tornadoes are expected.

A Warning has been issued for the counties north of Philadelphia until 7PM.

Line appears to have weakened, only a few cells capable of small hail.

Technical Analysis "Scorecard"

Currently being updated!

1. Dewpoints- YES
70F dewpoints are optimal for Thunderstorms, and the area under the Thunderstorm watch has dewpoints at 70F+

2. 850 mb Dewpoints- YES
14C Dewpoints are optimal, and we have around 16C dewpoints in the area under the warning

3. Precipitable Water-YES
1.5 inches is optimal, and we have around 1.7+ in the warning area

4. K Index- YES
38-40 provides best potential, we have around 38-40

5. LI (Lifted Index)- OK
-6 to -9 is very unstable, SE PA warning area has -6 as an LI Index

6. CAPE Values- OK
Best CAPE Values are 2500+, SE PA warning area has around 2000J CAPE

7. Bulk Richardson Number- YES++
BRN over 50 suggest multicellular thunderstorms but not necessarily severe weather. Mesoscale boundaries will help in this case: SE PA around 80-100


Severe Weather Storm Squall Line

Updated: 10:31 PM GMT on July 07, 2012


About weatherenthusiast1

The purpose of this blog is to give the public in the Mid Atlantic region the background behind the forecasts.