Weather Analysis & Forecasting
Chapter 12
- Weather Forecasts
-
Hunter College,
Geography Department Weather Station
- National Weather Service (a branch of National
Oceanic and Atmospheric Administration, NOAA)
- Provides the following forecasts and warnings for the US
and its territories, free:
- Weather
- Hydrologic
- Climate
- Most important services include forecasts and warnings of
hazardous weather including:
- thunderstorms
- flooding
- hurricanes
- tornadoes
- winter weather
- extreme heat
- Emergency Management Agency says 80% of all declared
emergencies are weather related.
- DOT states that more than 6000 fatalities per year can be
attributed to the weather.
- Heat waves claim approximately 1000 lives per year.
- The 1993 Mississippi River Valley flood claimed 48 lives
and caused more than $15 billion in damages.
- Property damage due to wind, hail, snow and tornadoes
increased more than 500% from 1986 to 1995.
- The process of providing weather forecasts and warnings
occurs in three stages:
- collect and analyze global atmospheric data to provide a
picture of its current state.
- apply a variety of techniques to establish the future state
of the atmosphere - weather forecasting.
- Disseminate the forecasts to the public, mainly through the
private sector (e.g., The Weather Channel, AccuWeather, CNN).
- Weather forecasting is EXTREMELY important to us.
- Weather Analysis (current atmospheric conditions)
- World Meteorological Organization (WMO) is
responsible for international exchange of weather data.
- Data collected four times each day (at 0000, 0600, 1200 and
1800 Greenwich Mean Time) from:
- 10,000 land surface stations.
- 7,000 ships.
- 3,000 data buoys.
- Data also collected from:
- weather satellites
- radiosondes (weather balloons)
- US Weather Data Collection
- International and domestic weather data collected by the
National Center for Environmental Prediction near Washington, DC. This
branch of the NWS prepares weather maps, charts and forecasts on a global and
national scale.
- Weather information is disseminated to the 119 Weather
Forecast Offices where it is used to produce local and regional weather
forecasts. These offices also gather and submit weather data to the NWS.
- The same information is provided free to private weather
companies such as AccuWeather and WeatherData.
- Debris Flow
Forecasting - San Francisco
- Synoptic (coincident in time) Weather Maps display weather
conditions at a given moment in time.
- Weather Forecasting - complex and quantitative.
- Synoptic Weather Forecasting - techniques are
employed to extrapolate future conditions from current conditions.
- Techniques include:
- persistence forecasting
- trend forecasting
- analog method
- Analog Method - looks at a developing cyclonic storm
and compares it to the behavior of similar weather systems from the past. Was
the primary method of weather forecasting in the 1950s and 1960s. Today, had
been replaced by other methods although still used for 24-48 hour forecasts
and to forecast specific events, such as when a rain storm will arrive at a
specific location.
- Numerical Weather Forecasting:
- Relies on the physical laws of the atmosphere to predict
its future state.
- Complex computer models are used that require billions of
calculations.
- Slight variations in initial conditions can produce very
different forecasts so multiple runs of the model are run.
- Forecasters make the final decision on which model run to
use.
- The final forecast is a blend of different model data and
input from satellite images, RADAR and other sources.
- The NWS produces generalized forecast charts of the future
condition of the atmosphere called prognostic charts.
- Meteorologists use the prognostic charts, their
professional experience and "rules of thumb" from the analog method to project
future sites of cyclogenesis.
- The general prognostic charts are sent to the 119 weather
forecasting offices where the data are blended with local conditions,
numerical predictions and the weather quirks of of the region into a
site-specific forecast.
- Statistical Methods - can be used to predict a
single aspect of the weather such as the daily high temperature.
- Techniques Used in Short-Range Forecasting
- Persistence Forecasts - simplest forecasting
technique based on the tendency of the weather, at a given site, to remain
unchanged for several hours, or even a day or so.
- Trend Forecasting - related to persistence
forecasting, assumes that the weather upstream will persist and move on to
affect the area in its path. Not good for predicting short-lived weather
situations or small-scale weather such as tornadoes, hail storms or
thunderstorms.
- Long-Range Forecasts - not a weather forecast in the
usual sense. Predicts whether an area will have near-normal temperature and
precipitation conditions or not.
- Forecast Accuracy - have improved significantly
during the past 20 years. Beyond 7 days, forecasts are no more accurate than
projections made from climatic data.
- Tools of Weather Forecasting
- Automated Surface
Observing Systems (ASOS) - about 1000 will be deployed in places
currently outside the observational network.
- Advanced Weather Interactive Processing Systems (AWIPS) -
computer network
- NEXRAD (Next Generation Weather RADAR) - not used to
predict small scale weather phenomena but to detect and track.
- Satellites in Weather Forecasting
- 1960 - TIROS (Television & Infra-Red
Observation Satellite) launched.
- 1964 - Second generation Nimbus satellite.
- Polar orbiting weather
satellites with 100 minute orbits.
- 1966 - Geostationary
satellites
- Types of imagery:
- Visible
- Emitted IR - used to view cloud tops. Higher clouds
are colder and have more precipitation.
- Water-vapor - 6.7 micrometer wavelength energy
emitted by water vapor. Bright regions mean high water vapor content.
- GOES (Geostationary Operational Environmental
Satellites) - provide visible,
IR and water vapor
images every 30 minutes.
