December 26, 2004 Winter Storm|
...”The Day after Christmas Ice and Snow Storm” in the Carolinas and Virginia, closed
portions of Interstate 95, stranded motorists and airline passengers, and left 20,000
households without electrical power...
...The storm was characterized by significant differences in precipitation amounts and
wintry precipitation types over short distances...
...Portions of Central and Eastern North Carolina received significant accumulations of snow, sleet,
and freezing rain...
A winter storm brought snow, sleet, and freezing rain to central and eastern
North Carolina during the morning hours of December 26th, 2004. The event was
short lived as much of the precipitation had moved offshore by late afternoon. The heaviest
precipitation, which consisted of a sleet and snow mixture, fell in close proximity to the Interstate 95
corridor where amounts reaching 3 inches occurred across sections of Hoke and
Scotland counties in southern North Carolina. A little further to the northeast,
the precipitation predominantly fell as snow, with a little sleet mixed in at times. The
snow and sleet accumulated up to
6 or 8 inches across much of Wilson, Edgecombe, and Nash counties. Snow
amounts in excess of 8 inches, ranging up to 11 inches, were reported across the
state’s northeastern counties, including Gates, Hertford, and Northampton. Meanwhile
significant amounts of ice from
freezing rain fell in a narrow band just
southeast of the snow and sleet regions across portions of southeastern North
Carolina. A coating of a quarter inch of ice occurred in southern Cumberland,
central Sampson and northern Duplin counties, while Robeson and Columbus counties experienced
an ice accrual up to a half inch.
This snow, sleet, and freezing rain event was associated with a
so-called Miller “A” pattern of cyclogenesis. This pattern is
characterized by a relatively simple mean sea level pressure
pattern where one relatively well organized surface low tracks
northeastward with a surface high pressure center located to
the north. With cold air in place over the Carolina’s and Virginia,
the surface low moved northeastward across the Gulf of Mexico
late on December 25th. The storm system then moved across Florida,
paralleling the coast of the Southeastern U.S. on the 26th.
Precipitation reached southern North Carolina shortly after
dark on Christmas evening. The precipitation shield then
spread northward and northeastward, covering much of central
and eastern North Carolina by daybreak on the 26th. The
resulting precipitation types and amounts were a function
of many meteorological factors. The surface low tracked well
offshore limiting the inland extent of the precipitation shield,
resulting in no snow or sleet in the more climatologically
favored areas of the Piedmont such as Roxboro and Triad areas.
The intensification of the coastal low once it passed Cape
Hatteras, contributed to the larger snowfall amounts in far
northeastern North Carolina.
The surface features were again consistent with the so-called so-called Miller “A” pattern of cyclogenesis.
Relative to this storm’s individual characteristics,
it is important to note that the surface low’s isobars showed
a rather elongated shape and relatively high central pressures
as it quickly passed by North Carolina’s southern coast. Meanwhile
the surface high to the north lacked a well defined ridge of
high pressure extending into the Carolinas. This configuration
is a signal to forecasters that there is a limited inflow of
warm air into the low and cold air from the high.
The meteorological features seen at 700 AM on December 26th at
the 850 MB level (typically located around 5,000 ft level
above ground) showed little advection of cold and warm air
into central and eastern North Carolina. When there is little or
no temperature advection in the atmosphere from ground level
through the 10,000 ft level or so, wintry precipitation types
can be subject to frequent changes (see the
meteogram from Fayetteville and
note the changes to the precipitation type in the "WX" row). These changes are often
associated initially with evaporative cooling as
precipitation falls into the dry sub cloud layer and then later by the precipitation
rates. Under these conditions the change of temperature in the
vertical from the ground through about 10,000 ft is very gradual
and often hovering near freezing through a deep layer. Indeed
with the “Day After Christmas Storm”, there were frequent
observations of changes between snow and sleet and a snow/sleet
mixture. Moreover, as the precipitation rates increased, the
barely above freezing melting layer extending through a relatively
deep layer that existed at Fayetteville at 600 AM on the 26th,
was erased by additional cooling from melting. The additional
cooling allowed the sleet or sleet/snow mixture to change to
snow. Once the precipitation rates diminished and cooling from
melting was lost, the snow would mix with or change again to sleet.
In addition to the configuration and evolution of the surface
and low level meteorological features; prominent features in
the upper levels of the atmosphere were key players in the
evolution of this winter event and its impact on central North
Carolina. A deep trough of low pressure, a strong vorticity
impulse moving around the base of the upper level trough, and
a dual upper level jet structure were all contributing energy
and moisture to the evolving low level low pressure system.
Prior to reaching North Carolina, the upper level trough and
its closely associated vorticity impulse had combined with
plentiful moisture and very cold air to produce unprecedented
snowfall in South Texas. It was the energy associated with the
upper level vorticity impulse that lead to the development of
the surface low in the Gulf of Mexico late on the Christmas Eve
that eventually produced the wintry precipitation across
central and eastern North Carolina on the 26th. The strong
south to southwest flow in the 500 – 300 MB layer provided
abundant moisture from the Pacific. The position of the dual
upper level jets produced strong divergence aloft that in
turn produced low level convergence and the development of
clouds and precipitation.
Snow / Sleet Accumulation Map
The corridor of heaviest snow and sleet accumulation fell near and just east of the I-95 corridor
with snow and sleet amounts ranging from 3 inches in southern North Carolina amounts in excess of
8 inches across northeastern North Carolina.
Freezing Rain / Glaze Accumulation Map
Significant freezing rain accrual was confined to southern and central portions of the costal plain and
eastern portions of the Sandhills. A coating to a quarter of an inch of glaze was reported over sections
of Sampson and Wayne counties. Immediately south of this region, ice accrual of a half inch was reported
in Robeson and Columbus counties.
High Resolution Visible Satellite Imagery Depicting Snow Cover
This image captured by the Terra MODIS instrument on Monday, December 27, 2004, shows the remaining snow
cover across portions of southern North Carolina, through Virginia, and across the Chesapeake Bay into Maryland.
Note how narrow the snow/sleet band is across North Carolina. Accurately forecasting the location of this band
was one of the biggest forecasting challenges associated with this event.
(Click on the image to enlarge.)