Evolution of Severe Convection in the New York City Region What are large-scale conditions favoring severe (tornadic) convective weather?


НазваEvolution of Severe Convection in the New York City Region What are large-scale conditions favoring severe (tornadic) convective weather?
Дата конвертації05.05.2013
Розмір496 b.
ТипПрезентации


Evolution of Severe Convection in the New York City Region


What are large-scale conditions favoring severe (tornadic) convective weather?

  • What are large-scale conditions favoring severe (tornadic) convective weather?

  • How does convection evolve in this coastal urban environment?

  • Importance of Mesonet and radars (TDWRs).



Sharp Gradient in Severe Convection Near Coast



Tornado Climatology for NYC and Long Island (1950-2007 – 32 events)





0600 UTC 7 August 2007





1500 UTC 7 August 2007

  • Convection over W PA weakens as it moves into a region of subsidence and weak frontogenetical forcing



0300 UTC 8 August 2007

  • Frontogenetical forcing and QG ascent increases during the evening hours over PA



Surface 06 UTC 8 Aug



Surface 10 UTC 8 Aug





RUC Max CAPE (lowest 180 mb), 925 mb V, ThetaE

  • Increase in CAPE along the coast and development of a low-level jet.



Evolution From Staten Is. To Brooklyn

  • DIX 88-D 1026 UTC



Vortex Evolution: TJFK (storm rel vel)

  • Tornado develops on north shore of Staten Island, weakens as it crosses Staten Island, and new one develops to NE strengthens after vortex merger and landfall at Brooklyn.



TJFK 1020Z-1029Z SRV

  • Intensifying tornadic circulation moves across northern Staten Island

  • Aliasing in SRV couplet at 1022Z - intense tornadic winds?

  • First tornado weakens/dissipates over Tompkinsville, then a second tornado develops near the northeast tip of Staten Island by 1027Z and crosses the Narrows toward Brooklyn



TJFK 1030Z-1041Z SRV

  • Tornado causes EF-2 damage as it moves across Bay Ridge, Kensington, and Flatbush sections of Brooklyn

  • More aliasing in SRV couplet indicative of intense tornadic winds



Benefit of TDWR Radar

  • DIX 88-D 1030 UTC



Composite of 18 LI/NYC Tornado Events (1979-2007) Using NARR (32-km)



Composite of 18 Events (1979-2007) 1000-mb Z, thetaE, V; sfc CAPE



Summary

  • NYC-Long Island tornadoes are most frequent during late summer (August) and can occur from early AM to early evening (1000-0000 UTC).

  • 7-8 August 2007 NYC tornado event had origins as a MCS over the Plains 30 h earlier along a W-E baroclinic zone.

  • Convection intensified in a region of large frontogenetical forcing, a nose of higher thetaE along the coast, and development of a LLJ.

  • Elevated mixed layer and the subsequent diabatic cooling from precipitation was likely important in destabilizing low levels.

  • There was rapid vortex evolution around Staten Island. (Role of the hills and land-water gradients??)



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