7/7/12: Severe Weather Update- Squall line or possible derecho approaches Philly Metr
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
Updated: 10:31 PM GMT en Julio 07, 2012
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