The NAO, which had been
neutral through the month of February, was just beginning to trend slightly
positive, as the polar vortex near Hudson Bay Canada was also retreating north
(Fig. 1a).The PNA was trending from
slight negative to neutral (Fig. 1b).A
high amplitude upper ridge developed over eastern Canada consistent with the neutral NAO trending slightly
positive (Fig. 2).This upper ridge
would play an important role in maintaining strong upper level confluence in
eastern Canada that supported a strong, cold surface high pressure
center that would keep the low-level cold air in place over much of the
interior northeastern U.S. during the 2 March storm.
1.Current and predicted
phases of the a) NAO and b) PNA.
2.Plot of 500 Mb heights,
height contours, wind barbs, and temperatures for 12Z 2 March 2007.Note the upper ridge around Hudson BayCanada.
This overall North American
upper-level pattern supported a more northerly storm track across the
continental 48 states, especially for strong southern-stream based systems
tracking out of the southwestern U.S associated with widespread
convection.In fact, the 2 March storm
originated in the eastern Pacific Ocean around 26 February, tracked into the
southwestern U.S. on the southern periphery of a strong upper low, and tracked
into the central plains on 28 February while phasing with northern stream upper
energy (Figs. 3a-e).By 1 March, the
system was tracking into the Midwest and western Great Lakes, as it continued to cut off from the main
westerlies, slowing the movement of the system through the Great Lakes (Figs. 3a-e).Severe weather and deadly tornadoes occurred during this time period in
the mid Mississippi valley.
Figure 3.Water vapor satellite images with lightning
overlay for a) 1800 UTC 27 February, b) 1800 UTC 28 February, c) 1800 UTC 1
March, d) 1800 UTC 2 March, and visible satellite images with lightning overlay
for e) 1800 UTC 28 February, and e) 1800 UTC 1 March.
Late on 1 March and through
2 March, a strengthening upper-level impulse tracked around the southern
periphery of the upper low, enhancing convection across the northern GulfCoastStates and TennesseeValley.Widespread severe weather and
deadly tornadoes occurred in along the Gulf Coast States and TennesseeValley, as the surface low pressure center developed in the OhioValley and mid Atlantic states, eventually strengthening
and tracking through southern New York and New
England the evening of 2
March (Figs. 4a-b).A very anomalously
long and broad 850 Mb jet with southerly V winds >5 SD above normal was
forecasted to track from the southeastern U.S. through the northeastern U.S. with peak winds of near 90 kt
(Figs. 5a-b). The “fist” of the 90 kt jet core (not “nose” since it was so wide
and strong, a “nose” just didn’t do justice to the width and magnitude of the
jet core) tracked through the mid-Atlantic and just south of Long Island (Figs.
6a-b), while 50 kt winds extended north into southern Canada. Due to the very
slow movement of the upper low center into the Great Lakes, only slight low-level cooling and drying occurred
behind the system that brought the mixed precipitation to the northeast U.S. and severe weather to the GulfCoast and TennesseeValley.The deeper cooling and drying
would have to wait until Sunday and Monday as the upper low finally exited into
and through southeastern Canada.
Figure 4.Mean Sea Level Pressure forecasts from the
12Z 1 March NAM12 and GFS40 at a) 30 hours valid 1800 UTC 2 March and b) 36
hours valid 0000 UTC 3 March.
Figure 5.850 Mb wind barbs (kt)
and U and V winds (shaded) for a) 30 hour Short Range Ensemble Forecast valid 1800
UTC 2 March and b) 30 hour Medium Range Ensemble Forecast valid 1800 UTC 2
Figure 6.Plot of 850 Mb wind barbs,
heights and isotachs (shaded) for a) 1200 UTC 2 March
and b) 0000 UTC 3 March.Note the
90 kt maximum along and the North
1200 UTC 2 March and east of Maine
at 0000 UTC 3 March.Also note 50 kt winds into the northeastern U.S.
at 1200 UTC 2 March.
It was clear several days in
advance of the storm, that mixed precipitation would affect most of the
region.Defining regions for each
precipitation type, accumulations, and timing transitions would be critical to
the forecast.Contributing to the
difficulty of the forecast was the wide variety of model solutions for
forecasted temperature profiles throughout our region during the storm.The one high-confidence aspect of the
forecast was high QPF, with guidance consistently forecasting around 2” of
liquid equivalent in southern areas and .75” to 1.5” liquid equivalent in
central and northern areas (Figs. 7a-b).
Figure 7.Quantitative Precipitation Forecasts from the
1200 UTC 1 March a) NAM12 and b) GFS.
The forecast models were
also very inconsistent in the days leading up to the event, with regard to
low-level temperatures (850 mb and 925 mb), which were crucial in determining precipitation
type.Three to four days prior to the
event, the GFS was the “colder” model, while the NAM was forecasting “warmer” temperatures.Then, one to two days prior to the event,
they flip-flopped drastically, with the NAM depicting colder temps in the low levels, while the
GFS was suddenly warmer.This
discrepancy between the operational models also carried over to the ensemble
solutions, which were divided into two camps just prior to the event:the colder MREF, and warmer SREF.This made forecasting precipitation types a
very difficult challenge, especially one to four days in advance of the system.It also became evident that due to
uncertainty, long lead times would not be attainable for this event.
There was a general
consensus by the afternoon of 28 February, that areas from the southern
Catskills through Poughkeepsie and northwestern CT would see mostly rain.The consensus from the majority of guidance
sources forecasted temperatures at least in the lower 40s, adding to concerns
for potential flooding due to snow melt, rainfall, blocked storm drains from
plowed snow, and the outside chance for ice jams, so a Flood Watch was
There was also a general
consensus by the afternoon of 28 February, that the Adirondacks, Lake George Area and southern VT had the best
chance for mostly snow, with possibilities of sleet mixing with at times.Converting the liquid
equivalent QPF using a ratio of 8-10:1 and accounting for some sleet as well,
warning level snow and sleet was expected over this region.A Winter Storm Watch was issued.
The low confidence part of
the forecast was the precipitation type and transitions across the Mohawk and SchoharieValleys into the Capital District, northern Catskills and Berkshires.Would there be warning
level snow, sleet, or freezing rain, or a combination (Figs 8a-c)?A Winter Storm Watch was issued for these
areas on the afternoon of 28 February, with the understanding that it would be
updated to a Warning or Advisory once the details about precipitation types
Figure 8.Plume diagrams from a) 06Z 1 March MREF and
b) 15Z 1 March SREF and c) 18Z MREF.Note the sleet as the predominant precipitation type in most of the
By early on 1 March, several
runs of the operational models and ensembles had shown some loose consistency
on the expected evolution of the system approaching our region, and the evolution
of the sensible weather in the broad mixed precipitation zone.The important Canadian surface high centered
just south of Hudson Bay was setting up with its axis just east of Montreal and Quebec City, nosing south into northern and central New England.All sources
of guidance were indicating that as the new surface low developed along the
triple point of the occluded front, warm front and cold front, and tracked
across southern New York and New England, strong warm advection associated with
the strong 850 Mb jet would push temperatures above freezing in a shallow layer
around 850-800 Mb from the western Mohawk Valley to the Capital District and
Berkshires (Figs 9a-f and 10 a-d), with deeper warm advection further south,
more proximate to the “fist” of the 850 Mb jet core.
Figure 9.850 Mb temperatures from the 1200 UTC 1 March
NAM12 for a) 18 hours valid 0600 UTC 2 March, b) 21 hours valid 0900 UTC 2
March, c) 24 hours valid 1200 UTC 2 March, d) 27 hours valid 1500 UTC 2 March,
e) 30 hours valid 1800 UTC 2 March and f) 33 hours valid 2100 UTC 2 March.Note the temperatures above freezing as solid
contours and below freezing as dashed contours.
Figure 10.850 Mb temperature spread and mean contours
from a) 15Z 1 March SREF valid 15Z 2 March, b) 15Z 1 March SREF valid 18Z 2
March, c) 12Z 1 March MREF valid 12Z 2 March, and d) 12Z 1 March MREF valid 18Z
The surface temperatures
were forecasted to reach just above freezing along and south of the MohawkValley and Berkshires during the last few hours of precipitation.However, the forecasted temperatures at
around 925 Mb were forecasted to be below -2C through the entire precipitation
duration in this region (Figs 11a-d).The operational model soundings (Figs. 12a-e), thermal profiles, Bufkit
data (Figs. 13a-f), and SREF and MREF Plumes (as shown in figure 8) suggested a
few inches of snow changing to 1-3” of sleet for the Mohawk Valley and Capital
District to the Berkshires, ending as a few hours of cold rain with surface
temperatures just above freezing.There
were a few ensemble members suggesting freezing rain to rain.The surface-based cold layer was forecasted
to be shallower over the western part of the MohawkValley suggesting a possible prolonged period of freezing rain (suggested by
the 925 Mb and 850 Mb temperature forecasts in figures 9 and 10).
Figure 11.925 Mb temperatures from the 1200 UTC 1 March
NAM12 for a) 18 hours valid 0600 UTC 2 March, b) 24 hours valid 1200 UTC 2
March, c) 30 hours valid 1800 UTC 2 March, and d) 36 hours valid 0000 UTC 3
March.Note the temperatures above
freezing as solid contours and below freezing as dashed contours.
Figure 12.1200 UTC 1 March model forecast soundings for
Albany, NY from a) NAM12 18 hour forecast valid 06Z 2 March, b) GFS40 18 hour
forecast valid 06Z 2 March, c) NAM12 24 hour forecast valid 12Z 2 March, d)
GFS40 24 hour forecast valid 12Z 2 March, e) NAM12 30 hour forecast valid 18Z 2
March, and f) GFS40 30 hour forecast valid 18Z 2 March.Note in a-d that the
isotherm is touching the 0C isotherm, and warmer than 0C in e and f.
Figure 13.BUFKIT precipitation overviews from a) 1200 UTC
NAM for Albany, NY, b) 1200 UTC GFS for Albany, NY, c) 1200 UTC NAM for Glens
Falls, NY, d) 1200 UTC GFS for Glens Falls, NY, e) 1200 UTC NAM for
Poughkeepsie, NY, and f) 1200 UTC GFS for Poughkeepsie, NY.Blue is snow, orange is sleet, red is freezing
rain and green is rain.
The progress of the HPC WWD
forecasts reflected the low confidence in the precipitation type forecast and
location of the precipitation transition zone (not shown).The ice forecast for central and eastern NY
was generally ¼” to ½” and the zone shifted north and south with each
forecast.Mostly snow was forecasted
along and north of the MohawkValley through the Adirondacks, Lake
George and Saratoga regions into southern VT.
During the early morning
hours of 1 March, a Winter Storm Warning was issued for the Adirondacks, Lake George Region and southern VT, where 7” or
more of a snow and sleet combination was expected.This was based on a high confidence of mostly
snow and sleet for this region, and the anticipated liquid equivalent QPF
converted to snow using 8-10:1.Even
with the relatively wet snow expected, ensemble and operational model output
over the course of 2 or more days were showing 850 Mb U wind anomalies of -4 SD
or less over northern New
England and northeastern New York (Figs. 5a-b), suggesting high probability of
exceeding warning level snows where all snow was expected.The 250 Mb U wind anomalies of -2.5 SD or
less were displaced north of the western Great Lakes, associated with the main upper low, which was
forecasted to track just north of our region, so a prolonged precipitation
event was not expected, as the upper deformation precipitation would not affect
our region.The Winter Storm Watch was
maintained over the Mohawk and SchoharieValleys, Capital District, Berkshires and northern Catskills, due to very low
confidence on whether any one precipitation type or combination would reach
Throughout the day on 1
March, it was clearly evident that there was widespread severe convection associated
with the system, even into the cold sector into the Great Lakes area.This
suggested that downstream upper ridging and dynamic tropopause processes would
result in the system tracking closest to the guidance depicting the further
north and west track, and would favor warmer air at the boundary layer.Surface temperatures were a dilemma, though,
with the strong Canadian surface high pressure center continuing to build into
The decision during the
afternoon of 1 March was to upgrade southern Herkimer County to a Winter Storm
Warning for mostly ice, upgrade the Berkshires for snow and sleet at higher
elevations, and convert the rest of the Watch area to a Winter Weather Advisory
for a few inches of snow changing to an inch or two of sleet, and a few hours
of freezing rain or rain before ending.All the Warnings and Advisories were collaborated with surrounding
offices and were reasonably consistent.Extra staffing was planned for the shift on 2 March with the evening intern able to stay over on the shift to do climate and/or a 06Z sounding if
necessary, and an extra forecaster was scheduled.
A band of snow developed
along the leading edge of the upper-level warm advection that tracked northeast
into our region during the late afternoon and evening of 1 March (Fig.
14).The low levels were so dry that
most of the precipitation did not reach the ground.During the late evening, just prior to , the leading edge of the deeper moisture rapidly
spread north and east across our region (Fig. 15).Precipitation began as a brief period of snow
and sleet from the MohawkValley and SchoharieValleys through the Catskills, Poughkeepsie area and northwestern CT.The precipitation began as snow in the
eastern Adirondacks, Lake George Area, southern VT and the
Figure 14.Regional radar mosaic of composite reflectivity valid 2200 UTC 1
March. (Courtesy NCAR)
Figure 15.Regional radar mosaic of composite reflectivity valid 0400 UTC 2
The precipitation quickly
changed to rain over the southern Catskills and Poughkeepsie area, as freezing rain and an occasional mix with
sleet became the predominant precipitation type across the Mohawk and SchoharieValleys, northern Catskills, Capital District, Berkshires and parts of
northwestern CT between and sunrise.Based on this rapid
precipitation transition, it was decided around on 2 March to lower Winter Storm Warnings in
southern Herkimer and the Berkshires to Winter Weather Advisory.This change was still well collaborated with
surrounding offices, where Advisories and Warnings continued adjacent to
Snow mixed with sleet after
sunrise in the Adirondacks and Lake
George area, while sleet
and freezing rain pushed to GFL and southern VT.Freezing rain and sleet continued in the
Mohawk and SchoharieValleys into the Capital District, Berkshires and northwestern CT through the
morning, becoming just rain in many areas before .Much of the Adirondacks and higher elevations of southern VT had mostly snow
and sleet throughout the storm.Freezing
rain and sleet persisted in favored, protected regions of the Mohawk and SchoharieValleys, Capital District, Berkshires and northwestern CT through much of the
morning of 2 March (Figs. 16a-b).Our
Winter Weather Advisory was cancelled in Litchfield County, CT at around 2 March, while NWS Taunton converted their Advisory in CT and MA to a
Freezing Rain Advisory.NWS Upton
maintained their Winter Weather Advisory in southern CT.The cancellation of the Advisory in Litchfield County, CT was not consistent with Winter Weather and Freezing
Rain Advisories that surrounded LitchfieldCounty from our surrounding offices.However, NWS Upton cancelled their Advisories for southern CT around 2 March.Our
office addressed the localized continuation of freezing rain and sleet in Litchfield County, CT with Special Weather Statements.
Figure 16.Regional radar mosaic of composite reflectivity valid a) 0900 UTC 2
March and b) 1600 UTC 2 March.(Courtesy NCAR)
Hartford, CT media called shortly after inquiring about our office canceling the Winter
Weather Advisory for LitchfieldCounty.They called
at least 2 more times before
and e-mailed pictures of ice in LitchfieldCounty (Figs. 17a-d).Looking at the
pictures, it was difficult to see how much accumulation had occurred on
objects, and whether accumulation was continuing, or if melting had begun.Details on the discussion with Hartford, CT media and the decision-making process for canceling
the Advisory will be provided in the lessons learned.
Figure 17.Pictures from
County, CT sent by WFSB in Hartford CT, e-mailed to our office around 1200 UTC 2 March.
The combination of moderate
to heavy rain and blocked storm drains required Urban and Small Stream Flood
Warnings by mid morning for the Capital District, parts of the MohawkValley, Catskills, Taconics and northwestern CT.Later in the day, rainfall runoff required a
river flood warning for Brookfield, CT.
In general, warning level
snows, with some sleet, fell in the Adirondacks and
higher elevations of southern VT.Warning level ice accumulated in southern Herkimer, parts of Montgomery (Figs. 18a-b) and LitchfieldCounties (Figs. 19a-b).All other areas
except the southern Catskills and Poughkeepsie area received advisory level snow, sleet and ice.
Figure 18.Ice pictures
from the morning of 2 March from near Amsterdam, NY.
Figure 19.Pictures from Litchfield County, CT on the morning of 2 March.
Recognizing widespread convection associated
with the system gave clues that despite the initial low-level dry, cold
conditions, rapid and deep warming would take place, due to the downstream
upper ridging and more northwesterly track of the system.The 850 Mb jet forecast also hinted at a
warmer scenario.This suggested
more freezing rain potential and less initial snow and sleet in the precipitation
transition zone, as the warm layer would be deeper than models
suggested.Model guidance still
needs to improve precipitation type forecasting, but until then, pattern
recognition can help improve our precipitation type forecasts.A local 06Z ALB sounding would have been
helpful as well (Figs. 20a-b).
data through MSAS or LAPS can increase confidence in Warning/Advisory
cancellation/continuation decision making.Derived fields such as Ageostrophic Winds
and Temperature Advection can provide important information on temperature
trends, in addition to monitoring hourly MSLP analyses (Figs. 21a-c).
We must carefully try to determine the weather
in locations between observation points.Using MADIS data on the internet is helpful (Figs. 22, 23a-c, and
Figure 20.Soundings at
Albany, NY from a) 0000 UTC 2 March and b) 1200 UTC 2 March.
Figure 21.MSAS Ageostrophic wind barbs MSLP and temperature advection
valid a) 04Z 2 March, b) 09Z 2 March and c) 12Z 2 March.
Figure 22.Plot of
observation points available from the FSL MADIS web site.
Figure 23.MADIS data
(MSLP, temperatures, dewpoints, winds and precipitation)
and trends from observation points in and upstream, based on surface wind flow,
from southern Herkimer County around 0445 UTC 2 March for a) Poland, Cold
Brook, Fort Plain and Hessville, b) Cooperstown,
Milford and Ballston Spa, and c) Palatine Bridge, Colonie
Figure 24.MADIS data
(MSLP, temperatures, dewpoints, winds and
precipitation) and trends from observation points in and upstream, based on
surface wind flow, from Litchfield, County, CT around 1230 UTC 2 March for a)
Avon, Wolcott, Southington, and Sherman, b) Torrington, Thomaston, West
Simsbury, Litchfield, c) New Hartford, Torrington2.