10 February 2010 storm (Click on image for larger display)

 

 

This was the second major snowstorm to affect the east coast in less than a week. This storm tracked a little further north than the 5-6 February storm, and the northern periphery of the precipitation shield was quite a challenge to forecast. The uncertainty affected the forecast process in southern NY and southern New England.

 

This storm was interesting in that the main energy that drove it, came from the polar jet stream versus the over active southern jet stream where storms had been impacting the mid-Altlantic for the past month. A strong upper level low dived south from Canada, across the midwest on Monday. This system interacted with energy from the southern stream as it moved eastward very close to the Interstate 70 corridor from Saint Louis to the eastern shore of Maryland.

 

Teleconnections for this storm included a continued persistent negative NAO, a moderate ENSO and the MJO went into its phase 8, a favorable position for east coast storms. The ultimate track of the storm was handled fairly well with few exceptions by most of the longer range models. Initially, the GFS and Canadian Long Range Models correctly tracked the main center of upper energy and associated surface low pressure well south of Long Island by over 100 miles. However, the ECMWF during the 3-6 day period, forecasted the upper air low and associated surface storm to trach more to the northeast, right off (and in one run, actually tracking well inland of Long Island!)

 

By Monday, two days prior to the event, most of the model guidance indicated that the initial upper air low/surface storm tracking through the Ohio valley would transfer energy to a much stronger storm off the Mid Atlantic coast. The dilemma remained, how far north would this storm and associated frontogenesis get.

 

Unlike the past storms that had slipped to our south, there was little if any blocking surface high to the north with this event. Also, the 850 hPa circulation indicated an easterly flow (as opposed to a northerly flow) well to the north of Albany which implied there would be little inhibition of the precipitation once it began moving north.

 

The QPF associated with the storm was extremely challenging. By Monday afternoon, the 12Z NAM and 12Z GFS both backed off QPF amounts in the Capital District indicating little if any locally, virtually none north. Both models kept the storm moving tracking more to the east as opposed to northeast. They both still however indicated half an inch or more to the south. The 00z ECMWF was pretty much on its own, still tracking the storm very close Long Island, indicating more of a snowstorm impacting most (if not all) of our area with significant snow. The 12Z ECMWF came in, and not only turned the storm more to the east, more in line (if not even further south) than the GFS/NAM, but had the lowest QPF of all. It barely gave anything to Albany and points north, and gave less than half an inch to most areas south.

 

As we head into Monday and especially Tuesday morning, both the GFS and NAM trended considerably higher with the QPF while shifting the surface and upper air low only very slight north. However, there was nothing significantly different in the forecasted mass fields, yet the QPF was quite different, ramping upward, especially with the 12z NAM. The 12Z NAM was around half an inch of QPF locally, closer to an inch south and even a quarter inch well north and west.

 

The locally generated WRF forecasted even higher amounts, three quarters of an inch to Albany, and well over an inch to the south. That model implied nearly two feet of snow could pile up in our southern Catskills! This model was actually supported by the 12Z Canadian GEM which produce nearly half an inch of liquid equivalent to Albany and about an inch south. Another important piece of information was that the TRENDS of both the 12z MREFS and especially 12Z SREFS all indicated a significant upward bump in QPF. The average of both the 12Z MREF/SREFS was around a quarter inch for Albany. Unfortunately there are no sites for plumes in our southern areas around Poughkeepsie. Bufkit and Model Cross Sections indicated good frontegenetic forcing in our southern areas, with EPV on top of the frontal slope, indicative and potentially good snow banding.

 

The 12Z Tuesday European model came with only a slight upward trend QPF but basically held its ground keeping the upper air low/surface low and frontogenetic band well south of our entire region. It gave Albany about a tenth of an inch QPF, still higher than reality, but turned a lot closer to the truth. This model also indicated less than half an inch of liquid even in our southern areas, which verified.

 

The 18Z on Tuesday considerably cut back the QPF from Albany north, but still had hefty amounts well over an inch just to the south. The 18z GFS came in with a similar trend but not as dramatic.

 

The 00Z Wednesday NAM run essentially kept the .01 QPF line right around Albany, but still give brought heavy amounts to nearly an inch to the Catskills. Later runs were more consistent on this idea. The 00Z European was the most consistent, bringing only 0.05 inches to Albany, and amounts to less than half an inch to our southern areas. This model was supported by the 00Z GFS.

 

Later runs of the RUC and NAM continued to show very high amounts of QPF in our southern areas, with a fairly sharp cutoff to the north. While the northward trend was correct, the models continued to seriously overforecast QPF amounts in our southern areas. The 12z NAM on Wednesday finally started to get the QPF close, but it was too late to make any changes on its own.

 

The "real" snow began in our southern areas well before sunrise Wednesday but did not reach Albany proper until about 800 AM and areas north after that. Snow made it as far north as Glens Falls. The heaviest snow associated with the frontogenetic forcing never really made it into our area.

 

What was interesting is that the precipitation shield looked more "cellular" than stratiform on the radar. Little "bandlets" of snow would form. Out our window, the snow flakes were initially small, but got fairly large indicative of some ascent in the "optimal" snow growth area. The bandlets produced a few tenths of an inch to an inch locally. It just appeared as the surface storm "exploded" to our south, and tracked east (instead of northeast) it probably robbed moisture to north of the area. It is still unkown as to why the shield was more cellular than stratiform. Had it been a uniform shield of moisture, there would have been snowfall around the entire area. So in summary, the storm track remained just south of the area, putting us on the edge of the heavy QPF.

 

The forecasts of the northern edge of the precipitation shield from guidance shifted from run to run over the course of several days, which made decisions on watches and warnings very difficult. Some sense for the shifts in precipitation forecasts can be seen in the attached loops of the GEFS, SREF, NAM and GFS.

 

There were some issues regarding user dissatisfaction with the snowfall predictions along the northern periphery of the precipitation shield. There is always a high degree of uncertainty in snowfall predictions along the northern periphery of precipitation shields, and the forecasting community, including the NWS, broadcast media, and private sector likely did not communicate uncertainty effectively, leading to certain expectations from all user groups. When those expectations were not met, in other words, when less snow fell than was predicted, the user some segments of the user community expressed dissatisfaction with the forecasts. Click on this link for an e-mail discussion from the SUNYA MAP list about this issue.

 

Above Loops of successive runs of 850 hPa wind anomalies from the GEFS, SREF and NAM, valid 00Z 11 February.

 

 

Above Loops of successive runs of 24 hour snowfall from the GEFS, SREF and NAM, and liquid equivalent from the ECMWF valid 06Z 11 February.

 

Above Loops of successive runs of 24 hour probability of 1.00 liquid equivalent from the GEFS and SREF valid 06Z 11 February.

 

 

Above Loops of successive runs of 24 hour probability of 0.50 liquid equivalent from the SREF valid 15Z 11 February.

 

 

Above Visible satellite image at 1955Z 10 February. Note the storm had an eye as it tracked offshore southern NJ.

 

 

 

Above Storm was preliminarily ranked category 2 on NESIS Scale.

 

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