Thursday, November 08, 2012

So Close, Yet So Far Away For Philly From Snow

30 miles...maybe 40 miles...made all the difference in the Delaware Valley with yesterday's coastal storm. Ocean and Monmouth Counties were the big winners in yesterday's snowfall from the coastal storm, picking upwards of a foot in a few localized spots.  The jackpot of snow to our east was of little consolation to those in Philly who wanted a good snowfall...or to those to the west who couldn't get in on the storm at all and were merely dealing with the fringe effects of a nor'easter that could generate only showers and flakes in the western burbs.

Dry air is to blame west of the city.  Bands of moisture made little progress west of the city as dry air aloft began to weaken those bands of snow, leading to lighter precipitation that couldn't fall heavy enough to lead to much snow from the city on west.  The closest the "wall" of precipitation got was essentially a line from Mercer County south to Mount Holly to near Millville -- places east of there did much better than west.

You can watch the evolution of this over a four hour window -- first at 4:45 PM yesterday, followed by 6:45, and then 8:45.  As the storm's moisture lifted north up the coast, the wall held generally close to the same location over that four hour window.  The deformation band that pummeled Ocean and Monmouth County, north into New York City, with one inch per hour rates, overperformed for those areas at the expense of Philadelphia.

In many respects, snowfall amounts in this storm behaved similar to the snowfall event on December 30th, 2000 (Millennium Storm) in terms of a very sharp cutoff and a very, very localized placement of heavier snowfall.   That storm's snowfall placement was a touch farther west than yesterday's...and produced more snowfall in its maximum.  However, it did have a similar radar placement in terms of a proverbial "wall".

This storm's slight eastward jog also benefited the coast as gusty winds were not as high as feared -- the strongest gusts were generally in the 30-40 mph range at the Shore, as opposed to the 50-60 mph range that was feared in modeling.  Coastal flooding was generally in the minimal range although some places did have widespread minor flooding as the barrier islands are incredibly vulnerable thanks to Sandy.  The tidal gauges at Atlantic City and Cape May only reached "minor" flooding in last night's high tide.

In terms of forecast accumulations -- yeah, it was a bust for Philadelphia.  In terms of impact and snowfall in the region, it was not a bust and it was an overperformer for those east of the city.  30 or so miles in this storm made the difference between Philadelphia getting a few to perhaps several inches of snow, with South Jersey's suburbs getting in on the bullseye, and what the final result was.