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. Albany would set two daily snowfall records in 3 days (1.6" on 27 OCT, and 3.8" on 29 OCT)!!!

 

This storm picked up where last winter left off, as an anomalous early season Nor'easter tracked south and east of the New England coastline Saturday evening on OCT 29th, slamming our southern and eastern portions of our County Warning area with a historically heavy snowfall. Many deciduous trees were foliated in the valley locations and across southwestern New England. The wet snow, accumulating on the tree limbs and leaves, resulted in damage or even devastation of many of these trees. As the tree limbs and leaves fell, they took down many power lines which resulted in tens of thousands of people left in the dark, especially south and east of immediate Capital District.

 

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 NAM was the slowest to latch on).

 

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 Denver metropolitan area. Meanwhile, a stronger disturbance traversed from the northwest coast in the northern branch of the jet stream. The big question was whether or not these systems would merge or phase into a stronger storm. They did Friday night into Saturday morning.

 

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 Canada funneled the unseasonably cold air over much of the Northeast Friday into Saturday.

 

The two disturbances phased just as they reached the eastern seaboard, spinning a surface storm off the South Carolina coast. This system in turn, utilized 60-70F sea surface temperature water, still south and east of Cape Hatteras over the Gulf Stream. This storm tracked along or just north of the Gulf Stream, and rapidly deepened and intensified (rapid cyclogenesis), as it moved northeastward on Saturday. It tapped Atlantic and subtropical moisture. The storm was a fast mover, already to the east of Cape Cod Sunday morning. The cold conveyor belt and snow shield associated with the Nor'easter quickly moved eastward over northern and eastern New England by daybreak on Sunday.

 

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. Albany's concern was a further northward trend of the cyclone track and a drastic QPF shift continuing. It was suggested to let another 12-18 hours of model forecast cycles to see if a consistency in the trends continue. However, ALY updated the HWO to include locations south and east of Capital Region for the potential of a moderate to heavy wet snowfall, and a Winter Storm Watch, Advisory or Warning may be necessary, if the trends continue with the impact expanding northward. Watches were put up for portions of the ALY forecast area on the 28 OCT midnight shift, and expanded much further north and west to include the Northern Catskills, Schoharie Valley, Helderbergs, Greater Capital Region, central and northern Taconics, as well as southern Vermont. The Watch expansion was due to the good agreement between the SREFs mean, GEFS mean, GFS, ECMWF, and HPC Winter guidance. The Canadian Guidance and NAM were still outliers with less QPF north of the mid-Hudson Valley, and southwest New England due to a track further off the coast. It was emphasized the Watch was being issued based on the "societal impact" over the northern half of the watch area. It was likely the 7" or greater snow criteria wouldn't be reached, but 2-6" of heavy wet snow on foliated trees could produce scattered to numerous power outages. This dangerous situation setting up also allowed for an upgrade to a Winter Storm Warning over much of the area (excluding the southern Adirondack Region and western Mohawk Valley) by 28 OCT in the afternoon.

 

Snow began moving into the southern portion of the Albany forecast area late Saturday morning on October 29th. Slowly but surely, the leading edge of the precipitation shield reached into the Greater Capital District region by mid afternoon (between 2-4 pm). The ageostrophic northerly wind working down the Hudson Valley continued to feed dry air into the northern periphery of the precipitation shield, which resulted in it taking a long time to reach our northern areas. The virga persisted the longest over the northern tier of the forecast area. The precipitation quickly transitioned to snow due to evaporative cooling over the Capital region. The roads and valley locations were warmer, so it took a little while for the snow to stick. It was a much different story over the eastern Catskills, portions of the Mid Hudson Valley, Taconics, Litchfield Hills, and Berkshires, where the snow stuck early on and piled up quickly. The KENX radar showed initially "bandlets" or several "small feeder bands" moving over these locations. Snow rates were easily 1-3"/hour south and east of the Capital Region with reflectivity rates in the 30-40 dBZ range. We used the snow study done in mid '90s for ESTF's and Special Weather Statement highlighting these heavy snow rates. It seemed some locations in the Berkshires, Litchfield Hills, and south-central Taconics may have received as high as 4 or 5 inches in an hour! Basically, higher reflectivities (40-50 dBZ's) were anticipated to forecast those higher amounts. The problem was the varying snow to liquid ratios during the storm at many locations. The snow started out "heavy and wet" over the higher terrain (i.e. the Berkshires) but became fluffier and drier (a higher snow to liquid ratio) as the storm continued into the late afternoon and overnight period. The next issue was forecasting the evolution and modulation/track of a heavy single snow band with the storm in the 6-10 pm time frame.

 

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 Litchfield Counties during the late afternoon, then into Columbia and Berkshire counties after sunset. Between 6-7 pm, this band made a run into the Greater Capital District. However, the northerly low-level ageostrophic wind was still coming down the Hudson River Valley (cutting off the precipitation over the northern zones...but holding the ptype as all snow) coupled with the cyclone track slightly further south and east of Long Island (the cyclone followed the isallobaric rise-fall couplet further south and east of the Martha's Vineyard and Nantucket), were just enough to pivot this band to the east, stretching it over most of the Berkshires, but missing the northern portions of the Greater Capital District by a few miles. Locations just south and east of the Tri-Cities of Schenectady, Albany and Troy got hit the hardest. There was a tremendous snowfall gradient. Another interesting note, was the performance of the High Resolution Rapid Refresh (HRRR) guidance and the HIRES WRF. The HRRR 3-km Columnar Max Reflectivity product did fairly well, but "wobbled" from run to run how far north and west the 30-40 dBZ echoes would get across the region. Some runs in the morning had the heavy returns getting into the Greater Capital Region. The WRF forecasted reflectivity showed the main snow band a little further southeast than what was eventually observed. The NAM was the most stubborn bringing 0.75" to 1.00" of liquid equivalent over the Great Capital Region with its 00Z, 06Z, and 12Z runs on 29 OCT. The SREF and GEFs plume means and plan view graphics also supported up to 1.00" of liquid equivalent up to ALB all the way up to 12Z issuance on OCT 29th! It turned out the trends down to lower amounts of QPF based on the ECMWF, GFS, and Canadian Guidance were the way to go for locations north and west of Albany once the event was ongoing. The SREF and GEFS means were too high (in terms of QPF). However, the precipitation type of mainly snow was correct.

 

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 Albany area, second only to the 6.5 inches that fell on October 4th 1987. The outlying areas of the Capital Region had 6-12" (portions of Columbia...Greene...Rensselaer and Albany counties).

 

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 half to third 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 Union the Sunday morning that there were around 12,000 outages just in the Greater Capital Region. The 2 to 6 inches that fell over the immediate Capital District still was problematic (i.e. power was out at the intersection of Fuller and Washington Ave. outside of the office).

 

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 U.S. several days before the GEFS indicated a coastal storm impact.

 

 

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.

 

Plumes

 

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.

 

 

Above: Cross 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 Connecticut and the Berkshires.

 

Soundings

 

 

Above: 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 Upton sounding.

 

Surface Maps

 

 

Above: Surface maps over the lower 48 states (left) and the northeastern U.S. (right). Note the track was just southeast of Cape Cod, just southeast of the Cape Cod Canal benchmark that would maximize precipitation in Albany, NY.

 

NWS Albany, NY web page

 

 

Above: Snapshot of the NWS Albany web page showing the large area of winter storm warnings.

 

Satellite imagery

 

 

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.

 

Radar imagery

 

 

Above: Consecutive loops of radar reflectivity.

 

 

Above: Loop of the HIRES WRF forecast radar reflectivity initialized 1200 UTC 29 October. Compare to the actual radar imagery.

 

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.