Mesoscale Data
Forecasters at RAH routinely use the
SPC meso-analysis products during
severe weather operations. During this event, the SPC meso-analysis products
were consulted frequently to monitor the evolving environment, anticipate the
growing tornado threat, and locate the region of greatest threat. The images and discussion below
highlight several of the SPC meso-analysis products that provide insight into the
evolution of the severe weather event. These images are not only used in real time but they are archived locally
for use in post event analysis and training.
Analyzed surface Theta-e (green contours), Theta-e convergence (purple contours) and wind barbs from SPC at 0800 UTC on Saturday, November 15, 2008
By 0800 UTC, the coastal front had advanced inland into the Coastal Plain and it can be approximated by the warm side of the Theta-e gradient near the
340 degree isentrope. A second boundary at the eastern edge of the wedge air mass was located in the western Piedmont and Foothills. The tornadoes in the
RAH CWA developed in the vicinity of the coastal front between 200 and 400 AM EST and tracked northeastward. The availability of a nearby source of low
level instability near the surface likely played an important role in tornadogenesis.
(Click on the image below to enlarge)
850 mb heights, temperatures (red/blue), dew points (green), and wind barbs (black) from SPC at 0800 UTC on Saturday, November 15, 2008
An 850 mb trough was located across the central Tennesssee valley at 0800 UTC. Behind the trough, temperatures were approaching
zero degrees C across western Kentucky and western Tennessee. Ahead of the trough, the low level jet axis of around 55 kts
extended from near Atlanta, GA to Raleigh, NC. In fact, the winds near 850 mb at 5,000
feet as shown in the Raleigh profiler actually reached 70 kts at around 0600 UTC. Some subtle directional convergence is suggested in
the 850 mb layer across eastern NC.
(Click on the image below to enlarge)
Analyzed mixed layer convective available potential energy (MLCAPE) (red) and mixed layer based convective inhibition (MLCIN) (blue lines - shaded)
from SPC at 0800 UTC on Saturday, November 15, 2008
MLCAPE values ranged between 1000 and around 1500 J/kg across the central and northern
Coastal Plain near the coastal front. A small area of near zero convective inhibition (CIN) overlapped the MLCAPE values greater
than 1000 J/Kg in a narrow region extending northeast from Goldsboro. The region of moderate instability was favorable for
intense updrafts and stretching vorticity vertically to support tornadogenesis.
(Click on the image below to enlarge)
0-6 km Bulk Shear (blue) and storm motion (brown) from SPC at 0800 UTC on Saturday, November 15, 2008
The 0-6 km bulk shear values range between 60-65 knots across the Coastal Plain. Given sufficient instability,
thunderstorms tend to become more organized and persistent as vertical shear increases.
Supercells are commonly associated with vertical shear values of 35-40 knots and
the analysis at 0800 UTC supports the potential of supercells.
(Click on the image below to enlarge)
0-1 km Storm Relative Helicity (SRH) (shown in blue) and storm motion (brown) from SPC at 0800 UTC on Saturday, November 15, 2008
Note that the 0-1 km SRH values range between 200 and 250 m²/s² across the Coastal Plain of North Carolina. The
SRH is a measure of the potential for cyclonic updraft rotation in right-moving supercells. Studies have shown
that larger values of 0-1 km SRH, greater than 100 m²2/s², suggests an increased threat of tornadoes and that very
large values of 0-1 km SRH (perhaps greater than 200 to 300 m²/s²) are indicative of significant tornado potential.
(Click on the image below to enlarge)
0-3 km Storm Relative Helicity (SRH) (shown in blue) and storm motion (brown) from SPC at 0800 UTC on Saturday, November 15, 2008
Note that the 0-3 Km SRH values range between 200 and 300 m²/s² across the Coastal Plain of North Carolina. The
SRH is a measure of the potential for cyclonic updraft rotation in right-moving supercells. Larger values of 0-3 km SRH
(greater than 100 m²/s²) suggest an increased threat of supercells and tornadoes. Some studies suggest that the 0-3 km SRH
is a better indicator of storm rotation, which is related to tornadoes, but not directly the potential for tornadoes themselves.
(Click on the image below to enlarge)
Analyzed Significant Tornado Parameter (STP) (effective layer) (shown in yellow and red) and the mixed layer
convective inhibition (MLCIN) from SPC at 0800 UTC on Saturday, November 15, 2008
The STP is designed to highlight areas favoring right-moving tornadic supercells.
The STP is a multiple ingredient, composite index that includes effective bulk wind difference (EBWD),
effective storm-relative helicity (ESRH), 100-mb mean parcel CAPE (MLCAPE), 100-mb mean parcel
CIN (MLCIN), and 100-mb mean parcel LCL height (MLLCL). Analyzed values across central and eastern
North Carolina show that the tornado outbreak area was highlighted in and near a region with STP values
between 1 and 2. Additional details on the Analyzed Significant Tornado Parameter (STP) is
available in
this reference.
(Click on the image below to enlarge)
Analyzed Lifting Condensation Level (red, blue, and green) from SPC at 0800 UTC on Saturday, November 15, 2008
The LCL height is the height at which a parcel becomes saturated when lifted dry adiabatically.
The importance of LCL height is thought to relate to sub-cloud evaporation and the potential
for outflow dominance. Low LCL heights imply less evaporational cooling from precipitation
and less potential for a strong outflow that would likely inhibit low-level mesocyclone development.
Thunderstorms that produce significant tornadoes generally have a lower LCL height with LCL heights
less than 1,000 meters typically favorable for tornado development. The LCL values during this
event in the areas where tornadoes occurred ranged between 500 to 750 meters.
(Click on the image below to enlarge)
NWS composite radar reflectivity imagery from 0800 UTC on Saturday, November 15, 2008.
The composite reflectivity imagery is from the approximate time in which the analysis imagery above is valid.
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