The 2-3 January, 2002 Snow Event
over the Western Carolinas and Northeast Georgia
Bryan P. McAvoy
NOAA/National Weather Service
Greer, SC
Author's Note: The following report has not been subjected to the scientific peer review process.
1. Introduction
This was an unusual event for the Greenville-Spartanburg (GSP)
County Warning and Forecast Area (CWFA) in that the precipitation
fell as all snow. Local research shows that only about 10 percent
of our winter precipitation events are of this type (Moyer 2001).
Every county that was included in the initial winter storm watch
and warning verified with significant lead time. However, snow
began earlier than expected and farther to the northwest. While
the southeast part of the CWFA was almost perfectly forecast (see
Fig. 1 for snowfall totals) the surprise snow in the southeast
slopes of the mountains the afternoon of 2 January will be a large
part of this paper's focus. As it became evident that the area
of warning criteria snow would extend farther to the north and
west, additional warnings were issued shortly after midnight on
3 January. Most counties in this second area of warnings received
a very short lead time but they did verify.
Figure 1. Snowfall map, in inches, from the 2-3 January 2002
winter storm.
2. Synoptic Overview
Snowfall amounts ranged from an inch or less over most of the
North Carolina Mountains, to as much as 10 inches in the eastern
part of the CWFA (Fig. 1). Typical amounts for the storm were
from 4 to 6 inches. Amounts exceeded 1 foot over a large part
of central and eastern North Carolina. Much of the precipitation
in eastern North Carolina fell late on 3 January and early on
4 January, after a nearly twelve hour break in significant
precipitation between the warm advection snow and the
intensification of the upper level deformation zone, as the
upper level energy with the system crossed the area. Figure 3
shows how far upstream the 500 mb upper low was when heavy snow
was falling over parts of the GSP CWFA during the late afternoon
hours of 2 January. Accumulations associated with the passage
of the upper low, and attendant intensification of the deformation
zone, were only around one inch in the GSP CWFA. The significant
secondary snowfall was mainly along and east of Raleigh, North
Carolina. As a result, this review will not focus much on the
contribution of the upper low and intensification of the
deformation zone, but the interested reader may view this
summary from WFO Raleigh (RAH).
Figure 2. Eta model 500 mb geopotential heights and vorticity
valid at 2100 UTC 2 January from the 0000 UTC 2 January 2002
cycle. Moderate to heavy snow was occurring over the GSP CWFA
at this time. Click on the image for a loop of the 500 MB
heights from this run.
While the primary contribution to the heavy snow over the eastern
part of the GSP CWFA was from low level warm advection, the
precipitation which fell over the mountains of northeast Georgia,
South Carolina, and southern North Carolina was not in a region
of strong low level isentropic upglide seen on the 292K surface
at 2100 UTC from the 0000 UTC 2 January run of the Eta model.
While this run of the Eta model did not handle upper forcing
well for the afternoon hours of 2 January, all indications are
that its lower to middle tropospheric upglide was fairly accurate
if a little too far east. However, even though there was little
adiabatic omega, the atmosphere over the entire CWFA was saturated,
and not particularly stable, so it should not be surprising that
the forcing which developed resulted in a snow band.
Up to three inches of snow accumulation had occurred by late
afternoon with the narrow snow band, quite a problem as the
warnings did not go into effect until the second period (Wednesday
night) for areas farther to the east. While higher terrain was
certainly a factor in these snow totals (it was anticipated that
a dry low level airmass would delay precipitation onset in all
but the southernmost zones), this base reflectivity loop (valid
from 1200 UTC 2 January through 0700 UTC 3 January) clearly
indicates a northeast to southwest oriented band of precipitation
over this area in the afternoon from 1700-2100 UTC. Thus, the
precipitation in the mountains was likely the result of upper
level forcing, as well as the higher terrain. Even as significant
snow was falling in the mountains, the central part of the Upstate
had nothing but flurries and few heavier snow showers until the
early evening hours. This can be seen in these hourly decoded
METARS from KGSP for 2 January 2002. This part of the forecast
was exactly as expected. Snowfall totals did reach 2 to 3 inches
in the southeast-most zones by later afternoon as well. It was
anticipated that this might happen, and is not considered a
significant bust.
Figure 3. Eta model cross section of relative humidity over
Greenville-Spartanburg, SC (KGSP) from the 0000 UTC 02 January
2002 cycle.
The easiest way to compare the differences between the 2 January
0000 UTC run of the Eta and the 1200 UTC run, is through the use
of BUFKIT time sections, centered over KGSP. Figure 3 is from
the 0000 UTC run on 2 January. This was the run available to
the mid shift, when the warnings were issued. Notice how dry
the low levels were. Precipitation was not expected to make
significant "landfall" until the evening hours over most of
the CWFA. Not too far to the south, however, the Eta model
projected a much earlier onset time as can be seen on the 292K
surface at 1500 UTC. Figure 4 is from the 1200 UTC run of the
Eta on 2 January. Notice that the low levels are now completely
saturated over KGSP through the afternoon hours. Time sections
of omega over KGSP illustrate why the moistening occurred so
much more quickly. The 0000 UTC Eta omega time section showed
weak upward vertical velocity (UVV) over the region from 1800 UTC
to 0000 UTC. Strong UVV was not expected until overnight on
2 January and early on 3 January. The 1200 UTC Eta omega time
section was completely different, showing the strongest UVV
during the afternoon hours of 2 January.
Figure 4. As in Figure 3, except for the 1200 UTC
2 January 2002 model cycle.
A couple interesting features highlight why the upper-level
forcing developed. The EDAS 400 mb winds valid at 1800 UTC on
2 January show a distinct double jet structure, right above the
level of the strongest UVV on the 1200 UTC time sections. At
300 mb the jet was more consolidated, though the region was in
the entrance region of the jet. Considering the slight
anticyclonic curvature of the jet, the deep forcing is fairly
easy to intuit.
3. Forecast Performance
The first watches were issued on the afternoon forecast shift
of 1 January. Figure 5 shows the total model QPF from Eta model
runs from 0000 UTC and 1200 UTC on 1 and 2 January. It was the
1200 UTC run on 1 January which moved the precipitation track
farther to the west. Per the Meet-Me conference call held that
afternoon, a decision was made to issue a watch for parts of the
South Carolina Upstate and the southern North Carolina Piedmont.
 
 
Figure 5. Eta model total QPF from the model cycle at
0000 UTC 1 January (upper left), 1200 UTC 1 January (upper
right), 0000 UTC 2 January (lower left), and 1200 UTC
2 January (lower right).
A second period warning was issued for the southernmost
counties in the CWFA by the midnight shift early on the
morning of 2 January (Greenwood, Abbeville and Elbert). The
reason for issuing the second period warning was that only
around an inch of snow was anticipated by late in the first
period, but there was expected to be 4 inches of snow fairly
early in the second period. The reasons for this are detailed
in the previous section. The previous watch was continued and
also expanded to include the rest of the Upstate (the so-
called I-85 corridor), but not the mountains, and a significant
portion of the Piedmont of North Carolina. Even though the
2 January 0000 UTC Eta run had backed off a little in its QPF,
the Canadian GEM continued to advertise heavier precipitation
for the eastern half of the CWFA. The forecasters on the mid
shift had a great deal of confidence in the Canadian, a model
which had outperformed (in the estimate of the forecasters)
the Eta in significant winter events over the past two years.
The day shift on 2 January issued warnings for an area that
included the original watch area (the one from the previous
day shift), and issued advisories for the counties included
in the watch by the midnight shift.
During the early morning hours on 3 January, the mid shift
upgraded the advisory to a warning for the I-85 corridor of
the Upstate as well as the South Carolina and northeast Georgia
mountains. As near-winter storm criteria snow had fallen in
the mountains, these zones were upgraded to account for light
to moderate snow which continued to fall much of the night.
In the North Carolina Foothills and western Piedmont, warnings
were issued as the deformation zone developed farther west
than expected, spreading moderate to heavy snow into this
area during the late evening hours on 2 January and early on
3 January. This rather weak deformation zone diminished
considerably during the early morning hours. However, the
warnings were kept in effect for the entire day of 3 January
as some precipitation was expected along and north of the
track of the 500 mb low. Around an inch of light snow fell
over the southern part of the CWFA during the day associated
with this feature.
4. Discussion and Conclusion
A winter storm affected the GSP CWFA starting the afternoon
hours of 2 January, and lasting until the late afternoon hours
of 3 January. Precipitation fell in association with several
different forcing mechanisms during the event. A band of snow
associated with an upper level jet streak affected the southern
mountains during the afternoon hours of 2 January. This feature
was poorly handled by both the Eta model and the forecasters at
GSP. Lower to middle tropospheric isentropic upglide developed
over the eastern part of the CWFA during the late afternoon hours
of 2 January. This was fairly well handled by the Eta model and
forecasters. Snow did develop farther west then forecast during
the late evening of 2 January. This was the result of a weak
deformation zone in the nose of another 300 mb jet streak
ejecting out of the trough, coupled with the western most edge
of the strong low level upglide. Finally, light some persisted
most of the day on 3 January as a strong 500 mb upper low crossed
the southern CWFA. This low eventually lead to another bout of
heavy snow over eastern North Carolina late on 3 January.
While the event was handled well on the whole, snow consistently
developed farther west then expected. Mechanisms responsible for
this were upper level forcing caused by a series of jet streaks
that crossed the region in southwest flow ahead of a strong
500 mb trough. The Eta model had a poor handle on the ascent
caused by these features almost up until the time they developed.
In the future, it may benefit the office to issue watches and
warnings father west than what low level upglide would suggest,
perhaps as far west as the core of the 300 mb jet.
Here are a series of Javascript loops from the 0000 UTC and
1200 UTC runs of the Eta model from the 2 January 2002 model cycle.
References
Moyer, Benjamin W., 2001: A climatological analysis of winter
precipitation events at Greenville-Spartanburg, SC. Eastern
Region Technical Attachment 2001-01. 19 pp.
Acknowledgements
Patrick Moore reconfigured the page with the GSP web page template.
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