Wednesday, August 14, 2013

Recapping A Wild Morning In The Region

Yesterday's rains were fierce across Southeastern Pennsylvania and North Delaware, with lesser amounts across South Jersey.  Philadelphia picked up 2.02" of rain yesterday, bumping the month's total to 3.76" and the summer total to 27.56" -- and we still have over two weeks of August to go to add more onto that.

The good news is we won't add any rain to the bucket for the next few days thanks to high pressure.

The unfortunate news is yesterday's storms blazed a trail of flooding rain in a path from Lancaster County to Chester County to the Fort Washington area (with one particularly strong storm), with a second swath of heavy rain extending from Northeast Maryland across New Castle County and across South Jersey.  In both of these instances, the heaviest rains occurred just to the north of particularly strong storms that showed signs of rotating winds aloft.  In the Southeast Pennsylvania storm, it appears those winds didn't reach the ground although it did generate a severe thunderstorm warning during the 6 AM hour.

A second cell did show feistier signs of rotation and did produce tornado warnings from Northeast Maryland across Delaware and across South Jersey.  More damage was associated with this storm, especially across the Manahawkin area as well as across Monroe Township in Gloucester County.

As is the case with the type of robust upper level energy we were dealing with in a moisture-rich environment, brief spin-up tornadoes can occur.  Sometimes they are more like rotating downbursts, gusty winds that are pulled down to the ground quickly due to the volume of rain in a particularly soaking thunderstorm. Sometimes these can produce EF-0 or EF-1 level winds (up to or just over 100 mph).  You can see the rotation on the doppler radar below as the storm approached Manahawkin just after 10 AM -- the greens hooking around an area of yellow and pink, indicative of rotating winds within a thunderstorm.  This did produce a tornado in the Manahawkin area that rated EF-0 (lowest possible rating).

The storm was producing very intense rainfall, especially on the eastern flank of the cell.  Flooding occurred on parts of Long Beach Island besides the damage that occurred on the Mainland.

This cell's history was pretty ominous through most of South Jersey -- showing signs of rotating winds at various times from Mullica Hill east through Hammonton on east towards Manahawkin.

In this case -- the rotation couplet as it works through the Hammonton area was not as defined an hour prior to Manahawkin (the greens are weak in comparison to the yellows and pinks to its north). There were some rather gusty winds...and enough to cause some damage across the Pinelands in South Jersey. It probably was not tied to the rotation or any weak tornadoes that may have dropped farther west or at the Shore, but straight line winds and downbursts are certainly doable in this type of setup with heavy rain.  The rotation part is immaterial.

All of this put together, the upper level disturbance and mesolow that developed yesterday morning contributed a lot of headaches to commuters and non-commuters through the region, whether it was from the flooding rains or from the severe weather.