Warm Season Climatology of Convective Evolution Over the Coastal Northeast U.S. Michael Charles and Brian A. Colle Institute for Terrestrial and Planetary.

Warm Season Climatology of Convective Warm Season Climatology of Convective Evolution Over the Coastal Northeast U.S.Evolution Over the Coastal Northeast U.S.

Michael Charles and Brian A. ColleMichael Charles and Brian A. ColleInstitute for Terrestrial and Planetary SciencesInstitute for Terrestrial and Planetary Sciences

SUNY at Stony BrookSUNY at Stony Brook

Jeffrey TongueJeffrey TongueNOAA/NWS Upton, NYNOAA/NWS Upton, NY

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

Motivational Questions

1.1. What is the change in thunderstorm What is the change in thunderstorm distribution in the Northeast from early to distribution in the Northeast from early to late summer?late summer?

2.2. How do thunderstorms evolve as they How do thunderstorms evolve as they approach the coast?approach the coast?

3.3. Under what conditions does more Under what conditions does more significant convection occur at the coast significant convection occur at the coast even with cooler early summer SSTs?even with cooler early summer SSTs?

NLDN sensor locations in the USNLDN sensor locations in the US

Objective Analysis RoutineObjective Analysis Routine

Background• Last year’s NROW talk:Last year’s NROW talk:

– Northeast lightning climatology (2000-2002)Northeast lightning climatology (2000-2002)– Concluded that a coastal gradient existed in Concluded that a coastal gradient existed in

June, but not in August.June, but not in August.– Hypothesized that the cooler June SST’s lead Hypothesized that the cooler June SST’s lead

to a relatively cool marine boundary layer that to a relatively cool marine boundary layer that weakens convection approaching the coast.weakens convection approaching the coast.

• This year’s research:This year’s research:– Included two more years (2003-2004).Included two more years (2003-2004).– Investigate the inter-annual variability in the Investigate the inter-annual variability in the

lightning distribution – Is SST the whole story?lightning distribution – Is SST the whole story?

June Density – 2000-2002 - strikes per 100 km2

Sea Surface TemperaturesSea Surface Temperatures15 June 2000 15 August 2000

Average Lightning Distributions

June 2000-2004 August 2000-2004

Strikes per 100 km2 per month Strikes per 100 km2 per month

800 m

50 m

600 m

200 m400 m

100 m

Terrain

June 2000June 2000 June 2004June 2004

June – Sharp coastal gradient

Strikes per 100 km2 Strikes per 100 km2

800 m

50 m

600 m

200 m400 m

100 m

Terrain

June 2002June 2002 June 2003June 2003

Strikes per 100 km2 Strikes per 100 km2

June – More significant coastal lightning

800 m

50 m

600 m

200 m400 m

100 m

Terrain

August – Sharp coastal gradient

Strikes per 100 km2 Strikes per 100 km2

August 2002 August 2004800 m

50 m

600 m

200 m400 m

100 m

Terrain

August 2000August 2000 August 2001August 2001

Strikes per 100 km2 Strikes per 100 km2

August – More significant coastal lightning

800 m

50 m

600 m

200 m400 m

100 m

Terrain

Is synoptic forcing a factor in the lightning distribution?

Synoptic climatology

• Cases:Cases:• Lightning cases defined as days that New Jersey, southeast Lightning cases defined as days that New Jersey, southeast

New York or Connecticut received >10 lightning strikes. 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)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)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 Both types of convection were summed into monthly totals for each yearfor each year

Non-frontal: 11-12 June 2000 caseNon-frontal: 11-12 June 2000 case

00 UTC 12th NCEP sfc. analysis 00 UTC 12th OKX sounding

~100 km

storms

CAPE=258 J/kg

11 June 2000 Lightning Strikes (per 100 km2)11 June 2000 Lightning Strikes (per 100 km2)

800 m

50 m

600 m

200 m400 m

100 m

Terrain

Non-frontal: 11-12 June 2000 caseNon-frontal: 11-12 June 2000 case

00 UTC 28th NCEP sfc. analysis 00 UTC 28th OKX sounding

~100 km

storms

CAPE=793 J/kg

Frontal: 27-28 August 2001Frontal: 27-28 August 2001

21 August 2004 Lightning Strikes (per 100 km2)21 August 2004 Lightning Strikes (per 100 km2)

800 m

50 m

600 m

200 m400 m

100 m

Terrain

Frontal: 27-28 August 2001Frontal: 27-28 August 2001

June average lightning distribution

Frontal convection

Strikes per 100 km2 per month Strikes per 100 km2 per month

Pre-frontal convection

800 m

50 m

600 m

200 m400 m

100 m

Terrain

August average lightning distribution

Strikes per 100 km2 per month Strikes per 100 km2 per month

800 m

50 m

600 m

200 m400 m

100 m

Terrain

Frontal convection Pre-frontal convection

June - Little coastal lightning

2000

2004

2000

2004

June – Significant coastal lightning

2002

2003

2002

2003

August - Little coastal lightning

2002

2004

2002

2004

August – Significant coastal lightning

2000

2001

2000

2001

Conclusions• There are large spatial gradients in lightning (convection) There are large spatial gradients in lightning (convection)

across the Northeast U.S. because of terrain (e.g. across the Northeast U.S. because of terrain (e.g. Wasula et al. 2002) and land-sea contrasts.Wasula et al. 2002) and land-sea contrasts.

• The relatively cool SST’s in the early summer can lead The relatively cool SST’s in the early summer can lead to rapid weakening of convection near the coast, but to rapid weakening of convection near the coast, but there is a lot of inter-annual variability.there is a lot of inter-annual variability.

• The rapid weakening of coastal convection is favored for The rapid weakening of coastal convection is favored for prefrontal (propagating) convection. Convection prefrontal (propagating) convection. Convection supported by a surface cold/warm front weakens less supported by a surface cold/warm front weakens less approaching the coast.approaching the coast.

• Those months with significant lightning near the coast Those months with significant lightning near the coast have more anomalous upper-level troughing around the have more anomalous upper-level troughing around the U.S. Eastern Seaboard.U.S. Eastern Seaboard.

Future Work

• Convective mode:Convective mode:– Convection divided into two convective modes:Convection divided into two convective modes:

• Organized/long-livedOrganized/long-lived

• Disorganized/short-livedDisorganized/short-lived

• Determine the processes which favor more long-Determine the processes which favor more long-lived convection near the coast during warm lived convection near the coast during warm season frontal passages. Is the convection more season frontal passages. Is the convection more elevated?elevated?

• Mesoscale modeling of specific cases at < 5-km Mesoscale modeling of specific cases at < 5-km grid spacing using WRF.grid spacing using WRF.

The End