A strong cold front crossed through the eastern Carolinas
during the evening hours of April 3, 2006, producing an outbreak of severe
weather. At the upper levels strengthening wind fields and
unclimatologically steep lapse rates from an elevated mixed layer
originating across the southwestern United States helped produce an
environment conducive for deep convection. Wind fields were uniformly
southwest during the afternoon hours, becoming more westerly during the
evening. Damaging wind gusts became more of a factor during the evening as
a 700 mb wind max over 50 knots rotated across North Carolina. Shear and
helicity values were never tremendous during the event; lapse rates and CAPE
were the two indicies which were most useful in forecasting the potential of
a severe weather outbreak.
Surface dewpoints were initally quite moist during the
morning of April 3rd, ranging from the upper 50s to lower 60s across the
forecast area.
Early morning convection associated with the back edge of mid level warm
advection across North Carolina produced a synoptic area of outflow winds
containing quite dry air. This modified airmass spread south into much of
inland North Carolina and north-central South Carolina during the mid
morning hours. As temperatures warmed during the day, what moisture
remained was mixed out and diluted with drier air from aloft causing surface
dewpoints to plunge into the 40s from Columbia, SC through Florence and
Lumberton. It appeared for a time this would be enough to cap soundings and
prevent widespread convection from developing.
Around 3 p.m. convection began developing along the
eastern slopes of the mountains across upstate South Carolina, likely in
association with convergence into the lee side surface trough. Convection
quickly developed east of the mountains across much of north central South
Carolina over the next two hours as soundings apparently became uncapped
from a combination of surface temperatures rising well into the 80s and
increasing lift through much of the atmospheric column. Severe weather was
initially limited to large hail, but later transitioned to both hail and
wind as the stronger mid-level winds arrived. Very dry air above 850 mb
helped aid entrainment of this high-momentum air into the storm downdrafts,
enhancing the occurrence of damaging surface wind gusts. Storm motions
increased to nearly 70 mph toward the end of the event.
The atmospheric quickly stabilized as the front crossed
the area before midnight, ending the severe weather threat.
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