1. Warm Season Climatology of Convective Evolution Over the Coastal Northeast U.S. Michael Charles and Brian A. Colle Institute for Terrestrial and Planetary Sciences SUNY at Stony Brook Jeffrey Tongue NOAA/NWS Upton, NY

2. Forecasting Northeast coastal convection is very difficult… False Alarm Rate (FAR) = Unverified warnings/total warnings (Svr tstm/torn.) ALY, BOX, OKX, and PHI from 1/1/1986 – 10/16/2003

3. Motivational Questions 1.What is the change in thunderstorm distribution in the Northeast from early to late summer? 2.How do thunderstorms evolve as they approach the coast? 3.Under what conditions does more significant convection occur at the coast even with cooler early summer SSTs?

4. NLDN sensor locations in the US

5. Objective Analysis Routine

6. Background Last year’s NROW talk:Last year’s NROW talk: –Northeast lightning climatology (2000-2002) –Concluded that a coastal gradient existed in June, but not in August. –Hypothesized that the cooler June SST’s lead to a relatively cool marine boundary layer that weakens convection approaching the coast. This year’s research:This year’s research: –Included two more years (2003-2004). –Investigate the inter-annual variability in the lightning distribution – Is SST the whole story?

7. June Density – 2000-2002 - strikes per 100 km 2

8. Sea Surface Temperatures 15 June 200015 August 2000

9. Average Lightning Distributions June 2000-2004August 2000-2004 Strikes per 100 km 2 per month 800 m 50 m 600 m 200 m 400 m 100 m Terrain

10. June 2000 June 2004 June – Sharp coastal gradient Strikes per 100 km 2 800 m 50 m 600 m 200 m 400 m 100 m Terrain

11. June 2002 June 2003 Strikes per 100 km 2 June – More significant coastal lightning 800 m 50 m 600 m 200 m 400 m 100 m Terrain

12. August – Sharp coastal gradient Strikes per 100 km 2 August 2002August 2004 800 m 50 m 600 m 200 m 400 m 100 m Terrain

13. August 2000 August 2001 Strikes per 100 km 2 August – More significant coastal lightning 800 m 50 m 600 m 200 m 400 m 100 m Terrain

14. Is synoptic forcing a factor in the lightning distribution?

15. Synoptic climatology Cases:Cases: Lightning cases defined as days that New Jersey, southeast New York or Connecticut received >10 lightning strikes.Lightning cases defined as days that New Jersey, southeast New York or Connecticut received >10 lightning strikes. Divided convection into two categories:Divided convection into two categories: –Near Front (Frontally maintained, referred to as frontal) Along surface cold front (< 100 km ahead)Along surface cold front (< 100 km ahead) Less than 200 km ahead of surface warm frontLess than 200 km ahead of surface warm front –Non-frontally maintained (referred to as pre-frontal) Propagates or develops > 100 km ahead of a cold frontPropagates or develops > 100 km ahead of a cold front > 200 km ahead of a surface warm front> 200 km ahead of a surface warm front –Both types of convection were summed into monthly totals for each year

16. Non-frontal: 11-12 June 2000 case 00 UTC 12 th NCEP sfc. analysis00 UTC 12 th OKX sounding ~100 km storms CAPE=258 J/kg

17. 11 June 2000 Lightning Strikes (per 100 km2) 800 m 50 m 600 m 200 m 400 m 100 m Terrain Non-frontal: 11-12 June 2000 case

18. 00 UTC 28 th NCEP sfc. analysis00 UTC 28 th OKX sounding ~100 km storms CAPE=793 J/kg Frontal: 27-28 August 2001

19. 21 August 2004 Lightning Strikes (per 100 km2) 800 m 50 m 600 m 200 m 400 m 100 m Terrain Frontal: 27-28 August 2001

20. June average lightning distribution Frontal convection Strikes per 100 km 2 per month Pre-frontal convection 800 m 50 m 600 m 200 m 400 m 100 m Terrain

21. August average lightning distribution Strikes per 100 km 2 per month 800 m 50 m 600 m 200 m 400 m 100 m Terrain Frontal convectionPre-frontal convection

22. June - Little coastal lightning 2000 2004 2000 2004

23. June – Significant coastal lightning 2002 2003 2002 2003

24. August - Little coastal lightning 2002 2004 2002 2004

25. August – Significant coastal lightning 2000 2001 2000 2001

26. Conclusions There are large spatial gradients in lightning (convection) across the Northeast U.S. because of terrain (e.g. Wasula et al. 2002) and land-sea contrasts.There are large spatial gradients in lightning (convection) across the Northeast U.S. because of terrain (e.g. Wasula et al. 2002) and land-sea contrasts. The relatively cool SST’s in the early summer can lead to rapid weakening of convection near the coast, but there is a lot of inter-annual variability.The relatively cool SST’s in the early summer can lead to rapid weakening of convection near the coast, but there is a lot of inter-annual variability. The rapid weakening of coastal convection is favored for prefrontal (propagating) convection. Convection supported by a surface cold/warm front weakens less approaching the coast.The rapid weakening of coastal convection is favored for prefrontal (propagating) convection. Convection supported by a surface cold/warm front weakens less approaching the coast. Those months with significant lightning near the coast have more anomalous upper-level troughing around the U.S. Eastern Seaboard.Those months with significant lightning near the coast have more anomalous upper-level troughing around the U.S. Eastern Seaboard.

27. Future Work Convective mode:Convective mode: –Convection divided into two convective modes: Organized/long-livedOrganized/long-lived Disorganized/short-livedDisorganized/short-lived Determine the processes which favor more long- lived convection near the coast during warm season frontal passages. Is the convection more elevated?Determine the processes which favor more long- lived convection near the coast during warm season frontal passages. Is the convection more elevated? Mesoscale modeling of specific cases at < 5-km grid spacing using WRF. Mesoscale modeling of specific cases at < 5-km grid spacing using WRF.

28. The End