October (Pre-Halloween) Snowstorm 2011
This historic late October snowstorm came on the
heels of our first snowfall of the season on Thursday October 27th.
This storm picked up where last winter left off, as
an anomalous early season Nor'easter tracked south and east of the
The storm from the vast majority of the guidance
(ECMWF was an outlier holding on) disappeared until 48-72 hours before the
event. The storm 3-5 days out was supposed to miss most of the forecast area
and be further out to sea. The issue continues that the medium range guidance
struggles with coastal low track and development. This storm had some
similarities to the 26-27 DEC 2010 snowstorm. That storm was supposed to have
an impact late in the extended (days 6 or 7), then disappeared for 2 or 3 days,
then came back 48 to 72 hours before the actual event. This storm didn't start
showing a somewhat decent consensus with the guidance until 48 hours before the
event. The consensus did get better in the 36 to 48 hour timeframe (the
The European Center Medium Range Weather Forecast (ECMWF) model had the best handle at longer ranges (beyond a few days) on this nor'easter, by forecasting this event nearly a week out. The Global Forecast System (GFS) model did not pick up on the storm until only a few days before it occurred. The 12Z THU 27 OCT GFS started trending further north and west grazing the southern zones of the ALY forecast area. This trend north and west trend continued on the next several model runs.
The ECMWF still might be the best long range model during the "cold" season. However, we will have to monitor its "potential" successes on future Nor'easters. Also, no matter what time of year, when snow falls hard enough, it will accumulate as much as it does in the middle of winter. It should be noted the ECMWF QPF varied quite a bit on the areal extent north and west of the cyclone track. This makes it very challenging on where to place watch, warnings, and advisories. QPF distribution continues to be a big challenge with all the operational guidance with coastal cyclones.
The synoptic setup before the storm included weak
ridging upstream across the northwest CONUS. A short-wave was moving through
the southern branch of the jet stream and it produced a snowstorm in the
Two days before the unusual early season historical
"epic" snowstorm, a weak system nonetheless produced our first
snowfall on October 27th. Low pressure rippling along an ana-type cold front
(precipitation displaced behind the boundary) had just enough cold air to
change the rain to snow most places. After the departure of this first storm,
there was plenty of cold air in place the when the stronger began developing to
our southwest. A surface anticyclone over southeastern
The two disturbances phased just as they reached the
eastern seaboard, spinning a surface storm off the
It should be noted that a special conference call
(215 pm) was set up by WFO OKX with the HPC Winter Weather Desk Thursday
afternoon to discuss the northward trends of the storm impacting much of the
OKX area, as well as, BOX, GYX, ALY, PHL and portions of BGM's area. No
headlines were issued yet, since this was a drastic cyclone track "trend"
shift. HPC was following an ECMWF and GFS compromise for the track and QPF.
Snow began moving into the southern portion of the
As the upper level dynamics of the system interacted
with the tight thermal ribbon (best low-level baroclinic zone) well south of
the Capital District, the strong 850-700 hPa frontogensis produced an
impressive "single band" of heavy snow with snowfall rates up to 2-3+
inches per hour ! The band worked northward through Dutchess and
Snowfall totals were 2-6 inches in the immediate
Greater District with some minor isolated to scattered power interruptions.
That said, the 3.8 inch snowfall on the 29th easily smashed the previous
official daily snowfall record of just 0.4 inches set back in 2000. Also this
value was the second greatest daily snowfall for any October day in the
Further south, accumulations were much higher, in the 6-12 inch range in valley locations, 12-24+ inches over the higher terrain. Peru in Berkshire County, elevation 2250 feet, report and incredible 32 inches! Further north and west of the Capital District, there were only minor accumulations of less than 3 inches.
Snow to liquid ratios were extremely variable during and throughout the event. Locations in the valleys were as low as 5:1, and the locations in the higher terrain were as high as 15-20+:1.
The ensemble plume guidance over forecasted the QPF for ALY and the Capital Region. It did get the precipitation type right, but the mean QPF amounts were way too high by a factor of two even when the event was ongoing. The plan view graphics also overdid it.
The short-range models did an excellent job indicating the heaviest QPF and best low to mid-level frontogenesis would be over the southern of the forecast area. They did struggle on where the gradient of heaviest QPF would set up. The forecast staff did a good job outlining that locations south and east of Capital Region would be crippled with the heaviest snowfall and widespread power outages in the warning statements issued Friday afternoon.
Based on the forecaster thinking and collaboration
with other offices, it was decided to issue watches and warnings based on the
"large societal impact" of this historic early season snowstorm.
Despite snowfall amounts falling below watch and warning snowfall criteria,
especially in the Hudson River Valley, Capital District and points north and
west, the enhanced headlines for Watches and Warnings was the way to go. A few
inches of heavy wet snow did bring down leafed tree limbs, trees, and
powerlines across the region. It was reported from the Times
The application of CSTAR Cool Season mesocale band research (Novak et al.) worked well for identifying the heavy snow potential associated with the band(s) in advance and in real-time. The evolution, placement and movement of the single band was very challenging. The small band-lets/multi-bands dominated early on before the transition to the single band. Forecasting "gradients" of snowfall continues to be challenging. The track of the bombing cyclone off the coast and the movement of the single "intense" mesoscale snowband was difficult.
Comparison of successive GFSEnsemble and ECMWF runs
Above: Loop of GEFS MSLP forecasts from 1200 UTC 24 October through 0000Z 29 October. Notice the GEFS was not indicating a coastal storm impact until about 1 to 2 days prior to onset.
Above: Loop of
ECMWF MSLP forecasts from 0000 UTC 25 October through 0000 UTC 29 October (top)
and 1200 UTC 24 October through 1200 UTC 28 October (bottom). Note the ECMWF was predicting a coastal storm
impact in the northeastern
Above: SREF 4 panel initialized at 0300 UTC 29 October showing MSLP (upper left), 500 hPa heights (upper right), 24 hour probability of >8” of snow (lower left) and 24 hour probability for 1 inch liquid equivalent precipitation (lower right). Note the SREF was consistent with the other guidance just prior to the onset of the storm.
Above: Verification of the ECMWF (blue) and GFS (red) compared to the Global Data Assimilation System (green) position based on observations.
Some basic GEFS and SREF forecast parameters
Above: GEFS 850 hPa winds and anomalies (left) and SREF 850 hPa winds and anomalies(right). Note the 850 hPa winds and anomalies exceeded -4 SD which supports localized extreme snowfall amounts. The GEFS and SREF began to capture the magnitude of the anomalies on about the same initialization time, around 27 October.
Above: GEFS 24 hour probability for 1 inch of liquid equivalent precipitation (left) and SREF 24 hour probability for 1 inch of liquid equivalent precipitation (right). The GEFS and SREF began to capture the probabilities for 1 inch of liquid equivalent precipitation on about the same initialization time, around 27 October.
Above: Same as above but probabilities for 2 inches of liquid equivalent precipitation.
Above: GEFS plume diagrams for Albany NY, Monticello NY, and Bradley Field CT. Notice the clustering at or above 1 inch of liquid equivalent precipitation at all three sites as the storm onset approached, with Bradley Field, CT showing the possibility for around 2 inches of liquid equivalent precipitation.
Above: Same as above except from the SREF. Note the spreads in the plumes were greater than in the GEFS but the clustering and maxima were similar.
AWIPS D2D images of model derived fields
Above: Four panel displays of 500 hPa heights and vorticity (color filled) from the NAM (upper left), GFS (upper right), ECMWF (lower left) and GFSEnsemble mean for 5 consecutive runs between 0000 UTC 27 October and 0000 UTC 29 October. Note that as the onset of the storm drew nearer, the guidance came to more of a consensus. Also note that the ECMWF showed a consistently more amplified system in each model run.
Above: Four panel displays of MSLP from the NAM (upper left), GFS (upper right), ECMWF (lower left) and GFSEnsemble mean for 5 consecutive runs between 0000 UTC 27 October and 0000 UTC 29 October. Note that the ECMWF showed a consistent signal for a coastal storm in each model run, and the spread in the GFSEnsemble decreased as the onset of the storm drew nearer.
Above: Four panel displays of liquid equivalent precipitation from the NAM (upper left), GFS (upper right), ECMWF (lower left) and 24 hour probability for 1 inch from the GFSEnsemble mean for 5 consecutive runs between 0000 UTC 27 October and 0000 UTC 29 October. Note that the ECMWF showed precipitation over the northeastern U.S. well before any of the other models and GFSEnsemble.
Above: Four panel display of 850 hPa temperatures (top) and 925 hPa temperatures (bottom) from the GFS (left) and NAM (right). Note the temperature profile was showing below freezing temperatures through the layer.
Above: Four panel display of 850-700 hPa winds and isotachs (top) and frontogenesis (bottom) from the the GFS (left) and NAM (right). Notice the very tight thermal gradient nearly parallel to the wind flow and the unusually strong frontogenesis.
Above: Time sections from the NAM showing temperatures, omega and relative humidity for the southern Berkshires (upper left), Albany, NY (upper right), the Catskills (lower left) and Glens Falls, NY (lower right). Note the maximum upward motion penetrates the dendritic growth zone above 700 hPa in the Berkshires and above 600 hPa at the other locations, with the most elevated core of upward motion in Glens Falls, the furthest northwest location.
section from the NAM showing temperatures, omega and relative humidity from
south of eastern Long Island, NY through Connecticut, the Berkshires and to
about Albany, NY. Note the strongest
upward motion in
Soundings from 0000 UTC 30 October from Albany, NY (left) and Upton, NY
(right). Note the thermal profiles are
below freezing in Albany, and just a little above freezing between 850-700 hPa
at Upton, NY. Also note the convective
instability indicated in the
maps over the lower 48 states (left) and the northeastern U.S. (right). Note the track was just southeast of
NWS Albany, NY web page
Snapshot of the NWS
Above: Visible satellite picture of the departing storm showing the eye like feature (left) and snowfall (right).
Above: Water vapor imagery.
Above: Visible satellite imagery.
Above: Consecutive loops of radar reflectivity.
Pictures and NESIS Scale
Above: Picture from Great Barrington, MA (left) and from a Weathernet 6 spotter in Pittsfield, MA (right).
Above: Preliminary NESIS Scale is a 1 out of 5, or notable.