Forecasting ConvectionAn overview of how radar can help in the forecast

process.

Presentation to MSC radar course, March 24, 2010By James Cummine, Lead Meteorologist

PASPC – WinnipegWinnipeg, MB CANADA

james.cummine@ec.gc.ca

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About me…

• Started as a Severe Weather assistant (summer student) in 1985 in Winnipeg

• Forecast for the Prairies most of my 25 year career

• Some time in Science Division in mid 1990’s

• Worked on evapotranspiration studies – “Role of ET in Convection on the Prairies”

• COMET liaison meteorologist 2005 – 2008

• Olympic forecaster – 2010 Winter Olympics

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Goal of this presentation

• Not to teach you about convection– All very well explained in the COMET modules and other places

• Not to teach you about specific radar products or URP

• But to help you understand what you are seeing and ANTICIPATE how it will evolve.

• We want to forecast the weather, not observe it!

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Introduction

• Radar observes the weather

• Forecasters use the observations to help make a diagnosis

• With the diagnosis, forecasters can then make a prognosis

• Warnings are issued based on the diagnosis from radar observations

• The Radar does NOT forecast!

• Thus forecasters need to understand what they are looking at!

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Summary

• Don’t rely solely on the radar

• Use the radar (with caution) to aid in the forecast process – (Observation/analysis – Diagnosis – Prognosis)

• A strong understanding of conceptual models and situational awareness lead to quick and accurate decisions in “short-fuse” situations

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Radar in Operations

• Variety of Products

• Different GUI’s (Graphical User Interface) and ways to view the products

• Animation

• Algorithms

• Experience and understanding

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Experience and understanding

• Know strengths and limitations of radar– Products – Algorithms– Scanning strategy– Colour enhancements

• Situational awareness– Pre-storm environment– Most probable area for development

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Radar Limitations

• Distance from radar of convective cell– Height of the beam above ground (where is it really sampling the

cell in a CAPPI)

• Attenuation– Dome wetting– Behind another cell

• Time between scans– Scanning strategy

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Situational Awareness

• A good work-up– Dynamic features– Thermodynamic parameters

• Monitor evolution of situation– Cap strength– Moisture flux– Surface convergence– Changing stability (convective temperature)

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Anticipation

• What types of storms are most likely to develop and how will they evolve?

– Super cell– Multicell lines (bow echo’s, Derecho, etc)– “popcorn” convection

• Plan warning strategy in advance– Are watches already issued?– What is the “expected” motion (including a “right deviator”)– Be aware of any heavily populated areas/activities

▪ Campgrounds, outdoor concerts, fairs, etc.

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Final moments

• Why are you waiting for one more scan?

• Be proactive and warning “in advance” don’t observe and react.

• Be confident of your analysis and diagnosis

• Radar shows you what you already think will happen…however, don’t deny what you see; make sure you understand it.

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Identifying Features

• Knowledge of conceptual models– Super cell– Squall line, usually with super cells embedded (or at end)– Bow Echo, Derecho– Outflow boundary, Sea/lake breeze convergence boundary

• Use animation – motion and evolution

• Use all products (CAPPI, doppler velocity, cross sections, etc.)

• Remember radar limitations (attenuation, dome wetting)

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Super Cell

• Classic super cell

• Lemon conceptual model

• Overhang/BWER

• RFD/outflow boundary

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Squall Line/Bow Echo

• May have to connect the dots

• Development typically on south end (in NA/NH)

• Watch for embedded super cells (“right-movers” or “left-movers”)

• Cells developing out ahead of the line

• Atypical synoptic flows (northwest vs southwest)

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Outflow boundary/Convergence zones

• Use lowest level scan

• Only close to radar

• Remember height of beam above ground

• Extrapolate motion

• Anticipate collisions/rapid development

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Wind/Gust Fronts

• “Who has seen the wind?”

• Radar detects targets – usually precipitation

• Watch for descending jets (RFD)

• Keep in mind storm motion and synoptic flow (adding/subtracting from speed)

• Remember beam elevation and “wind on the ground” (slope)

• Warn before it gets there!

Examples

Some “pretty pictures”

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“Big Storm- the no brainer”

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“Lots of storms – which ones are severe”

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“A line”

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“A Boundary”

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“Value of animation”

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Waiting for one more scan…the danger!

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Final Wrap-up

• Radars are a great tool for observations

Leads to better diagnosis

• By using a knowledge of convective storms, good situational

awareness and recent radar observations

Forecasters can issue warnings in advance of event reaching a location!