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The Heavy Snow of 29-30 January 2010

Laurence G. Lee and Patrick D. Moore
NOAA/National Weather Service
Greer, SC

Author's Note: The following report has not been subjected to the scientific peer review process.

1.  Introduction
A major winter storm affected portions of the southeastern United States 
on the 29th and 30th of January 2010.  Heavy snow, along with sleet and 
freezing rain, fell across much of western North Carolina and a small 
part of Upstate South Carolina and extreme northeast Georgia (Fig. 1).  
The storm also produced significant snowfall across the northern half of 
North Carolina and the Tidewater region of Virginia.  The greatest snow 
accumulations across the County Warning Area (CWA) of the National Weather 
Service (NWS) office at the Greenville - Spartanburg Airport (GSP) extended 
from just south of Asheville, North Carolina, east-northeast to Catawba, 
Iredell, and Davie counties in North Carolina.  Observers at several 
locations measured a foot of snow.  Rain was the predominant form of 
precipitation over southern portions of the CWA.  The primary weather 
features responsible for the wintry weather were a high pressure system 
over the northeastern United States and a low pressure system that traveled 
eastward across the Gulf Coast states, then northward along the coast of 
the Carolinas where it moved out to sea.
Click here to view a summary of snowfall reports for the event.
Storm Total Snowfall for 29-30 January 2010
Figure 1.  Storm total snow accumulation for 29 and 30 January 2010.
Click on image to enlarge.
2.  Development
At 1200 UTC on 29 January 2010, the surface analysis from the 
Hydrometeorological Prediction Center (HPC) showed a developing low 
pressure system located near the Texas Gulf Coast (Fig. 2).  A high 
pressure system was centered over the upper Mississippi River Valley.  
A cold front extended from the Atlantic Ocean west through south Georgia 
and the southern Gulf Coast states to the Texas low.  A 500 mb low was 
over the Texas-New Mexico border (Fig. 3).  Clouds and precipitation 
covered much of the lower Mississippi and Ohio river valleys west into 
the southern Great Plains (Figs. 4 and 5).
Click here to view a 36 frame Java loop of GOES-12 water vapor satellite 
imagery from 1245 UTC on 29 January to 2345 UTC on 30 January.
HPC Surface fronts and pressure analysis at 1200 UTC 29 January 2010
Figure 2.  HPC Surface fronts and pressure analysis at 1200 UTC on 
29 January 2010.  Click on image to enlarge.
500 mb geopotential height, temperature, and wind barbs at 1200 UTC on 29 January 2010
Figure 3.  Storm Prediction Center (SPC) objective analysis of 500 mb 
geopotential height (dm; dark gray contours), wind (kt; barbs), and 
temperature (degrees C; dashed red contours) at 1200 UTC on 29 January.  
Click on image to enlarge.
GOES-12 Infrared satellite image at  1215 UTC 29 January 2010
Figure 4.  GOES-12 infrared satellite image at 1215 UTC on 29 January.  
Cloud top temperatures are given by the color table in the upper left 
corner.  Click on image to enlarge.
RIDGE National NEXRAD mosaic at 1208 UTC 29 January 2010
Figure 5.  National radar reflectivity mosaic at 1208 UTC on 29 January.  
Rain intensity is given by the color table on the right.  Click on image 
to enlarge.
A look at several diagnostic charts from the North American Mesoscale (NAM)
model (80 km horizontal grid spacing, hereafter referred to as the NAM-80)
revealed why upward motion was occurring across the area from the Texas 
Gulf Coast to the mid-Mississippi Valley (Fig. 6):
1.  500 mb trough and cyclonic vorticity advection were approaching the 
    surface trough over the western Gulf of Mexico,
2.  Differential cyclonic vorticity advection (500-300 mb) was occurring 
    east of the cutoff low,
3.  Divergence aloft (250 mb) and convergence near the surface (850 mb) 
    were over eastern Texas and Oklahoma into the Lower Mississippi River 
    valley,
4.  An axis of strong isentropic lift (e.g., 300K surface) extended along 
    the Texas coast northeast through Arkansas to Tennessee and Kentucky,
5.  Frontogenetical forcing and upward motion existed in a deep layer from 
    the surface near the Gulf Coast to approximately 400 mb over Oklahoma 
    and Kansas, and
6.  Strong Q-vector convergence in the 500-250 mb layer extended from 
    Oklahoma south through Texas

NAM-80 initial analysis of 500 mb geopotential height, vorticity, and mean sea level pressure at 1200 UTC 29 January 2010NAM-80 initial analysis of 500-300 mb mean geopotential height and differential vorticity advection at 1200 UTC 29 January 2010

NAM-80 initial analysis of divergence at 300 mb and 1000 mb at 1200 UTC 29 January 2010NAM-80 initial analysis of pressure, wind, and omega on the 300K surface at 1200 UTC 29 January 2010

NAM-80 initial analysis cross-section of frontogenesis and omega at 1200 UTC 29 January 2010NAM-80 initial analysis of 500-250 mb Q vectors and divergence of Q at 1200 UTC 29 January 2010

Figure 6.  Diagnostic charts from the NAM-80 model initial analysis at 
1200 UTC on 29 January showing (a) 500 mb geopotential height (dm; green 
contours), vorticity (10-5 s-1; dashed orange contours and color fill), and 
mean sea level pressure (mb; blue contours), (b) 500-300 mb mean 
geopotential height (dm; green contours) and differential vorticity 
advection (10-9 s-1; tan contours and color fill), (c) 300 mb divergence 
(10-5 s-1; color fill) and 1000 mb divergence (10-5 s-1; blue contours, 
dashed negative), (d) 300 K isentropic analysis of pressure (mb, green 
contours), wind (kt; barbs), and omega (microbars s-1; orange contours and 
color fill, warm shades upward), (e) cross-section from South Dakota (left) 
to the southern Gulf of Mexico (right) showing frontogenesis (K m-1 x 10-10 s-1; 
color fill), and omega (microbars s-1; tan contours), and (f) 500-250 mb 
Q vectors (K m-2 x 10-12 s-1; light blue arrows) and divergence of Q 
(K m-2 x 10-16 s-1; green contours (upward) and color fill (warm colors 
upward)).  Click on each image to enlarge.
The divergence aloft and convergence near the surface were occurring in the 
right rear quadrant of an upper level wind maximum (170 kt at 300 mb) that 
extended from Missouri east through the northern mid-Atlantic states and 
offshore (Fig. 7). The upper level divergence and low level convergence were 
also just ahead of a smaller, but nonetheless strong (105 kt at 300 mb), 
wind maximum over southwest Texas.
300 mb isotachs, streamlines, and divergence at 1200 UTC 29 January 2010
Figure 7.  SPC objective analysis of 300 mb wind (kt; barbs), isotachs (kt; 
dark gray contours and color fill), streamlines (black contours), and 
divergence (yellow contours) at 1200 UTC on 29 January.  Click on image to 
enlarge.
Another cross-section view from the 80-km NAM model initialization at 
1200 UTC, this time from the Gulf of Mexico to North Dakota (Fig. 8), showed 
the vertical motion linked to the processes mentioned above.  The potential 
temperature isotherms sloped upward toward the north through a deep layer 
of the atmosphere, the isotherms being analogous to surfaces along which 
air parcels moved in response to the southerly wind flow ahead of the trough 
over west Texas.  The cross-section also depicted the upward motion (omega) 
and wind speed.  On the 300K potential temperature surface (Fig. 6d), a 
vertical motion maximum over northern Louisiana and southern Arkansas 
coincided with the region where the highest wind speeds were ascending the 
steeply sloped 300K surface.
cross section from North Dakota to the southern Gulf of Mexico at 1200 UTC 29 January 2010
Figure 8.  NAM-80 model initial analysis cross-section of potential 
temperature (K; green contours), vertical motion (microbars s-1; white 
contours (solid upward, dashed downward), and isotachs (kt; light blue 
contours and color fill above 70 kt) from North Dakota (left) to the 
southern Gulf of Mexico (right) at 1200 UTC on 29 January.  Click on image 
to enlarge.
3.  Precipitation Expands
By 1800 UTC on 29 January, the surface low pressure system was consolidating 
over Louisiana (Fig. 9).  The forcing for upward motion, depicted by the 
convergence of Q in the upper levels, had moved eastward just ahead of the 
trough (Fig. 10).  The moist, confluent southwest wind flow ascending the 
300K surface was a key factor in producing the prefrontal precipitation and 
the expanding rain shield over the lower Mississippi River valley.  The 
eastward spread of precipitation from Oklahoma to Tennessee can be 
attributed to the forcing for upward motion provided by the frontogenesis 
in the 850-500 mb layer seen in Fig. 11.
HPC Surface fronts and pressure analysis at 1800 UTC 29 January 2010
Figure 9.  As in Fig. 2, except at 1800 UTC on 29 January.  Click on image 
to enlarge.
NAM-80 initial analysis of 500-250mb average height, Q vectors and divergence of Q at 1800 UTC 29 January 2010
Figure 10.  NAM-80 model initial analysis of 500-250 mb average geopotential 
height (dm; green contours), Q vectors (K m-2 x 10-12 sec-1; blue arrows), and 
divergence of Q (K m-2 x 10-16 sec-1; color fill, blue and purple indicate 
forcing for upward motion) at 1800 UTC on 29 January.  Click on image to 
enlarge.
NAM-40 initial analysis of 850-500mb layer frontogenesis at 1800 UTC 29 January 2010
Figure 11.  NAM-40 model initial analysis of 850-500 mb layer frontogenesis 
(K m-1 x 10-10 sec-1; green contours and color fill) at 1800 UTC on 29 January.  
Maximum values are dark green and orange.  Click on image to enlarge.
The high pressure system was still centered over Wisconsin at 1800 UTC, but 
a surface ridge extended southeast into Virginia and the Carolinas.  A 
northeast surface wind indicated the dry, cold air over the mid-Atlantic 
states was spreading south, to the east of the Appalachians.  Dewpoints were 
in the teens in Upstate South Carolina and much of central and western North 
Carolina (Table 1).  Single digit dewpoints were common in Virginia.  The 
low dew points in combination with dry bulb temperatures in the 30s and 40s 
indicated the potential existed for precipitation to lower the surface 
temperature to near, or below, freezing. 
Station
Dry Bulb Temperature (oF)
Dew Point Temperature (oF)
Wet Bulb Temperature (oF)
Asheville Regional Arpt, NC
38
17
31
Hickory Airport, NC
38
13
30
Charlotte, NC
43
12
33
Greenville -Spartanburg, SC
45
18
35
Anderson, SC
46
19
36
Table 1.  Surface temperature observations taken at selected sites across the
western Carolinas at 1800 UTC on 29 January 2010.
The subfreezing wet bulb temperatures at the Asheville Regional Airport (AVL) 
and Hickory Regional Airport (HKY) focused attention on the likelihood of 
freezing or frozen precipitation.  The Charlotte-Douglas International 
Airport (CLT), GSP, and Anderson wet bulb temperatures were above freezing 
but sufficiently close to 32oF so that, absent cold advection, the height of 
the freezing level and the potential for cooling by melting snow would be 
critical in determining whether or not frozen precipitation reached the 
surface before completely melting. 
An examination of model soundings revealed the vertical temperature and 
moisture structure across the region in advance of the precipitation.  
The initial hour profiles from the 1800 UTC run of the NAM-80 model at 
AVL and HKY were quite dry, but a visual inspection showed the wet bulb 
temperature through the entire layer at both locations was subfreezing 
(Fig. 12).  The wet bulb temperature on the CLT and GSP profiles (Fig. 13) 
was below freezing except at the surface.  A northeast low-level wind 
associated with shallow cold air damming was seen in wind profiles at HKY, 
CLT, and GSP.
NAM-80 initial analysis profile for AVL at 1800 UTC 29 January 2010 NAM-80 initial analysis profile for HKY at 1800 UTC 29 January 2010
Figure 12.  NAM-80 initial analysis skew-T, log P diagram of temperature 
(right curve), dewpoint (left curve), and wind profile for Asheville (AVL; 
top) and Hickory (HKY; bottom) at 1800 UTC on 29 January.  The zero degree 
Celsius isotherm is highlighted white.  The vertical coordinate is pressure 
(mb).  Click on images to enlarge.
NAM-80 initial analysis profile for CLT at 1800 UTC 29 January 2010 NAM-80 initial analysis profile for GSP at 1800 UTC 29 January 2010
Figure 13.  NAM-80 initial analysis skew-T, log P diagram of temperature 
(red curve), dewpoint (green curve), and wind speed and direction (lines and 
numbers on the right) for Charlotte (CLT; left) and Greenville-Spartanburg 
(GSP; right) at 1800 UTC on 29 January.  The zero degree Celsius isotherm 
is highlighted white.  The vertical coordinate is thousands of feet.  Click 
on images to enlarge.
Close examination of the 1800 UTC radar mosaic (Fig. 14) revealed a narrow 
eastward extension of the precipitation area from the Tennessee River valley 
to the western tip of North Carolina and Upstate South Carolina.  The NWS 
Doppler radar at the Greenville - Spartanburg Regional Airport (the KGSP
radar) provided a more detailed view (Fig. 15).  At that time, precipitation 
in the form of snow had already started in the North Carolina-Georgia-South 
Carolina border area.  Apparently, the near-surface, above-freezing 
temperature was decreased by cooling caused by melting snow.  The rapid 
eastward spread and slow northward drift of snow in this narrow band can be 
seen in the KGSP radar displays from 1905 UTC, 2002 UTC, and 2105 UTC 
(Fig. 16).  The small bands of enhanced reflectivity embedded within the 
larger ribbon of precipitation indicated rapid rates of precipitation.  
Indeed, a public report from south Asheville revealed 2.8 inches of snow 
fell between 2130 and 2230 UTC.  Spotter reports elsewhere across the region 
documented the significant precipitation associated with the east-west 
oriented radar reflectivity maximum.  At 2245 UTC, an 8.0 inch accumulation 
was reported about five miles north of Franklin in Macon County, North 
Carolina.  Four miles west of Robbinsville in Graham County, North Carolina, 
at an elevation of 4,000 ft MSL, 6.0 inches of snow was measured at 2320 UTC.
Click here to view a 13 frame Java loop of a regional reflectivity mosaic 
from 1158 UTC to 2359 UTC on 29 January.
RIDGE National NEXRAD mosaic at 1808 UTC 29 January 2010
Figure 14.  As in Fig. 5, except at 1808 UTC on 29 January.  Click on image 
to enlarge.
KGSP composite reflectivity at 1802 UTC 29 January 2010
Figure 15.  KGSP composite reflectivity at 1802 UTC on 29 January.  
Reflectivity values are given by the color table at the upper left.  Click 
on image to enlarge.

KGSP composite reflectivity at 1905 UTC 29 January 2010KGSP composite reflectivity at 2002 UTC 29 January 2010KGSP composite reflectivity at 2105 UTC 29 January 2010

Figure 16.  As in Fig. 15, except for 1905 UTC (left), 2002 UTC (center), 
and 2105 (right) on 29 January.  Click on images to enlarge.
Light snow began at AVL at 1946 UTC when the surface temperature was 37oF.  
The snow became heavy and the temperature decreased to 32oF at 2008 UTC.  
Moderate to heavy snow continued for the next four hours, then the 
precipitation intensity became light.  The snow changed to freezing rain 
and sleet during the early morning hours on Saturday, 30 January.
As the band of enhanced radar reflectivity developed rapidly eastward 
across western North Carolina and Upstate South Carolina, snow spread into 
the southern Piedmont of North Carolina.  Light snow reached CLT at 2047 UTC 
while the temperature was 39oF.  The temperature dropped steadily, finally 
reaching the freezing mark at 2252 UTC.  Snow continued at CLT, with a 
couple of interruptions, until 0723 UTC on 30 January when the precipitation 
became mixed with freezing rain and sleet.
The rather narrow band of precipitation developed northward reaching HKY at 
2143 UTC.  Light snow became heavy at 2215 UTC and lasted for about an hour 
a half before once again becoming light in intensity.  Light snow or sleet 
continued until approximately 1730 UTC the next day.  The onset of heavy 
snow coincided with the presence of a small area of enhanced radar 
reflectivity.  Careful examination of the composite reflectivity from the 
KGSP radar at 2230 UTC (Fig. 17) showed the highest reflectivity (indicated 
by the darkest shade of green) extending from Burke County, North Carolina, 
into Catawba County, North Carolina.
Click below to view weather observations on 29 January 2010.
Station
Hourly Observations
Asheville Regional Airport, NC
Charlotte Douglas Intl Airport, NC
Hickory Regional Airport, NC
Greenville -Spartanburg Intl Arpt, SC
Table 2.  Surface observations taken at selected sites across the
western Carolinas during the calendar day of 29 January 2010.  
Click on the four-letter identifier to view the observations.
KGSP composite reflectivity at 2230 UTC 29 January 2010
Figure 17.  As in Fig. 15, except for 2230 UTC on 29 January.  Click on 
image to enlarge.
The vertically pointing MicroRain Radar (MRR) located at Newton in central 
Catawba County, operated by the Renaissance Computing Institute (RENCI), 
provided another interesting view of the heavy snow in the Hickory area.  
The onset of precipitation occurred with the rapid increase in reflectivity 
through a deep layer at approximately 2100 UTC (Fig. 18).  The heavy snow 
was associated with even higher reflectivities detected at approximately 
2230 UTC.  Precipitation intensity decreased near 2330 UTC, but another 
period of heavy snow occurred at 0130 UTC on 30 January.  The fall velocity, 
also in Fig. 18, showed precipitation particles were descending at around 
2 ms-1 or less, values typically associated with snow.
MRR vertically pointing radar reflectivity at 1600 UTC 29 January 2010 MRR fall velocity at 1600 UTC 29 January 2010
Figure 18.  Vertically pointing radar reflectivity (top) and fall velocity 
(bottom) at Newton, North Carolina, at 1600 UTC on 29 January.  The values 
are given by the color tables on the right.  The vertical coordinate is 
feet above ground.  Click on images to enlarge.
Frontogenesis was the primary forcing mechanism that helped identify the 
reason for the narrow east-west band of precipitation.  The NAM 700 mb 
frontogenetical forcing at 2100 UTC and 0000 UTC (Fig. 19) showed the 
strong southwest wind (greater than 60 knot over north Georgia) at 700 mb 
blowing nearly perpendicular to the tight temperature gradient.  This 
tended to enhance the gradient even further thus producing the atmosphere’s 
response in the form of vertical motion along that boundary. 

NAM-80 initial analysis 700 mb frontogenesis, height, and temperature at 2100 UTC 29 January 2010NAM-80 initial analysis 700 mb frontogenesis, height, and temperature at 0000 UTC 30 January 2010

Figure 19.  NAM-80 model forecast of 700 mb frontogenesis (K m-1 x 10-10 s-1; 
color fill), geopotential height (dm; green contours), and temperature 
(degrees C; red contours) from the 1800 UTC 29 January cycle valid at 
2100 UTC 29 January (left) and at 0000 UTC 30 January (right).  Click on 
each image to enlarge.
The 2100 UTC composite reflectivity and the NAM 500 mb 3-hour forecast 
500 mb omega pattern valid at 2100 UTC showed an areal distribution of 
precipitation that was very similar to the upward motion defined by the 
omega field (Fig. 20).  As a matter of fact, the axis of highest 
reflectivity was nearly coincident with the axis of highest omega values.  
The cross-section from southeast Georgia to eastern Kentucky in Fig. 21 
showed the upward motion was maximized over western North Carolina between 
400 and 500 mb.  The corresponding 3-hour NAM 310K isentropic forecast 
(Fig. 22) showed a narrow band of upward motion from southern Tennessee, 
east to north Georgia, and the western Carolinas.  A 70 knot wind maximum 
on this isentropic surface where the slope was quite steep (corresponding 
to the tight temperature gradient on the 700 mb pressure surface) over 
north Georgia contributed to the upward motion maximum.  The condensation 
pressure deficit (not shown) across the Southeast revealed that air 
parcels streaming northeastward did not reach saturation until arriving 
over the lower Tennessee River valley and southern Appalachians.  The 
orientation of the isentropic surface along which the air parcels were 
ascending contributed to the east-west orientation of the major 
precipitation.
KGSP composite reflectivity and NAM-80 3-hr 500 mb omega forecast at 2100 UTC 29 January 2010
Figure 20.  KGSP composite reflectivity (color fill, table at upper left) 
and NAM-80 three-hour forecast of omega (microbars s-1; yellow contours, 
solid lines denote upward motion) valid at 2100 UTC on 29 January.  
Click on image to enlarge.
NAM-80 3-hr forecast cross-section of omega and potential temperature valid at 2100 UTC 29 January 2010
Figure 21.  NAM-80 model forecast cross-section of potential temperature 
(K; green contours) and omega (microbars s-1; purple contours and color 
fill) from eastern Kentucky (left) to southeast Georgia (right) from the 
1800 UTC model cycle valid at 2100 UTC on 29 January.  Click on image to 
enlarge.
NAM-80 3-hr forecast of omega, wind, and pressure on the 310K surface valid at 2100 UTC 29 January 2010
Figure 22.  NAM-80 model forecast of omega (microbars s-1; color fill), 
wind (kt; yellow barbs), wind speed (kt; orange contours), and pressure 
(mb; green contours) on the 310K surface from the 1800 UTC model cycle 
valid at 2100 UTC on 29 January.  Click on image to enlarge.
4.  Warming Aloft and Mixed Precipitation 
The pattern continued into the evening hours producing an extended period 
of precipitation in central and western North Carolina.  Light snow occurred 
across northern parts of Upstate South Carolina and northern counties in 
western North Carolina, but the significant snowfall rates were limited to 
the narrow region of frontogenetical forcing and strongest isentropic lift.
By 0000 UTC on 30 January, the 500 mb trough was over the Red River between 
Oklahoma and Texas and the surface low pressure system was over southeast 
Louisiana.  The previously-referenced diagnostic tools displayed 
the following characteristics (not shown):


1.  The differential cyclonic vorticity advection (300-500 mb) was maximized 
    from the Mississippi River delta region across Mississippi to Alabama,   
2.  The upper level (250 mb) divergence maximum was nearly coincident with 
    the low level (1000 mb) convergence maximum over southern Mississippi 
    and Alabama,   
3.  The 310K isentropic analysis showed the omega maximum still oriented 
    east-west across North Carolina (aligned with the frontogenetical 
    forcing maximum), and another omega maximum over Alabama and Mississippi, 
    apparently related to the forcing associated with upper level trough,
4.  Frontogenetical forcing was maximized over the southern Appalachians, and
5.  The upper-level (300-500 mb) forcing indicated by the convergence of Q 
    was strongest from Missouri south to northern Louisiana.
An interesting feature of the upper level divergence and low level 
convergence pattern was the lack of significant influence across the 
Carolinas where moderate to heavy snow occurred.  This observation 
highlighted the importance of the mid-level frontogenetical forcing and 
resulting upward motion seen on the isentropic charts.
The moderate to heavy snow that occurred in the Asheville area during the 
first six hours of the event became light, but continuous, as the heaviest 
precipitation in the frontogenetically-forced band moved east across the 
Piedmont.
The cold air damming, although relatively weak, persisted and maintained a 
light northeast wind that kept the surface temperature near or below 
freezing across most of the area (Table 3).
Station
Dry Bulb Temperature (oF)
Dew Point Temperature (oF)
Wet Bulb Temperature (oF)
Asheville Regional Arpt, NC
30
29
30
Hickory Airport, NC
30
29
28
Charlotte, NC
33
30
32
Greenville -Spartanburg, SC
33
30
32
Anderson, SC
38
27
34
Table 3.  Surface temperature observations taken at selected sites across the
western Carolinas at 0000 UTC on 30 January 2010.
An ensemble of the NAM model soundings at 0000 UTC at AVL, CLT, GSP, and 
HKY showed most stations were experiencing southwest winds above the 
surface-based cold layer where northeast winds predominated (Fig. 23).  The 
exception was at AVL which had a southeast wind.  Each temperature profile 
was subfreezing above the surface except at GSP (blue lines in the figure) 
where warm air advection near 850 mb had increased the temperature to +1 oC.  
In response to the warming, the light snow at GSP changed to sleet and 
freezing rain just before 0500 UTC.  The mixed precipitation continued for 
the next 14 hours before changing to light snow prior to ending at 1900 UTC.
Click below to view weather observations on 30 January 2010.
Station
Hourly Observations
Asheville Regional Airport, NC
Charlotte Douglas Intl Airport, NC
Hickory Regional Airport, NC
Greenville -Spartanburg Intl Arpt, SC
Table 4.  Surface observations taken at selected sites across the
western Carolinas during the calendar day of 30 January 2010.  
Click on the four-letter identifier to view the observations.
NAM-80 initial hour profiles of temperature, dewpoint, and wind at HKY, GSP, CLT, and AVL at 0000 UTC 30 January 2010
Figure 23.  NAM-80 initial hour profiles of temperature, dewpoint, and wind 
at HKY (light brown), GSP (blue), CLT (dark brown), and AVL (green) at 
0000 UTC on 30 January.  Click on image to enlarge.
The surface low pressure system was over southern Alabama at 0600 UTC on 
30 January.  Precipitation was widespread, although the extreme southern 
portion of the CWA along with portions of central South Carolina and 
Georgia had less coverage (Fig. 24).  The NAM six-hour 310 K isentropic 
forecast showed the maximum upward motion over east Tennessee and far 
western North Carolina.

Regional composite reflectivity mosaic at 0600 UTC 30 January 2010

Figure 24.  Regional mosaic of composite reflectivity at 0600 UTC on 
30 January.  Click on image to enlarge.
Cold air damming was evident in the isotherm pattern along and to the east 
of the Appalachians on the 0600 UTC NAM 850 mb analysis (Fig. 25).  However, 
one of the most significant features was the region of strong warm air 
advection from northern Alabama across north Georgia to Upstate South 
Carolina.  The warm advection was the major factor in altering the vertical 
temperature structure so that the snow became mixed with and changed to 
sleet and freezing rain at nearly all observing sites during the overnight 
and morning hours on 30 January.
NAM-40 initial analysis of 850 mb geopotential height, temperature, and temperature advection at 0600 UTC 30 January 2010
Figure 25.  NAM-40 initial analysis of 850 mb geopotential height (dm; 
green contours), temperature (C; red contours), and temperature advection 
(C 12hr-1; color fill) at 0600 UTC on 30 January.  Click on image to enlarge.
The cold air damming that kept surface temperatures near or below freezing 
in combination with the warming aloft contributed to a common winter storm 
scenario across the western Carolinas in which snow becomes mixed with, or 
changes to, other forms of precipitation.  During the period from 0000 UTC
to 0600 UTC on 30 January, temperatures dropped at all sites, and fell 
below freezing at GSP and CLT (Table 4).
Station
Dry Bulb Temperature (oF)
Dew Point Temperature (oF)
Wet Bulb Temperature (oF)
Asheville Regional Arpt, NC
27
26
27
Hickory Airport, NC
28
27
26
Charlotte, NC
30
28
29
Greenville -Spartanburg, SC
31
29
30
Anderson, SC
33
30
32
Table 5.  Surface temperature observations taken at selected sites across the
western Carolinas at 0600 UTC on 30 January.
5.  Diminishing Precipitation 
The 1200 UTC surface analysis placed the low pressure system over south 
Georgia, but a weak wave was beginning to develop near the coast on the 
warm front that stretched east over the Atlantic.  By this time, much 
of the precipitation had moved east of the CWA (Fig. 26).  The NAM 310 K 
isentropic analysis showed the strongest upward motion moving across 
central and eastern North Carolina.  The wind flow on the 310K surface 
across northeast Georgia and the western Carolinas was nearly parallel 
to the pressure contours indicating virtually no upglide existed.
Click here to view a 19 frame Java loop of a regional reflectivity mosaic 
from 2359 UTC on 29 January to 1800 UTC on 30 January.
Regional composite reflectivity mosaic at 1200 UTC 30 January 2010
Figure 26.  As in Fig. 24, except for 1200 UTC on 30 January.  Click on 
image to enlarge.
The upper-level pattern also indicated the best forcing was moving away 
from the region.  The NAM analysis in Fig. 27 showed the maximum upward 
motion at 500 mb had shifted eastward in the right rear quadrant of the 
250 mb wind maximum south of Nova Scotia and ahead of the weaker wind 
maximum over the Gulf Coast.  The divergence of Q in the 500-300 mb layer
(Fig. 28) clearly indicated forcing for upward motion was along the East 
Coast and forcing for downward motion was moving into the central and 
southern Appalachians.
NAM-80 initial analysis of 250 mb geopotential height, isotachs, and 500 mb vertical motion at 1200 UTC 30 January 2010
Figure 27.  NAM-80 initial analysis of 250 mb geopotential height (dm; 
green contours), isotachs (kt; blue contours), and 500 mb vertical motion 
(microbars sec-1; color fill, orange to red shades upward) at 1200 UTC on 
30 January.  Click on image to enlarge.
NAM-80 initial analysis of 500-300 mb average geopotential height and divergence of Q at 1200 UTC 30 January 2010
Figure 28.  NAM-80 initial analysis of 500-300 mb average geopotential 
height (dm; green contours) and divergence of Q (K m-2 x 10-16 sec-1; color 
fill, warm shades upward and cool shades downward) at 1200 UTC on 30 January.  
Click on image to enlarge.
The 1200 UTC surface temperatures were freezing or below at all sites 
except in the extreme southern and far western portions of the CWA (Table 4).  
Even though surface temperatures were cold enough to support snow, many 
observations indicated sleet or freezing rain.  The warm advection that 
was quite strong at 850 mb at 0600 UTC continued during the early morning 
hours and caused temperatures to rise above the melting point (except at 
HKY) in a layer that extended from approximately 4,000 to 10,000 feet 
above the surface.  Vertical temperature profiles for AVL, CLT, GSP, and 
HKY confirmed the presence of the warm layer (Fig. 29).
Station
Dry Bulb Temperature (oF)
Dew Point Temperature (oF)
Wet Bulb Temperature (oF)
Asheville Regional Arpt, NC
27
25
26
Hickory Airport, NC
26
24
25
Charlotte, NC
29
26
28
Greenville -Spartanburg, SC
30
28
29
Anderson, SC
32
29
31
Table 4.  Surface temperature observations taken at selected sites across the
western Carolinas at 1200 UTC on 30 January 2010.

NAM-12 initial hour profile of temperature and dewpoint at AVL at 1200 UTC 30 January 2010NAM-12 initial hour profile of temperature and dewpoint at CLT at 1200 UTC 30 January 2010

NAM-12 initial hour profile of temperature and dewpoint at GSP at 1200 UTC 30 January 2010NAM-12 initial hour profile of temperature and dewpoint at HKY at 1200 UTC 30 January 2010

Figure 29.  NAM-12 model initial hour profiles of temperature and dewpoint 
for AVL (upper left), CLT (upper right), GSP (lower left), and HKY (lower 
right) valid 1200 UTC 30 January.  Click on each image to enlarge.
Between 1200 and 1800 UTC, the precipitation rapidly diminished from west 
to east.  By 1800 UTC, the surface pressure analysis displayed a complex 
organization consisting of several centers of low pressure extending from 
southeast Georgia to the vicinity of Cape Hatteras.  The eastward 
progression of the upper-level trough and wind maxima caused the significant 
upward motion to shift offshore and toward the mid-Atlantic region where 
consolidation of the low pressure centers subsequently occurred.
6.  Summary 
The low pressure system that moved across the Gulf Coast states to the 
Georgia and Carolina coast on the 29th and 30th of January 2010 resulted 
in a major winter storm for western North Carolina and adjoining parts 
of northeast Georgia and Upstate South Carolina.  Snowfall totals in 
excess of a foot occurred in portions of the Mountains, Foothills, and 
Piedmont of North Carolina.  The greatest accumulation was at Mills 
River in Henderson County which is about three miles southwest of AVL.  
The 12.0 inch accumulation at AVL made this the first winter season on 
record that had two 10.0 inch or greater events in the Asheville area.  
(The previous event was on 18 December 2009 when 10.1 inches fell.)  The 
meteorological features of this event were typical of winter storms in 
the southern Appalachian and Piedmont regions.  The low pressure system 
traveled from the Gulf Coast to a position along the Carolina coast before 
moving out to sea.  A high pressure system centered north of the area 
contributed to a cold air damming event east of the Appalachians that 
supplied subfreezing surface wet bulb temperatures for the CWA.  A strong 
southwest wind near 850 mb eventually warmed the temperature profile so 
that snow changed to sleet and freezing rain before the precipitation ended.  
Acknowledgements
Blair Holloway prepared the snowfall accumulation map and created it using
ArcView GIS.  The surface pressure and fronts analyses were obtained from
the Hydrometeorological Prediction Center.  The upper air analyses were 
obtained from the Storm Prediction Center.  The regional reflectivity 
mosaics, water vapor imagery, and regional surface plots were obtained from 
the University Corporation for Atmospheric Research.  The national radar 
mosaics and surface observations were obtained from the National Climatic 
Data Center.  The Renaissance Computing Institute (RENCI) provided the 
images from the MicroRain Radar.


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