June 23, 2004 Severe Weather Outbreak

Event Summary
National Weather Service, Raleigh NC

June 23, 2004 Severe Weather Outbreak
Updated 2004/06/30

Event Headlines -
...Wind Damage Associated with Multi-cell Thunderstorms...
...Elevated Reflectivity Cores and Deviate Right Motion Best Indicators of Severe...
...10 Warnings Issued - 7 Warnings Verified....

Event Overview - Showers and thunderstorms swept across North Carolina ahead of a cold front during the afternoon and evening of June 23, 2004 (radar loop from 259 PM EDT Wednesday June 23, 2004 through 958 PM EDT Wednesday June 23, 2004). Several clusters of thunderstorms became severe with numerous reports of damaging winds, a few damaging hail reports, and even a tornado across eastern North Carolina in Craven county.

Synoptic Overview - A cold front that was oriented east to west across central Virginia early Wednesday morning (June 23rd) dropped slowly south into northern North Carolina later Wednesday evening. A weak area of low pressure developed along the front in northeastern North Carolina during the late afternoon hours. The airmass across much of central and eastern North Carolina was unstable. Afternoon heating allowed surface temperatures to reach the lower 90s. Surface dewpoints generally ranged in the lower 70s.

The 12Z Greensboro sounding indicated an unstable airmass favorable for multi-cell thunderstorms with damaging winds. Modified CAPE values ranged around 2300 J/kg. The wind profile was not very impressive with little directional shear and limited speed shear. The wet bulb zero height was near 12,000 feet which reduced the hail threat. The low level flow was weak with a light west to southwesterly flow across the Carolinas (850 MB Upper Air Plot from 12Z June 23, 2004). Central North Carolina was on the southern edge of the upper-level wind maximum that was located over the Ohio Valley and Mid Atlantic states with an area of upper-level divergence noted across the Carolinas (250 MB Upper Air Plot from 12Z June 23, 2004).

Severe Weather Reports - Note that the severe weather reports were concentrated near the North Carolina / Virginia border, the southwestern Piedmont, the central coastal plain and near the Albemarle Sound.

Severe weather reports from June 23, 2004. Note that most of the reports were concentrated near the North Carolina / Virginia border, the southwestern Piedmont, the central coastal plain and near the Albemarle Sound

Archived Text Data from the June 23, 2004 Severe Weather Outbreak

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Surface Data

NCEP Surface Analysis at 21Z on Wednesday, June 23, 2004 (5 PM EDT).

Java Loop of Surface Analysis from 12Z (8 Am EDT), Wednesday June 23 through 06Z (2 Am EDT), Thursday June 24, 2004.

Radar Imagery

KRAX Base Reflectivity Image from 2030Z (430 PM EDT) Wednesday, June 23, 2004.
Click on the image to enlarge.

KRAX Base Reflectivity Imagery - Click to enlarge

Java Loop of base reflectivity imagery from krax WSR-88D.
The loop is from 1859Z (259 PM EDT) Wednesday June 23, 2004 through 0158Z (958 PM EDT) Wednesday June 23, 2004. The thunderstorms were organized into multi-cell segments. Note that the outflow boundaries from thunderstorms just northwest of Raleigh became better defined as they moved past the Raleigh area, producing additional thunderstorms in locations southeast of Raleigh.

In terms of storm structure as indicated by radar imagery and by wind damage reports, the most impressive storm of the day was located in western Halifax County between 4:20 and 4:35 PM EDT (2020Z - 2035Z)”.

The 4-Panel image contains Composite Reflectivity (CR) imagery in the upper left, Vertically Integrated Liquid (VIL) in the upper right,"8-bit" Reflectivity imagery “(0.5 slice)” in the lower left, and "8-bit" Storm Relative Velocity imagery “(0.5. slice)” in the lower right.

While the storm relative velocity imagery shows at weak mesocylone, it is the strong reflectivity cores in the CR and the “8 bit” imagery along with the high VILS that indicate a severe weather threat.

4-Panel KRAX radar imagery from 2035Z (435 PM EDT) Wednesday, June 23, 2004.
Click on the image to enlarge.

4-Panel Imagery from krax WSR-88D - Click to enlarge

The 4-Panel image contains Composite Reflectivity (CR) imagery in the upper left, Vertically Integrated Liquid (VIL) in the upper right, "8-bit" Reflectivity imagery “(0.5. slice)” in the lower left, and "8-bit" Storm Relative Velocity imagery “(0.5. slice)” in the lower right.

KRAX plan view and cross section of the Thunderstorm that produced widespread wind damage across much of western Halifax county from 2020Z (420 PM EDT) on Wednesday, June 23, 2004. Note the greater than 65 dBZ elevated core ranging from 12,000 to 29,000 feet “and the storm’s “overhang”, indicative of a strong and sustained updraft.

krax WSR-88D Composite Reflectivity imagery, the white line is the location in which the cross section is taken - Click to enlarge

krax WSR-88D Reflectivity Cross Section (RCS) taken along the white line in the Composite Reflectivity (CR) image looking east- Click to enlarge

The image on the left is of Composite Reflectivity (CR) from KRAX. The white line is the location in which the cross section is taken. The image on the right is of a Reflectivity Cross Section (RCS) taken along the white line in the Composite Reflectivity (CR) image looking east. Note the greater than 65 dBZ elevated core ranging from 12,000 to 29,000 feet.

Warning Decision Process

Most of the thunderstorms moved from west to east. But the two clusters of thunderstorms that were sustained the longest and produced the most damage across central North Carolina were right-movers. One severe thunderstorm cluster moved across Rockingham, Caswell, and Orange counties, while the second severe thunderstorm cluster moved across Vance, Warren, and Halifax counties.

In addition to the deviate right moving motion of the two severe thunderstorm clusters, elevated reflectivity cores exceeding 65 dBZ in a 4 panel display were the best indicators of severe storms. Other severe storm indicators included thunderstorm cell mergers and splitting storms.

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Mike Brennan
Doug Schneider
Jeff Orrock
Kermit Keeter
Jonathan Blaes

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