16 February 2010 Overachiever Storm (Click on image for larger display)

 

On 16 February a quick-moving storm tracked across southern NY and southern New England. The storm was associated with a small but dynamic closed upper low, with a very cold pool aloft. The consensus on the timing, track and QPF for the storm from all guidance sources was good, and the storm overall was well predicted across the northeastern U.S. Temperatures were predicted to be within a few degrees of freezing, and the liquid:snow ratios were expected to be around the climatological 12:1, or a little wetter, perhaps as low as 10:1 due to the relatively warm air at the surface and through the boundary layer.

 

Widespread advisory-level snows were expected across the region, with as much as 4-8 of snow in some of the high terrain in and around the Catskills and Helderbergs, and 2-4 or 3-6 in most other areas of the region. However, liquid:snow ratios ended up being 15:1 and in some cases nearly 20:1, so observed snowfall was on the higher end of predicted ranges, resulting in many areas receiving 4-7 of snow, which is near warning levels.

 

Looking at the forecast guidance, the magnitude of cold air aloft was generally overlooked, and based on analyses, the favored -12C to -18C layer was situated at or above 700 hPa over most of our region, right in the heart of the strongest vertical motion. The ideal dendritic growth region and vertical motion may have contributed to the most efficient precipitation production and intermittent heavy snowfall rates. The Graphics below show the forecast guidance, and the observed snow totals.

 

 

 

Above: GFS liquid equivalent QPF from the 12Z 15 February and 00Z 16 February initializations. Note the 0.25-0.60 liquid equivalent that was being predicted.

 

 

Above: NAM12 and NAM80 liquid equivalent QPF from the 12Z 15 February and 00Z 16 February initializations. Note the 0.25-0.60 liquid equivalent that was being predicted.

 

 

Above: GFS snowfall forecast from the 12Z 15 February and 00Z 16 February initializations. Note the general 2-5 that was being predicted.

 

 

Above: NAM12 and NAM80 snowfall forecast from the 12Z 15 February and 00Z 16 February initializations. Note the general 2-5 that was being predicted.

 

 

 

Above: Temperature forecast from 00Z 16 February GFS for 700 hPa, and SREF probability for >4 inches of snow in 12 hours from the 09Z 15 February and 03Z 16 February initializations. Note the -12C to -18C temperatures at 700 hPa. Also note the highest probabilities for >4 inches of snow were well east of our forecast area.

 

 

Above: GFS time/height display of temperature (dashed) vertical motion (solid contour) and relative humidity (color shaded) from the 12Z 15 February and 00Z 16 February initializations for Albany, NY. Note the vertical motion and nearly saturated relative humidity within the region of -12C to -18C temperatures.

 

 

Above: NAM time/height display of temperature (dashed) vertical motion (solid contour) and relative humidity (color shaded) from the 12Z 15 February and 00Z 16 February initializations for Albany, NY. Note the vertical motion and nearly saturated relative humidity within the region of -12C to -18C temperatures.

 

 

Above: Daily snowfall analysis 12Z 16 February though 12Z 17 February. Note that most of our area outside of the Adirondacks (that received little to no snow) received 4 or more inches of snow.

 

Any comments, questions or suggestions, please mail to:Neil.Stuart@noaa.gov