1. A Forecasting Success A negatively tilting mid level trough approaching North Carolina, combined with strong instability and increasing deep layer shear, created the ideal setup not only for severe weather but also for excessive amounts of lightning across central North Carolina on 8 July 2008. Experimental Lightning Forecasting in a National Weather Service Forecast Office Gail Hartfield NOAA/National Weather Service Raleigh, North Carolina Experimental Lightning Forecasting in a National Weather Service Forecast Office Gail Hartfield NOAA/National Weather Service Raleigh, North Carolina Why attempt this? From 1990-2003, North Carolina ranked 5 th in the nation in lightning deaths. Nationwide, over the last 30 years, lightning ranks as the second leading cause of weather-related deaths. Accurate lightning outlooks could greatly benefit NWS partners and customers within the aviation, utility, forestry, and recreation communities, as well as the general public. Since an exceptionally high strike density means a greater probability of individuals or structures being hit, providing a prediction of such events could give those affected time to take action to reduce the threat to life and property. The Goal: To produce a qualitative 3-24 hour lightning “outlook”, included in the early morning Hazardous Weather Outlook product. The focus is on anticipating days of exceptional amounts of lightning. What we’ve done… An operational forecasting checklist, consisting of parameters drawn from published studies of lightning production (particularly excessive lightning) as well as on past excessive lightning cases, was developed. Forecasters filled out the checklist daily from May to September 2008. The Forecast Process This checklist helps forecasters assess the expected near-storm environment, including the two primary factors which favor lightning production: Available moisture (the presence of graupel is essential for electrification) Instability, especially aloft (greater buoyancy = more vigorous updrafts) Moisture and instability Instability (esp. in critical mixed phase layer) SPC products (multi-parameter) Free text (moisture, forcing mechanisms) Benefits: Incorporates forecaster experience Based on preferred model-of-the-day, rather than a single predetermined model The varied-source input reduces forced reliance on one particular model, which may not pinpoint convection properly Forecaster can weigh each parameter differently based on the weather situation Increases forecasters’ understanding of the pre-storm environment Awareness of environments favoring severe hail has also increased Promotes inter- and intra-office discussion about the dominant weather threats Challenges: Assessing parameters from multiple sources proved cumbersome at times; process needs streamlining Some parameters were occasionally unavailable On occasion, the forecaster-chosen model proved incorrect Checklist requiring manual input is low-tech Acknowledgements: Special thanks goes to Barrett Smith and Jonathan Blaes, WFO Raleigh, and Phillip Bothwell, Storm Prediction Center, for their help and support. Much appreciation goes to the WFO Raleigh staff for their daily completion of the checklist. Some gridded verification data above courtesy of Vaisala, Inc. Layer CAPE information from the RAOB program, a product of Environmental Research Services. Historical lightning stats courtesy of Ronald Holle, Vaisala, Inc. Future Work Continued assessment of this season’s results and refinement of the forecast technique Further analysis of the “top ten” exceptional lightning days to determine the most significant predictors Improve the forecast methodology to allow for: o Easier and quicker retrieval and assimilation of forecast parameters o Better assessment of the technique’s successes and failures Possible normalization of key parameters and development of a “lightning number” “GIVEN THE DEGREE OF MID LEVEL INSTABILITY... HAIL AND NEARLY CONTINUOUS LIGHTNING WILL BE THE PRIMARY WEATHER THREATS THROUGH TONIGHT... ALTHOUGH WITH THE 30+ C VERTICAL THETA-E DIFFERENCE IN THE GSO SOUNDING... DAMAGING WINDS CANNOT BE RULED OUT EITHER. FINALLY... SEVERAL PARAMETERS INCLUDING THE HIGH CAPE (BOTH MUCAPE AND -10 TO -30C CAPE)... K-INDEX OF 33-36... AND NORMALIZED CAPE OF 0.25 ALL SUPPORT VERY VIGOROUS UPDRAFTS AND RAPID CHARGE SEPARATION... THUS THE MENTION OF FREQUENT LIGHTNING HAS BEEN ADDED TO THE FORECAST THROUGH TONIGHT.” “GIVEN THE DEGREE OF MID LEVEL INSTABILITY... HAIL AND NEARLY CONTINUOUS LIGHTNING WILL BE THE PRIMARY WEATHER THREATS THROUGH TONIGHT... ALTHOUGH WITH THE 30+ C VERTICAL THETA-E DIFFERENCE IN THE GSO SOUNDING... DAMAGING WINDS CANNOT BE RULED OUT EITHER. FINALLY... SEVERAL PARAMETERS INCLUDING THE HIGH CAPE (BOTH MUCAPE AND -10 TO -30C CAPE)... K-INDEX OF 33-36... AND NORMALIZED CAPE OF 0.25 ALL SUPPORT VERY VIGOROUS UPDRAFTS AND RAPID CHARGE SEPARATION... THUS THE MENTION OF FREQUENT LIGHTNING HAS BEEN ADDED TO THE FORECAST THROUGH TONIGHT.” Verification: In addition to the 58 severe events that were reported, there were 11,734 cloud to ground (CG) strikes across the Raleigh area of responsibility (31 counties in central North Carolina) during the 24 hour period ending 12 UTC 9 July 2008. Over Anson county alone, from 2245-2300 UTC 8 July, there were 573 CG strikes, or more than 38 strikes per minute. Based on these lightning-favorable parameters, a mention of high frequency lightning was added to the forecast. From the Area Forecast Discussion early that morning: Here is the checklist completed at 06 UTC (200 am LT) on 8 July 2008. NWS Doppler radar image from 0058 UTC on 9 July 2008. NWS Storm Prediction Center plot of observed severe weather events which occurred 12 UTC 8 July – 12 UTC 9 July. Total CG strikes, as plotted in the Graphical Forecast Editor (GFE) program. 12 UTC 8 July – 12 UTC 9 July. Orange and red colors indicate more than 130 strikes in that 5 km x 5 km grid box. Plotted numbers are total CG strikes within 40 km x 40 km grid boxes, from 12 UTC 8 July – 12 UTC 9 July. (Contours are Storm Prediction Center forecast probabilities of any strikes during this time period.) Note the 3048 CG strikes in one grid box over south central North Carolina. 500 hPa heights (dam) and temperatures (C), 12 UTC 8 July 2008. Surface-based convective available potential temperature (CAPE) and convective inhibition (CIN) (J/kg), 21 UTC 8 July 2008. CAPE in the -10C to -30C layer, along with freezing level (m) and 0-6 km shear (kt), 22 UTC 8 July 2008. Normalized CAPE (CAPE divided by the buoyant layer, from the level of free convection to the equilibrium level), 22 UTC 8 July 2008. Surface equivalent potential temperature (K) and advection (K hr - 1 ), 21 UTC 8 July 2008. Precipitable water in the lowest 400 hPa (inches), 01 UTC 9 July 2008.