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Weather Forecasting - I

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Title: Weather Forecasting - I


1
Weather Forecasting - I
2
Review of Chapter 12
  • The polar front model (Norwegian model) of a
    developing mid-latitude cyclonic storm represents
    a simplified but useful model of how an ideal
    storm progresses through the stages of birth,
    maturity and dissipation.
  • Cyclogenesis, lee-side lows, northeasters, bombs.
  • For a surface mid-latitude cyclonic storm to
    form, there must be an area of upper-level
    divergence above the surface low. For the surface
    storm to intensify, this region of upper level
    divergence must be greater than surface
    convergence.

3
Another way of looking at it.
4
Review of Chapter 12
  • When the polar-front jet stream develops into a
    looping wave, it provides an area of upper-level
    divergence for the development of surface
    mid-latitude cyclonic storms.

5
Review of Chapter 12
  • The curving nature of the polar-front jet stream
    tends to direct surface mid-latitude cyclonic
    storms northeastward and surface anticyclones
    southeastward.
  • Skip the sections Conveyor belt model of
    mid-latitude cyclones. A developing mid-latitude
    cyclone the March storm of 1993. Vorticity,
    divergence, and developing mid-latitude cyclones.
    Earth vorticity, relative vorticity and absolute
    vorticity. Putting it all together a monstrous
    snowstorm. Polar lows.

6
Importance of forecasting air-travel
7
Importance of forecasting
8
Importance of forecasting
9
Acquisition of Weather Information
  • Surface measurements (surface weather stations)
  • Land (more than 10,000 stations)
  • Ocean (ships, buoys, drifting automatic stations)
  • Upper air data radiosondes, aircraft,
    satellites

10
Collection and Exchange of Weather Information
  • The World Meteorological Organization (WMO) UN
    agency, 175 nations, standardization and exchange
    of data.
  • World Meteorological Centers Melbourne, Moscow,
    Washington D.C.
  • National Center for Environmental Prediction
    (NCEP)
  • Camp Springs, MD.
  • Data analysis, preparation of weather maps,
    prediction of the weather over the country.
  • Weather Forecast Offices (WFO)
  • Regional weather maps
  • National Weather Service
  • Advisories and warnings for severe weather
  • Advisory less hazardous conditions due to wind,
    dust, fog, snow, sleet, freezing rain
  • Watch atmospheric conditions favor hazardous
    weather, actual location and timing of occurrence
    is uncertain
  • Warning hazardous weather is imminent or
    actually occurring

11
Organizational structure
  • US Department of Commerce
  • National Oceanic and Atmospheric Administration
    (NOAA)
  • National Ocean Service (NOS) and National
    Geodetic Survey (NGS)
  • National Environmental Satellite, Data, and
    Information Service (NESDIS)
  • National Marine Fisheries Service (NMFS)
  • Program Planning and Integration (PPI)
  • Office of Oceanic and Atmospheric Research (OAR)
  • National Weather Service (NWS)
  • National Centers for Environmental Prediction
    (NCEP)
  • Aviation Weather Center (AWC)
  • Climate Prediction Center (CPC)
  • Environmental Modeling Center (EMC)
  • Hydrometeorological Prediction Center (HPC)
  • Ocean Prediction Center (OPC)
  • NCEP Central Operations
  • Space Environment Center (SEC)
  • Storm Prediction Center (SPC)
  • Tropical Prediction Center (TPC)
  • - National Hurricane Center (NHC)

Gary Locke
12
Weather Warnings
  • Wind Advisory Winds between 25-39 mph
  • High Wind Warnings Winds above 40 mph
  • Wind Chill Advisory Wind-chill temperatures -30
    to -35F and below
  • Heat Advisory/warning Daytime heat index reaches
    105F/115F or higher for 3 or more hours.
  • Flash Flood Watch Heavy rain may result in
    flash flood in the area.
  • Flash Flood Warning Flash flooding is occurring
    in the area.
  • Severe Thunderstorm Watch Thunderstorm with
    winds above 57 mph are possible.
  • Severe Thunderstorm Warning Thunderstorms with
    winds above 57 mph have been visually sighted

13
Weather Warnings
  • Tornado Watch/Warning Tornado may/has
    develop(ed) in the area
  • Snow Advisory There is a substantial snowfall
    expected in the area 2 in. or more in 12 hrs or
    3 in. or more in 24 hrs.
  • Blizzard Warning Snow with winds exceeding 35
    mph, visibility less than ¼ mi for several hours.
  • Small Craft Advisories Winds from 21-39 mph can
    be expected.
  • Gale Warnings Winds range from 39-54 mph in the
    area.
  • Hurricane Watch A hurricane or a tropical storm
    is a threat to a costal line. Be prepared!
  • Hurricane Warning The storm appears to be
    striking the area within 24 h. It is time to get
    out!

14
Forecasting Methods
  • Weather prediction by hand
  • Charts and maps have been drawn and analyzed by
    hand.
  • The upper air motion determines the general
    direction of movement of the weather systems and
    the likely location for the development of
    storms.
  • Relatively accurate short term forecasts.
  • Impractical for long term forecasts.
  • Numerical weather prediction
  • An atmospheric numerical model is used to
    describe the atmosphere set of equations that
    describe how the atmospheric temperature,
    pressure, winds, moisture will change with time.
  • The area of interest is covered by a
    3-dimensional grid, the equations are solved at
    the grid points (4 km or more apart)
  • The current atm. conditions are used to calculate
    the atm. properties after some time (time step).
  • The process is repeated as the calculated atm
    parameters are used to make a new calculation

15
Current Weather Conditions
16
Gainesville 10-day forecast
Do you believe the 10th day forecast?
17
Why the forecasts are not perfect?
  • Short term forecasts (3-5 days) are usually
    rather accurate.
  • Long term forecasts have large uncertainties
  • Sources for errors
  • Observations
  • Inaccuracy in the measurements
  • Uneven distribution of the observing stations
  • The coverage of the Earth is not complete
  • The theoretical models
  • The models are somewhat simplified.
  • Not all the physics is well understood
  • The computer simulations
  • Round-off errors
  • Model grid resolution
  • Small scale turbulence and chaotic processes are
    rather typical for the atmosphere and this makes
    predictions difficult.

18
Prognostic charts (progs) from two different
models
  • Somewhat different results but the trend is the
    same!

Upper level maps of pressure at constant height
surfaces.
19
Forecasting Tools
  • AWIPS Advanced Weather Interactive Processing
    System
  • Meteogram collection of observations at a given
    station over some time
  • Sounding vertical profile of the temperature,
    due point T and wind.

20
Forecasting Methods (1)
  • Persistent forecast (short term forecast) There
    is no reason for the weather conditions to
    change.
  • Steady state forecast (trend method). If we know
    the speed and the direction of the weather
    system, we can extrapolate its future location.
  • Analogue forecast (pattern recognition) I have
    seen this atmospheric conditions before and based
    on what happened back then, I can predict the
    weather today or tomorrow.
  • Statistical forecast the forecast is made based
    on past computer simulations that are weighted
    for the actual humidity, cloud cover, wind
    direction.

21
Forecasting Methods (2)
  • Probability forecast based on historical data.
    What is the chance to snow in Gainesville on
    Christmas?
  • Weather type. Uses general criteria such as the
    position of the subtropical highs, upper-level
    flow, prevailing storm track
  • Climatological forecast Based on information for
    the typical weather conditions at a given
    location for a given season.

22
Probability of a White Christmas
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