Subjective Probability Forecasts at the NWS Storm Prediction Center

Subjective Probability Forecasts at the NWS Storm Prediction Center

Dr. Russell S. Schneider

Steven J. Weiss

NWS Storm Prediction Center

Model Development Laboratory - December 2009

“Where America’s Weather and Climate Services Begin”

Outline

• Motivation

• Background

• SPC Probabilistic Products

• SPC Unique Guidance & Forecast Tools

• Advanced Verification

• Current Development

• Challenges

NOAA NWS Storm Prediction Center

• Forecast tornadoes, thunderstorms, and wildfires nationwide• Forecast information from 8 days to a few minutes in advance

• World class team engaged with the research community• Partner with over 120 local National Weather Service offices

Each Year: About 1,500 tornadoes touch down across the United States causing an estimated

$1.1 billion in damages and over 80 deaths

Motivation for Probabilities• Capture forecaster’s assessment

• Quantify uncertainty inherent in a forecast

• Enable partner-specific risk assessment & decision support

• Improve depth & quality end-to-end of forecast process

Scientific Background• Subjective Probability Forecasting (Sanders, 1963)

• Probability is proper internal language of forecasters • Forecasters use: Sorting Process & Labeling Process

• Murphy and Collaborators (1974-1995)• Early work with SPC (NSSFC) Forecast Process

• Murphy & Winkler (1982): SPC Tornado Watches in 1976-1977

• Murphy et al. (1993): Experimental Convective Outlooks

• Other notable papers• Murphy (1991): Probabilities, Odds, and Forecasts of Rare Events

• Murphy (1993): Essay on the Nature of Forecast Goodness– Need to effectively capture forecaster judgment

– Avoid forecaster product-embedded estimates of user cost-loss model

Basic Methodology• Guidance & Forecast Tools

• Forecaster Experience (rare events)• SPC Specialists for Severe Convection• Jack Hales: Lead for 35 years = over 1/5th

• Conceptual models important with limited data

• Capture Forecaster Information

• Communicate Information (multi-tier)

• Timely & Effective Feedback

SPC Probabilistic Products

• Tornadoes, Hail & Wind

• Fire weather (Day 1- 8)• Winter weather• Excessive rainfall

Storm Prediction Center

Hazardous Phenomena

“Super Tuesday” Outbreak5 February 2008

56 Fatalities - 15th Largest Death Toll

since 1950

Day 4-8 Convective OutlookOperational since March

200730% Probability of an Event within 25 mi of a point

(“high end” Slight Risk)“Potential too Low”

<30 % Probability

“Predictability too

Low” Widespread severe weather possible, but too much

uncertainty to forecast

an area

Graphic & Short Discussion

Issued at 4:00 am Central

Day 3 & Day 2 Convective Outlook

Operational since: 2001 & 1986 (categorical); 2001 &

2000 (probabilistic)Probability of Severe Weather within 25 miles of a point

Hatched Area --- 10% or greater chance of an extreme event

(EF2 or greater tornado, 2” or larger hail, 65 kt or faster gust)

Graphic & DiscussionValid for 24 hour period 1200 UTC – 1200 UTC

Issued at 2:30 am Central Issued at 1:00 am Central& updated at 1730 UTC

DAY AFTER TOMORROW TOMORROW

Day 1 Convective Outlook

Operational since 1955 (catagorical) & 2000 (probabilistic)Probability of individual hazards within 25 miles of a pointHatched Areas --- 10% or greater chance of an extreme event

(F2 or greater tornado, 2” or larger hail, 65 kt or faster gust)

Issued at 0600 UTC; updated at 1300, 1630, 2000, 0100 UTCValid for period ending at 1200 UTC

Categorical Risk

Hail Probability

Tornado Probability

Wind Probability

Hail Probabilities

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100

Forecast (%)

Obse

rved

POD

(%)

20042005200620072008

Reliability of Probabilistic Day 1 Outlooks

Gust Probabilities

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100

Forecast (%)

Obse

rved

POD

(%)

20042005200620072008

Tornado Probabilities

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100

Forecast (%)

Obse

rved

POD

(%)

20042005200620072008

2008 Forecast Obs10% Sig Torn 7.2%

10% Sig Gust 4.5% 10% Sig Hail 7.6%

All 2008 Day 1 Outlook Tornado Probabilities

0102030405060708090

100

0 20 40 60 80 100False Alarm Rate (%)

POD (

%)

All 2008 Day 1 Outlook Gust Probabilities

0102030405060708090

100

0 20 40 60 80 100False Alarm Rate (%)

POD (

%)

All 2008 Day 1 Outlook Hail Probabilities

0102030405060708090

100

0 20 40 60 80 100False Alarm Rate (%)

POD (

%)

All 2008 Day 2 Outlook Any Severe

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100False Alarm Rate (%)

POD (

%)

Day 2 Forecast Observed10% Prob. Sig 13.3%

All 2008 Day 3 Outlook Any Severe

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100False Alarm Rate (%)

POD (

%)Convective Outlook Probabilities ROC Charts

The concaveness of the ROC curve wrt to the diagonal indicates the value the forecast

Day 3 Forecast Observed

10% Prob. Sig 9.1%

POD = fraction of events that were correctly forecast

FAR = fraction of nonevents that were incorrectly forecast

Relationship betweenRelationship betweenCategorical and Probabilistic OutlooksCategorical and Probabilistic Outlooks

Watch Hazard Probabilities

All watches are not created equal

Use the probabilities to refine the specific threat within the watch and

gauge forecaster confidence in the specific convective hazards

Operational since 2006

0 1

F o re c a st (%)

2006 2007 2008

Reliability of Watch Hazard ProbabilitiesProbabiliy 2 or more Tornadoes

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100

Forecast (%)

Obse

rved

POD

(%)

Probability of 10 or more Gust Reports

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100

Forecast (%)

Obse

rved

POD

(%)

Probability of 10 or more Hail Reports

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100

Forecast (%)

Obse

rved

POD

(%)

2006

2007

2008

Probabiliy of an F2 or Greater Tornado

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100

Forecast (%)

Probability of a Gust Faster than 65 kts

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100

Forecast (%)

Probability Hail Larger than 2"

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100

Forecast (%)

2006

2007

2008

Problem with “significant wind gusts …Observational issue, few measurements…

Most estimated from damage(e.g., only 193 reports in 2008)

All Watch Hazard Probabilies

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100

Forecast (%)

Probabiliy 6 or more non-Tornadic reports

0102030405060708090

1000 10 20 30 40 50 60 70 80 90 100

Forecast (%)

All 2008 Watch Hazard Probabilities

0102030405060708090

100

0 20 40 60 80 100False Alarm Rate (%)

POD

(%)

All 2008 Watch Hazard Probabilies

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100

Forecast (%)

2008 Watch Hazard Probability VerificationWorst CaseBest Case

2008 Probability of a Gust Faster than 65 kts

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100

Forecast (%)

2008 Probability of a Gust Faster than 65 kts

0102030405060708090

100

0 20 40 60 80 100False Alarm Rate (%)

POD

(%)

POD = fraction of events that were correctly forecast

FAR = fraction of nonevents that were incorrectly forecast

Thunderstorm Outlooks to Support Aviation

1300UTC 9 April 20091300Z 9 April 09

VT 16Z-20Z

1300Z 9 April 09

VT 00Z-04Z

1300Z 9 April 09

VT 20Z-00Z

0600Z 9 April 09

VT 20Z-00Z

0600UTC 9 April 20090600Z 9 April 09

VT 16Z-20Z

0600Z 9 April 09

VT 00Z-04Z

Observed Cloud-to-Ground Lightning 16Z-20Z 20Z-00Z 00Z-04Z

SPC Scientific Approach• Engage the Community (SSB & Forecasters)

• Professional Meetings and Conferences • Collaborative Research Projects• Hazardous Weather Testbed

• Sift & Winnow• Eye toward specialized mission specific data & tools• Hazardous Weather Testbed (key intermediate step)

• Early integration of ensemble forecast systems• Storm-resolving WRF NWP• Storm-scale Ensemble Forecast System

• SSB focus on Science Enabling “Structure”• Flexible. Adapt to specific trends as path becomes clear• Multiple dimensions for success and synergy

SPC Science Support Branch Foci• Collaborative Research

• HWT Spring Experiments• NSSL, OU, EMC, NCAR, GSD, U. of Albany, Pacific NW Fire Lab• Steve Weiss, David Bright, Phillip Bothwell, Jason Levit, Chris

Siewert

• Forecast Tools & Guidance• Regional Scale NWP Information Extraction (e.g. SREF guidance)• Storm Scale NWP Information Extraction (e.g. storm scale ensemble)• Interactive Forecast Tools (e.g. NSHARP)• David Bright, Phillip Bothwell, Jason Levit & Steve Weiss

• Forecast Product & Storm Environment Database• SPC Administrative & Context Based Verification• Understanding Storms & Supporting Forecast Tools• Andy Dean, Phillip Bothwell, Greg Carbin

additional support: Gregg Grosshans, Jay Liang, Joe

Byerly

Guidance & Forecast Tools

Forecaster GUI for Probabilities… climatology as a reference

constrained by “policy” and based on climatology

Perfect Prog. Lightning Forecastsincluding Dry Thunderstorm Potential (Bothwell, 2008)

NOAA Hazardous Weather Testbed

EFP

EWPGOE

S-R PG

ExperimentalForecastProgram

ExperimentalWarningProgram

Prediction of hazardous weather events from a few hours to a

week in advance

Detection and prediction of hazardous weather events up to

several hours in advance

Key HWT Contributions to Advances in SPC Operations

• Short Range Ensemble Forecast System (SREF)• SREF Workshop (NCEP 1994)

• Collaboration on SREF with EMC & NSSL (1999-2002)

• SPC focused SREF guidance in Operations (2003)

• Developing additional calibrated high impact wx. guidance

• Global Ensemble Forecast System (GEFS)• SPC Focused GEFS Guidance in Operations (2005)

• Working toward NAEFS tools (2010)

• Convection Allowing High Resolution NWP• Experimental WRF data in Operations (2004)

• Operational WRF data in Operations (2008)

Example of 39 Hour SREF Calibrated Thunderstorm Forecast

Valid: 03-06 UTC 03 May 2008

Bright et al. 2005

Logistic Regression applied to sounding parameters, yielded the following significant predictors:

1) maximum bulk shear (m/s) in the 0-1 and 6-10 km layer2) 3-8 km lapse rate (degrees C/km)3) most unstable CAPE4) 3-12 km mean wind speed (m/s)

Probability of MCS Maintenance

Coniglio et al. 2006

Post-Processed Short Range Ensemble Forecast

Calibrated Severe Thunderstorm Probability

Calibration – Computed from conditional probability of Severe Weather given a Thunderstorm Bright & Wandishin 2006

Wide range of high impact SREF guidance are available at the

SPC websitehttp://www.spc.noaa.gov/exper/sref/

MDL has a Distinguished History of Probabilistic Forecast Guidance

• Pioneering work documented in formal publications• Charba (MWR 1979)

• Reap and Foster (JAM 1979)

• Technical Reports & Conferences with SPC• R. M. Reap, D. S. Foster, and S. J. Weiss, 1981

• R. M. Reap, D. S. Foster, and S. J. Weiss, 1982

• S. J. Weiss and R. M. Reap, 1984

SPC Day 3 Probabilistic Outlookfor Tuesday 8 December

Day 3 SPC Outlook valid 12Z 8 Dec.

24hr Unconditional Severe Thunderstorm Probability (within 25 mi of point)

Preliminary Reports valid 12Z 8 Dec.

24hr Compilation 12Z-12Z

NAM & GFS based Severe Thunderstorm Probabilities

NAM MOS: 72hr Projection valid 12Z 8 Dec.

24hr Unconditional Severe Thunderstorm Probability

GFS MOS: 72hr Projection valid 12Z 8 Dec.

24hr Unconditional Severe Thunderstorm Probability

SREF based Calibrated Severe Thunderstorm Probabilities

SREF 69hr Projection valid 12Z 8 Dec.

24hr Calibrated Unconditional Severe Thunderstorm Probability

We need data … robust verification

• In a World Without Data, Opinion Prevails• We tend to research the atmosphere, but not ourselves

From Scholtes (1998) “The Leader’s Handbook”

Context Based Verification

• Support a dynamic learning environment• Provide insights into tactical & strategic challenges

• Data & Methodology:– Severe weather reports for 2003-2008 (2009 through August)

– Environmental estimate from hourly SPC - RUC meso-analysis– Extract from nearest grid point at hour prior to event

– Link report and estimated environment databases by event time & location

175,658 reports | 8334 tornadoes

High CAPE - Strong Shear Low CAPE - Strong ShearSevere Reports

Environment Hours

~50hr/yr

~100hr/yr

• 24 % of F2+ tornadoes

• local axis ~ 40 hr / year


• widespread ~ 80 hr / year

All Tornadoes (total of 6643)0-

6 km

She

ar

100 mb ML CAPE

Thunderstor

ms

Common

Significant

Tornadoes

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

0-6

km S

hear

100 mb ML CAPE

Conditional Probability of Tornadoes (given lightning)

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

0-6

km S

hear

100 mb ML CAPE

All Watches: Probability of Tornado Detection

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

Overall POD: 0.69; F2+: 0.94

0-6

km S

hear

100 mb ML CAPE

Tornado Watch: Probability of Tornado Detection

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

Overall POD: 0.58; F2+: 0.83

0-6

km S

hear

100 mb ML CAPE

Tornado Watch: Probability of Tornado Detection

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

Overall POD: 0.58; F2+: 0.83> 60%

0-6

km S

hear

100 mb ML CAPE

Tornado Watch: Fraction of Missed Tornadoes

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

0-6

km S

hear

100 mb ML CAPE

Tornado Watch: False Alarm Area

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

0-6

km S

hear

100 mb ML CAPE

Tornado Watch: Fraction of Missed Tornadoes

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

Regional Tornado Variability0-

6 km

She

ar

100 mb ML CAPE

High

False Alarm Area

High Torna

do

POD (in tor)

Overall POD: 0.58; F2+: 0.83

All Tornadoes 2003-2008 (total of 9178)0-

6 km

She

ar

100 mb ML CAPE

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

All Central Region Tornadoes (total of 4369)0-

6 km

She

ar

100 mb ML CAPE

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

All Southern Region Tornadoes (total of 3622)0-

6 km

She

ar

100 mb ML CAPE

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

All Eastern Region Tornadoes (total of 981)0-

6 km

She

ar

100 mb ML CAPE

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

Tornado Variability (Tornado in Tornado Watch)0-

6 km

She

ar

100 mb ML CAPE

High

False Alarm Area

High Torna

do

POD (in tor)

Overall POD: 0.58; F2+: 0.83

Tornadoes: 2003 (1484 tornado segments)0-

6 km

She

ar

100 mb ML CAPE

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

Overall POD: 0.61; F2+: 0.90


6 km

She

ar

100 mb ML CAPE

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

Overall POD: 0.57; F2+: 0.82


6 km

She

ar

100 mb ML CAPE

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

Overall POD: 0.60; F2+: 0.77


6 km

She

ar

100 mb ML CAPE

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

Overall POD: 0.55; F2+: 0.82


6 km

She

ar

100 mb ML CAPE

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

Overall POD: 0.60; F2+: 0.84


6 km

She

ar

100 mb ML CAPE

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

Overall POD: 0.70; F2+: 0.82

Tornadoes: 2009 (Jan-Aug) (1130 tornado segments)0-

6 km

She

ar

100 mb ML CAPE

20 ms-1

10 ms-1

30 ms-1

40 ms-1

50 ms-1

Summary

• Tornado forecast improvement needed for marginally supportive environments

• Low CAPE – High Shear Environments– low conditional probability, very high potential impact

– distinct challenges for communication and societal response

• Modest CAPE – Modest Shear Environments

• Dimensions of Forecast Skill Variability• Regional & Annual Variation in Environments

• Supports queries to explore research and operational questions

• Provides an initial estimate of forecast difficulty

New Guidance

NOAA Hazardous Weather Testbed

EFP

EWPGOE

S-R PG

ExperimentalForecastProgram

ExperimentalWarningProgram

Prediction of hazardous weather events from a few hours to a

week in advance

Detection and prediction of hazardous weather events up to

several hours in advance

HWT strategy is to engage wider range of community

Testbed R20 Process

pathway for operational assessment and feedback

SPC-NSSL HWT

Forecast Focused Community Collaboration

Forecast Focused Community Collaboration

• Collaboration has grown steadily since 1997

• Focus on making an experimental forecasts

• Forecasters, Researchers, Numerical Modelers

• Community contributed experimental forecasts

• NOAA (NSSL, ESRL, NCEP)

• University of Oklahoma (CAPS)

• NCAR, AFWA, UK Meteorological Office

• Collaborations have spurred community momentum

We are rapidly approaching a new era in numerical weather prediction

High-resolution models can provide details important to prediction of high impact weather events

21 hour forecasts for a tornado outbreak on 15 Nov 2005

12 km North

American

Model

3 hour

precipitation

Experimental

4.5 km WRF-

NMM

Radar

Reflectivity

2005 Capability

Ensembles: Explore & Define UncertaintyARW – CNARW – CN ARW – C0ARW – C0 NMM – CNNMM – CN NMM – C0NMM – C0 ARPS – CNARPS – CN ARPS – C0ARPS – C0

Observed Radar ReflectivityObserved Radar Reflectivity

18 hr Forecast - 1 km “Radar”18 hr Forecast - 1 km “Radar”

HWT 2009

Spring Experiment

HWT 2009

Spring Experiment

Probability Updraft Helicity > 50 m2/s2

Supercell Forecast (26 hour)

Radar BREF 0142 UTC 22

Apr 2008

F026: Valid 02 UTC 22 Apr

2008

Updaft Helicity > 50 m2s-2 within

25 miles

Supercell Observed

Probability Updraft Helicity > 50 m2/s2

Looking south from Norman, OK (0145 UTC 22 Apr 2008)(Numerous large hail reports up to 2.25 inch)

Jack Hales

Vision: Warn-on-Forecast

NSSL Warn on Forecast Briefing March 5, 2007

The warning issued based on the computer model forecast(s) includes detailed information on the expected event

Radar and Initial Forecast at 2100 CST Radar at 2130 CST: Accurate Forecast

MostLikely

TornadoPath

T=2120 CST

T=2150

T=2130T=2140

70%

50%

30%

T=2200 CST

Developing Thunderstorm

MostLikely

TornadoPath

T=2120 CST

T=2150

T=2130T=2140

T=2200 CST

An ensemble of storm-scale NWP models predict the path of a potentially

tornadic storm. A Warning is Issued!

70%

50%

30%

• Triple current Tornado Warning lead times

• Support enhanced community response

Aviation Impacts from Thunderstorms

Observed Aviation impacts

7:00 pm 18 April 2008

26 hour Forecast of a Squall Line at 7:00 pm 18 April 2008

Hazardous Weather Testbed Experimental

Forecast

• Adverse weather costs approximately $30B / year• Thunderstorms cause two-thirds of all delays

• Support improved airspace management

Challenges• Service & Societal Challenges

• Effective communication of threat & uncertainty• Create a continuous decision support hazardous weather

information stream

• Major Science Challenges• the convective initiation challenge • impacts of mesoscale variability on storm predictability• appropriate NWP resolutions for severe storm prediction• advanced cloud microphysics & BL for storm scale NWP• radar (& other) data assimilation for storm scale NWP• extraction of storm information from high resolution NWP• perturbation strategies for storm scale ensembles • extraction of probabilistic information from storm scale

ensembles

New Software Tools

Real Time Queries to Storm DB

Ensemble Vertical Profiles

New Verification

• Support a dynamic learning environment• Provide insights into tactical & strategic challenges

Daily Context Based Verification

• 70 % of all tornadoes (2006)


• 13 % of tornadoes (2006)


All Supercells (2006)

Weak Storm Organization (2006)

QLCS & Bows - no Supercells (2006)

All “Significant” Reports (2006)

Future DB & Verification Work

• Add storm attributes • supercell, bow echo, QLCS

• Also applicable to NWS Warning problem

• Automated storm categorization algorithms in future

• Improve near Real Time Forecaster Feedback• Refine measures of forecast difficulty• Provide interactive forecaster access to database• Extend using climate reanalysis• Both Strategic & Tactical (Forecaster) Efforts

Forecast InformationDecision Support Services

Watch Hazard Probabilities

All watches are not created equal

Use the probabilities to refine the specific threat within the watch and

gauge forecaster confidence in the specific convective hazards

Operational since 2006

Current Internet Test for Public Watch… Hazard Probability Based Message (CTA)

URGENT - IMMEDIATE BROADCAST REQUESTED SEVERE THUNDERSTORM WATCH NUMBER 266 NWS STORM PREDICTION CENTER NORMAN OK

455 AM CDT FRI MAY 8 2009

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

NORTHERN ARKANSAS SOUTHEAST KANSAS SOUTHERN MISSOURI

NORTHEAST OKLAHOMA

EFFECTIVE THIS FRIDAY MORNING FROM 455 AM UNTIL NOON CDT.

...THIS IS A PARTICULARLY DANGEROUS SITUATION...

STORMS WITHIN THE WATCH AREA ARE EXPECTED TO PRODUCE

WIDESPREAD DAMAGING WINDS... WITH WIND GUSTS TO 80 MPH LIKELY.

WIDESPREAD LARGE HAIL TO 2.0 INCHES IN DIAMETER. ISOLATED TORNADOES.

DANGEROUS LIGHTNING WILL ALSO ACCOMPANY THESE STORMS.

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 …

A Derecho is

Forecast

Current Internet Test for Public Watch … Hazard Probability Based Message (CTA)

URGENT - IMMEDIATE BROADCAST REQUESTED SEVERE THUNDERSTORM WATCH NUMBER 266 NWS STORM PREDICTION CENTER NORMAN OK

455 AM CDT FRI MAY 8 2009

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

NORTHERN ARKANSAS SOUTHEAST KANSAS SOUTHERN MISSOURI

NORTHEAST OKLAHOMA

EFFECTIVE THIS FRIDAY MORNING FROM 455 AM UNTIL NOON CDT.

...THIS IS A PARTICULARLY DANGEROUS SITUATION...

STORMS WITHIN THE WATCH AREA ARE EXPECTED TO PRODUCE

WIDESPREAD DAMAGING WINDS... WITH WIND GUSTS TO 80 MPH LIKELY.

WIDESPREAD LARGE HAIL TO 2.0 INCHES IN DIAMETER. ISOLATED TORNADOES.

DANGEROUS LIGHTNING WILL ALSO ACCOMPANY THESE STORMS.

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 …

A Derecho is

Forecast

Add Societal Dimensions

U.S. Population Density Data (persons km-2) 2000 Census: 30 arc sec grid (calculations

on 1km grid)

May 5, 2007 Tornado High Risk

•354,381 people in risk area

•1.7% of area has pop >10/km2


Feb 5, 2008 Tornado High Risk

•2,826,940 people in risk area



Hypothetical Tornado High Risk

•9,893,380 people in risk area



Some Current SPC Initiatives• Refine and Expand Public Weather Outlook

• Add criteria based on potential societal impact

• Overnight violent tornado threat (began 1 December)

• Refine message to focus response & improve dissemination

• Work with partners to identify additional needs

• Refine Convective Watch Suite (FY11)• Hazard probability based wording to highlight threat

• Refine focus on partner & customer needs

• Adapt HWT for Diverse Challenges• Aviation, Cool Season Severe, Regional Hazards

• Science, Forecast Tools, Services & Society

Continuing SPC Challenges• Services to Support Improved Decisions

• continuous stream of probabilistic hazard information– rapid update, enhanced-time-resolution outlooks

– evolving convective watches with partner driven attributes

– support and seamlessly blend with local office & partner services

– support cascade to Warn-on-Forecast (Warn-on-Detection)

• distinguish forecast information from service delivery

• Adapt services to evolving needs– high impact weather (severe, fire, aviation, convection, OCONUS)

• Adapt staff to evolving science & business model• Create a dynamic and sustained learning environment

www.spc.noaa.gov

[email protected]

Subjective Probability Forecasts at the NWS Storm Prediction Center

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