Forecasting Convection An overview of how radar can help in the forecast process. Presentation to...

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

Page 2 –

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!

Page 4 –

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

Page 7 –

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

Page 8 –

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.

Page 12 –

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)

Page 15 –

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”

Page 18 –

“Big Storm- the no brainer”

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“Lots of storms – which ones are severe”

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“A line”

Page 21 –

“A Boundary”

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“Value of animation”

Page 23 –

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!