Anticipating Cloud-to-Ground (CG) Lightning Utilizing Reflectivity Data from the WSR-88D. Pete Wolf,...

Anticipating Cloud-to-Ground (CG) LightningUtilizing Reflectivity Data from the WSR-88D.

Pete Wolf, SOONational Weather Service

Jacksonville, Florida

Image from NOAA

Should We Do More?• CG lightning as weather-related killer…2nd 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 FindingsThe results suggested skill in producing probabilistic guidance based on the 40 dBZ echo height…

PROBABILITY OF:No CG CG Nmrs CG

Lgtng Lgtng Strikes

40dBZ height < -10C level – 8 kft 100% 0% 0%40dBZ height = -10C level – 5 to 7 kft 87% 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 kft 22% 78% 0%40dBZ height = -10C level + 5 to 7 kft 0% 100% 18%40dBZ height = -10C level + 8 to 10 kft 5% 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…UpdateUpdated results through mid 2006, incorporating a total of 835+ convective cells:

PROBABILITY OF:No CG CG Nmrs CG

Lgtng Lgtng Strikes

40dBZ height < -10C level – 8 kft 100% 0% 0%40dBZ height = -10C level – 5 to 7 kft 92% 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 kft 16% 84% 0%40dBZ height = -10C level + 5 to 7 kft 1% 99% 11%40dBZ height = -10C level + 8 to 10 kft 2% 98% 35%40dBZ height > -10C level + 11 to 14 kft 2% 98% 45%40dBZ height > -10C level + > 14 kft 0% 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 EXAMPLES40dBZ height relative Prob of CG lightningProb of numerous strikesto updraft -10C level (1+ per 5 min period) (> 10 per 5 min period)-8+ kft-7 kft 5%-6 kft 10%-5 kft 15%-4 kft 20%-3 kft 30%-2 kft 40%-1 kft 50%0 kft 60%+1 kft 70%+2 kft 75%+3 kft 80%+4 kft 85% 5%+5 kft 90% 10%+6 kft 95% 15%+7 kft 95% 20%+8 kft 95% 25%+9 kft 95% 30%+10 kft 99% 40%+11 kft 99% 50%+12 kft 99% 60%+13 kft 99% 70%+14 kft 99% 80%> +14 kft 99% 90%

1640z

March 22, 2005Part I

1645z1645z

1655z1655

1700z1700z

1705z

1705z

1710z1710z

1715z1715z

1725z1725z

1815z

P A U S E

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

2135z

99(90)

2145z

P A U S E

1725zJune 27, 2005

1825z

P A U S E

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%

L4C8J3

20 70 20 90

20 40 70

95 50 80 75 20 25

50 75 85

95 20

90 60

CG Lightning Probability

THE NEXT STEP…

Pete Wolf, SOO [email protected]

NWS Jacksonville FL 904-741-5186 ext 224

Develop algorithm, that produces radar-based CG lightning (and numerous strike) probabilities, for field evaluation.

QUESTIONS / COMMENTS ???

Anticipating Cloud-to-Ground (CG) Lightning Utilizing Reflectivity Data from the WSR-88D. Pete Wolf,...

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