10 May 2000

by

Richard H. Grumm

and

Michael Dangelo

Event Type: mini supercells with hail production

Synoptic Type: WSRB (Warm Sector Rainbands)

Overview:

Characterized by fast spin-up supercells. Most of these storms produced hail and minor wind damage. Three storms had strong and persistent mesocyclones, one of which produced a short-lived F0 tornado in Lancaster County.

Between 1300 and 1400 UTC, a distinct line of thunderstorms was present in western PA (FIG01.gif). By 1515 this line increased in strength and a broken line of supercells began developing over the lower Susquehanna Valley (Fig02.gif). The line to the west had tilted storms with elevated cores of 60-90 dBZ to 14kft. The supercell over Perry County had 50 dBZ cores to 25kft.

By 1544 UTC the supercell over Perry County had moved over Dauphin County with

a core of 70 dBZ reflectivity’s up to 20kft (Figx01.gif). The plan view showed the supercell and over Dauphin County and a smaller one over York County. A strong storm along the western line was present in Clearfield County. Three low-topped storms were present along the lines. All three storms had echo cores lower then 14kft. A series of cross sections revealed very little vertical extent or structure in these western storms.

Lower Susquehanna Supercells:

The first supercell had a well developed mesocyclone by 1556 UTC as seen in Figsrm01.gif The reflectivity cross section (DA01x.gif) revealed a deep thunderstorm over Dauphin County (DA01.gif). This storm tracked eastward, passing just north of Lebanon County enroute to Schuylkill County (DA02.gif).The storm weakened as it moved across Schuylkill County (DA03.gif). A second storm developed over Perry County and followed the same track as the first

(DA04.gif). The mesocyclone was very compact in this short-lived storm (DASRM04.gif).

A supercell storm developed around 1701 UTC in eastern Lebanon and western Berks County. This storm entered Schuylkill County around 1712 UTC and is visible in DA04.gif.

Another storm developed over Perry County and moved across northern Dauphin County around 1741 UTC. This storm can be seen in DA05.gif and a cross section in DA05x.gif. The storm showed 70 dBZ cores to 27kft. The SRM data showed strong mid-level convergence within the storm (DASRM05.gif). The cross section showed the mid-level convergence and strong storm-top divergence (DASRM05x.gif).

This storm strengthened as it moved across Dauphin County (DA06.gif). But weakened as it moved into western Schuylkill County.

The Lancaster Tornadic Storm

a. The beginnings of the Lancaster Tornadic Storm- Maryland to York County

East-central PA was covered by a broken line of thunderstorms by 1800 UTC.

These storms moved eastward with time. One large storm remained just south of the Maryland border. This storms large; front-flank downdraft was visible in the SRM data over southeastern Franklin County (FASRM01.gif) and in the reflectivity data (FA01.gif). The mesocyclone was just south of the PA/MD border at this time. This storm split and the northern cell moved over

Adams County (FA02.gif) This storm began developing its own mesocyclone by 1903 UTC. Although rather weak, the mesocyclone in this storm was quite deep (FASRMX02.gif). This storm weakened over eastern Adams County but began to redevelop over western York County by 1938 UTC (FA03.gif). To the north, yet another supercell thunderstorm had developed over northern Dauphin County.

b. Hail storm spin-up over York County

c. Lampeter Tornadic Stage

d. Quarryville supercell

e. Other storms of note

Conclusions:

a. Many storms tracked along terrain features. The southerly flow seemed to favor storms to the lee or in this case, to the north of the ridges.

b. Storms developed rapidly

c. Storms had a bean shape on radar with many having mini-supercell characteristics

d. The main line of storms, which developed over western PA, were very forward tilted and were not as high as the eastern storms.

e. Hail was the dominant severe weather type.

f. Satellite imagery revealed the stronger storms had noticeable enhanced-V signatures and were associated with the stronger storms.

To Do:

Will need more RIDDS data through 23 UTC. Did not load it all.

Show some satellite images in relation to the radar and the severe weather.

Get the PNS and LSR.