A view of Pilot Mountain, which is located north of Balsam Grove in western Transylvania County, North Carolina, from a vantage point on the north side of Rocky Mountain, north of Lake Toxaway, North Carolina. Note the glaze covering the tree branches in the foreground as the result of precipitation changing to freezing rain before ending. Image courtesy of Arthur Raynolds.

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

1.  Introduction

Another in a series of low pressure systems moved across the Deep 
South during the first week of February 2010.  Precipitation developed 
across northeast Georgia late in the afternoon of Thursday, 4 February, 
and spread northeast across the western Carolinas that evening.  Cold
air at the outset was expected to provide a favorable environment for
wintry precipitation across the mountains and foothills.  Precipitation 
became widespread and heavy late that night and into the morning of 
Friday, 5 February, due to strong northward moisture transport and
deep forcing.  Thus, flooding rain threatened the western Carolinas
in addition to the possibility of winter precipitation across mainly 
the mountains and foothills of North Carolina.  The passage of this 
low pressure system produced a three to five inch swath of heavy snow 
from Transylvania County, North Carolina, across the upper part of the 
French Broad River Valley, to the Blue Ridge and northern foothills of 
North Carolina (Fig. 1).  Most of the snow fell late Thursday night 
across these areas and changed over to a period of freezing rain in 
the pre-dawn hours on Friday, and finally to rain by mid-morning on 
5 February.  In the meantime, in excess of two inches of rain fell 
across most of northeast Georgia, Upstate South Carolina, and the 
Piedmont of North Carolina.  The excessive rain resulted in flooding
in parts of the French Broad River, Broad River, and Catawba River 
basins.  Heavy rain and snow melt also contributed to a debris flow
that moved down Rich Cove near Maggie Valley (Haywood County), North 
Carolina.  The dual threat of winter precipitation and heavy rain made 
this a particularly challenging event.

Click here to view a list of unofficial snowfall reports from across 
the forecast area of the Greenville/Spartanburg National Weather 
Service office.

Figure 1.  Total snowfall for the period from 4 February to 6 February
2010 across the forecast area of the Greenville/Spartanburg National 
Weather Service office.  Click on image to enlarge.

The low pressure system moved off Cape Hatteras, North Carolina, on 
the morning of 6 February and deepened off the coast of the Delmarva 
Peninsula, which resulted in a major winter storm for the Mid-Atlantic 
region (Fig. 2).  Heavy snow fell across southwest Virginia and the 
New River Valley, while the Baltimore/Washington metro area was buried 
under 18-36 inches of snow.  Heavy snow and blizzard conditions also 
occurred over the northern Delmarva, southern New Jersey, and the 
Philadelphia metro area.  The storm was rated a category 3 on the 
Northeast Snowfall Impact Scale (NESIS, Kocin and Uccellini 2004).

Click here to view a 22 frame Java loop of surface fronts and pressure 
from 1200 UTC 4 February to 0000 UTC 7 February.

Figure 2.  Preliminary snowfall analysis and NESIS rating for the 
4-7 February 2010 East Coast snowstorm.  Image obtained from the National
Climatic Data Center.  Click on image to enlarge.

[Note:  All times in this document are given in Universal Time 
Coordinated (UTC), which is Eastern Standard Time (EST) plus five hours.  
To convert to EST, subtract five hours from the UTC time.]

2.  Synoptic Features

a. 1200 UTC - 4 February to 0600 UTC - 5 February

At 1200 UTC on 4 February, the upper air pattern was characterized by 
split flow at 500 mb (Fig. 3). A pronounced western ridge and eastern 
trough were present in the northern stream across Canada and the 
northeastern United States, while a deep trough in the southern stream 
extended from the Rocky Mountains down across northern Mexico to the 
eastern Pacific.  A strong subtropical jet streak in excess of 150 kt 
was lifting out of the trough across the southern Plains (Fig. 4) which 
contributed to upper divergence over east Texas, Louisiana, and the 
northwest Gulf of Mexico.  Northward moisture transport was inferred 
from the 850 mb analysis (Fig. 5) over east Texas and the Mississippi 
Delta region.  At the surface, the Hydrometeorological Prediction 
Center (HPC) analyzed a low pressure center along the south Texas Gulf 
Coast while a 1031 mb high was centered over Lake Erie (Fig. 5).

Figure 3.  Objective analysis of 500 mb geopotential height (black 
contours), temperature (red dashed contours), and wind barbs at 1200 UTC 
on 4 February 2010.  Click on image to enlarge.

Figure 4.  Objective analysis of 300 mb wind barbs, isotachs (black 
contours and color fill), streamlines, and divergence (yellow contours)
at 1200 UTC on 4 February 2010.  Click on image to enlarge.

Figure 5.  Objective analysis of 850 mb geopotential height (black 
contours), temperature (red and blue dashed contours), dewpoint (green 
contours), and wind barbs at 1200 UTC on 4 February 2010.  Click on image 
to enlarge.

Figure 6.  HPC Surface fronts and pressure analysis at 1200 UTC on 
4 February 2010.  Click on image to enlarge.

During the early part of the afternoon, the center of low pressure 
moved out over the northwest Gulf of Mexico and a ridge of high pressure 
extended down to the lee of the Appalachians in a familiar pattern for 
cold air damming.  A band of light precipitation developed across north 
Georgia and the Midlands of South Carolina (Fig. 7), although it was 
not reaching the ground east of the Savannah River at 1800 UTC.  The 
precipitation was forced by a combination of upper divergence on the 
warm side of the subtropical jet, differential positive vorticity 
advection in the 700-400 mb layer, and frontogenesis in the 850-700 mb 
and 700-500 mb layers (Fig. 8).

Figure 7.  Composite reflectivity mosaic centered on GSP at 1757 UTC on  
4 February 2010.  Click on image to enlarge.

Figure 8.  Storm Prediction Center objective mesoanalysis at 1800 UTC on
4 February 2010 showing (A) 300 mb isotachs (kt; dashed black contours
and color fill), geopotential height (dm; solid black contours), 700-500 mb
layer average omega (microbars s-1; magenta contours are up and red contours 
are down), and ageostrophic wind (kt, barbs); (B) 500 mb geopotential
height (dm; black contours), vorticity (10-5 s-1; dashed black contours 
and color fill), and 700-400 mb differential vorticity advection (10-9 s-1; 
blue contours); (C) 700-500 mb layer mean geopotential height (dm, solid
black contours), temperature (oC; dashed blue contours), wind (kt; barbs), 
and 2-D frontogenesis (orange contours and color fill); and (D) 850-700 mb 
layer average geopotential height (dm; black contours), temperature (oC;
dashed blue contours), wind (kt; barbs), and 2-D frontogenesis (orange
contours and color fill).  Click on images to enlarge.

The center of low pressure moved near the mouth of the Mississippi 
River by 2100 UTC while the center of high pressure had migrated to 
Virginia (Fig. 9).  This orientation favored in-situ cold air damming 
once precipitation reached the ground east of the mountains.  Through 
2100 UTC, the band of precipitation lifted north over northeast Georgia 
and Upstate South Carolina (Fig. 10), where surface wet bulb temperatures 
(Fig. 11) were in the mid-30s (degrees F).  Rain reached the ground across 
Upstate South Carolina from west to east from 2000 UTC to 2100 UTC and 
was briefly mixed with snow at the outset across the area roughly along 
and north of Interstate 85.  The precipitation continued to spread north 
over the North Carolina Mountains, where the boundary layer average 
temperature was below freezing, and surface temperatures were below 
freezing over the upper part of the French Broad Valley at 2200 UTC 
(Fig. 12).  The precipitation began as snow at the Asheville Regional 
Airport (AVL) at 2141 UTC.

Click below to view weather observations on 4 February 2010.

Table 1.  Surface observations taken at selected sites across the
western Carolinas during the calendar day of 4 February 2010.  
Click on the four-letter identifier to view the observations.

Figure 9.  HPC surface fronts and pressure analysis at 2100 UTC on 
4 February 2010.  Click on image to enlarge.

Figure 10.  As in Fig. 7, except for 2057 UTC on 4 February 2010.  
Click on image to enlarge.

Figure 11.  SPC objective mesoanalysis of mean sea level pressure (black 
contours), wind (barbs), and wet bulb temperature (degrees F, dashed red 
and purple contours) at 2100 UTC on 4 February 2010.  Click on image to 
enlarge.

Figure 12.  SPC objective mesoanalysis of freezing level (kft; purple 
contours),  boundary layer zero C isotherm (red contour), relative 
humidity (color fill), and model freezing level at the surface (thick 
black contour) at 2200 UTC on 4 February 2010.  Click on image to 
enlarge.

The upper air analysis at 0000 UTC on 5 February suggested that the bulk 
of the deeper forcing remained to the west.  At 500 mb, the axis of the 
upper trough remained over the southern Plains with short waves noted 
over east Texas and the Arklatex region (Fig. 13).  Divergence was 
located from the Tennessee Valley to the northwestern Gulf of Mexico at 
300 mb (Fig. 14).  At 850 mb, a southerly flow had developed from the 
eastern Gulf of Mexico to the Tennessee Valley and western Carolinas, 
with a low level jet over Mississippi (Fig. 15).  An upper air sounding 
taken at Blacksburg, Virginia (RNK, Fig. 16), was representative of the 
profile over the mountains of North Carolina before precipitation began.  
The wet bulb temperature profile supported temperatures cooling such that 
snow would reach the ground, and in fact that was the predominant 
precipitation type across the mountains and northern foothills of North 
Carolina through at least 0600 UTC on 5 February.  Meanwhile, the upper 
air sounding at Peachtree City, Georgia (FFC, Fig. 17), showed a warm 
nose just below 850 mb as warm advection spread northward from the Gulf 
Coast.  Warm advection at low levels, associated with the warm conveyor
belt flow ahead of the upper trough, was expected to change the snow to
freezing rain across the North Carolina Mountains as the warm nose
lifted northward.  Meanwhile, rain fell across northeast Georgia and 
Upstate South Carolina through the evening of 4 February, and developed 
northeast across the Piedmont of North Carolina.

Figure 13.  Objective analysis of 500 mb geopotential height (black 
contours), temperature (red dashed contours), and wind barbs at 0000 UTC 
on 5 February 2010.  Click on image to enlarge.

Figure 14.  Objective analysis of 300 mb wind barbs, isotachs (black 
contours and color fill), streamlines, and divergence (yellow contours)
at 0000 UTC on 5 February 2010.  Click on image to enlarge.

Figure 15.  Objective analysis of 850 mb geopotential height (black 
contours), temperature (red and blue dashed contours), dewpoint (green 
contours), and wind barbs at 0000 UTC on 5 February 2010.  Click on image 
to enlarge.

Figure 16.  Skew T, log P diagram for upper air sounding taken at RNK 
at 0000 UTC on 5 February 2010.  A hodograph is shown in the upper right 
corner and a table of convective parameters is provided at the bottom.  
Click on image to enlarge.

Figure 17.  As in Fig, 16, except for FFC.  Click on image to enlarge.

Click here to view a 19 frame Java loop of GOES-12 water vapor satellite 
imagery from 1145 UTC 4 February to 0545 UTC 5 February.

Click here to view a 19 frame Java loop of composite reflectivity from 
1200 UTC 4 February to 0558 UTC 5 February.

b. 0600 UTC - 5 February to 0000 UTC - 6 February

The leading edge of the warm conveyor belt precipitation had moved 
across north Georgia by 0600 UTC and encroached upon the western 
Carolinas (Fig. 18).  Ahead of the warm conveyor belt, warm advection 
at 850 mb covered northeast Georgia and Upstate South Carolina, and 
was gradually spreading north over the mountains of North Carolina 
(Fig. 19).  The warm advection raised the temperature around 1 km aloft, 
which showed as a warm nose on a special upper air sounding taken at 
Greensboro, North Carolina (GSO, Fig. 20), just below 850 mb.  As a 
result, the precipitation changed to freezing rain at AVL at 0604 UTC.  
The area east of the Blue Ridge and north of Interstate 40 remained 
deeper in the colder air through the early morning hours, so snow was 
predominant at Hickory, North Carolina (HKY).  The strengthening warm 
nose eventually changed the precipitation to rain at HKY at 0926 UTC, 
although the observation incorrectly reported this as freezing rain 
with a surface temperature above 32o F.  Surface temperatures continued 
to cool early in the morning of 5 February, which allowed the 
precipitation to change to freezing rain at 1153 UTC.

Figure 18.  SPC composite reflectivity mosaic at 0600 UTC on 5 February.  
Click on image to enlarge.

Figure 19.  SPC objective mesoanalysis of 850 mb geopotential height (m; 
black contours), temperature (oC, dashed red contours), wind (kt; barbs), 
and temperature advection (oC/12 hr; color fill) at 0600 UTC on 5 February.  
Click on image to enlarge.

Figure 20.  As in Fig. 16, except for GSO at 0600 UTC on 5 February.  
Click on image to enlarge.

After 0600 UTC, the warm conveyor belt precipitation translated slowly 
east and covered the western half of the Carolinas by 1200 UTC (Fig. 21).   
The warm conveyor belt was manifested as a 40-50 kt low level jet at 
850 mb that stretched from north Florida, across Georgia, to eastern 
Tennessee (Fig. 22).   The center of low pressure at the surface moved 
slowly to the western Panhandle of Florida by 1200 UTC (Fig. 23), perhaps 
in response to the main short wave still rounding the bottom of the long 
wave upper trough located over east Texas and the western Gulf of Mexico 
(Fig. 24).   A large area of upper divergence associated with the right 
entrance region of the upper jet was poised to move east from Mississippi 
and Alabama (Fig. 25).  Mid-level frontogenesis was maximized across the 
North Carolina Mountains (Fig. 26a), although the deeper forcing was 
located over northeast Alabama, northwest Georgia, and eastern Tennessee 
as evidenced by a maximum of 850-250 mb differential divergence (Fig. 26b).  
The eastward movement of the deep forcing was expected to drive the warm 
conveyor belt slowly east across the region through the daylight hours.
Precipitation fell at the rate of one- to two-tenths of an inch per hour 
at most locations with the passage of the warm conveyor belt from
roughly 1200 UTC to 2100 UTC.  Precipitation changed to rain at HKY and 
AVL at 1348 UTC and 1354 UTC, respectively.  From that time onward, 
precipitation types other than rain were confined to localized areas near 
the Blue Ridge over the northern foothills of North Carolina near
Morganton and Lenoir.

Click below to view weather observations on 5 February 2010.

Table 2.  Surface observations taken at selected sites across the
western Carolinas during the calendar day of 5 February 2010.  
Click on the four-letter identifier to view the observations.

Figure 21.  As in Fig. 18, except for 1200 UTC on 5 February.  
Click on image to enlarge.

Figure 22.  Objective analysis of 850 mb geopotential height (black 
contours), temperature (red and blue dashed contours), dewpoint (green 
contours), and wind barbs at 1200 UTC on 5 February 2010.  Click on image 
to enlarge.

Figure 23.  HPC Surface fronts and pressure analysis at 1200 UTC on 
5 February 2010.  Click on image to enlarge.

Figure 24.  Objective analysis of 500 mb geopotential height (black 
contours), temperature (red dashed contours), and wind barbs at 1200 UTC 
on 5 February 2010.  Click on image to enlarge.

Figure 25.  Objective analysis of 300 mb wind barbs, isotachs (black 
contours and color fill), streamlines, and divergence (yellow contours)
at 1200 UTC on 5 February 2010.  Click on image to enlarge.

Figure 26.  SPC objective mesoanalysis at 1200 UTC on 5 February showing 
(A) 850-700 mb layer average height, temperature, wind, and frontogenesis,
and (B) 850-250 mb differential divergence.  Click on images to enlarge.

The back edge of the warm conveyor belt precipitation crossed the GSP 
forecast area between 1700 UTC and 2300 UTC.  Behind the warm conveyor
belt, another broken band of precipitation developed at the leading
edge of the dry air stream wrapping around the system at mid-levels
and the cold front aloft.  Water vapor imagery showed the dry air at
2100 UTC (Fig. 27) moving over south Alabama and the western Panhandle 
of Florida, with a moisture gradient along the Alabama - Georgia border. 
At 850 mb, a tongue of slightly warmer air extended north across Georgia, 
the western tip of North Carolina, and eastern Tennessee (Fig. 28), in
between the primary surface low over east central Georgia and an occluded
low over the Cumberland Plateau (Fig. 29). This precipitation fell 
almost exclusively as rain across the western Carolinas.

Figure 27.  GOES-12 water vapor imagery at 2045 UTC on 5 February 2010.  
Red colors signify relative dryness.  Click on image to enlarge.

Figure 28.  SPC objective mesoanalysis of 850 mb geopotential height (dm; 
black contours), temperature (oC; dashed red and blue contours), dewpoint 
(oC; green contours), and wind (kt; barbs) at 2100 UTC on 5 February.  
Click on image to enlarge.

Figure 29.  Surface fronts and pressure analysis at 2100 UTC on 
5 February 2010.  Click on image to enlarge.

Click here to view an 11 frame Java loop of GOES-12 visible satellite 
imagery from 1245 UTC to 2215 UTC on 5 February.

Click here to view a 31 frame Java loop of GOES-12 water vapor satellite 
imagery from 0545 UTC 5 February to 2345 UTC 6 February.

Click here to view a 23 frame Java loop of a composite reflectivity 
mosaic from 0558 UTC 5 February to 0359 UTC 6 February.

The vertically-pointing MicroRain Radar (MRR) located in Newton, North 
Carolina (about 12 miles southeast of HKY) and operated by RENCI 
(RENaissance Computing Institute) provided another vantage point of
the precipitation moving across the foothills of North Carolina during
the event.  A time vs. height display of radar reflectivity (Fig. 30)
showed the passage of three distinct bands of precipitation.  The first
period occurred from about 2300 UTC on 4 February through about 0600 UTC
on 5 February, although not continuously.  The higher band of reflectivity
seen between 4000 ft and 6000 ft above ground level corresponded to a 
near-freezing layer noted in the GSO upper air sounding at 0000 UTC on 
5 February.  It is thought that the warm nose seen in the FFC sounding 
shown in Fig. 17 extended north across the foothills at this time.  If 
that was the case, the higher reflectivity was the result of melting
snow crystals in the warm layer aloft.  The relatively sharp decrease
in reflectivity around 0600 UTC corresponded to the time that the
precipitation changed over to snow at HKY (see Table 2).  A period of
relatively high reflectivity was observed from 1600 UTC to 2000 UTC on
5 February, which was during the time that the main precipitation band
associated with the warm conveyor belt moved across the foothills.
After a lull of a few hours, the third band of precipitation passed over 
the MRR between 0000 UTC and 0200 UTC on 6 February.

Figure 30.  Vertical profile of radar reflectivity from MRR at Newton, 
North Carolina, from 0700 UTC 4 February to 0500 UTC on 6 February 2010.  
Horizontal axis is time (EST).  Vertical axis is height above ground 
level (ft).  Click on image to enlarge.

The radar-derived particle fall velocity product from the MRR gave 
additional information about precipitation type in the column above 
the radar (Fig. 31).  The initial period of precipitation at HKY varied
from snow to rain until right around 0600 UTC, when it changed over to 
snow.  The smaller fall velocity (blue colors) corresponded to the time
when snow reached the ground at HKY for about a two hour period through
0800 UTC.  After this time, the precipitation type was reported as
freezing rain and the MRR fall velocity went up.  During the passage
of the warm conveyor belt rain band from 1600 UTC to 2000 UTC, the
freezing level could be seen around 8000 ft above ground level, at 
which height snow crystals melted and began to fall at a much higher
velocity.  A similar display was noted with the passage of the third 
rain band after 0000 UTC on 6 February, during which rain was observed
at HKY.

Figure 31.  Vertical profile of radar-derived particle fall velocity 
from MRR at Newton, North Carolina, from 1300 UTC 4 February to 0500 UTC
6 February 2010.  Horizontal axis is time (EST).  Vertical axis is height 
above ground level (ft).  Click on image to enlarge.

c. After 0000 UTC - 6 February

At 0000 UTC on 6 February, the main short wave at 500 mb lifted out of 
the upper trough over Georgia (Fig. 32), while the primary surface low 
was moving northeast over the Coastal Plain of the Carolinas (Fig. 33).
The movement of the short wave pushed the second band of precipitation 
quickly east across the Piedmont of the Carolinas from 0000 UTC to 
0300 UTC.  Very little precipitation fell across the region after 
0300 UTC and was limited to the mountains.  Some northwest flow snow 
occurred along the Tennessee border on the morning of 6 February as the 
main surface low was off the Mid-Atlantic Coast.

Figure 32.  Objective analysis of 500 mb geopotential height (black 
contours), temperature (red dashed contours), and wind barbs at 0000 UTC 
on 6 February 2010.  Click on image to enlarge.

Figure 33.  HPC surface fronts and pressure analysis at 0000 UTC on 
6 February 2010.  Click on image to enlarge.

3.  Hydrologic Impacts

Several ingredients necessary for main stem river flooding were coming 
into place on 5 February.  At 1200 UTC, strong northward moisture 
transport from the Gulf of Mexico at 850 mb (Fig. 34) had raised 
precipitable water values above 1.0 inches across most of the southeast
United States (Fig. 35).  The precipitable water in the 1200 UTC upper 
air observation taken at FFC was measured at 1.04 inches, which was 
nearly two standard deviations above the median for that location in 
early February.  Relatively wet antecedent conditions allowed for 
more runoff than usual.

Figure 34.  SPC objective mesoanalysis of 850 mb geopotential height (m; 
black contours), equivalent potential temperature (oK; dashed green 
contours), and moisture transport (vectors and color fill) at 1200 UTC 
on 5 February.  Click on image to enlarge.

Figure 35.  SPC objective mesoanalysis of precipitable water (inches; 
dashed black contours and color fill) at 2100 UTC on 5 February.  Click 
on image to enlarge.

The passage of the warm conveyor belt resulted in a prolonged period 
of moderate to heavy rain over the headwaters of the French Broad River 
during the morning of 5 February.  Snow melt contributed additional 
runoff to the upper reaches of the French Broad basin which pushed the 
river above flood stage (16 feet) at Blantyre, North Carolina, but not 
until about 0800 UTC on 6 February (Fig. 36).  That a significant portion 
of the precipitation fell as snow probably contributed to the relatively 
slow response of the river.  The French Broad River remained in flood at 
Blantyre through the day on 6 February, and finally dropped below flood 
stage around 2100 UTC on 7 February.

Figure 36.  Hydrograph for the French Broad River gage at Blantyre, North 
Carolina, from 0000 UTC 4 February to 0000 UTC 9 February 2010.  The 
river stage is shown by the blue line.  Flood stage (16 ft) is indicated 
by the orange line.  Click on image to enlarge.

Excessive rain also fell over the Broad River basin and the Catawba 
River basin.  The South Fork of the Catawba River at Lowell, North
Carolina, rose above flood stage (10 feet) at around 2000 UTC on 
5 February, and reached a crest around 12 feet during the morning of 
6 February (Fig. 37).  The river fell below flood stage at Lowell at 
0900 UTC on 7 February.  On the Broad River (Fig. 38), flood stage was 
exceeded at Blacksburg, South Carolina (16 feet) at around 0300 UTC on 
6 February.  The river crested 1t 16.6 feet around 1000 UTC on 
6 February and quickly fell back below flood stage around 1300 UTC.

Figure 37.  Hydrograph for the South Fork of the Catawba River gage at 
Lowell, North Carolina, from 0000 UTC 4 February to 0000 UTC 8 February 
2010.  The river stage is shown by the blue line.  Flood stage (10 ft) 
is indicated by the orange line.  Click on image to enlarge.

Figure 38.  Hydrograph for the Broad River gage at Blacksburg, South 
Carolina, from 0000 UTC 4 February to 0000 UTC 8 February 2010.  The 
river stage is shown by the blue line.  Flood stage (16 ft) is indicated 
by the orange line.  Click on image to enlarge.

4.  The Rich Cove Debris Flow 

At approximately 2328 UTC on 5 February, a retaining wall failed at 
the top of a ridge (elevation about 4600 feet MSL) above Rich Cove 
(Fig. 39).  A large volume of earthen material behind the retaining 
wall proceeded to flow from the top of the ridge down into Rich Cove, 
picking up debris along the way (Fig. 40).  The debris flow damaged 
at least four houses and crossed Rich Cove Road in three locations 
(Fig. 41), before ending near the base of the ridge around 2330 UTC.

Figure 39.  Map showing the location of the Ghost Town - Rich Cove
debris flow near Maggie Valley, North Carolina, on 5 February 2010.   
The location of the Jonathan Creek rain gage is shown.  The path of 
the debris flow is indicated by the red line.  Image created using 
Google Earth Pro.  Click to enlarge.

Figure 40.  The Rich Cove Debris Flow began at the top of a ridge near 
Maggie Valley, North Carolina.  Image taken by Patrick Parton, Haywood 
County, and provided by Rick Wooten, North Carolina Geological Survey.

Figure 41.  The debris flow moved down the drainage of Rich Cove and
crossed Rich Cove Rd three times.  At least four houses were damaged 
before the debris flow ended near the base of the ridge.  Image 
courtesy of Rick Wooten, North Carolina Geological Survey.

Antecedent conditions were relatively wet near Maggie Valley due to 
several precipitation events during the late Autumn and early Winter.
Cooperative observers at Cullowhee and near Waynesville (both in 
Haywood County) recorded nine events dating back to 1 November 2009
when precipitation exceeded one inch.  Unlike other notable recent
slope failure events, the precipitation did not meet or exceed five
inches in the 24 hours prior to the event.  In fact, the Rich Cove
event happened with the least amount of precipitation compared to
other recent slope failure events known to the NWS.  The closest 
recording station at Jonathan Creek (Fig. 42) only measured a liquid 
equivalent of 1.93 inches through 2300 UTC on 5 February.  It is 
speculated that at least some of the shortfall was overcome by snow 
melt.  The cooperative observer located one mile east of Waynesville 
reported a snow depth of two inches on 4 February, with a modeled 
liquid equivalent of about 0.6 inches.  The amount of snow cover 
prior to the event was unknown.

Figure 42.  Precipitation accumulation at Jonathan Creek automated rain 
gage from 1700 UTC on 4 February until 1700 UTC on 6 February 2010.  
Image created from the North Carolina Division of Emergency Management 
Rain and Stream Gage Monitoring Network.  Click on image to enlarge.

5.  Summary 

The 4-6 February 2010 event was challenging in that two distinct threats
were present across parts of the NWS Greenville - Spartanburg forecast
area.  A transition of precipitation type was expected between primarily 
rain across northeast Georgia, Upstate South Carolina, and the western 
Piedmont of North Carolina, and a period of wet snow then freezing rain 
across parts of the Mountains and Foothills of North Carolina.  The 
precipitation was expected to be heavy enough that Winter Storm Warning 
criteria would be met with either heavy snow or a damaging accumulation
of ice.  Because heavy precipitation in the form of rain was expected 
along the Blue Ridge and across the Piedmont of the Carolinas, there
was also the possibility of flooding given the wet antecedent conditions.
In the end, a large part of the mountains east of the French Broad Valley,
and the northern Foothills of North Carolina, reached winter storm
criteria.  The heavy rain pushed three river forecast points above 
flood stage and contributed to a debris flow in Haywood County.

Snow and ice accumulation images taken by Bob Child, location near Lake 
Junaluska (Haywood County), North Carolina at 3800 ft elevation, on the 
morning of 5 February 2010.  Click on images to enlarge.

Snow and ice accumulation north of Lake Toxaway (Transylvania County), 
North Carolina at 3400 ft elevation, on the morning of 6 February 2010.  
Image courtesy of Arthur Raynolds.  Click on image to enlarge.

References

Kocin, P. J., and L. W. Uccellini, 2004: A Snowfall Impact Scale 
     Derived From Northeast Storm Snowfall Distributions.  Bull. 
     Amer. Meteor. Soc., 85, 177-194.

Acknowledgements

The snow accumulation map was prepared by Blair Holloway (NWS).  Chris
Horne (NWS) contributed to the hydrologic impact section.  Laurence
Lee (NWS) and Rick Wooten (North Carolina Geological Survey) contributed
to the debris flow section.  The upper air analyses and soundings were 
obtained from the Storm Prediction Center.  The mesoscale analyses were 
created by the Storm Prediction Center, but were obtained from the 
archive at NWS Omaha.  The surface fronts and pressure analyses were 
obtained from the Hydrometeorological Prediction Center.  Radar mosaics 
and satellite imagery were obtained from the University Corporation for 
Atmospheric Research.  The NESIS snowfall analysis map and the daily 
surface observation forms were obtained from the National Climatic Data 
Center.  The MRR images were obtained from the Renaissance Computing 
Institute.  The meteograms were obtained from Plymouth State College.