Overview

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Overview

• Introduction
• Model and Methods
• Results
• Summary

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1. Introduction

• Severe convection poses a risk for safety of life
  and property - and is a fascinating subject to
  study
• Two main modes of severe convection events over
  southern New England were observed
• sustained convection convection enters region
  from west and translates over entire area,
  including the southeastern most parts
• dissipating convection convection enters region
  from west and translates over the area, but not
  over the southeastern most parts

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Terminology Definitions

• Severe Convection occurrence of hail ? 0.75
  inches in diameter and/or wind gusts ? 50
  knots and/or
  presence of tornado (NWS
  definition)
• CAPE Convective Available Potential Energy
• maximum energy available to ascending
  parcel, i.e. the positive area in a
  thermodynamic diagram
• CIN Convective Inhibition energy
  needed to pseudoadiabatically lift parcel
  from original level to its level of free
  convection (LFC), i.e. the negative area
  in a skew-T diagram

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• Ri CAPE/(windshearsurface - equilibrium
  level)2 gives an indication on what kind of
  cells are most likely to form
• theta-e is conserved for dry-adiabatic and
  pseudo- adiabatic displacements. Serves as a
  proxy for parcel energy. The vertical
  distribution tells whether the atmosphere can
  be destabilized by large scale vertical
  displacement
• lhf evaporation of soil moisture provides one
  excellent source for latent heat which can be
  released at other locations in the atmosphere,
  transported by turbulent eddies

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Methods used

• Data for 11 cases was collected over the summer
  2001, 9 dates with sustained convection, 2
  days with dissipating convection - 4 legacy cases
  from 2000 were also examined
• Examine DIFAX-maps for the selected cases
  (analysis of surface and height-fields from 12
  UTC 00 UTC) radar data
• Generate composites for the two scenarios,
  horizontal maps and vertical cross-sections,
  meteograms etc.
• to be continued

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Methods continued

• using GrADS to plot meteorological fields and
  extract data from output files, developed various
  scripts and Fortran code to manipulate data and
  used Matlab to plot curves
• Calculate CAPE etc. for pseudo-observation
  stations, zones and composites
• Perform a Harmonics Analysis on the data -- wont
  be shown today

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PSM
EEN
MHT
II
LWM
BVY
ORE
BED
V
BOS
III
IV
ORH
CEF
OWD
BAF
PYM
BDL
SFZ
EWB
PVD
IJD
HFD
I
MVY
UUU
WST
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Synoptic overview
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sustained convection
500 mb Jun 20, 12Z
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dissipating convection
500 mb Aug 17, 12Z
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sustained convection
surface Jun 20, 12Z
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dissipating convection
surface Aug 17, 12Z
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Composite reflectivity for dissipating convection
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Composite reflectivity for sustained convection
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Composite windfield for dissipating convection,
lowest level
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Composite windfield for sustained convection,
lowest level
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Composite theta-e for dissipating convection
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Composite theta-e for sustained convection
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Composite latent heat flux for dissipating
convection
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Composite latent heat flux for sustained
convection
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The main factors

• Wind field westerly component over most areas,
  weaker, less homogenous low-level windfield with
  stronger wind aloft seems favorable
• Theta-e higher values over much of the area,
  especially the southeastern parts!
• lhf same applies as for theta-e, with decent
  amounts from early-on in the forecast period
  (started at 12 UTC)

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Summary of Results from 2002

• 17 Cases of Convection in Massachusetts
• 4 Cases had Convection Sustained to the Coast
• Only 1 of these cases did NOT fit the patterns

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May 31, 2002 dissipating convection Theta-e --
15 UTC
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May 31, 2002 dissipating convection Theta-e --
18 UTC
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May 31, 2002 dissipating convection Theta-e --
21 UTC
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May 31, 2002 dissipating convection Theta-e --
00 UTC
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May 31, 2002 dissipating convection Latent
Heat Flux -- 15 UTC
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May 31, 2002 dissipating convection Latent
Heat Flux -- 18 UTC
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May 31, 2002 dissipating convection Latent
Heat Flux -- 21 UTC
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May 31, 2002 dissipating convection Winds --
15 UTC
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May 31, 2002 dissipating convection Winds --
18 UTC
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May 31, 2002 dissipating convection Winds --
21 UTC
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May 31, 2002 dissipating convection Winds --
00 UTC
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May 31, 2002 dissipating convection Model
Reflectivity -- 18 UTC
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May 31, 2002 dissipating convection Model
Reflectivity -- 21 UTC
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May 31, 2002 dissipating convection Model
Reflectivity -- 00 UTC
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July 23, 2002 sustained convection Theta-e --
15 UTC
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July 23, 2002 sustained convection Theta-e --
18 UTC
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July 23, 2002 sustained convection Theta-e --
21 UTC
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July 23, 2002 sustained convection Theta-e --
00 UTC
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July 23, 2002 sustained convection Latent Heat
Flux -- 15 UTC
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July 23, 2002 sustained convection Latent Heat
Flux -- 18 UTC
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July 23, 2002 sustained convection Latent Heat
Flux -- 21 UTC
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July 23, 2002 sustained convection Latent Heat
Flux -- 00 UTC
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July 23, 2002 sustained convection Winds -- 15
UTC
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July 23, 2002 sustained convection Winds -- 18
UTC
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July 23, 2002 sustained convection Winds -- 21
UTC
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July 23, 2002 sustained convection Winds -- 00
UTC
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July 23, 2002 sustained convection Model
Reflectivity -- 18 UTC
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July 23, 2002 sustained convection Model
Reflectivity -- 21 UTC
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July 23, 2002 sustained convection Model
Reflectivity -- 00 UTC
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July 23, 2002 sustained convection Model
Reflectivity -- 03 UTC
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July 23, 2002 sustained convection Model
Reflectivity -- 06 UTC
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modifications to main factors

• Wind field westerly component over most areas,
  weaker, less homogenous low-level windfield with
  stronger wind aloft seems favorable -- SAME
• Theta-e high values with area of maximum values
  over southeastern Mass!

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modifications to main factors

• lhf same applies as for theta-e, with decent
  amounts from early-on in the forecast period --
  SAME, but this pattern doesnt seem to vary as
  much from sustained to dissipating cases as does
  Theta-e.
• Model Reflectivity widespread model
  reflectivity seems to indicate that the
  atmosphere is more supportive of convection.

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conclusions
Careful examination of patterns of
Theta-e Latent Heat Flux can prove helpful to
forecast convective behavior.

• Use of other tools, such as forecasts of CAPE,
  CIN, and wind shear are also needed.

Thank you!