A Climatology of the Convective System Morphology over Northeast United States

Kelly Lombardo & Brian Colle

School of Marine and Atmospheric SciencesStony Brook University

(m)

(Gallus et al. 2008)

Convective Structures

IC: Isolated CellsCC: Cluster of CellsBL: Broken Line

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

NL: Nonlinear

>60

50-60

40-50

30-40

<30

dBZ

Motivational Questions

What are the convective structures across the NE and how do they compare to the Central US?

What is the evolution of the convective types across the domain?

Are there specific ambient conditions that favor each type?

Is there a preferred type of severe weather associated with these structures ?

070803 1530 UTC – 070804 0800 UTC

Data & Methods

• Examined 2 km NOWrad (available from NCAR) every 15 minutes from May-August 2007.

• Identified the structure of convection across the Northeast U.S., matching the structures defined by Gallus et al. 2008.

• Noted the time and location of initiation and decay for each structure.

• Multiple structures can exist across the entire domain. All were cataloged.

Structural Distribution

Central Plains(Gallus et al. 2008)

925 events+24 LS & PS (Parker and Johnson 2000)

Northeast454 events

Upslope18%

HighTerrain

34%

East Slope&

Coastal Plain24%

Coastal Ocean

24%

Where do the convective types initiate?Methodology:*Noted domain & time of initiation.*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.

Types of Evolutions

• Upscale growth from cellular to linear and/or nonlinear systems.

• Cellular with no upscale growth.• MCS propagating into the region from upstream.• Embedded convection within widespread

precipitation and banding features associated with baroclinic systems.

• Example of upscale growth…

070627 1700 UTC 070627 2000 UTC 070627 2115 UTC

070627 2245 UTC 070628 0100 UTC 070628 0300 UTC

Cluster of Cells No Stratiform Bow Echo

Trailing Stratiform Trailing Stratiform Nonlinear

KALB070627 1200 UTCCAPE 1154 Jkg-1

June 27 2007 Transition Event

Surface AnalysisSounding

070627 1800 UTC

900 hPa

700 hPa

500 hPa

600 hPa

400 hPa

mean sea level pressure (blue solid), surface thte (K, green dashed), surface wind (ms-1), CAPE (Jkg-1, shaded)

Composite of Transition Events:

Included 17 events

Selected at random from May-August, 2005-2007

20 km RUC analyses

Closest time within 3 hrs prior to the first sign of cellular convection

070627 event was excluded from the composite

850 hPa hght (blue contours), 850 hPa wind (ms-1), 850 hPa thte (K, shaded), 850 hPa tmpc (light blue dashed)

700 hPa hght (blue contours), 700 hPa relative vorticity (*10-5 s-1, black dashed contours), 300 hPa mag wind (ms-1, shaded)

Composite of Transition Events

What convective type is associated with themost severe wind reports?

(Gallus et al. 2008)

Methodology:*SPC svr storm report archive.*Noted the time and lat/lon point of each individual storm report.*Examined NOWrad data for that time.*Noted the structure of precip at lat/lon point of svr wx report.*That convective structure was responsible for that svr wx report.*Normalized by the total number of events.

IC: Isolated Cells CC: Cluster of CellsBL: Broken Line NS: No StratiformTS: Trailing Stratiform PS: Parallel StratiformLS: Leading Statiform

BE: Bow Echo NL: Nonlinear

Trailing Stratiform070609:0000

IC CC BL NL NS TS LS PS BE

IC CC BL NL NS TS LS PS BE

Number of svr wind reports per event

What convective type is associated with themost hail reports?

(Gallus et al. 2008)

Clusters of Cells070713:2045

Broken Line070510:1800

IC CC BL NL NS TS LS PS BE

What convective type is associated with themost tornado reports?

(Gallus et al. 2008)

Bow Echo070809:1530

Nonlinear070808:1015

IC CC BL NL NS TS LS PS BE

Summary• Northeast U.S. has a similar distribution of different convective

structures as the Central Plains, perhaps more clusters of convection over the NE.

• Convective initiation (IC, CC, NL) begins in the UP & HT regions early in the day, peaking 18–00 UTC. This initiation shifts eastward to the coast & becomes more linear/NL later in the day.

• Transition events (isolated cell to linear) have moderate instability, westerly flow, weak shear & weak synoptic forcing.

• TS systems are associated with the largest number of severe wind reports per event in the NE, but the largest number of tornados per event are produced by BE.

Future Work• Include more warm season events in climatology.• Obtain a better understanding of the reasons for the convective

evolution and structures over the NE.