MRX: LMA data gives confidence to NOT warn
June 4, 2009 by NASA SPoRT Center
Author: Doug Schneider (NWS Morristown/Knoxville WFO)
posted by Kevin Fuell (SPoRT)
“On June 3, WFO Morristown, TN used LMA data in the warning decision-making process. The data were used mainly to decide NOT to warn on several storms. These storms were pulse storms, and reflectivity signatures indicated that they were close to severe criteria. On this day, we were looking for 50 dBZ heights to around 29,000 feet and VILs around 50. Several storms were very close to this criteria, and produced a large amount of cloud-to-ground lightning strikes, but the LMA data showed that they generally did not produce a large increase in source density. Using the LMA data increased confidence in the decision NOT to warn.
The reflectivity and VIL images below show some of the storms that were evaluated. One of the storms (the storm in the image taken at 2017Z) did produce severe weather – several trees were blown down in Meigs and Rhea counties betwen 2035-2045Z. A warning was issued on this storm based on the elevated reflectivity cores and high VIL.”
(3 of the 5 examples from Doug are shown below)
1916Z – June 3, 2009
LMA source density of about 25 sources over N. Bledsoe county at 1916 (same as reflectivity below). From 1912 - 1920 an increase from 0 to ~40 sources occurred. Some sustained total lightning activity occurred after 1920 UTC. However, this small increase indicated that severe weather was not likely, though the reflectivity shown below was near severe thresholds for the day. Red line indicates the MRX western CWA line.
Radar reflectivity at various tilts and VIL for cell over N Bledsoe county at 1916 UTC. Yellow line indicates the MRX western CWA line. Reflectivity at 26,200 ft is at 45 DBz with VIL at 40 to 45 kg/m^3, just below the thresold for severe.
2017Z – June 3, 2009
LMA source density at 2018 over E. Rhea / W. Meigs countys of about 15 sources. Total lightning activity start at 2012, peaked at ~25 sources at 2020 and continued at ~15 sources till 2038 UTC. Then dropped off at 2040 UTC. As noted in the paragraph, a report of a few trees down was the result. The LMA did not really show a jump, but a warning was issued based on reflectivity and VIL. This cell was near the eastern edge of the LMA domain where the detection efficiency is less.
4 panel reflectivity and VIL for HTX at 2017 UTC on June 3, 2009. Large reflectivity at 3.4 tilt around 27,000 ft and hight VIL values led to a warning being issued, while the LMA did not show a significant jump. A report of trees down at 2035 UTC did occur.
2040Z – June 3, 2009
North Alabama LMA source density over Bledsoe county. From 2028 to 2032 UTC the values went from near 0 to ~35 sources (4 minutes). Compare to the 2040 reflectivity below at the 3.4 tilt. The relatively low source density values led to a decision to not issue a severe thunderstorm warning.
2040 Z reflectivity at the 3.4 tilt from HTX on June 3, 2009 over Bledsoe county in SE Tennessee.