Kelly Lombardo & Brian Colle School of Marine and Atmospheric Sciences Stony Brook University

1. A Climatology of Convective Types over the Northeast US: Ambient Conditions and the Role of the Appalachian Lee on Initiation What is the convective structural distribution across the NE and how does it compare to the Midwest? What environments support these structures? Where do these structures initiate? What is the role of the Appalachian lee in convective initiation? What ambient conditions support convection initiation in this region? Kelly Lombardo & Brian Colle School of Marine and Atmospheric Sciences Stony Brook University

2. What are the structures? • 2-km NOWRad radar • reflectivity, every 15-min • May-Aug 2007 & randomly • selected warm season (2002-2006) • Identified structure according to • Gallus et al. (2008) • Multiple structures can exists • across the domain TS & IC CC & BE LS PS IC: Isolated Cells CC: Cluster of Cells BL: Broken Line NS: No Stratiform TS: Trailing Stratiform PS: Parallel Stratiform LS: Leading Statiform BE: Bow Echo NL: Nonlinear BL NS & NL

3. Comparison to Midwest Structural Distribution Northeast IC: Isolated Cells CC: Cluster of Cells BL: Broken Line NL: Nonlinear NS: No Stratiform TS: Trailing Stratiform PS: Parallel Stratiform LS: Leading Statiform BE: Bow Echo • Categorized Gallus’ June 2002 data for Midwest • Came up with my own % distribution for dataset • Found the difference between mine and Gallus’ = Correction factor • Applied this correction factor to total Gallus distribution 1071 Events

4. Comparison to Midwest Structural Distribution Northeast IC: Isolated Cells CC: Cluster of Cells BL: Broken Line NL: Nonlinear NS: No Stratiform TS: Trailing Stratiform PS: Parallel Stratiform LS: Leading Statiform BE: Bow Echo • Categorized Gallus’ June 2002 data for Midwest • Came up with my own % distribution for dataset • Found the difference between mine and Gallus’ = Correction factor • Applied this correction factor to total Gallus distribution 1071 Events

5. Comparison to Midwest Structural Distribution Northeast IC: Isolated Cells CC: Cluster of Cells BL: Broken Line NL: Nonlinear NS: No Stratiform TS: Trailing Stratiform PS: Parallel Stratiform LS: Leading Statiform BE: Bow Echo • Categorized Gallus’ June 2002 data for Midwest • Came up with my own % distribution for dataset • Found the difference between mine and Gallus’ = Correction factor • Applied this correction factor to total Gallus distribution 1071 Events

6. Comparison to Midwest Structural Distribution Northeast Midwest 1071 Events 949 Events

7. Ambient conditions that support these structures • Examined 2-km NOWRad data, every 15-min (primarily 2007) • Selected 29 days with clearly dominant structure • Cellular (7 days), linear (9 days), nonlinear (13 days) • Used NARR data to calculate the ambient conditions associated with these events; conditions spatially closest & just prior to convective development • Created scatterplots of various thermodynamic and dynamic quantities Cellular Nonlinear Linear

8. CAPE & PWTR CAPE & 1000:700 shear • Cells & linear similar CAPE • Nonlinear little to no CAPE • Higher pwtr for linear vs. cellular • Broad pwtr range for nonlinear • Higher shear for linear vs cells • Broad shear range for nonlinear

9. 500 vor adv & 850 tmp adv 700 q-vec conv & 950 frontogenesis • Cells forms under weak ava to 0 & weak waa • Linear & nonlinear form with cva &/or waa • Nonlinear forcing larger than linear • Cells weak q-vec conv, no frontogen • Over half linear & nonlinear form under q-vec conv &/or frontogen • Nonlinear forcing larger than linear

10. Where and when do the convective types initiate? Methodology: *Noted domain & time of initiation for 2 warm seasons. *Binned the times into 6 hr increments: 00-06 UTC, 06-12 UTC, 12-18 UTC, 18-00 UTC. *Normalized to account for variations in domain size. Upslope 18% High Terrain 34% East Slope & Coastal Plain 24% Coastal Ocean 24%

12. Role of Appalachian Terrain on Convective Initiation Monthly frequency of lightning strikes per km2 (Murray 2009) Enhanced convective activity within the Appalachian lee, intensification &/or initiation. What is the role of the lee in convective initiation? 0.15 0.30 0.45 0.60 0.75 0.90 1.05

13. Lee Event Criteria • NOWRad 2km 2002-2007. • Initiation within the lee of the • terrain or the coastal plain. • Initiation separated by 1.5o • from surrounding convection • outside the lee domain. • Temporal Criteria: Minimum • of 3 hours of convection. • Reflectivity Criteria: Minimum of 50 dBZ. • Density Criteria: Multiple cells initiating within a 1ox1o latitude/longitude box. • Events were selected by eye (not automated).

14. 69 events = 10% of all warm season days Initiation time: 3 hr bins 45+ dBZ within 2 hrs of initiation • Over half of the events develop • 1500 – 1800 UTC • 1. PA coastal plain • 2. NE PA confluence zone • 3. So NJ coastal plain

15. Categorize Initiation by Surface Boundaries • Utilized surface data & RUC analyses at 20/40 km. • Identified surface boundaries and associated synoptic conditions. • Lee trough developed in situ in the lee of the Appalachians. • Onshore flow includes sea breeze events. Understand dynamical evolution associated with initiation scenarios, processes leading to convective initiation Composites utilizing RUC analyses …

16. 900 hghts (black), 900 wnds (kts), CAPE (shaded), 900 thte (blue) Lee Trough: 13 events MSLP (black), 1000 wnds (kts), 950 conv (shaded *10-5), 850 omeg (green *10-3) 500 hghts (black), 300 wnds (shaded, m s-1), 700 omeg (blue *10-3)

17. Lee trough event: 070710 1800 UTC 1800 UTC CAPE (shaded), 900 thte (blue), 900 hght (black), 900 wnds (kts)

18. MSLP (black), 1000 wnds (kts), 1000 conv (shaded *10-5), 850 omeg (green *10-3) Onshore flow: 13 events 900 hghts (black), 900 wnds (kts), CAPE (shaded), 900 thte (blue) 850 tmpc (black), 850 wnds (kts), 850 tmp adv (shaded *10-5), 700 omeg (green *10-3) 500 hghts (black), 300 wnds (shaded, m s-1), 500 omeg (blue *10-3)

19. Summary • Compared to the Midwest, the Northeast has a smaller percentage of cellular structures (61% MW, 47% NE), a greater percentage of nonlinear systems (21% MW, 33% NE) , and a similar percentage of linear systems (18% MW, 20% NE). • Cellular: moderate surface based CAPE (1000-2250 J kg-1), pwtr values ranging from 28-44 mm, but little low- to mid-level forcing. • Linear: moderate surface based CAPE (1250-2250 J kg-1), pwtr ranging from 34-48 mm, weak dynamical forcing (850 hPa wam air advection, 500 hPa cyclonic vorticity advection, 950 hPa frontogenesis, 700 hPa Q-vector convergence). • Nonlinear: little or no surface based CAPE, weak dependence on moisture (pwtr values from 16-50 mm), and the strongest synoptic forcing of the 3 convective types. • Lee events preferentially initiate between 1500-1800 UTC. • Lee convection develops in association with a variety of synoptic regimes including propagating troughs and fronts (39%), lee troughs (20%), onshore flow (25%), uniform wind scenarios (12%).

21. Most of the nonlinear and linear that are 0 & -1 have 850 ascent, not convectively contaminated. So something is forcing these events.