Weather ForecastingWeather Forecasting

This chapter discusses:This chapter discusses:

1.1. Various weather forecasting methods, their tools, Various weather forecasting methods, their tools, and forecasting accuracy and skilland forecasting accuracy and skill

2.2. Images for the forecasting of 6 citiesImages for the forecasting of 6 cities

Analysis to PrognosisAnalysis to Prognosis

Figure 14.1AFigure 14.1A Figure 14.1BFigure 14.1B

Three important forecasting steps are:Three important forecasting steps are: 1) Assess the present state, called the analysis, by 1) Assess the present state, called the analysis, by plotting 6 hourly surface and 12 hourly sounding dataplotting 6 hourly surface and 12 hourly sounding data

2) Predict a future state by either running a computer 2) Predict a future state by either running a computer model of weather changes or using some other forecast model of weather changes or using some other forecast method.method.

3) Interpret the model results, called a prognostic chart, 3) Interpret the model results, called a prognostic chart, given forecasting experiencegiven forecasting experience

Here are two different model 500 mb progs.Here are two different model 500 mb progs.

Viewing Data with AWIPSViewing Data with AWIPS

Figure 14.2Figure 14.2

Viewing weather images, overlays, and graphs in multiple windows Viewing weather images, overlays, and graphs in multiple windows is facilitated with the National Weather Service's Advanced is facilitated with the National Weather Service's Advanced Weather Interactive Processing System (AWIPS), which gathers Weather Interactive Processing System (AWIPS), which gathers data from the Automated Surface Observing System among other data from the Automated Surface Observing System among other sources.sources.

WSR-88D Doppler RadarWSR-88D Doppler Radar

Weather Surveillance Radar - 1988 Weather Surveillance Radar - 1988 Doppler, also known as next Doppler, also known as next generation radar (NEXRAD), detects generation radar (NEXRAD), detects severe weather size, movement, and severe weather size, movement, and intensity.intensity.

Data received by the NEXRAD unit Data received by the NEXRAD unit are processed by algorithms to assist are processed by algorithms to assist the forecaster in weather the forecaster in weather interpretation.interpretation.

Figure 14.3Figure 14.3

Meteogram DisplayMeteogram Display

Predicted trends in Predicted trends in several weather several weather variables are variables are plotted for a 60 plotted for a 60 hour period on a hour period on a meteogram.meteogram.

Patterns in Patterns in variable response, variable response, such as rising such as rising pressure and a pressure and a stop in stop in precipitation, are precipitation, are readily observed.readily observed.

Figure 14.4Figure 14.4

Vertical Sounding ProfileVertical Sounding Profile

Figure 14.5Figure 14.5

Radiosonde Radiosonde instruments attached instruments attached to pilot balloons are to pilot balloons are launched twice daily launched twice daily to profile weather to profile weather variables with height.variables with height.

These January 14, These January 14, 1999 data show winds 1999 data show winds veering from easterly veering from easterly at the surface to at the surface to southwesterly aloft southwesterly aloft that may change the that may change the freezing rain in the freezing rain in the saturated lower saturated lower atmosphere to non-atmosphere to non-freezing rain.freezing rain.

Probability ForecastsProbability Forecasts

Figure 14.6Figure 14.6

Climate records, often 30 years of data, are used to generate Climate records, often 30 years of data, are used to generate probability forecasts for a given event.probability forecasts for a given event.

In this case, most of Texas has a less than 5% chance of snow on In this case, most of Texas has a less than 5% chance of snow on December 25th, while northern Minnesota has had snow on that December 25th, while northern Minnesota has had snow on that date for each of the past 30 years.date for each of the past 30 years.

Weather Forecasting MethodsWeather Forecasting Methods

Figure 14.7Figure 14.7

Several methods are used to forecast weather, and Several methods are used to forecast weather, and include:include: 1) Persistence - the future will be like the present1) Persistence - the future will be like the present

2) Trend - the future will be like upwind weather2) Trend - the future will be like upwind weather

3) Analogue - the future will be like weather that 3) Analogue - the future will be like weather that historically occurred when similar conditions were historically occurred when similar conditions were presentpresent

In this figure, the forecasting method is called weather In this figure, the forecasting method is called weather types, which is a type of long range analogue forecast.types, which is a type of long range analogue forecast.

Weekly & Monthly ForecastsWeekly & Monthly Forecasts

Figure 14.8AFigure 14.8A

Stationary Stationary weather weather systems often systems often allow for trend allow for trend based extended based extended weather weather forecasts, while forecasts, while multiple runs multiple runs of numerical of numerical weather weather models, known models, known as ensemble as ensemble forecasts, allow forecasts, allow for 30 to 90 day for 30 to 90 day outlooks.outlooks.

Figure 14.8BFigure 14.8B

Forecasting with Surface ChartsForecasting with Surface Charts

Figure 14.9Figure 14.9

Many of the following figures analyze and predict weather for 6 Many of the following figures analyze and predict weather for 6 U.S. cities.U.S. cities.

This simplified 6 AM Tuesday surface weather map is useful for This simplified 6 AM Tuesday surface weather map is useful for short time interval predictions of fronts and associated weather.short time interval predictions of fronts and associated weather.

Surface Chart PredictionsSurface Chart Predictions

3-hour pressure tendencies plotted on isallobar maps help predict 3-hour pressure tendencies plotted on isallobar maps help predict the movement of highs and lows and indicate how rapidly pressure the movement of highs and lows and indicate how rapidly pressure systems are changing.systems are changing.

Lows tend to move toward the region of greatest pressure fall, while Lows tend to move toward the region of greatest pressure fall, while highs move toward the region of greatest rise.highs move toward the region of greatest rise.

The low from the previous map will likely move to the NE, while the The low from the previous map will likely move to the NE, while the high will move to the SE.high will move to the SE.

Figure 14.10Figure 14.10

Upper Level ChartsUpper Level Charts

Upper level winds, particularly those at 5500 m, which is a common Upper level winds, particularly those at 5500 m, which is a common elevation for the 500 mb surface, often guide the path of surface elevation for the 500 mb surface, often guide the path of surface pressure systems.pressure systems.

These upper level winds, however, travel at nearly twice the speed These upper level winds, however, travel at nearly twice the speed as the surface systems.as the surface systems.

Here again, we see the low will head to the NE, while the high will Here again, we see the low will head to the NE, while the high will head SE.head SE.

Figure 14.11Figure 14.11

Observed Movement of FrontsObserved Movement of Fronts

Figure 14.12Figure 14.12

Surface weather Surface weather observations observations from 6 PM from 6 PM Tuesday and 6 Tuesday and 6 AM Wednesday AM Wednesday show how the show how the fronts, pressure fronts, pressure systems, and systems, and precipitation precipitation have moved as have moved as predicted.predicted.

Surface Weather for 6 AM WednesdaySurface Weather for 6 AM Wednesday

Figure 14.13Figure 14.13

Surface Weather for 4 PM SundaySurface Weather for 4 PM Sunday

Figure 14.14Figure 14.14

500 mb Chart for 4 PM Sunday500 mb Chart for 4 PM Sunday

Figure 14.15Figure 14.15

Computer Drawn 12, 24, &36 hr ProgsComputer Drawn 12, 24, &36 hr Progs

Figure 14.16Figure 14.16

Surface Weather Map for 4 AM SundaySurface Weather Map for 4 AM Sunday

Figure 14.17Figure 14.17

500 mb Chart for 4 AM Sunday500 mb Chart for 4 AM Sunday

Figure 14.18Figure 14.18

Infrared Satellite Image for 6:Infrared Satellite Image for 6:45 AM Monday45 AM Monday

Figure 14.19Figure 14.19

Surface Weather Map for 4 AM MondaySurface Weather Map for 4 AM Monday

Figure 14.20Figure 14.20

Visible Satellite Image for 9 AM TuesdayVisible Satellite Image for 9 AM Tuesday

Figure 14.21Figure 14.21