Anticipating Cloud-to-Ground (CG) Lightning Utilizing Reflectivity Data from the WSR-88D. Pete Wolf, SOO National Weather Service Jacksonville, Florida Image from NOAA

Should We Do More? CG lightning as weather-related killer…2 nd to floods. CG lightning among leading weather-related causes of property damage, and most frequent damage claim. –$2 billion+ annually in U.S. alone. Lightning is the most frequent threat to life/property. Our current effort is primarily focused on public awareness. –30/30 rule, “Take Cover if you Hear Thunder”, Lightning Awareness Week, etc. –In real-time, we do more to alert people of penny-sized hail than CG lightning. –More is not done due to belief that all t-storms produce deadly lightning.

Is CG Lightning Predictable (or at least “Nowcast”-able) A study on CG lightning initiation radar clues at the Kennedy Space Center (KSC) determined that skill in anticipating CG lightning was achievable. –The study involved about 40 thunderstorms around the KSC area. –Results showed the best correlation when the 40dBZ core reached at least the -10C height…yielding a POD around 0.85, an average lead time of 7.5 minutes, and a low FAR.

WFO Jacksonville FL Study A more ambitious study was completed in 2005, involving 420+ convective cells across northern FL, southern GA and other areas of the southern U.S. The study included a mix of single cell, multi-cell, and supercell events occurring during various times of the year (a few cases were in prior years). –Nearly 320 cells for CG initiation study, 109 not producing CG lightning. –Additional 109 cells producing numerous CG strikes after initially producing isolated/scattered strikes The study compared storms producing… –No CG strikes (that had 40dBZ core up to at least 10 Kft, with an echo top up to at least 22 Kft) –Isolated/Scattered strikes (defined as 1-10 CG strikes per 5-minute period) –Numerous/Excessive strikes (defined as > 10 CG strikes per 5- minute period)

WFO Jacksonville FL Study KSC Study: –Used Environ. -10C level –Used 40 dBZ echo height JAX Study –Used “Updraft” -10C level –Used 40 dBZ echo height Updr -10C Envir -10C

WFO Jacksonville Findings Due to a number of issues, a probabilistic approach to the results was taken. –Radar issues (e.g. interpolation, calibration, etc). –NLDN output accuracy issues. –Specific values issue (is there a difference between 40 dBZ and 38 dBZ or 42 dBZ?)

WFO Jacksonville Findings The results suggested skill in producing probabilistic guidance based on the 40 dBZ echo height… PROBABILITY OF: No CGCGNmrs CG Lgtng Lgtng Strikes 40dBZ height < -10C level – 8 kft100%0%0% 40dBZ height = -10C level – 5 to 7 kft87%13%0% 40dBZ height = -10C level – 2 to 4 kft (~ -6/-7C level)67%33%0% 40dBZ height = -10C level +/- 1 kft (apprch/exceed -10C)23%77%0% 40dBZ height = -10C level + 2 to 4 kft22%78%0% 40dBZ height = -10C level + 5 to 7 kft0%100%18% 40dBZ height = -10C level + 8 to 10 kft5%95%41% 40dBZ height > -10C level + 11 to 14 kft 1%99%75% 40dBZ height > -10C level + > 14 kft 0%100%92% (51%) Note skill in predicting CG strikes when 40dBZ height reaches -10C height in updraft. Note skill in predicting numerous CG strikes when 40 dBZ height > -10C height + 10kft. Note CG lightning is unlikely when the 40dBZ height is no higher than -10C level - 5kft The probability patterns above suggest probabilistic guidance can be generated for CG lightning.

WFO Jacksonville Findings…Update Updated results through mid 2006, incorporating a total of 835+ convective cells: PROBABILITY OF: No CGCGNmrs CG Lgtng Lgtng Strikes 40dBZ height < -10C level – 8 kft100%0%0% 40dBZ height = -10C level – 5 to 7 kft92%8%0% 40dBZ height = -10C level – 2 to 4 kft (~ -6/-7C level)79%21%0% 40dBZ height = -10C level +/- 1 kft (apprch/exceed -10C)39%61%0% 40dBZ height = -10C level + 2 to 4 kft16%84%0% 40dBZ height = -10C level + 5 to 7 kft1%99%11% 40dBZ height = -10C level + 8 to 10 kft2%98%35% 40dBZ height > -10C level + 11 to 14 kft 2%98%45% 40dBZ height > -10C level + > 14 kft0%100%92% (57%) Note skill in predicting CG strikes when 40dBZ height reaches -10C height in updraft. Note skill in predicting numerous CG strikes when 40 dBZ height > -10C height + 10kft. Note CG lightning is unlikely when the 40dBZ height is no higher than -10C level - 5kft The probability patterns change little, again suggesting probabilistic guidance can be generated for CG lightning.

Failure Areas This concept does not work well for: –Lengthy anvils, that may not have 40dBZ echo, yet can yield “bolts from the blue”. –Widespread MCS stratiform regions. It is possible to relate these failures to a sufficiently high 40dBZ core within the upstream (storm-relative) updraft region. Manual intervention needed to account for these failure areas.

CASE EXAMPLES Let’s take a look at a few cases, to demonstrate what the results suggest…an ability to anticipate occurrence and amount of CG lightning, based on WSR-88D reflectivity data. –April 22, 2005: Supercell/bow echo case –June 27, 2005: Pulse storm case The following are 5-min CG lightning displays (from NLDN), with CG lightning probabilities overlaid (numerous strike…>10 per 5 min…probabilities in parentheses). Very High Probability…90%+ (80%+) High Probability…60-85% (50-75%) Moderate Probability…30-50% (25-45%) Low Probability…5-25% (5-20%)

PROBABILITIES USED IN EXAMPLES 40dBZ height relative Prob of CG lightningProb of numerous strikes to updraft -10C level(1+ per 5 min period)(> 10 per 5 min period) -8+ kft -7 kft5% -6 kft10% -5 kft15% -4 kft20% -3 kft30% -2 kft40% -1 kft50% 0 kft60% +1 kft70% +2 kft75% +3 kft80% +4 kft85%5% +5 kft90%10% +6 kft95%15% +7 kft95%20% +8 kft95%25% +9 kft95%30% +10 kft99%40% +11 kft99%50% +12 kft99%60% +13 kft99%70% +14 kft99%80% > +14 kft99%90%

1640z March 22, 2005 Part I

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2045z March 22, 2005 Part II (2 ½ hrs later)

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How Can We Utilize This? Develop a WSR-88D algorithm that shows CG lightning/ numerous strike probabilities for detected cells. –Currently, SCAN only has detected CG rate. –Have algorithm update after every slice. Develop a web page display of CG lightning/ numerous strike probabilities, based on WSR-88D data. –Private sector could develop program to alert customers based on desired probability level. Issue CG lightning alerts for communities. –Some offices include lightning potential (especially excessive strikes) in significant weather alert SPS products. CG Lgtng Any Nmrs 95% 70% 75% 20% 40% 5% L4 C8 J CG Lightning Probability

THE NEXT STEP… Pete Wolf, SOO NWS Jacksonville FL ext 224 Develop algorithm, that produces radar-based CG lightning (and numerous strike) probabilities, for field evaluation. QUESTIONS / COMMENTS ???