February 10, 2008 High Wind and Fire Weather Event|
Event Headlines -
...A strong, dry cold front and high winds caused hazardous weather across much of North Carolina...
...Widespread wind damage was reported as winds gusted to over 45 mph...
...Over 300 wildfires burned more than 9,000 acres of land across North Carolina on February 10, with the 9,000 acres representing
over 46% of the typical number of acres that burn in a year...
...A variety of online resources are available for meteorologists to maintain awareness of the weather's impact including
power outage maps from power companies...
Event Overview -
A very strong mid-level jet, channeled between a mid-level ridge over the Western U.S. and
an anomalous low drifting across the Great Lakes Region, and a surface cold front
surged southeastward through the Upper Midwest during the early morning hours of February 10th.
A cold frontal passage across the Mid-Atlantic States the previous day left dewpoints in the upper
teens and lower 20's throughout the Piedmont and Foothills of Virginia and North Carolina. Temperatures
on the 10th ranged from the upper 50's to mid 60's across the area, creating relative humidities in the
15 to 23 percent range. When the mid-level jet nosed across the Appalachian Mountains during the mid-morning
hours, a developing deep mixed layer reaching up to near 750 mb allowed winds in excess of 40 mph to
be mixed down to the surface. Low relative humidities (< 20%) and strong winds (sustained > 20 mph and gusts >30 mph)
are known to cause conditions favorable for fire development and growth. The National Weather Service in Raleigh issued
a Red Flag Warning from 9am to 9pm on the 10th, as well as a Wind Advisory that lasted through the day until 9pm.
High Wind Warnings were issued by NWS offices in Blacksburg, VA and Greenville-Spartanburg, SC for
even higher wind gusts of 60mph or higher. By mid-afternoon, many measured wind gusts of 40+ mph and a few above 50 mph,
had been reported, and hundreds of fires had developed across Central North Carolina.
Synoptic Overview -
On Saturday, February 9, 2008, an anomalously low (around 400 meters) 500 mb low center was developing
over the Great Lakes region. Behind the upper-level low, a strong jet was digging southeastward
into the Upper Midwest. The strong winds extended down into the mid-levels of the atmosphere, where over
110 knots was observed at 500 mb, and over 70 knots at 700 mb.
A strong cold front, seen in the strong 850 mb temperature gradient, was also pushing through the
Upper Midwest, as 850 mb temperatures fell to less than 30
below zero in some locations near the Canadian border. Model forecasts from 00 UTC on February 10 (Saturday evening) predicted a rapid strengthening of the wind
field, particularly below 500 mb. Winds at 700 mb were forecast to strengthen to nearly 90 knots over
Virginia, with over 70 knots over the NWS Raleigh County Warning Area (CWA) during the day on
Sunday (February 10).
Upper-air analysis of the 12 UTC February 10 RAOB data verified the forecast strengthening, as 500 mb winds increased to over 180 knots
and 700 mb winds up to 90 knots from Iowa to Indiana. In addition to the strong winds moving into the Mid-Atlantic region, deep mixing in the
boundary layer was also poised to take place. The upper-air sounding from Greensboro (GSO)
from Saturday evening revealed a mixed layer extending to near 650 mb, or over 10,000 feet. With little change in the synoptic pattern,
a similar deep mixed layer was expected during the day on Sunday. The 12 UTC sounding on Sunday
February 10 shows the residual mixed layer above the surface inversion. As the strong winds
rounded the base of the upper-level trough and crossed the Appalachian Mountains, wind
speeds of 60 to 70 knots were located at the top of the mixed layer. As temperatures during the day on Sunday climbed into the upper 50's to
mid 60's across Central North Carolina, the low-level inversion eroded, and the high
winds began to be realized at the surface.
Most locations across North Carolina started reporting wind gusts of 20 knots or higher during the early morning
hours (around 14 UTC or 9am LST). The mixed layer reached to near 700 mb on Sunday afternoon,
where winds were in excess of 75 knots. Wind gusts steadily increased throughout the day as deeper mixing and the passage of the
strongest mid-level winds occurred. By early afternoon (around 18 UTC), wind gusts over 40 mph were reported at many locations, with a
sites gusting to over 50mph (see the official Public Information Statement for a full list of maximum wind gusts).
There were numerous reports of damage to homes, and downed trees and power lines closed many local roads and interstates.
In addition to the wind, fire danger was also a concern statewide. A series of dry cold fronts swept across North Carolina during the first full week of February 2008, under a
relatively flat, zonal mean flow across the Central US. This kept dewpoints in the low to mid 30s throughout the week.
With nearly all of North Carolina in the midst of a persistent, exceptional drought,
not only was the air dry, but fuel moistures (the percent water content of vegetation)
were also very low. These conditions placed North Carolina under a level of
high fire danger.
Many fires began in the early afternoon, as relative humidities fell to around 20% and winds increased. The image below shows widespread
fires across the Deep South and Southeast U.S. at 18Z on Sunday afternoon.
Maximum Wind Gust Map