Mini-supercell hail storms of 12 May 2000
By
Richard H. Grumm
And
Michael Dangelo
National Weather Service State College PA 16803
Last updated: 31 Aug 1999
Introduction:
During the later afternoon hours of 12 May 2000, several small supercell thunderstorms developed over north central Pennsylvania. Hail was reported from all of these storms and severe hail, in the 0.75 to 1.25 inch range was observed from supercell thunderstorms over Potter and Lycoming Counties. No wind damage was reported with these storms.
These storms formed in northwesterly flow with weak low-level southwesterly flow. The threat was from large hail. All the severe hail producing storms appeared showed supercell characteristics in both the reflectivity and velocity data. The storms moved from about 310 degrees at 25 kts. Storm relative motions showed weak mesocyclones in both severe hail producing supercells.
Method:
Archive II data were used to examine these storms from our RIDDS tapes. Storm reports came from locally collected data. A list of all available radar images is available here. Our radar archive begins at 0549 UTC, shortly after the initiation of heavy rains.
RESULTS:
This storm produced 1.00 inch hail around 555 PM 10 miles northwest of Galeton . On radar, this storm showed the characteristic hook or appendage and rotation was observed in both the SRM and radial velocity data.
The supercell which produced the damage formed over southern NY and can be seen over central Potter County at 540 PM. By 546 PM, this storm had a distinct appendage on the rear flank of the storm.
The maximum VIL of 55 was reached at 2215 UTC in this storm. A storm to the south over Lycoming County achieved a VIL of 60 at 2204 UTC. A previous storm a few hours earlier had reach a VIL of 44 near Galeton. No hail was reported from that storm.
VIL PRODUCTS: 2152 | 2158 | 2204 | 2209 | 2215 | 2221 |
This storm formed out of the remenants of the Potter County storm. It can be seen at 731 PM over northern Lycoming County.
The maximum VIL (55) achieved in this storm was reached at 2355 UTC.
CONCLUSIONS:
These mini-supercell hail storms were isolated over north central PA. The formed in northwesterly flow and moved from northwest to southeast across the area. Cross sections and velocity data revealed weak mesocyclones and updrafts which suspended upto 70 dBZ cores above 20kft in these storms.
Both hail storms achieved a maximum VIL in excess of 50. However, a storm with a 60 VIL did not produce any reportable hail.
