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Chapter 13 – Weather Analysis and Forecasting
Chapter 13 – Weather Analysis and Forecasting

Chapter 13 – Weather Analysis and Forecasting - PowerPoint Presentation

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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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Presentation on theme: "Chapter 13 – Weather Analysis and Forecasting"— Presentation transcript

Slide1

Chapter 13 – Weather Analysis and ForecastingSlide2

The National Weather Service

The National Weather Service (NWS) is responsible for forecasts several times dailySlide3

The National Weather Service

The National Weather Service (NWS) is responsible for forecasts several times dailyDifferent weather forecast offices (WFOs) are responsible for their specific regionSlide4

The National Weather Service

The National Weather Service (NWS) is responsible for forecasts several times dailyDifferent weather forecast offices (WFOs) are responsible for their specific region

WFOs are also responsible for warnings in their specific regionSlide5

The National Weather Service

The National Weather Service (NWS) is responsible for forecasts several times dailyDifferent weather forecast offices (WFOs) are responsible for their specific region

WFOs are also responsible for warnings in their specific regionNWS forecasters rely heavily on the Advanced Weather Information Processing System (AWIPS) to understand current conditions and make forecasts Slide6

The National Weather ServiceSlide7

The National Weather ServiceSlide8

The National Weather ServiceSlide9

The National Weather Service WFOsSlide10

The National Weather Service

A variety of products are created at NWS WFOsSlide11

The National Weather Service

A variety of products are created at NWS WFOsShort-term forecasts

7-day zone forecastsAviation forecastsMarine forecastsForecast discussionsSlide12

The National Weather Service

A variety of products are created at NWS WFOsShort-term forecasts

7-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 nowcastingSlide14

The Forecasting Process

Forecasts from now out to a few hours is called nowcastingStrongly based on observations (radar, satellite images, surface observations)Slide15

The Forecasting Process

Forecasts from now out to a few hours is called nowcastingStrongly based on observations (radar, satellite images, surface observations)

Forecasts beyond about 6 hours is based mostly on numerical weather prediction (NWP) modelsSlide16

Numerical Weather Prediction – The Analysis Phase

A gridded, 3-dimensional analysis is produced with 1) A previous forecastSlide17

Numerical Weather Prediction – The Analysis Phase

A gridded, 3-dimensional analysis is produced with 1) A previous forecast

2) ObservationsSlide18

Numerical Weather Prediction – The Analysis Phase

A gridded, 3-dimensional analysis is produced with 1) A previous forecast

2) ObservationsThe 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 uncertaintySlide20

Data Assimilation

Temperature at a single point (Lubbock):

T = 80

o

F

T

error

= 1

o

F

T = 86

o

F

T

error

= 10

o

F

Previous forecast

from model

ObservationSlide21

Data Assimilation

Temperature at a single point (Lubbock):

T = 80

o

F

T

error

= 1

o

F

T = 86

o

F

T

error

= 10

o

F

Previous forecast

from model

Observation

Analysis

T = 81

o

FSlide22

Data Assimilation

Temperature at a single point (Lubbock):

T = 80

o

F

T

error

= 10

o

F

T = 86

o

F

T

error

= 1

o

F

Previous forecast

from model

Observation

Analysis

T = 85

o

FSlide23

Data Assimilation

Temperature at a single point (Lubbock):

T = 80

o

F

T

error

= 5

o

F

T = 86

o

F

T

error

= 5

o

F

Previous forecast

from model

Observation

Analysis

T = 83

o

FSlide24

Data Assimilation

The resulting analysis is the most likely state of the atmosphere based on the given informationSlide25

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 momentumSlide26

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 massSlide27

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 energySlide28

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

Example:

F = ma = m = m

dv

dt

V

2

-V

1

∆tSlide29

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 uponSlide33

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-hrSlide35

Deterministic vs. Probabilistic Forecasting

Time = 00-hr

Time = 72-hrSlide36

Probabilistic Forecasting

10-day forecastsSlide37

Probabilistic Forecasting

Main challenge = Expressing uncertainty to the public in a way it will be usefulSlide38

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 modelSlide40

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 analysesSlide42

Initial Condition Error

Initial condition errors are always present in NWP analysesBecause 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 perfectSlide44

Physics Errors

The physics in NWP models aren’t perfect - Surface radiation processesSlide45

Physics Errors

The physics in NWP models aren’t perfect - Surface radiation processes

- Frictional turbulence of surface windsSlide46

Physics Errors

The physics in NWP models aren’t perfect - Surface radiation processes

- Frictional turbulence of surface winds - ConvectionSlide47

Physics Errors

The physics in NWP models aren’t perfect - Surface radiation processes

- Frictional turbulence of surface winds - Convection - Cloud processesSlide48

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 thicknessSlide51

NWP Post-processingSlide52

NWP Post-processingSlide53

NWP Post-processing

The final forecast product includes the human factor – judgments based on both a forecaster’s experience and NWP Slide54

NWP Post-processingSlide55

NWP Post-processing

Model Output Statistics (MOS) – a post-processing technique that correlates relationships between a model forecast and reality over many, many forecastsSlide56

NWP Post-processing

Model Output Statistics (MOS) – a post-processing technique that correlates relationships between a model forecast and reality over many, many forecastsMOS produces a forecast incorporating these statistical relationshipsSlide57

Other Forecasting Methods

Other forecasting methods include:

1) Persistence forecasting – a forecast identical to the previous day’s conditionsSlide58

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 daySlide59

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