This was a storm of
historical proportions, especially in terms of wind and rain. There was some
snow, sleet and freezing rain in higher elevations of the Catskills, Helderbergs, Berkshires,
All sources of guidance and
ensembles pointed to a major storm 5 or more days prior to onset, but as usual
the fine details of precipitation types, potential flood impacts and wind
impacts could not be determined until about 12-24 hours prior to onset. Part of
the problem was determining how much cold air would be able to anchor itself in
the region to produce winter precipitation. The ECMWF was most accurate in
depicting sub freezing temperatures at the surface over higher elevations, 5
days prior to onset. Although temperatures through the rest of the boundary layer
were less consistent from guidance sources. By 1-3 days prior to the event, the
GFS and GFSEnsembles suggested colder surface
temperatures in areas of higher terrain. By 1-2 days prior to the event, even
the NAM12 was focusing on colder temperatures around areas of higher terrain.
Another aspect of precipitation type that was exceptionally difficult to
resolve, was the elevation dependence of snow vs. sleet vs. freezing rain and
rain. The levels at which each precipitation type were occurring were not only
different from the Catskills to western
The pure model snowfall forecasts for snowfall in higher elevation were not consistent, with some guidance predicting feet of snow, and others <7 inches. Very short-fuse Winter Storm Warnings and Winter Weather Advisories were issues due to the high levels of uncertainty. It was decided that due to the multiple precipitation types in short distances and elevations, all precipitation types would be highlighted in the Warnings and Advisories, and some distinguishing of elevations would be provided in the statements. In fact, since some parts of the Berkshires reported up to 0.25" of ice, and parts of the Helderbergs reported accumulating sleet and snow, that further reinforced the idea to include all precipitation types in the WSW statements. We initially began the warning idea of 1500' elevation. However, by Saturday afternoon, several reports of sleet and ice were received at elevations around 1000'. We quickly made the change to lower the freezing levels which proved to be more correct.
The Flood Watch was issued
far in advance of the storm, due to the consistent signal in guidance for multiple
inches of liquid equivalent precipitation, especially in the Catskills and
Wind forecasts were another
challenge. The anomalous winds were expected to reach Wind Advisory criteria,
especially in areas of higher terrain, but there was the possibility for some
localized damage from stronger winds. Again, the winds exceeded -5 SD,
translating to 70+ knot winds, and the potential to mix the full force of the
wind to the surface was in question. Wind Advisories were issued for much of
the forecast area. Some of the observed winds outside the forecast area, from
Above: Heights and Vorticity
forecasts at 500 hPa from 00Z March 9, and 12Z March
12 from multiple sources of guidance.
Although there was broad agreement on the evolution and track of the
slow-moving upper level system, there were important differences when looking
at the specific tracks of the upper features in all sources of guidance. Subtle differences in track and timing could
result in significant differences in impacts throughout the northeastern
Above: MSLP forecasts from 00Z March 9, and 12Z March 12 from multiple sources of guidance. Although
there was broad agreement on the evolution and track of the slow-moving surface
low pressure center, there were important differences when looking at the
specific tracks of the surface low pressure centers in all sources of
guidance. Subtle differences in track
and timing could result in significant differences in impacts throughout the northeastern
Above: Ageostrophic winds at 925 hPa from 00Z March 9, and a forecast loop from 12Z March 12 from multiple sources of guidance. Note the strong north to northwest ageostrophic flow suggesting colder and dryer air continuing to advect into the region during the storm.
Above: Precipitation and snowfall forecasts from
multiple sources of guidance. Notice the
heaviest precipitation was forecasted to favor areas of higher terrain,
especially the Catskills and western
Above: Temperature forecasts at 850 hPa, 925 hPa and a loop of forecasted surface temperatures from multiple sources of guidance. Notice the 925 hPa and 850 hPa temperatures were suggesting changing precipitation types in different areas at different times, but still favoring snow, sleet and/or freezing rain at higher elevations. The different sources of guidance were in noticeable disagreement as to the evolution of the 850 hPa and 925 hPa temperatures, creating high uncertainty in precipitation type forecasts. Surface temperature forecasts from different sources of guidance were also in considerable disagreement, but generally showed the coldest temperatures in areas of highest terrain.
Above: Wind barbs and U wind anomalies at 850 hPa, valid 00Z 14 March from the GEFS and GFS. Notice the consistency from run-to-run, and as the event neared, the predicted anomalies increased due to better resolution of the system. Also notice the remarkable areal extent of anomalies exceeding -4 SD, illustrating some of the most widespread extreme wind anomalies ever observed in a cool season nor’easter.
Above: Wind barbs and U wind anomalies at 850 hPa, valid 00Z 14 March from the SREF and
Above: Wind barbs and U wind anomalies at 250 hPa, valid 00Z 14 March from the GEFS and GFS. Notice the remarkable areal extent of anomalies exceeding -3 SD. In some cases the wind anomalies exceeded -4 SD, which represents some of the most extreme 250 hPa U wind anomalies ever observed, illustrating how cut off the storm was from the steering flow.
Above: Wind barbs and U wind anomalies at 250 hPa, valid 00Z 14 March from the SREF and
Above: PWAT and anomalies from the GEFS and SREF showing anomalies of 2-3 SD above normal. The moisture being entrained into the storm was well above normal.
Above: MSLP and anomalies from the GEFS. Note the surface high over southeastern
Above: GEFS probabilities for 2.00”, 3.00” and 4.00” of liquid equivalent precipitation. Notice the very large area of high probabilities for >2.00”, and some of the largest areas of probabilities for 3.00” and 4.00” ever observed in a cool season nor’easter. Compare the probabilities with the locations of maxima in the observed precipitation at the bottom of this page.
Above: SREF probabilities for 2.00”, 3.00” and 4.00” of liquid equivalent precipitation. Notice the very large area of high probabilities for >2.00”, and some of the largest areas of probabilities for 3.00” and 4.00” ever observed in a cool season nor’easter. Also note the remarkable agreement between the GEFS and SREF with regard to the 3.00” and 4.00” probabilities. Compare the probabilities with the locations of maxima in the observed precipitation at the bottom of this page.
Loops of GEFS plumes from
Above: Loops of SREF plumes from
Above: Successive loops of water vapor satellite
imagery. Notice the large area that the
storm covered, and the multiple smaller impulses embedded within the larger
circulation. Also notice the barotropic circulations that developed over the
Above: Visible satellite imagery. Notice the large area that the storm covered, and the multiple smaller impulses embedded within the larger circulation. Also note the areas of convection and lightning embedded within the large circulation.
Above: Radar loop over the course of 2 days, showing the enhanced precipitation in higher elevations, and the break-up of the precipitation in valley areas.
Above: Radar loop from KDIX showing strong convection with high winds and hail locally just under 1” in diameter. The 12Z sounding from KOKX showed remarkable instability above 900 hPa that supported the development and maintenance of the convection.
Above: Observed stage 4 precipitation over the 3+
day storm. Notice the widespread 3”+
across NJ, southern NY and southern/eastern