Hourly 4 inch (0.1m) Soil Temperatures|
The image below (click on it to enlarge) shows the hourly 4 inch soil
temperatures at 8 locations across central North Carolina from midnight on
12/24 through midnight on 12/30, 2010.
First, note that the 4 inch soil temperatures were rather cold on 12/24,
with soil temperatures at most locations dropping into the mid 30s or colder on the morning of
12/24. Despite mostly sunny skies during the day and
high temperatures mainly in the lower to mid 40s,
soil temperatures only warmed slightly from the morning minimums with a diurnal
spread of between 4 and 8 degrees on 12/24. The nocturnal cooling of the soil was likely reduced by the
warmer air temperatures compared to previous nights. Air temperatures on the morning of 12/25
ranged in the lower to mid 30s with mostly cloudy skies.
Precipitation spread into the western Piedmont during the late morning hours on 12/25.
The precipitation was responsible for the early peak in the hourly soil temperature plot for stations
NCAT (NC A&T Research Farm) and HIGH (UNCG Lindale Farm Station) which are both located in Greensboro. Note that the max soil temperature for these two locations occurred around
noon local time. The other stations reached their maximum soil temperature around
the more typical time of 400 PM local time.
In general, most locations had a rather steady decline in soil temperatures as
precipitation fell across central North Carolina. Note that both LILE (Lilesville) and
HAML (Hamlet) had a more aggressive decline in soil temperatures between 200 AM and
600 AM. This decline appears coincident with a period of heavier precipitation which
cooled the boundary layer and allowed the rain to quickly change to snow and accumulate
during the pre dawn hours. It is also worth noting that there was very little diurnal
change in soil temperatures on 12/26 as snow accumulated across most of central
North Carolina through at least midday
On 12/27, the soil temperatures at most observing locations in central North Carolina
showed very little diurnal change. This was not too surprising given
the fresh snow cover across the area. Note that there was one exception, LILE
which had around a 3 degree diurnal change in soil temperatures during the day. South-central
NC where Lilesville is
located, received around 4 inches of snow during the storm which was
on the low end of the general 4 to 12 inches of accumulation that fell across central NC.
In addition, high temperatures on
12/27th approached 40 degrees in Lilesville which resulted in some additional melting.
By 12/28, sunshine along with daytime temperatures well into the 40s
resulted in considerable melting and allowed the diurnal spread in soil temperatures to increase. The diurnal spread was greatest
at LILE, HAML, and in Greensboro at the NCAT and HIGH where the snow melted more significantly compared to
CLIN (Clinton), GOLD (Goldsboro), CLA2 (Clayton) and SILR (Siler City) where the more significant snows were slower to melt.
Past experience has shown that when the max soil temperature during the day preceding a snow fall are
in the lower 40s or colder and given modest snow rates with surface temperatures at or near freezing,
the snow can be expected to accumulate. Max soil temperatures in most of central North Carolina were
in the lower to mid 40s on 12/24. During this event, the snow was slower to accumulate than then
12/16, 2010 event which had very cold temperatures preceding and during that event which allowed
the snow to readily accumulate, even on roadways. During this event, boundary layer temperatures in the eastern
Piedmont and Coastal Plain were near or just above freezing which initially limited accumulations.
Eventually, heavier precipitation and cooling from melting allowed air temperatures to fall to around or below freezing
and allow the snow to accumulate more efficiently.
NCAT - NC A&T Research Farm, Greensboro NC
HIGH - UNCG Lindale Farm Station, Greensboro NC
SILR - Siler City Airport, Siler City, NC
CLA2 - DAQ Clayton Profiler, Clayton, NC
LILE - NC Electric Cooperative Anson Peaking Plant, Lilesville, NC
HAML - Hamlet Tower, Hamlet, NC
GOLD - Cherry Research Station, Goldsboro, NC
CLIN - Horticultural Crops Research Station, Clinton, NC