chapter 1- Weather forecasting methods

Question 1

Weather Forecasting Methods

Answer 1

persistance

trends

climatology

analogue

numerical weather prediction

Question 2

The method a forecaster chooses depends upon

Answer 2

• the experience of the forecaster,
• the amount of information available to the forecaster,
• the level of difficulty that the forecast situation presents, and
• the degree of accuracy or
• confidence needed in the forecast

Question 3

Persistence

Answer 3

It is the simplest way of producing a forecast.

Question 4

The persistence method assumes that

Answer 4

the conditions at the time of the forecast will not change

Question 5

1.1 Persistence
It gives a prediction based on

Answer 5

the assumption that the weather in the future will be the same as it currently is

Question 6

Persistance

for example

Answer 6

if it is sunny and 47 degrees today, the persistence method predicts that it will be sunny and 47 degrees tomorrow

Question 7

The persistence method works well when

Answer 7

weather patterns change very little and features on the weather maps move very slowly.

Question 8

Persistence forecasts are generally good only for

Answer 8

short periods of a few hours and become less accurate as the time period lengthens.

Question 9

However, if weather conditions change significantly from day to day, the persistence method usually

Answer 9

breaks down and is not the best forecasting method

Question 10

Trend Forecasting

Answer 10

In this method, the forecaster is looking at the changes that are occurring in the weather systems; the fronts, air masses, high and low pressure systems, which are affecting the station and areas of clouds and precipitation.

Question 11

Trend forecasting

the forecast is based on

Answer 11

the assumption that these changes will continue at the same rate they have been occurring.

Question 12

Trend forecasting

example

Answer 12

if a storm system is 1000 km west of your location and moving to the east at 250 km per day, using the trends method you would predict it to arrive in your area in 4 days.
Similarly, if a cold air mass is moving toward the station and temperatures at stations within the air mass are dropping at 1o C per hour, then temperatures at the station for which you are forecasting will also drop at 1 o C per hour.

Question 13

For example, using the trend forecasting, what will the temperature forecast for 10.00 Hrs. and 19.00 Hrs.?

Answer 13

+40 –> 10

+38 –> 19

Question 14

The trends method works well when

Answer 14

systems continue to move at the same speed in the same direction for a long period of time. If they slow down, speed up, change intensity, or change direction, trends forecast will not work as well.

Question 15

Trend (steady‐state) forecasting gives a good guide to follow at least for

Answer 15

short periods of time. Attempting to use this method for a forecast greater than 24 hours will usually prove inaccurate.

Question 16

the method has proven successful for

Answer 16

forecasts of a few minutes to several hours

The method called now casting which refers to forecasts for the next several hours, are often based on such steady‐state techniques.

Question 17

Climatology

Answer 17

This method uses such guidelines as the average value of weather elements for a region, the maximum and minimum values of weather elements, the most or least time of occurrence of certain weather phenomena, etc. to make a prediction of the value of those weather elements for some future period.

Question 18

Climatology

it is based on

Answer 18

the assumption that the specific element value will not be significantly different than the values of that element from previous observations.

Question 19

climatology

example

Answer 19

if you were using the climatology method to predict the weather for a station on July 4th, you would go through all the weather data that has been recorded for every July 4th and take an average

Question 20

climatology

if you were making a forecast for temperature and precipitation then you would

Answer 20

use this recorded weather data to compute the averages for temperature and precipitation

Question 21

The climatology method only works well when

Answer 21

the weather pattern is similar to that expected for the chosen time of year. If the pattern is quite unusual for the given time of year, the climatology method will often fail.

Question 22

Analogue

Answer 22

The Analog Method is a slightly more complicated method of producing a forecast. It involves examining today’s forecast scenario and remembering a day in the past when the weather scenario looked very similar (an analog).

Question 23

Analogue

example

Answer 23

suppose today is very warm, but a cold front is approaching your area. You remember similar weather conditions one last week, also a warm day with cold front approaching.
• You also remember how heavy thunderstorms developed in the afternoon as the cold front pushed through the area.

Question 24

For example, suppose today is very warm, but a cold front is approaching your area. You remember similar weather conditions one last week, also a warm day with cold front approaching.
• You also remember how heavy thunderstorms developed in the afternoon as the cold front pushed through the area.
Therefore, using the analog method, you would

Answer 24

predict that this cold front will also produce thunderstorms in the afternoon

Question 25

The analog method is difficult to use because

Answer 25

it is virtually impossible to find a perfect analog. Various weather features rarely align themselves in the same locations they were in the previous time.

Question 26

Even small differences between the current time and the analog can lead to

Answer 26

very different results

Question 27

Even small differences between the current time and the analog can lead to very different results.
However,

Answer 27

as time passes and more weather data is archived, the chances of finding a “good match” analog for the current weather situation should improve, and so should analog forecasts.

Question 28

Numerical Weather Prediction uses

Answer 28

the power of computers to make a forecast

Question 29

Numerical Weather Prediction

It involves using

Answer 29

mathematical equations to describe the atmospheric processes that causes changes to weather elements; such as, temperature, pressure, winds etc., that make the state of the atmosphere.

Question 30

1.5 Numerical Weather Prediction

It involves using mathematical equations to describe the atmospheric processes
that causes changes to weather elements; such as, temperature, pressure, winds
etc., that make the state of the atmosphere.
This state of the atmosphere (initial conditions), is defined by

Answer 30

the value of weather at grid pints, (at ground or sea level and vertically in the atmosphere).

Question 31

This state of the atmosphere (initial conditions), is defined by the value of weather at grid pints, (at ground or sea level and vertically in the atmosphere).
Once weather observations are entered into the program, the computer can

Answer 31

generate the initial conditions and solve the equations to determine new values of the weather elements for some period in the future;

Question 32

Numerical Weather Prediction

example

Answer 32

ten minutes past the time the observation measurements were made.
• The computer then uses these new values to determine subsequent values at each grid point ten minutes later.
• This procedure continues until values have been determined for 12, 24, 36, 48 hours, and for some models even longer, into the future.

Question 33

Numerical Weather Prediction

limitations are due to

Answer 33

errors in forecast models and initial conditions

Question 34

NWP

Despite the limitations due to errors in forecast models and initial conditions, the NWP is the best method at

Answer 34

forecasting the day‐to‐day weather changes