Chapter 13 – Weather Analysis and Forecasting

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The National Weather Service. The National Weather Service (NWS) is responsible for forecasts several times daily. The National Weather Service. The National Weather Service (NWS) is responsible for forecasts several times daily. ID: 541098 Download Presentation

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Chapter 13 – Weather Analysis and Forecasting




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Presentations text content in Chapter 13 – Weather Analysis and Forecasting

Slide1

Chapter 13 – Weather Analysis and Forecasting

Slide2

The National Weather Service

The National Weather Service (NWS) is responsible for forecasts several times daily

Slide3

The National Weather Service

The National Weather Service (NWS) is responsible for forecasts several times daily

Different weather forecast offices (WFOs) are responsible for their specific region

Slide4

The National Weather Service

The National Weather Service (NWS) is responsible for forecasts several times daily

Different weather forecast offices (WFOs) are responsible for their specific region

WFOs are also responsible for warnings in their specific region

Slide5

The National Weather Service

The National Weather Service (NWS) is responsible for forecasts several times daily

Different weather forecast offices (WFOs) are responsible for their specific region

WFOs are also responsible for warnings in their specific region

NWS forecasters rely heavily on the Advanced Weather Information Processing System (AWIPS) to understand current conditions and make forecasts

Slide6

The National Weather Service

Slide7

The National Weather Service

Slide8

The National Weather Service

Slide9

The National Weather Service WFOs

Slide10

The National Weather Service

A variety of products are created at NWS WFOs

Slide11

The National Weather Service

A variety of products are created at NWS WFOs

Short-term forecasts

7-day zone forecasts

Aviation forecasts

Marine forecasts

Forecast discussions

Slide12

The National Weather Service

A variety of products are created at NWS WFOsShort-term forecasts7-day zone forecastsAviation forecastsMarine forecastsForecast discussions

Current Lubbock forecast discussion and 7-day zone forecast…

Slide13

The Forecasting Process

Forecasts from now out to a few hours is called

nowcasting

Slide14

The Forecasting Process

Forecasts from now out to a few hours is called

nowcasting

Strongly based on observations (radar, satellite images, surface observations)

Slide15

The Forecasting Process

Forecasts from now out to a few hours is called

nowcasting

Strongly based on observations (radar, satellite images, surface observations)

Forecasts beyond about 6 hours is based mostly on numerical weather prediction (NWP) models

Slide16

Numerical Weather Prediction – The Analysis Phase

A gridded, 3-dimensional analysis is produced with

1) A previous forecast

Slide17

Numerical Weather Prediction – The Analysis Phase

A gridded, 3-dimensional analysis is produced with

1) A previous forecast

2) Observations

Slide18

Numerical Weather Prediction – The Analysis Phase

A gridded, 3-dimensional analysis is produced with

1) A previous forecast

2) Observations

The process by which the above are combined is called

data assimilation

Slide19

Data Assimilation

Gridded atmospheric analyses are produced by combining the following:

1) A previous forecast

2) Forecast uncertainty

3) Observations

4) Observation uncertainty

Slide20

Data Assimilation

Temperature at a single point (Lubbock):

T = 80

o

FTerror = 1oF

T = 86oFTerror = 10oF

Previous forecast from model

Observation

Slide21

Data Assimilation

Temperature at a single point (Lubbock):

T = 80

o

FTerror = 1oF

T = 86oFTerror = 10oF

Previous forecast from model

Observation

Analysis

T = 81

oF

Slide22

Data Assimilation

Temperature at a single point (Lubbock):

T = 80

o

FTerror = 10oF

T = 86oFTerror = 1oF

Previous forecast from model

Observation

Analysis

T = 85

oF

Slide23

Data Assimilation

Temperature at a single point (Lubbock):

T = 80

o

FTerror = 5oF

T = 86oFTerror = 5oF

Previous forecast from model

Observation

Analysis

T = 83

oF

Slide24

Data Assimilation

The resulting analysis is the most likely state of the atmosphere based on the given information

Slide25

Numerical Weather Prediction – The Prediction Phase

The prediction phase of NWP involves calculating the future state of the atmosphere (starting point = the analysis) under the following

governing equations

:

1) Conservation of momentum

Slide26

Numerical Weather Prediction – The Prediction Phase

The prediction phase of NWP involves calculating the future state of the atmosphere (starting point = the analysis) under the following

governing equations

:

1) Conservation of momentum

2) Conservation of mass

Slide27

Numerical Weather Prediction – The Prediction Phase

The prediction phase of NWP involves calculating the future state of the atmosphere (starting point = the analysis) under the following

governing equations

:

1) Conservation of momentum

2) Conservation of mass

3) Conservation of energy

Slide28

Numerical Weather Prediction – The Prediction Phase

The prediction phase of NWP involves calculating the future state of the atmosphere (starting point = the analysis) under the following governing equations: 1) Conservation of momentum 2) Conservation of mass 3) Conservation of energyExample: F = ma = m = m

dv

dt

V

2-V1

∆t

Slide29

Numerical Weather Prediction – The Prediction Phase

NWP takes massive amounts of computing power!!!

Slide30

Numerical Weather Prediction – The Prediction Phase

NWP takes massive amounts of computing power!!!

1980s: U.S. nested grid model – 80-km

resolution over continental U.S.

(48-hr forecast runtime = hours)

Slide31

Numerical Weather Prediction – The Prediction Phase

NWP takes massive amounts of computing power!!!

1980s: U.S. nested grid model – 80-km

resolution over continental U.S.

(48-hr forecast runtime = hours)

Today: Weather Research and Forecasting

model – 12-km resolution over U.S.

(48-hr forecast runtime = 10 minutes)

Slide32

Numerical Weather Prediction – The Prediction Phase

NWP can be classified in 2 ways:

1)

Deterministic

– a single forecast is

produced and relied upon

Slide33

Numerical Weather Prediction – The Prediction Phase

NWP can be classified in 2 ways:

1)

Deterministic

– a single forecast is

produced and relied upon

2)

Probabilistic

– many forecasts are

produced and forecast probabilities can

be generated (

ensemble forecasting

)

Slide34

Deterministic vs. Probabilistic Forecasting

Time = 00-hr

Slide35

Deterministic vs. Probabilistic Forecasting

Time = 00-hr

Time = 72-hr

Slide36

Probabilistic Forecasting

10-day forecasts

Slide37

Probabilistic Forecasting

Main challenge

= Expressing uncertainty to the public in a way it will be useful

Slide38

Probabilistic Forecasting

Main challenge

= Expressing uncertainty to the public in a way it will be useful

- Do people want to hear what the high

temperature will be, or do they want to

know the possible range of high

temperatures?

Slide39

The Prediction Phase – How Can Forecasts Go Bad?

There are 2 main sources of error in NWP forecasts:

1)

Initial condition error

– errors in the

analysis of a NWP model

Slide40

The Prediction Phase – How Can Forecasts Go Bad?

There are 2 main sources of error in NWP forecasts:

1)

Initial condition error

– errors in the

analysis of a NWP model

2)

Physics errors

– physics that are

wrong in the NWP model (mostly

associated with surface processes)

Slide41

Initial Condition Error

Initial condition errors are always present in NWP analyses

Slide42

Initial Condition Error

Initial condition errors are always present in NWP analyses

Because of chaos, errors in the analysis will eventually grow to be large (forget about 30-day forecasts!)

Slide43

Physics Errors

The physics in NWP models aren’t perfect

Slide44

Physics Errors

The physics in NWP models aren’t perfect

- Surface radiation processes

Slide45

Physics Errors

The physics in NWP models aren’t perfect

- Surface radiation processes

- Frictional turbulence of surface winds

Slide46

Physics Errors

The physics in NWP models aren’t perfect

- Surface radiation processes

- Frictional turbulence of surface winds

- Convection

Slide47

Physics Errors

The physics in NWP models aren’t perfect

- Surface radiation processes

- Frictional turbulence of surface winds

- Convection

- Cloud processes

Slide48

Physics Errors

Physics errors often lead to model biases – consistent errors in certain model variables (e.g. surface temperature)

Slide49

Numerical Weather Prediction – The Post-processing Phase

The post-processing phase of NWP involves creating graphics of the forecast:

Slide50

Numerical Weather Prediction – The Post-processing Phase

The post-processing phase of NWP involves creating graphics of the forecast:

1) 500-mb height

2) SLP

3) Surface wind

4) 3-hr precipitation

5) 1000-500mb thickness

Slide51

NWP Post-processing

Slide52

NWP Post-processing

Slide53

NWP Post-processing

The final forecast product includes the human factor – judgments based on both a forecaster’s experience and NWP

Slide54

NWP Post-processing

Slide55

NWP Post-processing

Model Output Statistics (MOS) – a post-processing technique that correlates relationships between a model forecast and reality over many, many forecasts

Slide56

NWP Post-processing

Model Output Statistics (MOS) – a post-processing technique that correlates relationships between a model forecast and reality over many, many forecasts

MOS produces a forecast incorporating these statistical relationships

Slide57

Other Forecasting Methods

Other forecasting methods include:

1)

Persistence forecasting

– a forecast

identical to the previous day’s conditions

Slide58

Other Forecasting Methods

Other forecasting methods include:

1)

Persistence forecasting

– a forecast

identical to the previous day’s conditions

2)

Climatological forecasting

– a forecast

identical to the average conditions for

that day

Slide59

Forecast Verification

Forecast verification is the process of measuring the skill of a forecast (model, human forecaster, MOS…)

Slide60

Forecast Verification

Forecast verification is the process of measuring the skill of a forecast (model, human forecaster, MOS…)

Slide61

Long-range Forecasts

The Climate Prediction Center (CPC) is responsible for forecasts valid more than 1 week into the future (numerical models and statistics)

Slide62

Long-range Forecasts

The Climate Prediction Center (CPC) is responsible for forecasts valid more than 1 week into the future (numerical models and statistics)

Seasonal forecasts are also made by the CPC that indicate above or below probabilities of warm/cold or wet/dry seasons


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