January 26-27, 2015 Blizzard – a glancing blow to the NWS Albany, NY Forecast area (Click on images to enlarge)

 Overview:

A powerful, and in some areas historic Nor'easter affected parts of the Northeast U.S. from late on Monday Jan. 26 through much of Tuesday Jan. 27. This type of storm ended up resembling more of a Miller Type-B, as the primary (clipper low) weakened as it moved into the Ohio Valley and Penn and coastal development occurred just off the N. Carolina/Delmarva coast as multiple pieces of energy helped to dig the upper trough. The upper trough quickly became negatively tilted Mon. evening along the eastern seaboard, with a distinct baroclinic leaf evident in the water vapor imagery from the Mid-Atlantic region into parts of the Northeast. The surface cyclone then deepened rapidly as the mid/upper level circulation closed off Monday night. The storm ended up tracking very close to the 40/70 lat/lon intersection deepening to a 978 mb cyclone Tuesday morning, before gradually filling and tracking well east of Cape Cod.

With the storm taking a more easterly track, there was considerable snowfall across a swath from Long Island north and east to coastal CT, RI, central/southern MA, and coastal NH/ME. Blizzard conditions verified for areas along and near the coast with in some cases Hurricane force winds. The forecast confidence was high in these areas, with the precipitation directly associated with the coastal low, with warm advection/isentropic lift as well as cyclonic vorticity advection. The snow that fell across the Albany CWA was primarily from deformation, as well as Mohawk-Hudson convergence locally in the Capital District. So snowfall totals were at least close to the lower end of the range of our forecasts from around the Capital District northward (generally 4 to 8 inches), with much less snow than forecast to the south and east of Albany for areas such as the eastern Catskills, Mid-Hudson Valley, Taconics and western New England (1 to 11 inches observed, but 14 to 24+ inches forecast).

What was learned from this event:

This event posed significant challenges from both a forecasting and communication perspective. Being on the northwest periphery of a strong Nor’easter, there is usually quite a tight gradient in observed snowfall. As a result, typical probabilities for various snowfall forecasts are wide-ranging along this northwest periphery. From synoptic and sub-synoptic perspectives, typically the mechanism for ascent is deformation farther away from the main surface cyclone, which is usually more localized. However, closer to the coastal cyclone there are more favorable factors for large scale ascent from warm advection/isentropic lift and additionally from cyclonic vorticity advection and upper level divergence from coupled upper level jet structure. So the higher confidence forecast was for coastal areas of New England while across the interior there was much lower confidence in any one solution or snowfall range.

There was not a clear signal much ahead of time this coastal storm/nor’easter would develop. On Thursday the 22nd a northern stream low was expected to pass just to our southwest with widespread QPF possible for Monday. Guidance was not in agreement with the track or timing of the system. The GFS was slower and stronger than the ECMWF. On Friday the 23rd the guidance had come into better and had the low tracking farther to the south; missing the local area with QPF.

On Saturday the 24th guidance was stronger with the low passing even farther south and indicating a coastal storm would develop with rapidly deepening. Winter Weather Headlines were already in effect for current snow. When Winter Storm Warning for Litchfield County was downgraded to an advisory the HWO was upgraded and “THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.” was added to the outlook.

The nature of the Nor’easter not developing until Monday night while demands for deterministic forecasts from decision makers, as well as providing a consistent message from the NWS WFOs and WPC ahead of the event was extremely challenging. This in part was due to a wide range of solutions as recent as one day before the event (Monday Jan. 26) with regards to the track and more importantly the gradient on the northwest edge of the precipitation shield (through the ALY/OKX/PHI/BTV forecast areas). Also, based on the multi-member probabilistic snowfall from WPC, the probability range of snowfall for ALB varied from as little as a few inches at the 10% level, to as much as 18 inches at the 90% level. The 50% level range was 8-10 inches for ALB. This level of uncertainty is very difficult to communicate to our various groups of users. Probabilistic information can be conveyed to Emergency Managers in conference calls and briefing slides, but for the general public and other users most of the guidance people use is deterministic (point-and-click forecasts and the Storm Total Web graphic).

From a model perspective on Monday Jan. 26, comparing sources of operational guidance there was great discrepancy regarding the eventual track of the storm once significant cyclogenesis occurred. The eventual track played a crucial role in QPF and snowfall. There were two main camps of the single operational models from Monday Jan. 26 at 12Z. The NAM/ECMWF were farthest north and west and showed significant QPF from mainly the Capital Region eastward (highest totals in western New England), while the GFS/Canadian indicated a slightly farther track south and east, with the heaviest QPF generally limited to southern Taconics and southern portions of western New England. Ensemble guidance from the SREF indicated considerable spread in the 09Z Jan. 26 plumes at ALB, with QPF ranging from a few tenth of an inch to around 2 inches. This further bolstered the case for great uncertainty along the northwest periphery of the storm.

Early on Monday morning, the 26th, with the warnings already in place both the 00Z NAM and 00Z GFS came in with much lighter QPF than the previous runs. The SREFS and GEFS reflected this downward trend as well. This put us into a bind. If we followed this QPF we would have had to take down the warnings, or downgrade them to advisories. WPC graphics actually cut back snowfall amounts a bit. Had we followed them to the "tee" we would have been forced to downgrade the Capital region to an Advisory. The 00Z ECMWF came in with higher QPF amounts easily supporting Warning criteria. We decided to "stay the course" and collaborated that message with WPC and surrounding office, keeping most of the snowfall amounts at a very similar level as the previous shift. We did decide to cancel the Watches for the Mohawk Valley and Lake George Saratoga region, converting them into Advisories.

The potential for mesoscale banding was mentioned, especially across the southeast portion of the forecast area, but this never really developed since banding directly associated with the coastal storm was across Long Island and eastern/coastal New England.

Then both the 06Z NAM and especially 06Z GFS models came in with considerably higher QPF amounts again, mainly in the peripheral areas (like the Capital region). Since both of the guidance trended higher, our confidence increased about the Warnings.

An examination of the CIPS which attempts to analog events based on the overall synoptic pattern and the current ENSO cycle. The analogs indicated storms from February 25 1989 and other dates where little or no snow fell in the Capital region, heavier snows much further east and south.

The 00Z NAM trended a lot lower with QPF everywhere. Interestingly enough, the 00Z GFS guidance, while certainly lower than pervious runs, still indicated we could have a low end warning in at least our southern areas. However, the QPF clearly feel short (well under a quarter inch) from Albany north and west. We anxiously awaited the Euro, and finally, this was the first time it too really backed off the QPF everywhere. A band of snow attempted to make it into our eastern areas after midnight and we issued SPS/SVS for this band as it worked into Litchfield County.

The first band fizzled as it worked into the Dutchess County. Then a real synoptic mesoscale band began working into our eastern areas. We watched as this attempted to do so around 2-3 early morning. It too fizzled as it encountered too dry of air. Still it looked like snow could make it into the Hudson valley.

With all the guidance indicating much lower QPF (in some cases barely anything) for the Capital region, we decided to go ahead and downgrade the warning to an advisory. This was done by 400 AM with the ESTF update. The 06Z NAM came in with practically no QPF for the Capital region westward, but the GFS, while still lower, indicated advisory snow could still fall as far west the CD. By 600 Am, the band of light snow that worked into our eastern regions began shriveling up as it crossed the Hudson valley. I decided and discussed this with Monty, to downgrade on remaining Winter Storm warning in the Hudson valley and Taconics as it was obvious these areas would not reach winter storm criteria. Per coordination with BOX and OKX, we decided to leave the warnings up in adjacent New England.

Toward the end of the storm, there was no evidence that any deformation band would form that ultimately gave the Capital District and some surrounding areas 4-8 inches (enhanced by MHC). It looked to us as if the dry air was just to much for this incoming Atlantic moisture.

Mohawk-Hudson convergence likely occurred in the Capital District and surrounding areas within a broader area of deformation snow during the day Tuesday. Surface observations indicated westerly winds down the Mohawk Valley (at RME/NY0) and northerly winds down the Hudson Valley (at GFL/ALB). Enhancement for several hours was noted on the radar reflectivity, with a local maxima of 4-8 inches in the Capital District.

With the forecast through the extended completed; we added the potential storm to the HWO: A SLOW MOVING COASTAL STORM MAY BRING SNOWFALL TO THE REGION MONDAY NIGHT INTO TUESDAY. THERE IS A GREAT AMOUNT OF UNCERTAINTY REGARDING THE EXACT TRACK OF THIS SYSTEM...WHICH WILL HAVE AN IMPACT ON HOW MUCH SNOW OCCURS ACROSS OUR AREA. AT THE CURRENT TIME...EASTERN PARTS OF THE AREA HAVE THE HIGHEST RISK FOR SEEING A SIGNIFICANT SNOWFALL. 

Winter Storm Watches were issued on the midnight shift Saturday night into Sunday for most of our CWA. On Sunday many things occurred including the issuance of warnings, conference calls, collaborations and coordination of staffing.

Upgraded all of the watch to a warning with the exception of keeping a watch for northern Warren County and adding Montgomery and Fulton County to the watch and upgraded to a Blizzard Warning for Litchfield County after collaborating with BOX. OKX had already expanded their Blizzard Watch with the morning ESTF and were planning on Blizzard Warning for their entire CWA.  

To ensure forecast consistency used WPC QPF. Snowfall ratio with this storm were expected to be higher than climatology especially as you headed northwest across the forecast area. Used a ratio of 14:1.

 

a)  b)

Above:  Loops of GEFS 850 hPa winds and anomalies initialized at a) 00Z 24 January and b) 12Z 24 January.

a) b)

Above:  Loops of GEFS 850 hPa winds and anomalies initialized at a) 00Z 25 January and b) 12Z 25 January.

a) b)

Above:  Loops of GEFS 850 hPa winds and anomalies initialized at a) 00Z 26 January and b) 12Z 26 January.

a) b)

Above:  Loops of GEFS 850 hPa winds and anomalies initialized at a) 00Z 27 January and b) 12Z 27 January.

a) b)

Above:  Loops of SREF 850 hPa winds and anomalies initialized at a) 21Z 24 January and b) 09Z 25 January.

a) b) c)

Above:  Loops of GEFS plumes for Albany, NY initialized at a) 00Z 25 January, b) 00Z 26 January and c) 00Z 27 January.

a) b) c)

Above:  Loops of SREF plumes for Albany, NY initialized at a) 03Z 25 January, b) 03Z 26 January and c) 03Z 27 January.

Above:  Loop comparison of model MSLP forecasts.

Above:  Liquid Equivalent QPF from the GFS (upper left), ECMWF (upper right) and NAM12 (lower right) initialized on 26 January.

a) b)

Above:  Weather Prediction Center snow forecasts from a) the afternoon of 25 January and b) early morning 26 January.

Above:  Loop of MSLP and areas of falling/rising pressure (shaded).

Above:  Loop of water vapor satellite imagery.

a) b)

Above:  Radar loops from KENX of a) base reflectivity and b) base reflectivity with observations overlayed.

Above:  Snowfall totals.