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Advanced Severe Weather Spotter Course ‐ 2013

Advanced Severe Weather Spotter Course ‐ 2013

National Weather Service

Wakefield, VA

National Weather Service

Wakefield, VA

The National Weather Service (NWS) provides weather, hydrologic, and climate forecasts and warnings for the United States, its territories, adjacent waters and ocean areas, for the protection of life and property and the

enhancement of the national economy.

NWS data and products form a national information database and infrastructure which can be used by other governmental agencies, the private sector, the public,

and the global community.

The National Weather Service (NWS) provides weather, hydrologic, and climate forecasts and warnings for the United States, its territories, adjacent waters and ocean areas, for the protection of life and property and the

enhancement of the national economy.

NWS data and products form a national information database and infrastructure which can be used by other governmental agencies, the private sector, the public,

and the global community.

• Review of What to Report

• Review of Basic Weather (“The BIG Picture”)

• Severe Weather Ingredients

• Radar Basic Operations & Dual Polarization Radar

• Radar Signatures

• Break

• Severe Weather Signatures and Storm Intensity

• Understanding Rotation and Shear

• Review of What to Report

• Review of Basic Weather (“The BIG Picture”)

• Severe Weather Ingredients

• Radar Basic Operations & Dual Polarization Radar

• Radar Signatures

• Break

• Severe Weather Signatures and Storm Intensity

• Understanding Rotation and Shear

A Review of What to Report …

A Review of What to Report …

What Info Are We Looking For?

What Info Are We Looking For?

Answer 3 Basic Questions:

1) What Happened? … Type and Magnitude of the Event

2) When did it happen?... Also, event duration.

3). Where did it happen? … Location Referenced to City/Town, Portion of County, Major Intersection

a) Lat/Lon info is GREAT...but not needed.

Good & Bad Examples:1) "Hello, I'm a trained severe weather spotter. At 6:04 p.m., 3 miles northwest of

Richmond, I spotted a tornado a few miles to my north, heading northeast.

2) “We are having severe lightning here” …. “The wind is really blowing”

3) “I am a trained spotter and I would like to report mainly nickel size hail but some of the large stones are as big as the size of quarters…and it is still hailing 3 miles south of the city of Richmond.”

4) “It sounds bad out…are we under a warning?” (WHERE ARE YOU!?!)

5) “I would like to report trees and power lines down near the intersection of Wood St. and Blair Ave…5 NW of Jackson in Northampton County in NC.”

6) It is starting to get dark here!

How can we make these bad statements better ?? …think of some examples

Problems Spotters EncounterProblems Spotters Encounter

• Limited Visibility due to blockage by trees, hills, buildings, etc.

• Understanding the “big picture” of what is going on around them.

• Mobile access to radar data (improving).

• Judging distances to weather phenomena… generally underestimate.

• Limited Visibility due to blockage by trees, hills, buildings, etc.

• Understanding the “big picture” of what is going on around them.

• Mobile access to radar data (improving).

• Judging distances to weather phenomena… generally underestimate.

Copyright Simon Brewer

Copyright Greg Woods

Reporting Hail Size

“Marble” hail ambiguous…find another description!!!

Report Storm Damage April 28, 2008 –

Suffolk,VA

March 5, 2008 –Bertie, NC

Feb. 24, 2012 –Dorchester, MD

Urban Flooding

High Water

Rural Flooding

Flood Damage

Report Flooding

From a Place of Safety…From a Place of Safety…

1-800-737-8624

Let the NWS know what you observed, to help protect others!

For critical information, like a developing or on‐going tornado…

CALL US !

If you’re close enough to hear the thunder, you’re close enough to be struck by lightning!

Lightning SafetyLightning SafetyWarnings are not issued for lightning.

The Big Picture &

Thunderstorm

Ingredients

The Big PictureThe Big Picture• Low Pressure Systems = counter-clockwise flow, rising

motion, and typically the “weather makers”

• High Pressure Systems = clockwise flow, sinking motion, and typically tranquil weather

• Low Pressure Systems = counter-clockwise flow, rising motion, and typically the “weather makers”

• High Pressure Systems = clockwise flow, sinking motion, and typically tranquil weather

• Instability

• Shear

• Lift

► Instability = Heat and Moisture►Shear = Increasing Speed &

Veering (Clockwise turning) with height (SE S SW)

► Lift = An upward forcing of air

3 Ingredients for T-Storms3 Ingredients for T-Storms

Sheared environments foster the development of sustained storms

When winds increase strongly and / or change direction with height,

updraft (red arrow) is slanted;

rain-cooled storm outflow (blue) can then spread down shear away from updraft;

The storm therefore avoids tendency to self-destruct

(Moller et al. 1994; after Browning and Ludlam, 1962)

10 km

8 km

6 km

4 km

2 km

2-10 km Shear

Lifting mechanismsLifting mechanismsWarm & Cold Fronts large-scale lifting

Low Pressure Areas draw air in and lifts it

Dry Line dry air undercuts moist air

Thunderstorm Outflow cold air flowing out from astorm undercuts warm air

Hills / Mountains

Cold front

Warm front

Lift is neededLift is neededForcing of air upward by some mechanism

What Makes a Thunderstorm Severe ?What Makes a Thunderstorm Severe ?

• Damaging Winds 55-60+ mph

• Hail at least 1 inch in diameter (Quarter Size)

• Trees or power lines down, structural damage, etc. from wind or tornado

• Damaging Winds 55-60+ mph

• Hail at least 1 inch in diameter (Quarter Size)

• Trees or power lines down, structural damage, etc. from wind or tornado

Fundamental Definitions

Severe weather rarely happens without any warning!

Forecasts define broader areas of severe weather potential

Warnings pinpoint exact timing/location.

Severe weather rarely happens without any warning!

Forecasts define broader areas of severe weather potential

Warnings pinpoint exact timing/location.

BEFORE the Storm, Monitor: ► Hazardous Weather Outlook

► Convective Outlooks from the Storm Predictions Center

► TV and NOAA All Hazards Weather Radio for…► Watches and Warnings

Check the forecast several times daily, to

see if you are…or will be at risk for severe

weather.

NWS Wakefield Severe PageNWS Wakefield Severe Page

Mouse over “?” next to

each element for an

explanation of that

parameter!

http://www.erh.noaa.gov/er/akq/brief/severe.php

Basic Radar OperationsBasic Radar Operations

NWS Radar Web PageNWS Radar Web PageAccessing NWS Radar Data

NWS Doppler radar images are available on the Internet

at: radar.weather.gov

Click on the radar button from AKQ’s web site:

weather.gov/akq

►Base & Composite Reflectivity

Shows Energy returned to radar

Higher Reflectivity from heavy rain/ice

Composite Reflectivity= highest reflectivity in lowest 4 elevation scans

Radar ProductsRadar Productshttp://radar.weather.gov/

ReflectivityReflectivityBase reflectivity

data for the lowest (0.5 degree) elevation slice.

Composite ReflectivityHighest Reflectivity in lowest 4 elevation scans.

Higher intensity returns were above the lowest (0.5 degree) base reflectivity slice.

Composite ReflectivityHighest Reflectivity in lowest 4 elevation scans.

Higher intensity returns were above the lowest (0.5 degree) base reflectivity slice.

Now we’ll see a composite reflectivity image from the same time

VelocityVelocity

►Base Velocity

Product that puts the “Doppler” in Doppler Radar

One Dimensional Velocity– Motion Toward or Away From Radar

Motion Toward the Radar in GREEN, Away from the Radar in RED

►Base Velocity

Product that puts the “Doppler” in Doppler Radar

One Dimensional Velocity– Motion Toward or Away From Radar

Motion Toward the Radar in GREEN, Away from the Radar in RED

Base Velocity ExampleBase Velocity Example

Storm Relative Motion - SRMStorm Relative Motion - SRMSRM = Base Velocity MINUS Avg. Storm Motion

Useful in finding Mesocyclones /Tornado circulations.

SRM = Base Velocity MINUS Avg. Storm Motion

Useful in finding Mesocyclones /Tornado circulations.

Base Velocity Storm Relative Motion

Dual Polarization (Dual Pol) RadarDual Polarization (Dual Pol) Radar

https://www.youtube.com/watch?v=HXWPltFHRAA

• AKQ/DOX upgraded in late Winter 2012

• Available in GR2Analyst Software

• Will Assist in Forecast/Warning process with:

– Improved Precipitation Estimation

– Tracking Heavy Rainfall

– Ability to classify areas of Snow, Rain and Hail

– Ability to confirm Tornado on the Ground within 60-70 miles of radar (Tornado Debris Signature)

Dual-Pol Radar

Dual-Pol Radar (Cont’d)

• Dual Pol Radar

– Samples both horizontally/vertically.

– MUCH better sampling of shape of radar return!

• Non DP Radar

– Limited to Horizontal sampling of clouds and precipitation.

Base Data TerminologyBase Data Terminology• Data Types

– Z (Reflectivity),

– V (Velocity)

– SW (Spectrum Width)

• Dual Pol Base Variables

– CC,

– ZDR,

– KDP

• Data Types

– Z (Reflectivity),

– V (Velocity)

– SW (Spectrum Width)

• Dual Pol Base Variables

– CC,

– ZDR,

– KDP

Example Dual-Pol ImageExample Dual-Pol Image

Dual Polarization OnlineDual Polarization Online

• http://www.wdtb.noaa.gov/courses/dualpol/outreach/

• Online Module by WDTB on each product

• Courses for media & non-meteorologists available!

• http://www.wdtb.noaa.gov/courses/dualpol/outreach/

• Online Module by WDTB on each product

• Courses for media & non-meteorologists available!

Common Radar Signatures

Common Radar Signatures

Multiple Cell Storms ‐ Linear (Squall Line)Moderate to Strong Shear, Moisture and InstabilityMultiple Cell Storms ‐ Linear (Squall Line)Moderate to Strong Shear, Moisture and Instability

Radar Cross Section

Shelf Cloud

Rear Inflow

Jet

Downdraft

Updraft

Anvil

Inflow Notches

April 3rd 2006 1700z Reflectivity ImageApril 3rd 2006 1700z Reflectivity Image

Outflow BoundariesOutflow Boundaries

Outflow Boundary Interacts with Sea Breeze Boundary Over SE VA

Tornadic Supercell EvolutionTornadic Supercell EvolutionA. Early StageA. Early Stage

B. Developing hookB. Developing hook

C. Mature StageC. Mature Stage

Tornado Signatures on RadarTornado Signatures on RadarCouplets of Opposite Motion Close Together

Motion TOWARD the Radar in GREEN/BLUE

Motion AWAY FROM the Radar in RED/YELLOW

Line Echo Wave PatternLine Echo Wave Pattern

Meso Low

Tornadoes From “Broken S-Shaped” Signatures

Tornadoes From “Broken S-Shaped” Signatures

6 am 9/23/2003

Wilmington, NC – 11/07/1995 2124 - 2159 UTC Wilmington, NC – 11/07/1995 2124 - 2159 UTC

Series of

Boundaries

BREAK TIME!

We’ll Resume with Severe Weather Signatures in about 10 minutes!

Severe Weather Signatures

Severe Weather Signatures

A cornucopia of “indices”A cornucopia of “indices”

Vorticity Generation Parameter (VGP)*Supercell Composite Parameter (SCP)

This list is not nearly exhaustive!

K Index (KI)Total Totals (TT)

Severe Weather Threat (SWEAT)Lifted Index (LI)*

Showalter Index (SI)

Lapse Rate (LR)*CAP Strength (700 mb LI)

Relative Humidity (RH)*

Lifted Condensation Level (LCL)*Level of Free Convection (LFC)*Equilibrium Level (EL)*

* Can be calculated over many different layers/levels/parcels

Moisture Flux “Convergence” (MFC)*Equivalent Potential Temperature (e)*Precipitable Water (PW)*Warm Cloud Depth (WCD)*

Wet Bulb Zero (WBZ)Melting Level (MLT)

Convective Available Potential Energy (CAPE)*Convective Inhibition (CIN)*

Bulk Richardson Number (BRN)*

Storm-Relative Helicity (SRH)*

Bulk Vertical Wind Shear*Total Vertical Wind Shear*Storm-Relative Wind*

Downdraft CAPE (DCAPE)

Normalized CAPE (nCAPE)*

Bulk Richardson Number Shear (BRNSHR)

Dry Microburst Index (DMI)Theta-E Index (TEI)

Wind Index (WINDEX)

Wet Microburst Severity Index (WMSI)Microburst Day Potential Index (MDPI)

Energy-Helicity Index (EHI)*

Significant Tornado Parameter (STP)*Significant Hail Parameter (SHIP)Significant Severe Parameter (SSP)Strong Tornado Parameter (STP)

Indices of Indices (“Inbreeding”)

LSI = Lid Strength IndexDCI = Deep Convective IndexTQ Index = for “low-topped

instability”

HI = Haines Index*HMI = Hybrid Microburst Index

Mesoscale Convective System Forecast Index (MCS Index) a recent index published in WAF (2007)

The Result?The Result?Paralysis by analysis!

Types of ThunderstormsTypes of Thunderstorms

SingleCell

MulticellCluster

MulticellLine

Supercell

Weak updraft(non-severeor severe)

Slight threat

Moderate updraft (non-severe or severe)

Moderate threat

Intense updraft(Always severe)

Mesocyclone -Rotating updraft

High threat

Moderateupdraft (non-severeor severe)

Moderatethreat

“Squall Line”

Single Cell StormsSingle Cell Storms

May produce brief severe events

Single Cell StormsSingle Cell Storms

Multi-cell ThunderstormsMulti-cell Thunderstorms

Each cell lasts about 20 minutes, but a cluster can last for hours.

Each cell lasts about 20 minutes, but a cluster can last for hours.

Heavy rain is usually the main problem. However, strong winds, small hail and weak tornadoes are possible.

Heavy rain is usually the main problem. However, strong winds, small hail and weak tornadoes are possible.

Courtesy Alan Switzer

Ordinary non-organized storms with low severe threat

Multi-cell ThunderstormsMulti-cell ThunderstormsOrdinary non-organized storms with low severe threat

Multi-cell (Squall) LineMulti-cell (Squall) Line Leading edge of

Squall Line.

What to expect

Strong and possibly damaging wind

Heavy rain/hail

Worst is first; then comes the rain/hail.

Leading edge of Squall Line.

What to expect

Strong and possibly damaging wind

Heavy rain/hail

Worst is first; then comes the rain/hail.

Multi-cell Line (Bow Echo)Multi-cell Line (Bow Echo)

Supercell ThunderstormSupercell Thunderstorm

Contains a rotating updraft called a mesocyclone

Produce large hail, high winds, and violent tornadoes

Lasts for several hours

Contains a rotating updraft called a mesocyclone

Produce large hail, high winds, and violent tornadoes

Lasts for several hours

SupercellSupercellMain Features

Anvil

Overshooting Top

Rotating UpdraftMesocyclone

Supercell Thunderstorm3 Types of Supercells

Supercell Thunderstorm3 Types of Supercells

ClassicClassic

Low PrecipitationLow PrecipitationHigh PrecipitationHigh Precipitation

SupercellSupercell

DowndraftRear FlankDowndraft

NMain Features

Wall Cloud

Rain Free Base

-Supercell Thunderstorms--Supercell Thunderstorms-Rear Flank Downdraft (RFD)

This indicates an area of downward rushing air and at times just precedes the development of a tornado.

This indicates an area of downward rushing air and at times just precedes the development of a tornado.

Rear Flank DowndraftRear Flank Downdraft

Classic Supercell ThunderstormBird’s-eye View

Classic Supercell ThunderstormBird’s-eye View

0 5 10Nautical miles

Light Rain

Moderate/Heavy Rain & Hail

Supercell Thunderstorm(top view)

Anvil Edge

Gust Front

WSR-88D Radar Image

N

Hook echo

Hook echo

Rotating wall cloud under rain-free base

TT

TT

Shelf Cloud

RFDRFD

FFDFFDStorm Motion

Anvil Edge

Heavy Rain

Light Rain

Updraft

HP Supercell

N

Looking west

Top view

HP SupercellHP Supercell

Generally, there is not a good spot to view this type of storm since it is wrapped by a rain shield.


Copyright Jon Davies

LP Supercell(Most Common West of the Appalachians)

LP Supercell(Most Common West of the Appalachians)

Light Rain

Possible Hail

LP SupercellLP Supercell

Top Down ViewTop Down View

0 5 10

miles

Light Rain

Moderate/Heavy Rain & Hail

Supercell Thunderstorm

(top view)

Gust Front

Viewing angle

N Shelf CloudShelf Cloud

Wall CloudWall Cloud

Rain Free Base

Wall Cloud

Tail Cloud

Movement

Storm Intensity

Clues

Storm Intensity

Clues

Storm Strength CluesStorm Strength Clues

Wall cloud

Updraft

Overshooting Top

Flanking Line

Evaluating the SurroundingsEvaluating the Surroundings

An indication of a rapidly, intensifying

storm!

A thick, crisp anvil is another sign of a strong

updraft

Low Level Storm CluesLow Level Storm Clues

• Low, flat cloud base with little

visible precipitation

falling.

• On the back side of a

potentially tornadic storm.

Understanding Rotation

Understanding RotationUnderstanding Rotation

• In order to generate a tornado, a storm needs two basic things

1. Time – it must persist for an appreciable time – long lived updraft that doesn’t get choked by downdraft.

2. Wind shear that translates into vertical rotation.

• In order to generate a tornado, a storm needs two basic things

1. Time – it must persist for an appreciable time – long lived updraft that doesn’t get choked by downdraft.

2. Wind shear that translates into vertical rotation.

Updraft Weak Wind Speed Shear

Updraft Weak Wind Speed Shear

Updraft Strong Wind Speed Shear

Updraft Strong Wind Speed Shear

Wind ShearWind ShearDirectional wind shear Speed wind shear

ShearShear

• Very little separation between updraft and

downdraft. Downdraft chokes updraft causing

storm be short-lived.

• Tilted Updraft & downdraft are separated, so they co-exist. Therefore, the storm

lives longer.

Weak Strong

Supercell Structure/RFDSupercell Structure/RFD

Due to favorable shear, the downdraft does

NOT contaminate the updraft!

Secondary downdraft forms at rear of storm –called the Rear Flank Downdraft (RFD)

What is a Rear Flank Downdraft

(RFD)?

What is a Rear Flank Downdraft

(RFD)?


• Crucial to tornado development

• Downdraft on backside of updraft

tower

• Wraps around updraft to tighten

circulation

T

RFD

UPDRAFT

DOWNDRAFT

N

(Top view)


RFDRFD Rain/FFDRain/FFDWall CloudWall

Cloud

(Looking northwest)(Looking northwest)

Photo by Michael Peregrine


RFDRFD Wall CloudWall

Cloud

Signs of RotationSigns of Rotation

Spiral bands or striations in the

clouds serve as a rotation indicator!

Mesocyclone DevelopmentMesocyclone Development

Present with allSupercells!

Rotating updraft within the Rain-Free Cloud Base

How does mesocyclone develop and how can it last for 1 hour or more?

How does mesocyclone develop and how can it last for 1 hour or more?

MesocycloneMesocyclone

Mesocyclone gets it energy from vertical wind shear

concentrated in the lowest

10,000 feet of the atmosphere

Wall Cloud – time lapseWall Cloud – time lapse

Video

Rope

Tornado

Wedge

Supercell Tornado StagesSupercell Tornado Stages

Funnel CloudsFunnel Clouds

• Report Funnel Clouds

• If funnel extends more than half way to ground, circulation may likely be in contact – watch closely!

• Report Funnel Clouds

• If funnel extends more than half way to ground, circulation may likely be in contact – watch closely!

• Rotation aloft• Rotation aloft

Funnel CloudsFunnel Clouds

• Some funnels can form without a Supercell (“Cold Air Funnels”)

• No wall cloud - usually weaker

• Less lead time (if any); WATCH unlikely

• Some funnels can form without a Supercell (“Cold Air Funnels”)

• No wall cloud - usually weaker

• Less lead time (if any); WATCH unlikely

Photo by Chris Gullickson

Your perspective is the key!Your perspective is the key!

Copyright Chris Gullikson Copyright Chris Gullikson

This was simply low hanging cloud elements attached to the front of the shelf cloud. No rotation was present. ALWAYS look for rotation!

This is the same feature, but looking at it from a different perspective.

Where you are in relation to the storm?

Where you are in relation to the storm?

Looking South (1)Looking Northeast (2)

Looking Northwest (3)

Tornado 32

1

Shelf CloudShelf Cloud

Kiptopeke, VA - 081508

Shelf CloudShelf Cloud

OutflowOutflow

• Down and away…TOWARDS US!• Down and away…TOWARDS US!

OutflowOutflow

What is this feature?What is this feature?

Copyright Mike Umscheid

SHELF CLOUD

What is this? What is this?

WALL CLOUD

What are these?What are these?

Rain ShaftsTornadoes Shelf Clouds

Wall CloudsRain Shafts

For more information…For more information…

• See our website at:www.weather.gov/wakefieldOr just go to weather.gov and click on area of interest

• E-mail address:[email protected]

• Follow us on Facebook & Twitter

Spotter Hotline: 1-800-737-8624

• See our website at:www.weather.gov/wakefieldOr just go to weather.gov and click on area of interest

• E-mail address:[email protected]

• Follow us on Facebook & Twitter

Spotter Hotline: 1-800-737-8624

QUESTIONS ?QUESTIONS ?

?

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? ??

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