The Spring State College Supercell Thunderstorm

UPDATE: An EF-0 tornado was confirmed with this storm just east of State College! My time-lapse video and Kristi's hail video were featured on AccuWeather.com.

ORIGINAL BLOG 4/20:

Thunderstorms aren't unusual here in central Pennsylvania during the spring. In fact, some of our best storms have been in late May. Climatologically speaking (as shown by the graph below), there is a spike in early April, but late April is typically unimpressive.

That all changed yesterday. A massive supercell thunderstorm plowed into town, and I was here to see it. Here's a timelapse of the storm approaching me; I had a heck of a view from the top of the Beaver Avenue Parking Deck in downtown State College (I have a special agreement with the city to film there). Here's a wide-angle time-lapse from my GoPro (high-res on YouTube):

I also documented the rotation of the storm up-close in this time-lapse:

Here's what the radar looked like at the beginning of the time-lapse. You can see the classic supercell look to the storm, with a pronounced hook echo and hail core.

The hook echo caused a wall cloud to form, dissipate and reform in the storm as it moved toward me. I snapped a photo of (with my cell phone) it at its peak intensity:

Significant rotation was also detected on the velocity radar (air moving toward the radar co-located with air moving away from the radar). Looking at the hook echo in 3-D (by isolating a certain level of the radar data), it's clear that heavy rain was being drawn down into the "trunk of the elephant" as it were. This could mean that a funnel cloud or tornado was present, but I never saw the rotation indicating one from my perspective (which was admittedly not the best place to observe).

The hail was estimated to be as large as 2.57 inches in diameter by the radar. As is typical, the radar overestimated the hail size, although two spotters reported hail as wide as 1 inch in the path of the storm. More impressive was the size of the hail core and how much land it covered compared to other storms that day or historical storms in this area.

How did it all start? Pennsylvania Storm Chasers on Facebook noticed impressive model numbers as early as last Wednesday. On Friday, the three-day SPC forecast started out with a "Slight Risk" from the Storm Prediction Center. The area was expanded Saturday, but the forecast held until Sunday, when an "Enhanced Risk" (technically, a high-end "Slight Risk") was issued, which crept toward and over State College by Monday afternoon. (Because we're east of the Appalachians, storms are hard to come by here and forecasts usually get "better" (i.e. fewer storms), not worse, another surprise).

All told, the storm was one of the most impressive I have seen since moving here in 1997, and was almost as bad (hail coverage was wider, but sizes smaller) than "Hurricane Henry" in 2010.

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