Weather Forecasting

2009

Predicting the weather

• People have needed to predict the weather since the dawn of time.

• Hunting, farming, and all outdoor work depends on the weather.

• Folklore grew around the observations people made.

A ring around the sun or moon, means that rain will come real soon.

Red sky at night, sailor's delight; red sky in the morning, sailor's take warning.

Modern Forecasting

•Relies on:

•Observation using various instruments

•Computer models

•Previous trends and patterns in the weather.

•Can be accurate up to five days in the future.

Trends and Patterns

•Meteorologists: Scientists that study the causes of weather and try to predict it.

•They use data collected over the past 100 or more years to make their predictions.

•So when they say “There is a 40% chance of rain today,” they mean that in the past, when the conditions were similar, it rained 40% of the time.

Weather Instruments

•A thermometer measures temperature. A barometer measures air pressure. A rain gauge measures precipitation. An anemometer measures wind speed.

•Weather vanes find wind direction.

•A psychrometer measures relative humidity.

Weather Technology

•New technologies have made short range (2 to 5 days or so) forecasting fairly reliable.

•They are now working on long range predictions.

•Changes in technology are making this possible:

•Satellites and computers.

Computer Models

•Computers can take millions of pieces of data and process this information to make predictions.

•Predictions are only as good as the computer model.

Weather Radar

•Uses Doppler radar to track moving storms and precipitation.

•NEXRAD is the new generation Doppler radar that tracks wind and precipitation.

•This allows tornadoes to be accurately tracked.

Weather Balloons •Weather balloons carry equipment up to 30 kms high

• A radiosonde attached to a weather balloon measures weather high in the atmosphere.

•This equipment records data and sends it to weather stations

Weather Satellites •A lot of data comes from satellites

•They take pictures of the earth from outer space.

•They can also collect data on temperature, cloud height, and moisture.

•Then the satellites send their data to weather stations

Weather Maps

•There are many different kinds of weather maps.

•Data from local weather stations from all over the country is collected to create national weather maps.

Temperature Map

•Shows the current temperatures.

Radar Maps

•Shows precipitation.

National Wind Map

•Shows wind speed and direction.

Infrared Satellite

•Shows cloud top temperature.

Fronts

Visible Satellite

• Shows picture from space.

Precipitation

• Shows precipitation in inches.

Humidity

• Shows the relative humidity.

Isobars

•Show areas of equal pressure.

•Inner most circles will be the low or high pressure areas.

Isotherms

•Lines show areas of equal temperature.

•Isotherm maps show where temperatures are relatively high and low, and also where temperature changes are gradual or dramatic over a distance.

Weather Maps

•The National Weather Service produces weather

maps based on information gathered from about 1,000

weather stations across the United States.

Chapter 16 NWS and Maps

Weather Map Symbols •These are the symbols you would see on a weather map.

•The arrows or bumps point in the direction the front is moving.