Saturday, June 30, 2012

Wicked Winds

Having been through my share of derechos in the Midwest, I hate them. They're nasty storm complexes that cause a crapload of damage and impact as they steamroll over large swaths of real estate. From a meteorological perspective, they're impressive...from a cleanup perspective, not so fun.  Yesterday's derecho resulted in over 500 confirmed reports of severe weather from Iowa to Jersey, with the storm's brunt passing through generally Wilmington to Barnegat south, which was well placed by the Storm Prediction Center in their final severe weather update last night.   That said, thunderstorms did move through the city and suburbs as well last night, bringing a couple of tenths of an inch of rain to Philly and immediate vicinity along with a vivid sound and light show.

The derecho's origins in Iowa yesterday morning means the storm system tracked closer to a thousand miles but once it got into Indiana it became a potent windstorm, dropping 80-100 mile per hour winds in Indiana and Ohio and winds to around 80 miles per hour even nearby.

More:  What is a derecho? (Storm Prediction Center)

Locally, despite some hail reports the calling card of last night's squall line was powerful winds.  Wind gusts were reported as high as 81 miles per hour in Tuckerton(unofficial) and officially as high as 67 miles per hour in Millville.  As you can tell, the strongest winds were south of the city...and the lion's share of damage is down there as well.  As of 8 AM this morning, 168,000 were without powerin AC Electric's coverage area in South Jersey and another 20,000 in Delaware were without power.   Two fatalities have been reported so far near Pittsgrove from a tree falling on campers during the storm last night.

Thanks to a heat ridge that's positioned to our south and our position on the northern periphery of it, we're getting into the "ring of fire" that accompanies hot airmasses.  Thunderstorm complexes that develop tend to travel the highway around the northern fringe of heat, easily able to feed off of heat and humidity and providing a calling card of wind damage and sometimes hail.  These derecho complexes will often times track over a thousand miles and produce extensive damage...and even if a derecho doesn't develop, squall lines can on the edge of these heat ridges and do similar damage but over a smaller amount of real estate.

We're under a slight risk of severe weather today and we have to keep tabs on this complex of thunderstorms over Ohio (as of the time of this post) to see what it does over the next several hours.  This complex is working east...if it survives and holds together it would cross our region this afternoon (around 4 PM).  If it does weaken, it may help spawn a new complex of storms later on over Ohio or Western Pennsylvania that will push east and southeast.  The calling card threats for today's severe weather are predominately wind (30% chance of severe level wind within 25 miles of a point to the south and west of the city), followed by hail (15% shot of that within 25 miles of a point).  Modeling (as of this morning) is hinting that the best threat for any severe will be to the south of the city...whether that track is similar to last night's or north/south of that remains to be seen as the computer models are waffling with the "worst of the worst" track.  That waffling is to be expected as it is a "finer point" detail and tough to pin down with 100% accuracy until we see thunderstorms actually firing or approaching.  However, the timing element does appear to be this afternoon and evening regardless of how/where it tracks.