Friday, January 18, 2013

Too Little, Too Late

The Delaware and coastal South Jersey snowstarved looked like they were in line for at least *some* snow last night.  Unfortunately, outside of a short burst of snow that finally took over in the finale of yesterday's "on and off" event, that really wasn't the case for many of them.

One of the problems with yesterday's system down to the south was the presence of some low and mid level milder (and drier) air in the atmosphere.  Temperatures were slow to cool down, due in part to precipitation being modest during the evening hours. While it was raining, rains were modest in intensity and were unable to draw colder air down from aloft.  Dry air was edging in from the northwest (which was the reason why radar returns were suggesting it was raining aloft but little more than a few sprinkles, flakes, or sleet pellets reached the ground in the city) and was limiting the heavy, steady nature of precipitation.   The result was a slower than expected temperature decline, a slower-than-expected changeover to snow, and little to no accumulation in much of the areas where one to three inches fell.

Human forecasts weren't the only thing to bust.  Yesterday's European computer model tried, strongly, to suggest precipitation would be heavier and steadier across southern portions of the region and attempted to paint upwards of a quarter inch of precipitation in Philadelphia yesterday and tried to paint a half inch of precipitation in Atlantic City.  That didn't work too well.

There are varied excuses -- dry air, mild air, precip not heavy enough. In this case, those excuses are why we couldn't coax the changeover to snow down to our south until the very end of the event...and only why coating type accumulations could be the best some areas of Delaware could muster.