Introduction:

During the afternoon hours of Friday, 16 June 2000, a series of thunderstorms developed along the Allegheny front in Clearfield and Centre Counties. These storms moved east northeastward across Centre, Clinton, Lycoming and Sullivan Counties. The strongest echo cores followed the higher terrain of the front. Several storms developed weak cyclonic circulations as they moved eastward. One cell developed a mesocyclone over Lycoming County and then a tornado vortex signature. This storm spawned at least one tornado over southeastern Lycoming County and possibly a second, which then moved into Sullivan County.

The first tornado produced sporadic damage long a 17-mile path from the north end of Montoursville to Eagles Mere in Sullivan County. An off duty fireman captured the tornado with his camera near the Montoursville location. A second tornado downed some trees near Farragut. Both tornadoes were estimated to be off F1 intensity. Other strong pulse like storms developed in Huntingdon and Franklin Counties. The Franklin County storm developed rotation but produced no known damage.

The key to the Lycoming-Sullivan supercell storm appeared to be the wind direction relative to the terrain. Over recent years, there appears to be a local supercell and tornado maximum just in the valley locations of Lycoming County south of the Allegheny front. It is possible that the rear-flank downdrafts accelerate down the terrain into the valley enhancing the inflow and rotation into the storm. An event similar to this occurred in late July of 1999. This phenomenon is worthy of further study.

Method:

Archive II data from the local RIDDS machine was used in WATADS to make radar imagery. The data are archived for a possible PSU 418W follow-on study.

Volume scan numbers, mesocyclone ID’s and TVS ID’s are provide for follow-up study purposes.

Results:

The first supercell developed over eastern Clearfield County (31) around 1900 UTC (VOLUME SCAN 65) and moved to the northeast. This storm formed and tracked along the Allegheny front. This probably enhanced the inflow into the storm allowing it to sustain itself. The WSR-88D algorithm detected a tornado vortex around 2128 UTC. A weak circulation (76) had been detected in the storm five-volume scans earlier.

This circulation became a meso around 2143 UTC. By this time, a second supercell (18) was on the heels of the first storm and tracking about 4 miles south of the previous storm’s track. Initial results suggest this storm never developed quite the vertical depth or vertical circulation achieved by the lead storm.

A second TVS was detected in the first storm around 2148 UTC. This TVS persisted until 2203 UTC. A spotter took a picture of the storm north of Montoursville, confirming that this storm did indeed produce a tornado. The NWS verified this the next day. This mesocyclone dissipated by 2252 UTC over the higher terrain in Sullivan County.

Other large, rotating storms developed over Snyder County, to the south of these storms. But they too never achieved the circulation depth or vertical extent of the northern storms. Interestingly, the Snyder County storms formed along and followed the southwest to northeast oriented ridges with the strongest low-level circulation over the valley locations.

The tornadic supercell had its early development over the Allegheny front in Clearfield County shortly after 1800 UTC. The storm the moved over western Centre County by 1900 UTC where it took on a pendant like echo appearance. The storm continued to track along the front in northern Centre County, passing over I-80 around 1910 UTC. The storms Pendant echo evolution continued and a second storm was visible to the NE of the storm of interest. The Storm continued to move eastward and was about to enter Clinton County at 1934. The storm to the northeast began to weaken. The supercell began to weaken as it moved over Clinton County, losing its pendant shape. A third storm had developed to the west over Centre County. The supercell continued to weaken (#31) over Clinton County while the third storm strengthened to the west. By 2009 UTC, the supercell began to strengthen again. By this time, numerous pulse storms were present along the SW-NE oriented ridges of Centre County.

The supercell moved into Lycoming County around 2020 UTC, north of Jersey Shore. The storm then rapidly strengthened over southwester Lycoming County. To the SW, weaker storms moved northeastward and to the southeast face of the ridges in Centre and Huntingdon Counties. By 2044 UTC, Lycoming Storm had really begun to spin-up and strengthen. At 2056 UTC, the radar began to sense to reflectivity cores in storm 31 and assigned it a new number (50). By this time, what would now be known as storm 50 developed a pronounced mesoscale circulation in the storm relative velocity (SRM). By 2108 UTC, storm 50 was moving across Lycoming County with a second storm to its west. By 2119 storm 50 was still strong but storm 42 showed a hook like structure.

At 2128, storm 50 developed a TVS signature. Storm 42 split and was now assigned the number 18. At 2138 the storm had only a mesocyclone it. A second TVS was detected around 2148 , the storm and the TVS persisted at 2158 and a reflectivity cross section 2158 revealed the depth of this storm.

2056 Lycoming County circulation now in storm. 2108 Lycoming County new number 50 2119 Lycoming County new number 50 2128 Lycoming County TVS in storm. 2138 Lycoming County TVS in storm. 2148 Lycoming County TVS. 2158 Lycoming County TVS.

VELOCITY: showed the RFD nicely in the valley south of the Front

2138 : Velocity shows RFD in the Valley south of the terrain.

2148 : Strong RFD winds.

2158 : Strong RFD winds.

| SRMX | SRMX | SRMX | SRMX |

VIL were strong on this storm at times. VIL1 2208, 2218, and 2228.

All imagery can be found Imagery can be found here.

The NWS WSR-88D did an excellent job tracking the evolution of all the supercell storms, which formed on 16 June 2000. This allowed the NWS forecasters to issue a timely and accurate warning to the citizens of southern Lycoming and western Sullivan County. It should be mentioned that the WSR-88D algorithms performed well too.

The NWS in State College also attempted to verify this storm did indeed produce a tornado. This was facilitated by the Lycoming and Sullivan County Emergency management personnel and concerned citizens in the affected area.

These data will be used to improve how the NWS in State College uses the WSR-88D to warn. It appears this and similar cases may help improve anticipating supercell and tornado development along the uniquely shaped Allegheny front.

Lcoming-Sun Gazette, Lycoming EMA, Sullivan EMA, Dave Ondrejik-NWS Storm Survey, and Pete Jung and Kevin Fitzgerald for Warning and initial data archive.