The Challenge of Convective Forecasting: Forecasting Issues by

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The Challenge of Convective Forecasting
Forecasting Issuesby
Lance F. Bosart Department of Earth and
Atmospheric SciencesThe University at
Albany/SUNY/ES-2271400 Washington AvenueAlbany,
NY 12222
NCAR Colloquium on the Challenge of Convective
Forecasting 10-21 July 2006
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Forecasting Philosophy Bosart (2003)
What has happened? Why did it happen? What is
happening now? Why is it happening? What is
going to happen? Why is it going to happen?
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Why Does The ForecastGap Exist?

• Disconnect between research and operations.
• Inadequate technology transfer mechanisms.
• Inadequate communication processes.
• Inadequate representation of mesoscale weather
  systems.

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Mesoscale Forecasting RoadblocksA Personal
Perspective

• Communications bottlenecks.
• Inadequate use of event-driven forecasts.
• Problems that make it difficult for weather
  scientists to address messy operational
  issues.
• Inadequate computer resources.
• Managerial infatuation with technology for
  technologys sake independent of forecaster
  needs.
• Inadequate managerial appreciation of how human
  skills and resources are needed to extract
  the maximum operational advantage from
  technological advances.
• Inadequate technology transfer (e.g., use of
  mesoscale model information) into the
  operational sector.

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What Are Some Forecast Needs?

• Matching forecast and observed variability.
• Mesoscale substructure within cyclones.
• Analysis, synthesis, and understanding.
• Rain versus snow versus freezing rain.
• Convection, convection, convection.
• Boundaries rule.
• Uncertainty rules.

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"Customer Concern"
The weather that people care about lies,
like the devil, in the mesoscale details and not
in the S1 score or the AC coefficient.
Behind the Concern

• Coupled jets.
• Cold fronts aloft.
• QPF distribution within a cyclone.
• Severe weather and mesoscale heavy rains and
  flooding.
• Weak cyclones (death by a 1000 tiny cuts)

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What Ted Fujita Taught Us

• How to use time-to-space conversion processes to
  analyze and deduce important mesoscale storm
  structures.
• How to blend disparate datasets and sources to
  yield a meteorological story not available from
  an individual dataset/source alone.

What Ed Danielsen Taught Us

• How to understand cyclone lifecycles from a
  Lagrangian perspective.
• How to visualize the mesoscale importance of the
  dry slot.
• How to appreciate how wet and dry depositions
  patterns could be used to understand mesoscale
  cyclone structure from the PV/isentropic
  perspective.

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Why Can Mesoscale Weather Systems "Hide"?

• Mesoanalyses generally unavailable.
• Inadequate synthesis of disparate observations.
• Degradation of routine surface synoptic analyses.
  
• Quality problems with web-based analyses.
• Inadequate student education and training.

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Mesoscale PhilosophyCirca 1980
Analyze and represent synoptic scale features
and synoptic scale boundaries correctly and
forecast models will have a chance to simulate
properly some mesoscale weather systems that
depend upon these boundaries for their existence.
As model resolution has continued to improve,
this concept has proved useful in the forecasting
of mesoscale weather systems that are (1)
significantly influenced by terrain, (2)
dependent upon diurnally varying differential
heating and roughness, and (3) associated with
pre-existing low-level boundaries.
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Bulk Upscale Effects of Deep Moist Convection

• Continue to be poorly forecast by models
• Downstream ridging
• Downstream jet development
• Enhanced cyclonic vorticity advection over
  cyclone center
• Examples
• (a) Hurricanes David (1979) Floyd
  (1999)
• (b) Midlatitude cyclones 12-14
  March 1993 Superstorm 25-26 January 2000
  "Surprise" snowstorm

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Convection, Downstream Ridge/Jet Development,
and Cyclogenesis

• Downstream ridge and jet development.
• Tracton (1973) Fritsch and Maddox (1981)
  Anthes (1983) Boyle and Bosart (1986)
  Uccellini (1990) Bosart and Lackmann (1995)
  Zhang and Bao (1996a,b) Dickinson et al. (1997)
  Bosart (1999) Zhang et al. (1999a,b)
  Hurricanes Agnes (1972), Fran (1996), and Floyd
  (1999)
• Boundary layer preconditioning (moistening and
  destabilizing).
• Numerous authors
• Low-level PV growth.
• Numerous authors

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Mesoscale Lessons From Cyclone Studies

• Features such as coastal fronts, inverted
  troughs, dry lines/troughs, cold fronts aloft,
  moisture ribbons all play important roles in
  cyclone precipitation distribution.
• Widespread convection in the warm sectors of
  cyclones may "rob" the region poleward of the
  warm front of stratiform precipitation.
• Lateral shear profiles and the associated
  deformation characteristics of the large-scale
  flow contribute significantly to cyclone
  structure and life cycles.
• Forecasting relatively low-latitude
  subsynoptic-scale cyclogenesis is very sensitive
  to diabatic processes and the representation of
  PV anomalies near the surface and near the DT.
• Nonconservation of PV on the DT provides a good
  way to "view" mesoscale aspects of diabatic
  processes.
• Representation of low-level PV anomalies demands
  a better use of surface observations.

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Mesoscale Lessons From Cyclone
Studies(Continued)

• Ridges can play important roles in setting up
  positive PV advection and influencing mesoscale
  precipitation distribution.
• Precipitation distribution relative to the track
  of landfalling tropical cyclones depends strongly
  on the flow characteristics.
• Multiple genesis events may precede major
  cyclogenesis and in the presence of exceptionally
  strong forcing aloft rapid surface
  intensification may occur away from the primary
  baroclinic zones.
• The degree to which mesoscale processes
  associated with orographic forcing contributes to
  cyclogenesis is seasonally dependent.

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What Are Some Important Scientific Issues?

• Origin and evolution of mesoscale ascending
  sheets of air.
• Origin, evolution, and impact of coherent
  tropopause disturbances.
• Understanding and representing upscale effects of
  deep convection.
• Understanding how low-level boundaries
  preferentially impact mesoscale substructure and
  deep convection near boundaries and in cyclones.
• Understanding how "preconditioning" influences
  cyclone/frontal development.
• Understanding origin and evolution of mesoscale
  substructure (especially deep convection) within
  cyclones.

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a) PV distribution is known. b) A balance
relationship is assumed. c) Bottom/top boundary
temperatures are known.
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Forecasting Strategies
Lift Instability Moisture Boundaries When
forecasting always remember to go out on
a.. LIMB!