Synoptic Overview - On the morning hours of March 8, 2005 a deep, negatively tilted 500 mb trough was digging into western North Carolina. Further aloft, at 250 mb, a 180+ knot jet max existed over GA and off the GA/SC coast, with eastern NC in the left exit region. Strong divergence values and 50 knot cross-height ageostrophic wind components (towards higher heights) along and off the NC/SC coast showed just how much the atmosphere was advecting itself out of balance. The 12Z March 8, 2005 MHX upper-air sounding showed a 61 knot (70 mph) low level jet at just 1200 ft AGL! Before and throughout the event, little or no instability was present over eastern North Carolina. Instability during the event was quite weak, indeed, with only 500-750 J/kg or less of CAPE (assessed using the LAPS analysis), primarily directly ahead of the squall line. Ahead of the cold front, temperatures were in the upper 50s to low 60s and dewpoints were predominately in the low to mid 50s. Behind the cold front, temperatures were in the mid 30s to low 40s. At 1800Z (100 pm), after the cold front crossed the Albemarle Sound area, Elizabeth City, NC (KECG) reported peak wind gusts to 52 knots with thundersnow and temperatures near freezing while Kitty Hawk and Manteo, just 30 miles away, reported temperatures near 60 with severe thunderstorms!
The fact that such an extensive severe weather event occurred in the presence of such marginal moisture/instability is a testament to the important role that low-level wind shear and upper-level dynamics play in the development and sustainment of severe thunderstorms.
Mesoscale Overview - At around 1200Z (7am) on March 8, 2005 a squall line formed west of Charlotte, NC along a strong surface cold front and downstream of a deep, negatively-tilted upper trough. The squall line proceeded to rapidly propogate across the state. Severe thunderstorm warnings were issued by NWS offices in Greenville/Spartanburg, SC and Raleigh, NC as the line of storms continued to move east. The sustained, impressive radar characteristics of the squall line as it crossed the state and the extensive wind damage history that accompanied it allowed NWS Newport/Morehead City, NC forecasters ample time to prepare for warnings as the squall line approached eastern North Carolina. 0.5 degree radial velocities showed 70+ knot inbound winds embedded within the squall line as it approached and subsequently crossed the area.
Upper-Air Sounding - 12Z (7am) March 8, 2005 Newport/Morehead City, NC upper-air sounding showing 60+ kt (70+ mph) winds just above the surface through 500 mb. Note the dry air above 600 mb. Also note the absence of any CAPE in this sounding.
(Click the image to enlarge.)
Model Synoptic Analysis - 1600Z (1100am) March 8, 2005 0-HR RUC40 500mb Height and MSLP analysis showing a deep, negatively-tilted 500mb trough digging over North Carolina and a deeping surface low (981 mb) along the coast.
(Click the image to enlarge.)
Model Jet Analysis - 1600Z (1100am) March 8, 2005 0-hr RUC40 250mb heights (white), windspeed (image), ageostrophic wind component (barbs) and divergence (solid blue). Note the 180+ knot jet max over GA and off the GA/SC coast with eastern NC in the left exit region. Strong divergence values and up to 60 knot cross-height ageostrophic wind components (towards higher heights) along and off the NC/SC coast show how much the atmosphere was advecting itself out of balance.
(Click the image to enlarge.)
Visible Satellite Imagery - 1600Z (1100am) March 8, 2005 Visible satellite image showing the strong surface front crossing eastern North Carolina. Note the cloud streaks behind and perpendicular to the front, indicating very strong NW winds aloft. Also note Wilmington, NC gusting to 77 knots (89 mph) with the passage of the squall line along the cold front.
(Click the image to enlarge.)
Radar Imagery - 1558Z (1058am) 0.5 degree KMHX reflectivity image showing the squall line crossing eastern North Carolina. Note the bowing of the line in Onslow county, a visual clue that severe winds were occurring.
(Click the image to enlarge.)
Radar Imagery - 1558Z (1058am) 0.5 degree MHX radial velocity image showing a large area of 64+ knot inbound velocities associated with the squall line. Several pixels of 70+ knot inbound velocities can be found in portions of the squall line.
(Click the image to enlarge.)
Damage Pictures from Pitt County (Click the images to enlarge.)
Photos courtesy of Eric Christensen, MHX Spotter
Damage Pictures from Outer Banks Dare County (Click the images to enlarge.)
Photos courtesy of the Outer Banks Sentinel, used with permission.
Case Study Team:
Brandon Vincent
Chris Collins
|
|
