Transcript The continuing evolution of severe weather forecasting in

The Continuing Evolution Of
Severe Weather Forecasting In The
United States: Observations And
Forecasts, Watches and Warnings
John T. Snow
Dean, College of Geosciences and Professor of Meteorology
The University of Oklahoma
Norman, 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, hurricanetyphoon  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
Tornadoes
Lakeview, Texas, 19 April 1977
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
USERS
NWS
Forecast
Office
Storm Prediction Center (SPC)
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.
ZCZC MKCWWAMKC ALL 030300;370,1005 311,1015 311,1042 370,1035;
WWUS8 KMKC 030013
MKC WW-A 030013
NMZ000-TXZ000-OKZ000-0300300STATUS REPORT ON WW NUMBER 361 AND 362
IN WW 361 THE THREAT OF SEVERE WEATHER CONTINUES TO THE EAST OF A
LINE 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 TX
PANHANDLE AND WRN TX AND OK BY 02Z.
NUMEROUS SUPERCELLS CONTINUE DEVELOPING OVER THE SRN HIGH PLAINS
EAST OF THE DRYLINE IN AN AXIS THAT EXTENDS FROM NEAR WINK TX TO
NEAR CLAYTON NM. NUMEROUS REPORTS OF BASEBALL HAIL HAVE BEEN
RECEIVED. WV IMAGERY SHOWS SHORTWAVE LIFTING NEWD THROUGH UT AND
WRN CO. DEEP LAYER SHEAR PROFILES HAVE INCREASED TO 60 KT AS MID
LEVEL SPEED MAX ON THE SRN PERIPHERY OF SHORTWAVE LIFTS NEWD TOWARD
THE SRN PLAINS. INDIVIDUAL CELLS WERE MOVING NEWD AT AROUND 35 KT.
INCREASING LOW LEVEL INFLOW ASSOCIATED WITH DEVELOPING LOW LEVEL
JET WILL SUPPORT CONTINUED EWD DEVELOPMENT INTO THE EVENING.
INCREASING STORM RELATIVE FLOW AND SHEAR PROFILES SUGGEST THREAT
FOR SUPERCELLS WITH LARGE HAIL...DAMAGING WIND AND ISOLATED
TORNADOES WILL CONTINUE AS ACTIVITY DEVELOPS EWD INTO INSTABILITY
AXIS ACROSS THE TX AND OK PANHANDLES WHERE SBCAPES ARE AS HIGH AS
5000 J/KG.
..DIAL.. 06/02/99
NNNN
ZCZC MKCWWAMKC ALL 040300;335,0993 360,0993 360,0961 335,0962;
WWUS8 KMKC 032333
MKC WW-A 032333
OKZ000-040200-
STATUS REPORT ON WW NUMBER 195
CLUSTER OF INTENSE THUNDERSTORMS...INCLUDING STRONG TORNADIC
SUPERCELLS WEST/SOUTHWEST OF OKLAHOMA CITY AREA IS ONGOING. STRONG
AND INTENSIFYING DIVERGENT UPPER FLOW FIELD...ENHANCED BY MID/UPPER
JET DIGGING ACROSS THE SOUTHERN ROCKIES...WILL CONTINUE TO SUPPORT
EVOLUTION 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 AND
PARTS OF NORTH CENTRAL TEXAS WITHIN THE NEXT HOUR OR SO.
..KERR.. 05/03/99
NNNN
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
OHC169-130030BULLETIN - 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
$$
WFUS54 KHGX 171506
TORHOU
TXC321-481-171545BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
905 AM CST MON NOV 17 2003
THE NATIONAL WEATHER SERVICE IN LEAGUE CITY HAS ISSUED A
* TORNADO WARNING FOR...
WHARTON COUNTY IN SOUTHEAST TEXAS
MATAGORDA COUNTY IN SOUTHEAST TEXAS
* UNTIL 945 AM CST
* AT 900 AM CST...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A
TORNADO 8 MILES WEST OF MARKHAM...OR ABOUT 14 MILES WEST OF BAY CITY...MOVING NORTHEAST AT 20 MPH.
* LOCATIONS IN THE PATH OF THE SEVERE THUNDERSTORM INCLUDE...
MARKHAM AND BOLING
THE SAFEST PLACE TO BE DURING A TORNADO IS IN THE INTERIOR HALLWAY OR ROOM SUCH AS A CLOSET ON THE LOWEST LEVEL OF A
STURDY BUILDING. USE BLANKETS OR PILLOWS TO COVER YOUR BODY AND ALWAYS STAY AWAY FROM WINDOWS.
IF IN MOBILE HOMES OR VEHICLES...EVACUATE THEM AND GET INSIDE A SUBSTANTIAL SHELTER. IF NO SHELTER IS AVAILABLE...LIE FLAT
IN THE NEAREST DITCH OR OTHER LOW SPOT AND COVER YOUR HEAD WITH YOUR HANDS.
PLEASE REPORT SEVERE WEATHER TO THE COUNTY SHERIFF...LOCAL POLICE... OR DEPARTMENT OF PUBLIC SAFETY. THEY WILL RELAY
YOUR REPORT TO THE NATIONAL WEATHER SERVICE.
A TORNADO WATCH REMAINS IN EFFECT UNTIL 100 PM CST MONDAY AFTERNOON FOR SOUTHEAST TEXAS.
LAT...LON 2901 9631 2888 9617 2912 9586 2925 9602
$$
SPOTTERS
USERS
NWS
Forecast
Office
Oklahoma Weather Center
2002 Storm Spotter Talk Schedule
Calendar Table
National Weather Service Weather Forecast Office
National Weather Service
Forecast 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 transmitter
Volume scanning strategy
Reflectively 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 In
Severe Weather Warning
 TWDR
– FAA-controlled, focused on wind shear detection
– Same technology as WSR-88D, but 5 cm
 Commercial radars, mainly television
Types of Watches/Warnings
Flood / Flash Flood
Severe Thunderstorm
Tornado
Tropical Storm
Hurricane
Winter Storm
Excessive Heat
National Weather
Service
Average
Warning
Times
National
Weather
Service
Warnings
25
Minutes
20
15
Severe Thunderstorm
Tornado
10
5
0
1997 1998 1999 2000 2001 2002 2003
Radar => detects mesocyclones
 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
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 Improving
Storm 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
D/FW
6-hour Forecast
Storms on NEXRAD Radar
Oklahoma Weather Center
Center for Analysis and Prediction of Storms
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!
Enhanced Decision Support Systems
for Forecasters, Decision Makers
Courtesy National Severe Storms Laboratory
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 nearreal 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. Snow
Dean, College of Geosciences
The University of Oklahoma
Sarkeys Energy Center, Suite 710
100 E. Boyd Street
Norman, Oklahoma 73019
Tel: 405-325-3101
FAX: 405-325-3148
E-mail: [email protected]
Web: http://geosciences.ou.edu