A series of Pacific weather systems will bring several rounds of precipitation and wind to the western U.S. this week. Several inches of rain could fall in portions of WA, OR and CA, especially in the coastal ranges and foothills. Snow is forecast in the higher mountains. In addition, winds will be strong, especially in mountainous areas, which could pose a hazard to high-profile vehicles. Read More >
Some remnant energy from once Hurricane Issac moved across our area during the September 3-5, 2012 time frame. In addition, this enhanced the tropical moisture across the area with surface dew points in the lower to mid 70s. The atmospheric conditions were comprised of some instability and wind shear (change in direction and speed with height). Since the instability was not exceptionally high, thunderstorms that tended to develop did not achieve tall updrafts in general. A cold front finally moved through most of our region on September 5, 2012 that knocked down the dew points some.
There were two events that occurred, which involved weak tornadoes. The weak tornadoes, EF0 with winds between 65-85 mph, are typical of what occurs in our part of the country. These are mainly spin-ups that develop and dissipate quickly. This was again the case on September 3rd and 4th. The thunderstorms that spawned these weak and short-lived tornadoes were in the same environment. This was characterized by deep tropical moisture and also wind shear (wind shear is a change in wind direction with height and also even speed). This creates a rolling motion in the atmosphere, and when storms develop rotation, this can then be tilted vertically by the storms updraft resulting in a tornado. Because of the tropical moisture that was in place, the local condensation level, or LCL, was rather low. The lower this is to the ground, the greater chance of a tornado occurring given other favorable parameters such as wind shear.
The focus here is with the September 4th tornado that hit the Mount Ephraim, New Jersey (Camden County) area, as it occurred not too far from the Philadelphia Terminal Doppler Radar (TDWR, TPHL). Some brief information about the September 3rd Camden, Delaware tornado is also listed. The velocity data also showed as the hook became more pronounced, the wind strengthened and the velocity data tightened up.
Warnings and Storm Summary
The tornadoes typically in our area usually develop and then dissipate quickly. This was the case once again during these September 2012 events. In the case of the September 4, 2012 Mount Ephraim tornado, the funnel appeared to touch down for a brief time with the main rotation remaining disconnected from the ground. This would explain the limited damage despite the impressive look on the radar imagery.
Storm Pictures and Damage