Chapter 13 Weather Analysis and Forecasting Weather Studies Introduction to Atmospheric Science American Meteorological Society Credit: This presentation.

Chapter 13Chapter 13

Weather Analysis Weather Analysis

and Forecastingand Forecasting

Weather StudiesWeather Studies Introduction to Atmospheric ScienceIntroduction to Atmospheric Science

American Meteorological SocietyAmerican Meteorological Society

Credit: This presentation was prepared for AMS by Michael Leach, Professor of Geography at New Mexico State University - Grants

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Case-in-PointCase-in-Point Tornado forecasting began in the late 19Tornado forecasting began in the late 19thth century century

– Started by John P. Finley, U.S. Army Signal CorpsStarted by John P. Finley, U.S. Army Signal Corps 1884: about 950 “tornado reporters” were gathering data1884: about 950 “tornado reporters” were gathering data Finley established criteria for a valid tornado sightingFinley established criteria for a valid tornado sighting

– Finley’s forecasting lasted only 2 yearsFinley’s forecasting lasted only 2 years U.S. Army Signal Corps discontinued the program in 1886U.S. Army Signal Corps discontinued the program in 1886

– The word “tornado” was disallowed in Signal Corps forecasts The word “tornado” was disallowed in Signal Corps forecasts because it might cause the public to panicbecause it might cause the public to panic

– Late 1940s and early 1950s, Air Force meteorologists Fawbush and Miller Late 1940s and early 1950s, Air Force meteorologists Fawbush and Miller developed a method for forecasting tornadoesdeveloped a method for forecasting tornadoes Forecasts were primarily issued for military installationsForecasts were primarily issued for military installations Interest in tornado forecasting stemmed from tornado that struck Interest in tornado forecasting stemmed from tornado that struck

Tinker Air Force Base in Oklahoma City, OK on 20 March 1948Tinker Air Force Base in Oklahoma City, OK on 20 March 1948 Developed a list of six atmospheric conditions that preceded tornado Developed a list of six atmospheric conditions that preceded tornado

outbreakoutbreak– Those conditions reappeared 5 days laterThose conditions reappeared 5 days later– Issued first tornado forecastIssued first tornado forecast

– Eventually, U.S. Weather Bureau adopted/allowed tornado forecasting Eventually, U.S. Weather Bureau adopted/allowed tornado forecasting for public distributionfor public distribution

– Severe Local Storm Warning Center (now the Storm Prediction Severe Local Storm Warning Center (now the Storm Prediction Center) was established in Norman, OK Center) was established in Norman, OK

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Driving QuestionDriving Question What is the process involved in making a scientific What is the process involved in making a scientific

forecast of the weather?forecast of the weather?– Weather effects everyoneWeather effects everyone– Forecasts quite accurate out to 7 daysForecasts quite accurate out to 7 days– Weather prediction will never be perfectWeather prediction will never be perfect

Incomplete information on initial state of atmosphereIncomplete information on initial state of atmosphere Some scientific questions not yet answeredSome scientific questions not yet answered Short range forecasts still surprisingly accurateShort range forecasts still surprisingly accurate

– U.S. National Weather Service (NWS)U.S. National Weather Service (NWS) An agency of the National Oceanic and Atmospheric An agency of the National Oceanic and Atmospheric

Administration (NOAA)Administration (NOAA) Issues 24-hour forecasts with 85% accuracyIssues 24-hour forecasts with 85% accuracy

– This chapter covers: How forecasts are madeHow forecasts are made Limits of forecast accuracyLimits of forecast accuracy Making your own weather forecastsMaking your own weather forecasts

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International CooperationInternational Cooperation International Meteorological Organization (IMO) founded International Meteorological Organization (IMO) founded

in 1878in 1878 - - IMO became the World Meteorological OrganizationIMO became the World Meteorological Organization (WMO) (WMO)

Headquartered in Geneva, SwitzerlandHeadquartered in Geneva, Switzerland Agency of the United NationsAgency of the United Nations Coordinates the efforts of 189 nations and territories in global Coordinates the efforts of 189 nations and territories in global

weather-monitoring program called World Weather Watch (WWW)weather-monitoring program called World Weather Watch (WWW) - WWW makes meteorological information available - WWW makes meteorological information available

internationallyinternationally Global Observing SystemGlobal Observing System

– Data from 5 geostationary and 4 polar orbiting satellites,10,000 land Data from 5 geostationary and 4 polar orbiting satellites,10,000 land stations, 7,000 ships at sea, reconnaissance and commercial aircraft, stations, 7,000 ships at sea, reconnaissance and commercial aircraft, radar, radiosondes, and buoysradar, radiosondes, and buoys

– Data transmitted to 3 WMO Centers where maps and charts are Data transmitted to 3 WMO Centers where maps and charts are created. Forecasts can then be prepared.created. Forecasts can then be prepared.

– Maps/forecasts are sent to Regional Specialized Meteorological Maps/forecasts are sent to Regional Specialized Meteorological Centers.Centers.

– National Centers for Environmental Prediction (NCEP) National Centers for Environmental Prediction (NCEP) responsible for U.S. forecastsresponsible for U.S. forecasts

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International CooperationInternational Cooperation

- Weather forecasting entails:- Weather forecasting entails: Acquisition of present weather dataAcquisition of present weather data Graphical depiction of the state of the Graphical depiction of the state of the

atmosphereatmosphere Analysis of data and mapsAnalysis of data and maps Prediction of the future state of the Prediction of the future state of the

atmosphereatmosphere Dissemination of weather information and Dissemination of weather information and

forecasts to the publicforecasts to the public

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Acquisition of Weather DataAcquisition of Weather Data Surface Weather ObservationsSurface Weather Observations

– Over 2,000 stations across the U.S. Over 2,000 stations across the U.S. operated by:operated by: National Weather Service (NWS) National Weather Service (NWS)

personnelpersonnel Staff of other government agencies, Staff of other government agencies,

including the Federal Aviation including the Federal Aviation Administration (FAA)Administration (FAA)

Private citizens or businessesPrivate citizens or businesses

Automated stations also located in Automated stations also located in unmanned locationsunmanned locations National Data Buoy CenterNational Data Buoy Center

Data gathered for preparation of Data gathered for preparation of weather maps and forecasts, weather maps and forecasts, exchange with other nations, and use by exchange with other nations, and use by aviationaviation

– Observations taken simultaneouslyObservations taken simultaneously Use Coordinated Universal Time (UTC)Use Coordinated Universal Time (UTC)

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Acquisition of Weather DataAcquisition of Weather Data Surface Weather Observations, cont.

– Automated Surface Observing System (ASOS) and communication ports

Result of 1990s NWS modernization 862 ASOS units in continual operation Reports temperature (ambient, dewpoint),

pressure (sea-level, altimeter setting), wind (direction, speed), precipitation accumulation, visibility, obstruction to vision, present weather, and sky condition

– Automated Weather Observation System (AWOS)

Similar to ASOS Located at 429 smaller airports

– NWS Cooperative Observer Network Volunteers Provide daily precipitation, and temperature

readings

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Acquisition of Weather DataAcquisition of Weather Data Upper-Air Weather ObservationsUpper-Air Weather Observations

– RadiosondesRadiosondes Radio-equipped instrument packageRadio-equipped instrument package Transmits upper air information to a ground station (rawinsonde Transmits upper air information to a ground station (rawinsonde

observation)observation)

Map showing locations of rawinsonde stations. Sites in Map showing locations of rawinsonde stations. Sites in red are part of the International Global Climate Observing red are part of the International Global Climate Observing SystemSystem

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Weather Data Assimilation, Weather Data Assimilation, Depiction and AnalysisDepiction and Analysis

Weather reported by each observation station is depicted on a map by a station model


Surface weather Surface weather mapsmaps– IsobarsIsobars

Connect points Connect points of equal air of equal air pressurepressure

Isobaric analysis Isobaric analysis reveals locations reveals locations of anticyclones of anticyclones (highs) and (highs) and cyclones (lows), cyclones (lows), troughs and troughs and ridges, and ridges, and horizontal horizontal pressure pressure gradientsgradients

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Surface Weather Maps, continuedSurface Weather Maps, continued– Cyclone centers are indicated by the symbol Cyclone centers are indicated by the symbol L (Low)L (Low)

Closely spaced isobars around cyclone indicate steep pressure Closely spaced isobars around cyclone indicate steep pressure gradient and strong windsgradient and strong winds

Fronts originate at storm centersFronts originate at storm centers

– Anticyclone centers are mapped as an Anticyclone centers are mapped as an H (High)H (High) Usually a relatively weak horizontal pressure gradient, shown Usually a relatively weak horizontal pressure gradient, shown

by widely spaced isobars, resulting in weak or calm windsby widely spaced isobars, resulting in weak or calm winds

– Synoptic surface maps are drawn every 3 hours for Synoptic surface maps are drawn every 3 hours for North America, and every 6 hours for the Northern North America, and every 6 hours for the Northern

HemisphereHemisphere

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Weather Data Assimilation, Weather Data Assimilation, Depiction, and AnalysisDepiction, and Analysis

Upper-Air Weather Upper-Air Weather MapsMaps Plotted on constant- Plotted on constant-

pressure surfacespressure surfaces Height contours labeled in Height contours labeled in

meters above sea level, meters above sea level, drawn 60 m apartdrawn 60 m apart

Altitude of pressure Altitude of pressure surface varies primarily surface varies primarily because of mean because of mean temperature differencestemperature differences Air pressure drops Air pressure drops

more rapidly in cold air more rapidly in cold air than in warm, due to than in warm, due to density differencesdensity differences

Isotherms plotted as Isotherms plotted as dashed linesdashed lines

Sample 500-mb analysis (NOAA)Sample 500-mb analysis (NOAA)

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Upper-Air Weather Maps, continued– Cyclonic and anticyclonic curvature shown in contours by troughs

and ridges in the prevailing westerlies Center of a ridge is relatively warm with high height contours,

labeled with an H. Often linked to a warm-core anticyclone at the surface.

Center of a trough relatively cold with low height contours, labeled with an L. Often linked to a cold-core extra-tropical cyclone at the surface.

– Winds that blow across isotherms produce air advection Cold air advection occurs where winds blow from colder to

warmer locations Warm air advection occurs where winds blow from warmer to

colder locations


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AWIPS workstationAWIPS workstation

Deluge of real-time weather information spurred the development of computerized data management systems– McIDAS (Man-computer Interactive Data

Access System) Ingests weather data and organizes into

guidance products for potential users

– AWIPS (Advanced Weather Interactive Processing System)

Used by NWS Offices since 2000 Receives and organizes ASOS data plus

analysis and guidance products from NCEP Allows meteorologists to display, process,

and overlay images, graphics, and other data

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Weather PredictionWeather Prediction

Hydrometeorological Prediction CenterHydrometeorological Prediction Center– Issues short range 12, 24, 36, and 48-hr Issues short range 12, 24, 36, and 48-hr

forecastsforecasts– Medium range 3- to 7-day extended outlooks Medium range 3- to 7-day extended outlooks

issued each day, and outlooks up to 10 days issued each day, and outlooks up to 10 days are issued 3 times a weekare issued 3 times a week

Climate Prediction CenterClimate Prediction Center– Generates monthly (30-day), seasonal (90-day) Generates monthly (30-day), seasonal (90-day)

outlooks, and multi-seasonal outlooksoutlooks, and multi-seasonal outlooks

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Weather PredictionWeather Prediction Numerical Weather ForecastingNumerical Weather Forecasting

– Computers are programmed with a numerical model of Computers are programmed with a numerical model of the atmosphere; a model of mathematical equations that the atmosphere; a model of mathematical equations that relate wind, temperature, pressure, and water vapor relate wind, temperature, pressure, and water vapor concentrationconcentration

– Uses present data to predict values of atmospheric Uses present data to predict values of atmospheric properties for a grid of points on a uniform pressure properties for a grid of points on a uniform pressure surfacesurface

– Millions of computations go into 12, 24, 36, and 48-hr Millions of computations go into 12, 24, 36, and 48-hr forecastsforecasts

North American Mesosscale Model (NAM)North American Mesosscale Model (NAM)– Divides troposphere into 60 vertical layersDivides troposphere into 60 vertical layers– Forecasts every 6 hours out to 84 hoursForecasts every 6 hours out to 84 hours

Nested Grid Model (NGM)Nested Grid Model (NGM)– Atmosphere divided into 16 vertical layersAtmosphere divided into 16 vertical layers– Issues forecasts twice a dayIssues forecasts twice a day

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Eta ModelEta Model– Greater resolution than NGM, consists of 60 levelsGreater resolution than NGM, consists of 60 levels– Runs 4 times per dayRuns 4 times per day

Rapid Update Cycle (RUC)Rapid Update Cycle (RUC)– 50 levels with a horizontal resolution of 20 km50 levels with a horizontal resolution of 20 km– Short range (3–12 hrs) for general and aviation Short range (3–12 hrs) for general and aviation

forecastsforecasts– Frequency is every 1–3 hrsFrequency is every 1–3 hrs

Global Forecast System (GFS)Global Forecast System (GFS)– Has two 64 level models operating at different Has two 64 level models operating at different

resolutions and forecast periodsresolutions and forecast periods

Weather PredictionWeather Prediction Techniques used to optimize the skill of weather Techniques used to optimize the skill of weather

forecasting based on numerical models:forecasting based on numerical models:– Ensemble forecastingEnsemble forecasting

Numerical model generates several forecasts based on Numerical model generates several forecasts based on slightly different initial conditionsslightly different initial conditions

If forecasts are consistent, they are considered reliableIf forecasts are consistent, they are considered reliable

– Model ComparisonModel Comparison Comparison is made among forecasts produced by Comparison is made among forecasts produced by

different modelsdifferent models If they agree, the forecast is issued with a high level of If they agree, the forecast is issued with a high level of

confidenceconfidence

– If forecasts are inconsistent using either technique, If forecasts are inconsistent using either technique, forecast is considered unreliableforecast is considered unreliable

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Weather PredictionWeather Prediction Forecasting Tropical CyclonesForecasting Tropical Cyclones

U.S. Army Signal Corps was in charge of observation and forecasting U.S. Army Signal Corps was in charge of observation and forecasting early onearly on 1873: gathered reports from Cuba to help detect tropical cyclones1873: gathered reports from Cuba to help detect tropical cyclones

28 September 1874: first plotting of a hurricane28 September 1874: first plotting of a hurricane 1890: forecasting moved to civilians (U.S. Weather Bureau)1890: forecasting moved to civilians (U.S. Weather Bureau)

Little attention paid to tropical cyclonesLittle attention paid to tropical cyclones War caused increased interest in tropical cyclone forecastingWar caused increased interest in tropical cyclone forecasting

1898, Spanish-American War; fear that a hurricane could destroy U.S. 1898, Spanish-American War; fear that a hurricane could destroy U.S. fleetfleet

Increased number of weather stations in the CaribbeanIncreased number of weather stations in the Caribbean Technological advances greatly benefited understanding and Technological advances greatly benefited understanding and

monitoring of tropical cyclonesmonitoring of tropical cyclones Invention of radio allowed ship-to-shore reportsInvention of radio allowed ship-to-shore reports 1930s: upper air was monitored1930s: upper air was monitored 1950s: weather radar at coastal stations observed tropical storms1950s: weather radar at coastal stations observed tropical storms 1960s: remote sensing via satellites began1960s: remote sensing via satellites began Recently, buoys have provided additional informationRecently, buoys have provided additional information Aircraft can now deploy dropwindsondes (similar to a radiosonde) to Aircraft can now deploy dropwindsondes (similar to a radiosonde) to

receive sounding from inside stormreceive sounding from inside storm 1919

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Weather PredictionWeather Prediction Forecasting Tropical Cyclones, continuedForecasting Tropical Cyclones, continued

1940s: Atlantic hurricane forecasting split between Weather Bureau 1940s: Atlantic hurricane forecasting split between Weather Bureau offices in Miami, New Orleans, Washington, DC, Boston, and San Juanoffices in Miami, New Orleans, Washington, DC, Boston, and San Juan

1967: designated Miami office as the National Hurricane Center (NHC)1967: designated Miami office as the National Hurricane Center (NHC) Today, forecasting is split between NHC and the Central Pacific Today, forecasting is split between NHC and the Central Pacific

Hurricane Center in Honolulu.Hurricane Center in Honolulu. NHC responsible for issuing statements for tropical cyclones in Atlantic NHC responsible for issuing statements for tropical cyclones in Atlantic

basin and eastern Pacific basin to 140basin and eastern Pacific basin to 140°W°W CPHC activated when tropical cyclone develops in central Pacific CPHC activated when tropical cyclone develops in central Pacific Operates SLOSH model for prediction of storm surgesOperates SLOSH model for prediction of storm surges

NHC is a branch of the Tropical Prediction Center (TPC)NHC is a branch of the Tropical Prediction Center (TPC) TPC, under WMO agreement, has responsibility for prediction of tropical TPC, under WMO agreement, has responsibility for prediction of tropical

cyclones for 24 nationscyclones for 24 nations

Weather PredictionWeather Prediction Forecasting Tropical Cyclones, continuedForecasting Tropical Cyclones, continued

– Biggest challenge is predicting track and intensityBiggest challenge is predicting track and intensity Forecasts issued every 6 hours. Covered 72 hr periods until Forecasts issued every 6 hours. Covered 72 hr periods until

2001 when period was extended to 96 and 120 hrs2001 when period was extended to 96 and 120 hrs Track forecasts based on climatology, numerical models, and Track forecasts based on climatology, numerical models, and

experience of forecasterexperience of forecaster

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Track forecast for Hurricane Track forecast for Hurricane Katrina issued at 5 p.m. EDT Katrina issued at 5 p.m. EDT on 26 August 2005. The on 26 August 2005. The white area (“cone of white area (“cone of uncertainty”) encompasses uncertainty”) encompasses possible variations in the possible variations in the track based on output of track based on output of numerical models. (NOAA, numerical models. (NOAA, NHC) NHC)



Forecasting Tropical Cyclones, continuedForecasting Tropical Cyclones, continued SLOSH (Sea, Lake and Overland Surges from SLOSH (Sea, Lake and Overland Surges from

HurricanesHurricanes) model predicts location and height of storm predicts location and height of storm surgesurge

Probability forecast included in advisory statements Probability forecast included in advisory statements since 1983since 1983

Hurricane Watch: winds of at least 119 km (74 mi) Hurricane Watch: winds of at least 119 km (74 mi) possible with in the next 36 hourspossible with in the next 36 hours

Hurricane Warning: hurricane conditions expected in 24 Hurricane Warning: hurricane conditions expected in 24 hours or lesshours or less Watches and warnings also issues for tropical stormsWatches and warnings also issues for tropical storms

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During the 20During the 20thth century, tropical cyclone fatalities in century, tropical cyclone fatalities in the U.S. trended downward, whereas property the U.S. trended downward, whereas property damage trended upwarddamage trended upward

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Other Forecasting CentersOther Forecasting Centers Aviation Weather Center (AWC)Aviation Weather Center (AWC)

– Located in Kansas City, MOLocated in Kansas City, MO

– Supports FAASupports FAA

– Forecasts for aviation interestsForecasts for aviation interests

Storm Prediction Center (SPC)Storm Prediction Center (SPC)– Located in Norman, OKLocated in Norman, OK

– Forecasts severe stormsForecasts severe storms

– Also monitors fire weather, Also monitors fire weather, blizzardsblizzards

Other Forecasting CentersOther Forecasting Centers

River Forecast Centers River Forecast Centers (RFC)(RFC)– 13 centers located 13 centers located

nationwidenationwide– Develops river, reservoir, Develops river, reservoir,

and flood forecastsand flood forecasts– Monitors and forecasts Monitors and forecasts

river discharge and stageriver discharge and stage Marine ForecastingMarine Forecasting

– Ocean Prediction Center is Ocean Prediction Center is located in Camp Springs, located in Camp Springs, MDMD

– Issues forecasts, warnings, Issues forecasts, warnings, and guidance for mariners, and guidance for mariners, fisheries, and recreational fisheries, and recreational boatersboaters

Locations of RFCs and their Locations of RFCs and their regions of responsibilityregions of responsibility

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Weather PredictionWeather Prediction Forecast SkillForecast Skill

Weather forecasting skill declines rapidly for periods Weather forecasting skill declines rapidly for periods longer then 48 hrs, and is minimal beyond 10 dayslonger then 48 hrs, and is minimal beyond 10 days Missing or inaccurate observational dataMissing or inaccurate observational data Failure to detect all meso-scale and micro-scale Failure to detect all meso-scale and micro-scale

circulation systemscirculation systems Imprecise equations in numerical modelsImprecise equations in numerical models

1- to 5-day forecasting has shown slow but steady 1- to 5-day forecasting has shown slow but steady improvementimprovement Better understanding of atmospheric processesBetter understanding of atmospheric processes Larger and faster computersLarger and faster computers More reliable and sophisticated observational toolsMore reliable and sophisticated observational tools

Including Doppler radar and remote sensing by satelliteIncluding Doppler radar and remote sensing by satellite Denser weather observational networks worldwideDenser weather observational networks worldwide

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Weather PredictionWeather Prediction Computers aren’t likely to replace humansComputers aren’t likely to replace humans

The best forecasters rely on knowledge, experience, and The best forecasters rely on knowledge, experience, and intuition intuition

Begin with previous and current observationsBegin with previous and current observations Must analyze and interpret computerized predictionsMust analyze and interpret computerized predictions

Adapt those forecasts to regional and local circumstancesAdapt those forecasts to regional and local circumstances

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Weather PredictionWeather Prediction Long-Range ForecastingLong-Range Forecasting

Climate Prediction CenterClimate Prediction Center Camp Springs, MDCamp Springs, MD

Prepare 30-day (monthly) 90-day (seasonal) and 15-month (multi-Prepare 30-day (monthly) 90-day (seasonal) and 15-month (multi-seasonal) generalized climate outlooksseasonal) generalized climate outlooks

– Long range forecasting relies on Long range forecasting relies on teleconnectionsteleconnections: a : a linkage between changes in atmospheric circulation linkage between changes in atmospheric circulation occurring in widely separated regions of the globeoccurring in widely separated regions of the globe

30-day (monthly) outlooks rely on circulation patterns at 30-day (monthly) outlooks rely on circulation patterns at 700 mb level700 mb level Identifies areas of persistent warm and cold air advectionIdentifies areas of persistent warm and cold air advection

– 90-day (seasonal) outlooks rely on long-term trends and 90-day (seasonal) outlooks rely on long-term trends and recurring eventsrecurring events Computer attempts to match past trends with present conditionsComputer attempts to match past trends with present conditions

– 15-month (multi-seasonal) outlooks began in 199515-month (multi-seasonal) outlooks began in 1995 Each month 13 forecasts are issued, each covering a 3-month Each month 13 forecasts are issued, each covering a 3-month

period. Subsequent 3-month forecast overlaps the previous by period. Subsequent 3-month forecast overlaps the previous by two months.two months.

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Weather PredictionWeather Prediction Single-Station ForecastingSingle-Station Forecasting

Short-term weather prediction based on observations at one Short-term weather prediction based on observations at one locationlocation

Forecasts usually generalized and tentativeForecasts usually generalized and tentative– Fair-weather biasFair-weather bias

Fair-weather days outnumber stormy days almost everywhereFair-weather days outnumber stormy days almost everywhere Predicting all fair-weather days would be correct more then half the Predicting all fair-weather days would be correct more then half the

timetime

– PersistencePersistence Weather episodes persist for some period of time (i.e., if it has been Weather episodes persist for some period of time (i.e., if it has been

cold and storm for several days, it may continue that way for awhile)cold and storm for several days, it may continue that way for awhile)

– ClimatologyClimatology Forecast prepared based on previous years weatherForecast prepared based on previous years weather

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Weather Prediction


Private Sector ForecastingPrivate Sector ForecastingTelevision and radio stations, some Television and radio stations, some

newspapers, and private forecast servicesnewspapers, and private forecast servicesSome private meteorologists tailor forecasts to Some private meteorologists tailor forecasts to

specific needs of their commercial, agricultural, specific needs of their commercial, agricultural, or industrial clientsor industrial clients

Supplement the efforts of government Supplement the efforts of government forecastersforecasters

Communication and DisseminationCommunication and Dissemination

NCEP maps and charts transmitted to local NWS NCEP maps and charts transmitted to local NWS Forecast Offices to guide meteorologists in Forecast Offices to guide meteorologists in preparing local forecastspreparing local forecasts

Weather information then distributed to the publicWeather information then distributed to the public When hazardous weather threatens, NWS issues:When hazardous weather threatens, NWS issues:

Outlooks: provided for advanced noticeOutlooks: provided for advanced notice Watches: hazardous weather is possible based on Watches: hazardous weather is possible based on

current or anticipated conditionscurrent or anticipated conditions Warnings: hazardous weather is occurring in the region Warnings: hazardous weather is occurring in the region

or imminentor imminent Advisories: anticipated weather hazards; less serious Advisories: anticipated weather hazards; less serious

then those covered by warningsthen those covered by warnings

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Communication and DisseminationCommunication and Dissemination

NWS also issues:NWS also issues: Tornado Warning: detection of a thunderstorm that is Tornado Warning: detection of a thunderstorm that is

known or likely to produce a tornadoknown or likely to produce a tornado Heavy Snow Warning: snowfall of at least 10 to 15 cm Heavy Snow Warning: snowfall of at least 10 to 15 cm

(4 to 6 in.) expected in less then 12 hrs(4 to 6 in.) expected in less then 12 hrs Blizzard Warning: blowing or falling snow with sustained Blizzard Warning: blowing or falling snow with sustained

winds of 56 km (35 mi) per hr or higher, reducing winds of 56 km (35 mi) per hr or higher, reducing visibility to less then 400 m (1300 ft)visibility to less then 400 m (1300 ft)

Flash Flood Watch: flash flooding possible within watch Flash Flood Watch: flash flooding possible within watch areaarea

Flash Flood Warning: dangerously rapid rise in river Flash Flood Warning: dangerously rapid rise in river level is imminent or occurringlevel is imminent or occurring

Public receives weather reports and forecasts via Public receives weather reports and forecasts via radio, NOAA weather radio, TV, Internet, radio, NOAA weather radio, TV, Internet, newspapersnewspapers

Chapter 13 Weather Analysis and Forecasting Weather Studies Introduction to Atmospheric Science American Meteorological Society Credit: This presentation.

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