Transcript AMS Weather Studies

AMS Weather Studies
Introduction to Atmospheric Science, 5th Edition
Chapter 13
Weather Analysis
and Forecasting
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Driving Question
 What is the process involved in making a scientific
forecast of the weather?
 This chapter covers:
 How forecasts are made
 Limits of forecast accuracy
 Making your own weather forecasts
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Case-in-Point
Evolution of Tornado Forecasting
 Tornado forecasting
 1884: started by John P. Finley, U.S. Army Signal Corps
 950 “tornado reporters” were gathering data with criteria Finley established
 1886: program discontinued
 Word “tornado” disallowed in Signal Corps forecasts for fear of public panic
 1940-50s: Air Force meteorologists Fawbush and Miller developed method
for forecasting tornadoes
 Tornado struck Tinker Air Force Base in Oklahoma City, OK on 20 March 1948;
motivated Fawbush and Miller
 List of six atmospheric conditions that preceded tornado outbreak
 Those conditions reappeared 5 days later
 Issued first tornado forecast; accurate, saved lives and aircraft
 Primarily issued for military installations
 Eventually, U.S. Weather Bureau adopted/allowed tornado forecasting for
public distribution
 Severe Local Storm Warning Center (now the Storm Prediction Center)
established in Norman, OK
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 1952: ban on “tornado” with issue of first tornado watch
International Cooperation
 International Meteorological Organization (IMO) founded in 1878
 IMO became the World Meteorological Organization (WMO)
 Headquartered in Geneva, Switzerland, agency of the United Nations
 Coordinates the efforts of 189 nations and territories in global weathermonitoring program called World Weather Watch (WWW)
 Provides meteorological information available internationally
 Global Observing System
 Data from 6 geostationary and 3 polar orbiting satellites, 11,000 land stations,
4000 ships at sea, 3000 reconnaissance and commercial aircraft, radar, 1300
radiosonde stations, 1200 drifting and 1300 moored buoys
 Data transmitted to 3 WMO Centers where maps and charts are created,
forecasts prepared
 Maps/forecasts sent to Regional Specialized Meteorological Centers
 National Centers for Environmental Prediction (NCEP) responsible for
U.S. forecasts
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International Cooperation
Global Observing System
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International Cooperation
 Weather forecasting entails
 Acquisition of present weather data
 Graphical depiction of the state of the atmosphere
 Analysis of data and maps
 Prediction of the future state of the atmosphere
 Dissemination of weather information and forecasts
to the public
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Acquisition of Weather Data
 Surface Weather Observations
 Over 2,000 stations across the U.S. operated by
 National Weather Service (NWS) personnel
 Staff of other government agencies, including the
Federal Aviation Administration (FAA)
 Private citizens or businesses
 Automated stations also located in unmanned
locations
 National Data Buoy Center
 Data gathered for preparation of weather maps
and forecasts, exchange with other nations, and
use by aviation
 Observations taken simultaneously
 Use Coordinated Universal Time (UTC)
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Acquisition of Weather Data
 Surface Weather Observations, cont.
 Automated Surface Observing System (ASOS)
 Result of 1990s NWS modernization
 947 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, sky condition
 Automated Weather Observation System (AWOS)
 Similar to ASOS
 163 FAA-owned and 1149 non-Federal
 NWS Cooperative Observer Network
 Volunteers
 Provide daily precipitation, and temperature readings
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Acquisition of Weather Data
 Upper-Air Weather Observations
 Radiosondes
 Radio-equipped instrument package
 Transmits upper air information to a
ground station (rawinsonde
observation)
 92 radiosonde observation stations
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Acquisition of Weather Data
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Locations of radiosonde observation stations.
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Weather Data Assimilation, Depiction
and Analysis
Weather
reported by each
observation
station is
depicted on a
map by a station.
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Weather Data Assimilation, Depiction
and Analysis
 Surface weather maps
 Isobars:
 Connect points of
equal air pressure
 Isobaric analysis
reveals locations of
anticyclones and
cyclones, troughs and
ridges, horizontal
pressure gradients
 Drawn at 4-mb
intervals
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Weather Data Assimilation, Depiction
and Analysis
 Surface Weather Maps, cont.
 Cyclone centers are indicated by the symbol L (low)
 Closely spaced isobars around cyclone indicate steep pressure
gradient and strong winds
 Fronts originate at storm centers
 Anticyclone centers are mapped as an H (high)
 Usually a relatively weak horizontal pressure gradient, shown by
widely spaced isobars, resulting in weak or calm winds
 Synoptic surface maps are drawn every 3 hours for North
America, and every 6 hours for the Northern Hemisphere
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Weather Data Assimilation, Depiction
and Analysis
 Upper-Air Weather Maps
 Plotted on constant- pressure
surfaces
 Height contours labeled in
meters above sea level
 Drawn at 60 m intervals
Sample 500-mb analysis (NOAA)
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 Altitude of pressure surface
varies because of mean
temperature differences
 Air pressure drops more
rapidly in cold air than in
warm, due to density
differences
 Isotherms plotted as dashed
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lines
 Drawn at 5 C deg intervals
Weather Data Assimilation, Depiction
and Analysis
 Upper-Air Weather Maps, cont.
 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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Weather Data Assimilation, Depiction
and Analysis
 Computerized data management systems
 Spurred by deluge of real-time weather information
 AWIPS (Advanced Weather Interactive Processing System)
 Used by NWS Offices since 2000, AWIPS II began roll-out in 2011
 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 Prediction
 Hydrometeorological Prediction Center
 Short range: 12-, 24-, 36-, and 48-hr forecasts
 Medium range: 3- to 7-day extended outlooks
 Climate Prediction Center
 Long range: 6-10 day, 8-14 day, 30-day (monthly), 90-day (seasonal), and
multiseasonal outlook
 Numerical Weather Forecasting
 Computers programmed with numerical model of the atmosphere
 Model of equations relate wind, temperature, pressure, and water vapor
concentration
 Current data used to predict atmospheric properties only a few minutes
into the future, that prediction becomes the starting point for another few
minutes into the future, that prediction…
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 Repeated until 12-, 24-, 36-, and 48-hr forecasts are achieved
Weather Prediction
 Numerical Weather Forecasting
 Computers programmed with a numerical model of the
atmosphere
 Model of equations that relate wind, temperature, pressure, and
water vapor concentration
 Uses present data to predict values of atmospheric
properties for a grid of points on a uniform pressure surface
 Millions of computations go into 12, 24, 36, and 48-hr
forecasts
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Weather Prediction
 North American Mesoscale Model (NAM)
 Contains NOAA Environmental Modeling System (NEMS)
 Divides troposphere into 60 vertical layers
 Forecasts every 6 hours out to 84 hours
 Nested Window Run (NWR)
 Contains images from Weather Research and Forecast Model (WRF)
 Run 4x a day, forecasts at 3-hr increments to 2 days
 Rapid Update Cycle (RUC)
 Features 50 levels with horizontal resolution of 13 km
 Provides short-range, hourly numerical weather guidance
 Rapid Refresh (RR) scheduled to replace RUC
 Global Forecast System (GFS)
 64-level model operating at different19 resolutions and forecast periods
 Runs 4x a day
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Weather Prediction
 To optimize weather forecasting with numerical models:
 Ensemble forecasting
 Numerical model generates several forecasts based on slightly
different initial conditions
 If forecasts are consistent, they are considered reliable
 Model Comparison
 Comparison is made among forecasts produced by different
models
 If they agree, the forecast issued with a high level of
confidence
 If forecasts are inconsistent using either technique, forecast
is considered unreliable
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Weather Prediction
 Forecasting Tropical Cyclones
 U.S. Army Signal Corps initially in charge of observation/ forecasting
 1873: gathered reports from Cuba to help detect tropical cyclones
 28 September 1874: first plotted hurricane
 1890: forecasting moved to civilians (U.S. Weather Bureau)
 Little attention paid to tropical cyclones
 1898: Spanish-American War increased interest in tropical cyclone
forecasting
 Fear hurricane destroying U.S. fleet increased weather stations in the Caribbean
 Technological advances
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Invention of radio allowed ship-to-shore reports
1930s: upper air monitored
1950s: weather radar at coastal stations observed tropical storms
1960s: remote sensing via satellites began
Recently, buoys have provided additional information
Aircraft can now deploy dropwindsondes
(similar to a radiosonde) to receive
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sounding from inside storm
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Weather Prediction
 Forecasting Tropical Cyclones
 1940s: Atlantic hurricane forecasting split between Weather
Bureau offices in Miami, New Orleans, Washington, DC,
Boston, and San Juan
 1967: designated Miami office as the National Hurricane
Center (NHC)
 Today, forecasting split between NHC and the Central Pacific
Hurricane Center (CPHC) in Honolulu.
 NHC responsible for issuing statements for tropical cyclones in Atlantic
basin and eastern Pacific basin to 140°W
 Operates SLOSH model for prediction of storm surges
 CPHC activated when tropical cyclone develops in central Pacific
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Weather Prediction
 Forecasting Tropical Cyclones
 Predicting track and intensity
 Forecasts issued every 6 hours, up to 72, 96 and 120 hrs
 Track forecasts based on climatology, numerical models, and
experience of forecaster
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Weather Prediction
Atlantic hurricane track forecast error, and basin intensity forecast errors.
With lengthening forecast period, error increases.
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Weather Prediction
 Forecasting Tropical Cyclones
 SLOSH (Sea, Lake and Overland Surges from Hurricanes)
model predicts location and height of storm surge
 Probability forecast included in advisory statements since 1983
 Hurricane Watch: winds of at least 119 km (74 mi) possible
within the next 36 hours
 Hurricane Warning: hurricane conditions expected in 24
hours or less
 Watches and warnings also issued for tropical storms
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Weather Prediction
During the 20th century, tropical cyclone fatalities in the U.S.
generally trended downward. Property damage has trended
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upward since the 1980s
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Weather Prediction
 Aviation Weather Center (AWC)
 Located in Kansas City, MO
 Supports FAA
 Forecasts for aviation interests
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Weather Prediction
 Storm Prediction Center (SPC)
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Located in Norman, OK
Forecasts severe storms
Also monitors fire weather, blizzards
Convective outlooks identifying areas
expected to experience severe and nonsevere thunderstorms in 1-3 days.
 Issued several times a day
 Specify areas of severe thunderstorm risk
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Weather Prediction
SPC Day 1 convective outlook issued at 1259Z on 2 March 2012.
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Weather Prediction
 River Forecast Centers (RFC)
 13 centers located nationwide
 Develops river, reservoir, and flood forecasts
 Monitors and forecasts river discharge and stage
Locations of
River Forecast
Centers.
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Weather Prediction
 Marine Forecasting
 Ocean Prediction Center located in Camp Springs, MD
 Issues forecasts, warnings, guidance for mariners, fisheries
recreational boaters
 Space Weather Forecasting
 Space Weather Prediction Center (SWPC) located in Boulder, CO
 Monitors phenomena such as the aurora, solar wind, and solar cycle
 Scales used that rank severity from 1 to 5
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Weather Prediction
 Forecast Skill
 Declines rapidly after 48 hrs,
minimal beyond 10 days
 Missing or inaccurate observational data
 Failure to detect all mesoscale and micro-scale
circulation systems
 Imprecise equations in numerical models
 1-5 day forecasting
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Tracking an early winter cyclone.
Slow but steady improvement
Better understanding of atmospheric processes
Larger and faster computers
More reliable and sophisticated observational tools
Denser weather observational networks
worldwide
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Weather Prediction
 Computers won’t replace meteorologists
 The best forecasters rely on knowledge, experience, and intuition
 Begin with previous and current observations
 Must analyze and interpret computerized predictions
 Those forecasts are adapted to regional and local circumstances
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Weather Prediction
 Long-Range Forecasting
 Climate Prediction Center
 Monthly, seasonal and multi-seasonal generalized climate outlooks
 Long range forecasting relies on teleconnections
 Linkage between changes in atmospheric circulation occurring in widely
separated regions of the globe
 30-day (monthly) outlooks
 Relies on circulation patterns at 700 mb level
 Identifies areas of persistent warm and cold air advection
 90-day (seasonal) outlooks
 Relies on long-term trends and recurring events
 Computer attempts to match past trends with present conditions
 15-month (multi-seasonal) outlooks began in 1995
 Each month 13 forecasts are issued,
 Each covers a 3-month period
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 Subsequent 3-month forecast overlaps previous by 2 months
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Weather Prediction
 Single-Station Forecasting
 Short-term weather prediction based on
observations at one location
 Forecasts usually generalized and tentative
 Fair-weather bias
 Fair-weather days outnumber stormy days
almost everywhere
 Predicting all fair-weather days would be correct
more then half the time
 Persistence
 Weather episodes persist for some period of
time (if it has been cold and storm for several
days, it may continue that way for awhile)
 Climatology
 Forecast prepared based on previous years
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weather
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Weather Prediction
 Private Sector Forecasting
 Television and radio stations, some newspapers, and private
forecast services
 Some private meteorologists tailor forecasts to specific needs
of their commercial, agricultural, or industrial clients
 Supplement the efforts of government forecasters
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Communication and Dissemination
 NCEP maps and charts transmitted to local NWS
Forecast Offices to guide meteorologists in preparing
local forecasts
 Weather information then distributed to the public
 When hazardous weather threatens
 Outlooks: provided for advanced notice
 Watches: hazardous weather is possible based on current or
anticipated conditions
 Advisories: anticipated weather hazards; less serious then
those covered by warnings
 Warnings: hazardous weather is occurring in the region or
imminent
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Communication and Dissemination
 NWS also issues
 Tornado Warning: detection of a thunderstorm that is known or likely to
produce a tornado
 Heavy Snow Warning: snowfall of at least 10 to 15 cm (4 to 6 in.) expected
in less then 12 hrs
 Blizzard Warning: blowing or falling snow with sustained winds of 56 km
(35 mi) per hr or higher, reducing visibility to less then 400 m (1300 ft)
 Flash Flood Watch: flash flooding possible within watch area
 Flash Flood Warning: dangerously rapid rise in river level is imminent or
occurring
 Public receives weather reports and forecasts via radio, NOAA
weather radio, TV, Internet, newspapers
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