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 ColleSchool of Marine and Atmospheric Sciences

Stony Brook University

A Climatology of Convective Types over the Northeast US: Ambient Conditions and

the Role of the Appalachian Lee on Initiation

TS & IC

PS

CC & BE

LS

BL

NS & NL

IC: Isolated CellsCC: Cluster of CellsBL: Broken Line

NS: No StratiformTS: Trailing StratiformPS: Parallel StratiformLS: Leading StatiformBE: Bow Echo

NL: Nonlinear

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

1071 Events

Northeast

Comparison to Midwest Structural Distribution

o Categorized Gallus’ June 2002 data for Midwest

o Came up with my own % distribution for dataset

o Found the difference between mine and Gallus’ = Correction factor

o Applied this correction factor to total Gallus distribution

IC: Isolated CellsCC: Cluster of CellsBL: Broken Line

NL: Nonlinear

NS: No StratiformTS: Trailing StratiformPS: Parallel StratiformLS: Leading StatiformBE: Bow Echo

1071 Events

Northeast

Comparison to Midwest Structural Distribution

o Categorized Gallus’ June 2002 data for Midwest

o Came up with my own % distribution for dataset

o Found the difference between mine and Gallus’ = Correction factor

o Applied this correction factor to total Gallus distribution

IC: Isolated CellsCC: Cluster of CellsBL: Broken Line

NL: Nonlinear

NS: No StratiformTS: Trailing StratiformPS: Parallel StratiformLS: Leading StatiformBE: Bow Echo

1071 Events

Northeast

Comparison to Midwest Structural Distribution

o Categorized Gallus’ June 2002 data for Midwest

o Came up with my own % distribution for dataset

o Found the difference between mine and Gallus’ = Correction factor

o Applied this correction factor to total Gallus distribution

IC: Isolated CellsCC: Cluster of CellsBL: Broken Line

NL: Nonlinear

NS: No StratiformTS: Trailing StratiformPS: Parallel StratiformLS: Leading StatiformBE: Bow Echo

949 Events1071 Events

Northeast Midwest

Comparison to Midwest Structural Distribution

Cellular Linear Nonlinear

Ambient conditions that support these structures

o Examined 2-km NOWRad data, every 15-min (primarily 2007) o Selected 29 days with clearly dominant structureo Cellular (7 days), linear (9 days), nonlinear (13 days)o Used NARR data to calculate the ambient conditions associated with these events; conditions spatially closest & just prior to convective developmento Created scatterplots of various thermodynamic and dynamic quantities

CAPE & PWTR CAPE & 1000:700 shear

o Cells & linear similar CAPEo Nonlinear little to no CAPEo Higher pwtr for linear vs. cellularo Broad pwtr range for nonlinear

o Higher shear for linear vs cellso Broad shear range for nonlinear

500 vor adv & 850 tmp adv 700 q-vec conv & 950 frontogenesis

oCells forms under weak ava to 0 & weak waaoLinear & nonlinear form with cva &/or waaoNonlinear forcing larger than linear

oCells weak q-vec conv, no frontogenoOver half linear & nonlinear form under q-vec conv &/or frontogenoNonlinear forcing larger than linear

Upslope18%

HighTerrain

34%

East Slope&

Coastal Plain24%

Coastal Ocean

24%

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.

0.15 0.30 0.45 0.60 0.75 0.90 1.05

(Murray 2009)

Monthly frequency of lightning strikes per km2

Role of Appalachian Terrain on Convective

Initiation

Enhanced convective activity within the Appalachian lee, intensification &/or initiation.

What is the role of the lee in convective initiation?

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).

Initiation time: 3 hr bins

Over half of the events develop1500 – 1800 UTC

1. PA coastal plain2. NE PA confluence zone3. So NJ coastal plain

69 events =10% of all warm season days

45+ dBZ within 2 hrs of initiation

Categorize Initiation by Surface Boundaries

Surface Boundary No. of Events

Propagating trough/front 27

Lee Trough 14

Onshore flow 17

No wind boundary 8

Unclassified 3

• 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 …

500 hghts (black), 300 wnds (shaded, m s-1), 700 omeg (blue *10-3)

900 hghts (black), 900 wnds (kts), CAPE (shaded), 900 thte (blue)

MSLP (black), 1000 wnds (kts), 950 conv (shaded *10-5), 850 omeg (green *10-3)

Lee Trough: 13 events

Lee trough event: 070710 1800 UTC

CAPE (shaded), 900 thte (blue), 900 hght (black), 900 wnds (kts)

1800 UTC

MSLP (black), 1000 wnds (kts), 1000 conv (shaded *10-5), 850 omeg (green *10-3)

900 hghts (black), 900 wnds (kts), CAPE (shaded), 900 thte (blue)

Onshore flow: 13 events

500 hghts (black), 300 wnds (shaded, m s-1), 500 omeg (blue *10-3)

850 tmpc (black), 850 wnds (kts), 850 tmp adv (shaded *10-5), 700 omeg (green *10-3)

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%).

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