Severe Storms of July 30, 1999

An isolated thunderstorm developed in Tioga county during the early afternoon... as a trough/mid level energy combined with sunshine on an unstable atmosphere to produce convection. See the 2 pm Northeast Region Surface Analysis. The dotted line slicing through PA indicates the trough. Additional showers and thunderstorms formed rapidly during the mid and late afternoon across the eastern half of PA. By far the Susquehanna Valley got the worst of the storms... which were intense. The anvil tops of the cumulonimbus clouds could distinctly be seen 50-60 miles away!

Several intense severe thunderstorms moved south and tracked along and just west of the Susquehanna River... bringing large hail to numerous locations. Crop and vehicle damage was incurred in a number of locations. Also, three people were unfortunately injured in southern New York State from golfball size hail.

Unfortunately, I was out (ironically, performing a storm survey from a previous event!) and not able to save radar images prior to 5 pm. Here are the following radar images available:

5:03 pm reflectivity data indicates the parade of severe thunderstorms along the Susquehanna River. All were producing large hail, and strong (but not quite damaging) winds.

VIL from the same time shows the significant amount of hail present within these thunderstorms... especially the one currently in Lycoming county just north of Williamsport.

Reflectivity from 5:08 pm indicated the intense severe thunderstorms. A look at the Storm Information Table (SIT) overlaid shows that two cells had rotation within them (noted by a "YES" under the MESO column)... in this case a check the with velocity data indicated it was at the mid levels of the storm. The one labeled as "P6" was a couple miles northwest of my house... dropping hail in excess of 1 inch in diameter (besides its mid level rotation). The cell farther north in central Lycoming county (labeled as "P0") was dropping golfball size hail with DBZ values as high as 69.

5:13 pm reflectivity. Severe thunderstorms continue...

And continue...

With high tops and very high VIL.

Storms still going strong at 5:23 pm.

Check out the 5:33 pm reflectivity shot...

...And compare it with one from just a few minutes later. You'll note the severe thunderstorm in southwest Lycoming county has strengthened quite a bit in 5 minutes. DBZ value shot from 61 to 67 in that time. Also, the tops with this storm have risen to 50,000 feet! VIL is also very high.

From about 5:45 to 6:35 pm, I was out chasing that particular severe storm which was entering Union county. Thus radar images during this time frame were not saved.

At 6:37 pm, radar showed the area of thunderstorms moving through Snyder county and continuing south-southeast.

Radar at 7:27 pm indicated a severe thunderstorm in York county.

7:31 pm echo tops data indicates extremely powerful updrafts with the storm in York county at this time. The top shown - 62,000 feet - is rare. Over the past couple years, I can't remember seeing them that high on this radar site. Although it might have occurred a couple times and I missed it... it is a rare sight no doubt. Also an extremely rare sight was the VIL with this intense severe thunderstorm... right off the top of the scale! Values like this are close to record values for VIL seen in this area. A tornado warning was being issued for southern York county right about at the time of these images.

7:32 pm reflectivity.

The 7:32 pm visible satellite image, one of the last of the day, shows the overshooting top... confirming the echo tops data linked above. Note on the visible image the large shadow made by this extremely tall, severe thunderstorm.

See the Storm Total Precipitation product of Doppler Radar. You'll note the "training" effect that took place from south central NY... south through the Susquehanna Valley in PA.

Radar animations available:
4:35-5:16pm
1:30-6:30pm
6:30-11:30pm

Numerous reports of large hail and eventually damaging winds were received with today's severe thunderstorms. A tornado was suspected by some people in southern York county. However, after a damage survey by the NWS, no tornado was confirmed. All damage patterns pointed to downburt thunderstorm winds. Roofs were ripped off 2 houses in the York/West York area.. and hail 2 inches in diameter fell. For a list of many, but not all of the severe weather reports... see the NWS Local Storm Report (LSR). Also available is the warnings/statements issued by the NWS.

A complete listing of all images/text available for this event can be found here.