skywarn experimentallightnin gforecasts

Information about skywarn experimentallightnin gforecasts

Published on October 7, 2007

Author: Danielle

Source: authorstream.com

Content

Experimental Lightning Forecasts:  Experimental Lightning Forecasts Gail Hartfield Senior Forecaster NOAA/NWS Raleigh Central Carolina Skywarn Information Net Tuesday, August 7, 2007 Slide2:  Lightning Casualties and Damages in the United States Lightning was #2 source of weather related deaths behind flash + river flooding (tornado close #3) Lightning was #1 source of convective weather deaths from 1992 – 94 (tornado close runner-up). From Curran et al. (2000) For lightning (‘59-’94), North Carolina ranked #2 – Fatalities #4 – Injuries #4 – Casualties #4 – Damage in the United States Slide3:  Lightning Casualties in the United States From the National Lightning Safety Institute #5 So, how might we reduce lightning casualties? Lightning safety awareness efforts have been ongoing (www.lightningsafety.noaa.gov), and warnings and statements often address it (“storms are producing extreme lightning”), but what about forecasting lightning? WFO RAH’s long term vision::  WFO RAH’s long term vision: A qualitative 3-24 hour lightning “outlook”, included in 5 AM Hazardous Weather Outlook With high confidence, a potential event might be described more quantitatively; e.g. “STORMS MAY PRODUCE A DEADLY FLASH EVERY 15 TO 30 SECONDS…” Why do this?:  It’s still a big public safety issue Just one strike can kill, but numerous strikes raise the odds Only “planning” information we currently give is very generic Augment our local radar technique (which just gives a 20-30 minute lead time for the first strike) Much value can be gained from providing a skillful (even a little bit!) Day 1 lightning outlook Aviation Electric utilities Forestry agencies General public & recreation Great opportunity to do something new and valuable Why do this? How we’ve gone about this…:  How we’ve gone about this… Review of past research and lightning studies Created a checklist, which we are currently testing Worked with Storm Prediction Center on experimental model-based lightning probabilities (based on WRF-NMM and SREF) Will locally archive cloud-to-ground strikes (CGs) on a case-by-case basis this year, for conducting case studies during the winter First, what is “excessive” lightning? From the Federal Meteorological Handbook #1::  First, what is “excessive” lightning? From the Federal Meteorological Handbook #1: “Occasional”: < 1 flash/minute “Frequent”: 1 – 6 flashes/minute “Continuous”: 6 – 12 flashes/minute And, RAH’s addition, “Extreme/excessive”: > 12 flashes/minute (that’s more than a flash every 5 seconds) A lightning review:  A lightning review Necessary conditions for lightning::  Necessary conditions for lightning: Strong instability Strong updrafts Sufficient moisture above 0°C Rapid charge separation and electrification Operational checklist for lightning threat:  Parameters and thresholds pulled from past research and local case studies Intended to help assess two essential lightning ingredients: Available moisture (presence of graupel, needed for electrification) Instability aloft (favoring vigorous updrafts) Operational checklist for lightning threat #1: Sufficient moisture aloft:  Need sufficient graupel (small ball of soft ice or snow) in the -5° to -30°C layer for electrification An important charging mechanism results from the collision of ice crystals and rimed graupel in the presence of supercooled water Need to factor in entrainment & environment changes #1: Sufficient moisture aloft From Carey and Rutledge (2000) #2: K-Index:  Incorporates mid level lapse rate (instability) and moisture … KI = (T850mb- T500mb) + Td850mb - (T700mb -Td700mb) Because it includes both moisture and instability, it captures potential for Strong updrafts Presence of colliding ice crystals & rimed graupel, for charge separation #2: K-Index From Livingston et al (1996) and Shafer and Fuelberg (2006) #3 and #4: Showalter index and Convective Available Potential Energy (CAPE):  Both used to assess instability in the sounding Showalter: difference between the environmental and parcel temperature; more negative = more unstable CAPE is highest with warm/moist boundary layer & cool air aloft #3 and #4: Showalter index and Convective Available Potential Energy (CAPE) From Livingston et al (1996) From a study by Cope (2006):  From a study by Cope (2006) Most high-flash events had CAPEs > 1500 J/kg #5: N-CAPE (normalized CAPE):  Shows the “shape of the CAPE” Tall, skinny CAPE = weak vertical parcel accelerations (little or no lightning) Short, fat CAPE = strong parcel accelerations (favorable for frequent lightning) #5: N-CAPE (normalized CAPE) From Williams (1995 and 2000) and Blanchard (1998) #6: 850 mb theta-e ridge:  A surrogate for low level warm and moist air #6: 850 mb theta-e ridge From Livingston et al (1996) #7/#8: Experimental model output:  From Storm Prediction Center Each based on a different model #7/#8: Experimental model output From Livingston et al (1996) and Shafer and Fuelberg (2006) #9: Triggers:  Should help increase coverage and organize convection #9: Triggers #10: Persistence:  Did storms produce high flash rates yesterday? And is the weather regime relatively unchanged? #10: Persistence From Livingston et al (1996) and Shafer and Fuelberg (2006) Another consideration: “Mixed-phase CAPE”:  Presents instability isolated to just the layer where lightning production is focused, 0° to -40°C, or -10° to -30°C Much like the N-CAPE, it conveys the potential for vigorous updrafts within this critical layer Another consideration: “Mixed-phase CAPE” From Carey (2002) Example of CAPE -10° to -30° : 4/27/07, Eastern VA:  50+ strikes in 5 minutes! Example of CAPE -10° to -30° : 4/27/07, Eastern VA Example of CAPE -10° to -30° : 4/27/07, Eastern VA:  Example of CAPE -10° to -30° : 4/27/07, Eastern VA Future work: Case studies to hopefully lead to skilled, specific strike-frequency forecasts. Some future wording you might see in the HWO::  Future work: Case studies to hopefully lead to skilled, specific strike-frequency forecasts. Some future wording you might see in the HWO: “Storms which develop will be capable of producing nearly continuous dangerous lightning… more than 100 strikes in 10 minutes as they pass by.” “In addition to the threat of large hail… excessive deadly lightning is likely. Any storm could produce up to 10 strikes a minute.” Slide24:  Thank you very much for your time and attention, and thanks to all hams and Skywarn spotters for your excellent work throughout the year. Questions? [email protected]

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