Friday, July 27, 2012

Strong Line of Storms Hits, Thankfully Not Worst Case


Last night's storms were a pretty fierce line that produced over 370 reports of wind damage across the Northeast and Ohio Valley, including a fair share of wind damage locally.  The strongest wind gust in the Delaware Valley with last night's storms was 64 at Elverson in Chester County, with Philly getting a 46 mph gust as storms pushed through right around 8 PM. Rainfall ranged from very little in Atlantic City as storms fizzled as they approach the South Jersey coastline, to as much as 1.11" in Wilmington. Most of the region generally got between a third and two thirds of an inch of rain last night, all of which was pretty much needed.


As the storms pushed into Philadelphia, the line weakened a little bit locally, with the strongest storms concentrating themselves on the western and eastern flanks of the squall line.  You can see the radar image from 7 PM above showing the line snaking across New Jersey and Eastern Pennsylvania.  The portions of the line around Lancaster County (which produced that 64 mph gust)  and also across Western New Jersey at the time were the strongest portions of the line as they moved south and east, while the portion across the Lehigh Valley weakened a little bit as it slipped south.  The combination of declining daytime heating and earlier cloud cover may have aided in weakening things a little bit around here and preventing a worst or worse-case scenario locally.  That said, it looked rather eerie out there for a time last night as these storms marched in.

While the storms were bad, these were not as bad as the derecho that ripped through South Jersey four weeks ago tonight.  These were also well-warned if not well-hyped thunderstorms as the National Weather Services was providing nearly an hour to 75 minutes of warning lead time as this line was approaching and various media and forecast entities (including the Storm Prediction Center) were throwing around the "d" word like candy at a Halloween parade.  Regardless of if the technical criteria of a derecho were met (it looks it might have based on the damage reports in the Ohio Valley and Kentucky), we thankfully dodged a bit of a bullet as these storms pushed through given it certainly could have been worse.

With that said, I'm not so sure using the derecho term so freely over social media and in the media in general is a wise course of action. Not every line of thunderstorms is a derecho.  We have seen a few instances where some have hyped up potential derechos for what are effectively solid lines of severe weather but don't have the qualifications for a derecho (intensity, duration, geographic distance), such as a line of heat-busting thunder that fizzled on July 7th as it approached Philadelphia.  Using the term opens a bit of a pandora's box to "doom and gloom", with the thought that another DC type system is about to knock the power grid back to the 1800's.  Such sky-is-fallingism doesn't help when the reality isn't quite as bad as hyped, leading to the term losing its meaning and significance until one actually experiences a derecho.   Derechos are relatively rare storm systems and as such, the term should be used less frequently and really only in hindsight once we know that one has occurred or really is occurring (June 29th was clear cut case of a derecho).  You can still effectively get the message across by using "nasty of thunderstorms", "severe weather", "windswept thunder", "widespread outbreak of severe weather", and other such terms.  Let's save the derecho talk for once criteria is met...and not for hyped up hopes of hits, eyeballs, and viewers.