The Continuing Evolution Of Severe Weather Forecasting In The

United States: Observations And Forecasts, Watches and Warnings

John T. SnowDean, College of Geosciences and Professor of Meteorology

The University of OklahomaNorman, Oklahoma U.S.A.

Presented: 17 November 2004

Revised: 24 November 2003

Acknowledgements

This talk was prepared using materials from the websites maintained by the following organizations of the National Oceanic and Atmospheric Administration:

– National Severe Storms Laboratory– Storm Prediction Center– National Weather Service Office – Norman,

Oklahoma

The use of these materials is gratefully acknowledged. These folk are the experts on severe weather monitoring and prediction, and on the communication of watches and warnings to the public. Any misinterpretation of their materials is my personal responsibility.

Does The U.S. Have A Severe Weather Problem?

Severe and Hazardous Weather In the U.S.A. Tropical cyclone (depression, storm, hurricane-

typhoon winds, rain, storm surge) Thunderstorm (hail, strong winds, intense local rain,

lightning, tornadoes, downbursts) Winter Storm (blizzard, freezing rain, extreme cold) Wildfire (forest, grasslands) Strong winds from intense cyclonic systems (damaging

winds; blowing dust; ground blizzard) Flooding (flash; widespread) Stagnant situation (air quality - smog; in summer,

extreme heat) Obscurants - Fog, smoke, dust, blowing snow

Flash Floods - #1 Weather-Related Killer in US

Cheyenne, Wyoming – 1985: 12 fatalities, $61M in damage

Shadyside, Ohio – 1990: 26 fatalities, $8M in damage

Dallas, Texas – 1995: 16 fatalities, $1B, damage

Ft. Collins, Colorado – 1997: 5 fatalities, $100M in damage

Large Hail

Threat to property, agriculture

Tornadoes

Moore, Oklahoma, 3 May 1999

Lakeview, Texas, 19 April 1977

Tornadoes

The Past

Severe Weather Warning Operations Began in 1953 – What took so long?

General forecasts since 1880s, but not specific forecasts, warnings

Concerns re specific storm warnings– Panic!– Technical feasibility– Credibility– Effort required – cost/benefit

1953 – Waco, TX; Flint, MI; Worchester, MA – Congress directs USWB to begin storm warning services

Continuing Evolution 1950s: First operations – built on WW II technology

– Located Kansas City due to communications

– Combined USWB and AWS operation

– Combined operations (SELS) and research (NSSP)

– Primitive radars – WSR-3

1960s: Mature operations– National Severe Storms Laboratory (NSSL: Norman,

Oklahoma)

– National Severe Storms Forecast Center (NSSFC; Kansas City) -- blended with aviation weather forecasting

– First national weather radar network – WSR-57

1980s-1990s: Re-invention 1980s: Restructuring 1

– Deployment of new radar system -- WSR-88D

– Consolidation of NWS Forecast Offices around radars

– Co-location of selected offices on university campuses 1990s: Restructuring 2

– Move of operations to Norman, OK Storm Prediction Center (aviation operations to new Aviation Weather Center)

– Rejoining of operations with research importance of research, timely transfer to operations

2000s: Continuing upgrades– Radar – dual polarization retrofit

– Local mesoscale models

Why The Strong Focus On Tornadoes?

Major hazard over most of the U.S. east of the Rocky Mountains– Potential for major loss of life– Some events produce $1B+ in property losses

Scientific and Technical Challenge– Continually tests overall severe weather warning

systems– Pushes development of technology, techniques that

then has other applications

Political Realities

1998 Tornadoes(most fatalities since 1992)

1254 tornadoes in 48 contiguous states 129 fatalities. (67 in mobile homes) February: “Night of the Tornadoes,”

Orlando, FL – 42 deaths, 260 injured April: VA, MI, TE, GA - 50 fatalities, 272

injuries

May 3, 1999 Tornado Outbreak in Oklahoma

• 38 dead, 748 injured, $1 Billion damage• NWS warning based on NEXRAD detection of a tropospheric mesocyclone saved est. 600 lives• UMASS/UOklahoma radar captures the tornado on the ground, yielding highest spatial resolution images ever with W-band radar

Current Practices

Severe Weather Watches

What Is A Severe Weather Watch? A severe weather watch defines a region where a

specific form of severe weather is possible in the next several hours. It describes a general region, typically part of a state, the type of weather expected, the period in which the weather is likely to be severe, and provides reminders regarding appropriate actions.– Issued by the Storm Prediction Center (Tropical Prediction Center in the

case of tropical storms) as a forecast based on model output, forecaster judgment of the evolution of the situation

– It does not mean that the occurrence of severe weather is imminent, but that is it possible

– It is a first alert to the public to be watchful and prepared to go to appropriate shelter if the weather turns severe or a warning is issued.

Simplified Example Of A Watch Statement

11 am

Severe thunderstorms with large hail and damaging winds are expected in your area between 2 pm and 9 pm today

SEL9 URGENT - IMMEDIATE BROADCAST REQUESTED SEVERE THUNDERSTORM WATCH NUMBER 229 NWS STORM PREDICTION CENTER NORMAN OK 1210 AM CDT SUN MAY 4 2003

THE NWS STORM PREDICTION CENTER HAS ISSUED A SEVERE THUNDERSTORM WATCH FOR

PORTIONS OF SOUTHWEST IOWA NORTHEAST KANSAS NORTHWEST MISSOURI EASTERN NEBRASKA

EFFECTIVE THIS SUNDAY MORNING FROM 1210 AM UNTIL 600 AM CDT.

HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 55 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS ALONG AND 105 STATUTE MILES EAST AND WEST OF A LINE FROM 65 MILES NORTH OF OMAHA NEBRASKA TO 40 MILES EAST SOUTHEAST OF EMPORIA KANSAS.

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY DO PRODUCE TORNADOES.

National Centers for Environmental Prediction

NWSForecast

OfficeUSERS

The SPC is the element of the National Weather Service/National Centers for Environmental Prediction charged with providing timely and accurate forecasts and watches for severe weather over the contiguous United States, including thunderstorms/tornadoes, heavy rain, heavy snow, and fire weather events.

The SPC produces a suite of products to relay forecasts of organized severe weather as much as three days ahead of time, and continually refines the forecast up until the event has concluded. All products issued by the Storm Prediction Center are available on the World Wide Web. Its products are commonly used by National Weather Service offices, emergency managers, TV and radio meteorologists, private weather forecasting companies, the aviation industry, storm spotters, agriculture, educational institutions and many other groups.

Storm Prediction Center (SPC)

ZCZC MKCWWAMKC ALL 030300;370,1005 311,1015 311,1042 370,1035;WWUS8 KMKC 030013MKC WW-A 030013NMZ000-TXZ000-OKZ000-0300300-

STATUS REPORT ON WW NUMBER 361 AND 362

IN WW 361 THE THREAT OF SEVERE WEATHER CONTINUES TO THE EAST OF ALINE FROM 50 SW WINK TO 30 NE CNM TO 40 E ROW TO 65 W CVS.

IN WW 362...CONTINUE WW.

TORNADO WATCH WILL LIKELY BE REQUIRED FARTHER EAST INTO THE ERN TXPANHANDLE AND WRN TX AND OK BY 02Z.

NUMEROUS SUPERCELLS CONTINUE DEVELOPING OVER THE SRN HIGH PLAINSEAST OF THE DRYLINE IN AN AXIS THAT EXTENDS FROM NEAR WINK TX TONEAR CLAYTON NM. NUMEROUS REPORTS OF BASEBALL HAIL HAVE BEENRECEIVED. WV IMAGERY SHOWS SHORTWAVE LIFTING NEWD THROUGH UT ANDWRN CO. DEEP LAYER SHEAR PROFILES HAVE INCREASED TO 60 KT AS MIDLEVEL SPEED MAX ON THE SRN PERIPHERY OF SHORTWAVE LIFTS NEWD TOWARDTHE SRN PLAINS. INDIVIDUAL CELLS WERE MOVING NEWD AT AROUND 35 KT.INCREASING LOW LEVEL INFLOW ASSOCIATED WITH DEVELOPING LOW LEVELJET WILL SUPPORT CONTINUED EWD DEVELOPMENT INTO THE EVENING.

INCREASING STORM RELATIVE FLOW AND SHEAR PROFILES SUGGEST THREATFOR SUPERCELLS WITH LARGE HAIL...DAMAGING WIND AND ISOLATEDTORNADOES WILL CONTINUE AS ACTIVITY DEVELOPS EWD INTO INSTABILITYAXIS ACROSS THE TX AND OK PANHANDLES WHERE SBCAPES ARE AS HIGH AS5000 J/KG.

..DIAL.. 06/02/99NNNN

ZCZC MKCWWAMKC ALL 040300;335,0993 360,0993 360,0961 335,0962;WWUS8 KMKC 032333MKC WW-A 032333OKZ000-040200-

STATUS REPORT ON WW NUMBER 195

CLUSTER OF INTENSE THUNDERSTORMS...INCLUDING STRONG TORNADICSUPERCELLS WEST/SOUTHWEST OF OKLAHOMA CITY AREA IS ONGOING. STRONGAND INTENSIFYING DIVERGENT UPPER FLOW FIELD...ENHANCED BY MID/UPPERJET DIGGING ACROSS THE SOUTHERN ROCKIES...WILL CONTINUE TO SUPPORTEVOLUTION INTO LARGER SEVERE CONVECTIVE SYSTEM...AHEAD OF DRY LINE...THROUGH THE EVENING HOURS. GIVEN ONGOING AND EXPECTED TRENDS...WW MAY BE REPLACED WITH NEW WW INCLUDING NORTHERN OKLAHOMA ANDPARTS OF NORTH CENTRAL TEXAS WITHIN THE NEXT HOUR OR SO.

..KERR.. 05/03/99NNNN

Severe Weather Warnings

What Is A Severe Weather Warning?

A severe weather warning indicates that severe weather is occurring or is imminent for specific region. It describes the specific region being threatened, evidence for the occurrence of the severe weather, direction and speed of movement, and likely duration. Rapidly updated as necessary– Issued by the local National Weather Service Forecast Offices minutes to a

few hours in advance of the occurrence.

– Usually based on actual observations: spotters, law enforcement, or radar.

– It is an alert to the public that immediate action is required.

– Can be issued without a preceding Watch

Goal: No surprises to the public!

Simplified Example Of A Warning Statement

3:35 pm

Spotters report a severe thunderstorm with large hail and damaging winds near your vicinity, moving to the NE at 50 km/hour. Take shelter immediately, and remain in shelter for next 30 minutes.

WFUS51 KCLE 122345 TORCLE OHC169-130030-

BULLETIN - EAS ACTIVATION REQUESTED TORNADO WARNING NATIONAL WEATHER SERVICE CLEVELAND OH 644 PM EST WED NOV 12 2003

THE NATIONAL WEATHER SERVICE IN CLEVELAND HAS ISSUED A

* TORNADO WARNING FOR...   WAYNE COUNTY IN NORTHEAST OHIO...

* UNTIL 730 PM EST

* AT 644 PM EST NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO 10 MILES WEST OF   WOOSTER...MOVING EAST AT 50 MPH.

* SOME LOCATIONS NEAR THE PATH OF THIS STORM INCLUDE...   DALTON   DOYLESTOWN   ORRVILLE   WOOSTER

LAT...LON 4092 8199 4095 8177 4098 8165 4075 8165           4072 8212 4089 8212

$$

WFUS54 KHGX 171506 TORHOU TXC321-481-171545-

BULLETIN - EAS ACTIVATION REQUESTED TORNADO WARNING NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX 905 AM CST MON NOV 17 2003

THE NATIONAL WEATHER SERVICE IN LEAGUE CITY HAS ISSUED A

* TORNADO WARNING FOR...   WHARTON COUNTY IN SOUTHEAST TEXAS   MATAGORDA COUNTY IN SOUTHEAST TEXAS

* UNTIL 945 AM CST

* AT 900 AM CST...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A  SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO 8 MILES WEST OF MARKHAM...OR ABOUT 14 MILES WEST OF BAY CITY...MOVING NORTHEAST AT  20 MPH.

* LOCATIONS IN THE PATH OF THE SEVERE THUNDERSTORM INCLUDE... MARKHAM AND BOLING

THE SAFEST PLACE TO BE DURING A TORNADO IS IN THE INTERIOR HALLWAY OR ROOM SUCH AS A CLOSET ON THE LOWEST LEVEL OF A STURDY BUILDING. USE BLANKETS OR PILLOWS TO COVER YOUR BODY AND ALWAYS STAY AWAY FROM WINDOWS.

IF IN MOBILE HOMES OR VEHICLES...EVACUATE THEM AND GET INSIDE A SUBSTANTIAL SHELTER. IF NO SHELTER IS AVAILABLE...LIE FLAT IN THE NEAREST DITCH OR OTHER LOW SPOT AND COVER YOUR HEAD WITH YOUR HANDS.

PLEASE REPORT SEVERE WEATHER TO THE COUNTY SHERIFF...LOCAL POLICE... OR DEPARTMENT OF PUBLIC SAFETY. THEY WILL RELAY YOUR REPORT TO THE NATIONAL WEATHER SERVICE.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 100 PM CST MONDAY AFTERNOON FOR SOUTHEAST TEXAS.

LAT...LON 2901 9631 2888 9617 2912 9586 2925 9602

$$

NWSForecast

OfficeUSERS

SPOTTERS

Oklahoma Weather Center

            

    

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                                                

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

                     

         

2002 Storm Spotter Talk ScheduleCalendar Table

National Weather Service Weather Forecast Office

National Weather ServiceForecast Office – Key Personnel

Science Operations Officer (1) – training, review and assessment of severe warning team, infusion of new technology, techniques

Warning Coordination Meteorologist (1) – training of users (state, county, city emergency management personnel) and spotters (law enforcement, fire fighters, amateur radio clubs)

Journeyman/Lead Forecasters (3 to 5) – leads severe weather warning team; decides when conditions merit issuance of a warning

Key to Severe Weather Monitoring: The National Radar Network

WSR-88D Doppler Weather Surveillance Radar– A “national network”, but locally operated

NEXRAD: WSR-88D

8.5 meter antenna; ~1o beam width

500 kW transmitterVolume scanning strategyReflectively and Doppler field

outputs

138 installations across US

NEXRAD THUNDERSTORM (SUPERCELL) IMAGERY

Hook Echoes and Vortex Doppler “Couplets” reliably indicate the presence of mesocyclones in the troposphere

Image/Text/Data from the University of Illinois WW2010 Project.

Other Radars Used InSevere Weather Warning

TWDR– FAA-controlled, focused on wind shear detection

– Same technology as WSR-88D, but 5 cm

Commercial radars, mainly television

Flood / Flash Flood

Severe Thunderstorm Tornado

Tropical StormHurricane

Winter Storm

Excessive Heat

Types of Watches/Warnings

National Weather Service Warnings

0

5

10

15

20

25

1997 1998 1999 2000 2001 2002 2003

Min

ute

s

Severe Thunderstorm

Tornado

National Weather Service Average Warning Times

Probability of detection ~70%; Average warning time is ~11 minutes False alarm problem is significant since only

~30% of mesocyclones produce tornadoes (= intense columnar vortex in contact with the ground)– Situation best for largest, most long-lived events,

which pose greatest threat– Situation poorest for small, short-lived events

Radar => detects mesocyclones

Weather Advisories

What Is A Severe Weather Advisory? A severe weather advisory provides the public

information on a weather condition that may be hazardous to certain portions of the population or may cause great inconvenience. An advisory defines a region where a specific form of severe weather is possible in the next several hours. It describes a general region, typically part of a state, the type of weather expected, the period in which the weather is likely to be present, and provides reminders regarding appropriate actions.– Issued by the Storm Prediction Center (Tropical Prediction Center in

the case of tropical storms) or the local National Weather Service Forecast Office.

– Often used where conditions are threatening, but where established severe weather thresholds are not likely to be crossed.

A Few Types Of Advisories

Fog

Heavy Snow

High Wind/High Profile Vehicle

The Future

The Future

Dual Polarization Retrofit to WSR-88D– Hydrology flood warnings– Ground clutter removal

Improved scanning strategies GIS-based products Development of a centralized (national?

regional?) radar network, including FAA, possibly commercial radars national/regional high resolution composite, mosaics; adaptive operational strategies

The Future

Fill in the boundary layer – dense network of small, inexpensive radars on cell phone towers

Continuously updating model-based forecasts, out to 30, 60, 90 minutes, with update rates of a few minutes– Very fast local computing– Forecaster has access to seamless past, current,

future on a “smart” decision support system

Warn on prediction

Spread of State-/Region-Based Mesonetworks

• Conventional surface network + Oklahoma Mesonet + DoEnergy ARM Site and network + special networks

Continually ImprovingStorm Scale Models

Created the world’s first storm-scale numerical forecast system (ARPS) – now used operationally by American Airlines and others (FAA, NWS)

Direct, 4D Var assimilation of radar data

6-hour Forecast Storms on NEXRAD Radar

D/FW

Center for Analysis and Prediction of Storms

Oklahoma Weather Center

Developing Technology for The Next NEXRAD

$38M partnership among NSSL, OU, FAA, Navy, Lockheed Martin to apply Spy-1 military radar technology to meteorology

Totally solid state; can track weather and aircraft simultaneously Fast!

Courtesy National Severe Storms Laboratory

Enhanced Decision Support Systemsfor Forecasters, Decision Makers

Miscellany

What is needed to be a good severe weather forecaster?

The specialized storm prediction mission requires meteorologists with a high level of expertise in convective storm forecasting, as well as excessive precipitation, winter weather, and conditions leading to high fire dangers.

In the U.S., almost all severe weather forecasters have at least a BS degree in atmospheric science from a college or university; most have done graduate-level studies and/or hold a Master of Science degree.

At the Storm Prediction Center and in NWS FO, all lead forecasters have at least 5 years of specialized experience, with veteran forecasters having over 20 years of severe storm forecasting experience.

What is needed to be a good severe weather forecaster?

Motivation: Almost all severe storms forecasters are passionate about violent weather, with an intense desire to learn about and become better at predicting it. For many, this dates back into childhood -- a first-hand encounter with violent storms, images on TV or in books and magazines, or even a deep attraction to storms which goes back too far to recall. Others start out in other fields or college majors, then became fascinated with severe weather. In any case, this desire leads to...

Education: Consistently good severe storms forecasters have a solid educational background in atmospheric science which allows them to understand "textbook" concepts of thunderstorm formation. They don't stop with their college education, either. They constantly re-educate themselves in the latest discoveries about severe thunderstorms and tornadoes -- reading scientific journal articles on cutting-edge research, perhaps doing some research themselves. The understanding of storms which results lets the forecaster think of "conceptual models" -- visualizations of what the storms will do and how.

What is needed to be a good severe weather forecaster?

Flexibility: Because the atmosphere doesn't read textbooks or science journals, the forecaster must adapt those "classroom" ideas to an endless variety of day-to-day situations which may look a lot different. He or she also should be able to recognize when and why a forecast is not working out, and make the right adjustments. These skills come from...

Experience: In meteorology, history never repeats itself exactly. But certain types of situations do recur, allowing the forecaster to set a mental benchmark for what to expect. From there, he or she can better decide what data will be most important to examine, and what data will not be as relevant to the situation. Experienced forecasters are able to learn how bad forecasts went wrong and how good forecasts worked each time, building a more complete mental warehouse of severe storm forecast knowledge as time passes. When the experience is continually blended with motivation, flexibility and more education, he or she will keep improving as a forecaster.

Situational Awareness

Critical in recognizing when severe weather begins in an often-complex meteorological situation, and during situations with multiple hazards occurring simultaneously

Multi-tasking, mentally and physically Team coordination Requires continuous training/practice,

standardized techniques, technology, all properly integrated

Not everyone can do it!

3 May 1999 Tornado Tracks/Intensity

Courtesy Oklahoma City Area National Weather Service Forecast Office

Role of the Media

Local Media – Television and Radio National Media

– National Network Television– TLC, Discovery Channel– The Weather Channel

Point: Media are essential partners in both educating the public and communicating near-real time information regarding the onset of severe weather

References

Bradford, Marlene, 2001: Scanning the Skies – A history of tornado forecasting. The University of Oklahoma Press, Norman, Oklahoma. 220 pp. ISBN 0-8061-3302-3

European Conference on Severe Storms 2002. Special issue: Atmospheric Research, 67-68. 701 pp. ISSN 0169-8095

At Laughlin AFB in Del Rio, Texas, downburst winds on 24 May 2003 did significant damage to the radome of the KDFX WSR-88D.

It is estimated the wind which did this damage was in the range of 80-85 knots.

                                                                         

John T. SnowDean, College of GeosciencesThe University of Oklahoma

Sarkeys Energy Center, Suite 710100 E. Boyd Street

Norman, Oklahoma 73019

Tel: 405-325-3101FAX: 405-325-3148

E-mail: jsnow@ou.eduWeb: http://geosciences.ou.edu