2 This section discusses: Various weather forecasting methods, their tools, and forecasting accuracy and skillImages for the forecasting of 6 citiesApplications of weather forecasting
3 Four forecasting steps: 1) Assess the present state, called the analysis, by plotting 6 hourly surface and 12 hourly sounding data2) Predict a future state by running a computer model of weather changes…3) Interpret the model results, called a prognostic chart, given forecasting experience…apply ROTs (Table 14.1 page 369)4) Translate forecast into something that is useful
4 Forecasting methods Persistence Trend Analogue Climatology The future conditions here will be like the present conditions hereTrendThe future conditions here will be like the weather upstream is nowAnalogueThe future conditions here will be like weather that historically occurred when similar conditions were presentClimatologyFuture conditions here will be near the monthly average for hereNumerical Weather PredictionFuture conditions here will be as predicted by supercomputers running equations of atmospheric motion“Reading the Sky”Future conditions here can be predicted by using current conditions and forecasting rules of thumb (ROT)
5 Persistence ForecastThe persistence method works well when weather patterns change very little and features on the weather maps move very slowly. It also works well in places like southern California, where summertime weather conditions vary little from day to day.
10 Probability Forecasts Figure 14.6Climate records can be used to generate probability forecasts for a given event.Florida has less than a 5% chance of snow on December 25th, while northern Minnesota has had snow on that date for each of the past 30 years.
11 Numerical Weather Prediction (NWP) At 00Z and 12Z each day, data is collected and NWP models are runNWP is the 2nd largest user of super computers in the world
13 Local Weather “signs”Understanding how the atmosphere works (“red sky at morning…”, halo around the moon, clear skies at sunset, etc, etc, etc)Local rules of thumb (ROT) (for example--southerly flow in March)Table 14.3, page 378; and appendix E (page A11)If you have good “situational awareness” of the atmosphere, rudimentary wx measurements (temp, DP, pressure, winds), and good ROT—you can make a pretty good 0-24 hour forecast.
14 Forecast Periods Nowcasting (less than 6 hours) Mainly surface observations, weather satellite and radar, and persistence or trend forecastsShort-range (<3 days)Trend and analogue methods, weather charts and numerical weather forecast productsMedium range (3-8 days)Analogue forecasts, numerical weather forecast products, climatologyLong-range (>8 days)Climatology
15 Weekly & Monthly Forecasts Stationary weather systems often allow for trend based extended weather forecasts, while multiple runs of numerical weather models, known as ensemble forecasts, allow for 30 to 90 day outlooks.Figure 14.8AFigure 14.8B
16 Ensemble ModelingNumerical weather models are run multiple times with small changes in the initial conditionsGives forecaster a good estimate of the possible range of weather conditions at a future times
17 Accuracy and skill12-24 hours: very good, 2-5 days: fairly good, above 7 days: slightly more accurate than persistenceAccuracy—what is considered “right”?Skill—how complicated/hard is the forecast (Southern California in summer…)?Forecast skill is determined by comparing your forecast against either persistence or climatologyLonger-range climatological forecasting improvingTornadoes…where they are likely to form: 3 days in advance, but precise area struck is forecastable minutes-few hours in advance
20 Analysis to Prognosis--NWP Figure 14.1AFigure 14.1BTwo forecast model 500 mb progs for the same time.Forecast models lose accuracy over time due to errors in the model, chaos in the atmosphere, and measurement errors
21 Data Processing and Display Figure 14.2Viewing weather images, overlays, and graphs in multiple windows is done using the National Weather Service's Advanced Weather Interactive Processing System (AWIPS), which gathers data from the Automated Surface Observing System among other sources.
22 WSR-88D Doppler RadarWeather Surveillance Radar Doppler, also known as next generation radar (NEXRAD), detects severe weather size, movement, and intensity.Data received by the NEXRAD unit are processed by algorithms to assist the forecaster in weather interpretation.Figure 14.3
23 Meteogram DisplayPredicted trends in several weather variables are plotted for a 60 hour period on a meteogram.Patterns in variable response, such as rising pressure and a stop in precipitation, are readily observed.Figure 14.4
24 NWS Probability of Precipitation Probability of Precipitation (PoP) describes the chance of an event occurring at any point in the forecast area, over a certain period of time (usually 12 hours).PoP is defined as: PoP = Pa x Pc, where:Pa =the probability that precipitation will occur somewhere in the forecast area during the forecast period and Pc =the percent of the area that will receive measurable precipitation, if it does occur
25 Vertical Sounding Profile Radiosonde instruments attached to pilot balloons are launched twice daily to profile weather variables with height.This example shows winds veering (clockwise—warm advection is occurring) from easterly at the surface to southwesterly aloft that may change the freezing rain in the saturated lower atmosphere to non-freezing rain.Figure 14.5Vertical soundings are also used for strength and timing of convective wx, cloud types and heights, turbulence and icing, etc.
27 Surface Chart Predictions - 3-hour pressure tendencies plotted on isallobar maps help predict the movement of highs and lowsLows tend to move toward the region of greatest pressure fall, while highs move toward the region of greatest rise.Figure 14.10
28 Upper Level ChartsFigure 14.11Upper level winds guide the path of surface pressure systems.
29 Observed Movement of Fronts Surface weather observations from 6 PM Tuesday and 6 AM Wednesday show how the fronts, pressure systems, and precipitation have moved as predicted.Figure 14.12
30 ForecastUsing both trend and persistence forecast techniques, what is your forecast for 24 hours from now in:Denver? Dallas? Chicago? Memphis?Washington? Augusta?Tues 6amWed 6am
31 Observed Weather for 6 AM Wednesday Figure 14.13
32 Another Scenario: Forecast for central CA coast for tomorrow Slowly falling barometer and increasing high cloudsWeak low pressure in Pacific.....Will it rain, or not??
33 Surface Weather for 4 PM Sunday Figure 14.14Look at 500mb chart for clues:
34 500 mb Chart for 4 PM SundayFigure 14.15564 line across the area (local ROT); Omega High present…but cold advection and shortwave may change the stagnant upper pattern; upper-level divergence??
35 12, 24, & 36 hour ProgsForecaster has access to several forecast models-Which one is best?-- Choice is based on initialization and experience….
36 Surface Weather Map for 4 AM Sunday Figure 14.17
40 Weather Impacts on Aviation Mishaps 88% of all weather-related aircraft mishaps occurred under IMC (Instrument Meteorological Conditions)83% of fatal crashes involved FAR Part 91 (General Aviation) aircraft
45 Weather and Commercial Aviation Direct costs due to weather on airline operations can be separated into several categories: diversion, cancellation, delay and insurance. The cost of a diverted flight can be as high as $150,000 and a cancellation close to $40,000 (Irrgang and McKinney, 1992).A report from the Air Transport Association (ATA) states that the direct annual costs to sixteen member airlines of the first two categories listed above are $47 million and $222 million, respectively (Air Traffic Management in the Future Air Navigation System, 1994).
47 Weather Impacts on Economic Sectors Oil and gas exploration:improved forecasts of tropical weather conditions (wind, waves, disturbances) can reduce delays in drilling operations at a cost of up to $250,000 per rig per day (several thousand rigs in the Gulf).improved hurricane track predictions could reduce days of production shutdown, each day of which costs the industry and the U.S. treasury a combined $15,000,000.Vegetable processing:improved temperature and precipitation forecasts can lead to greater efficiency in chemical spraying (e.g., pesticides), which costs $10-$15 per acre per application for hundreds of thousands of acres.on a national scale the annual cost of lost production to the vegetable processing industry, primarily due to weather, is $42,500,000.Insurance:a single hurricane could lead to more than $50,000,000,000 in damages.weather-related catastrophes have led to more than $48,000,000,000 in property insurance claims over the period
48 Wx Impacts on Economy Rail transportation: it costs $2,000 per hour to stop a train. A single tornado warning covering 15 miles of track for 15 minutes can lead to seven stopped trains.most weather-related derailments cost $1,000,000 to $5,000,000.Electric power:using improved thunderstorm forecasts could save one utility $200,000 annually in reduced outage time.using "good QPF forecasts" could save one utility $2,000,000 over five years.using improved temperature forecasts could save "hundreds of millions annually nationwide for the utility sector".Aviation:every avoided cancellation saves $40,000, every avoided diverted flight saves $150,000.for the 16 members of the Air Transport Association, delays and cancellations cost $269,000,000 annually.
50 “Own the Weather” Understand organization’s mission and operations Decision cyclesRisk adversityLeadership and their goalsUnderstand how weather impacts the organization and its competitionTaking the knowledge of weather effects, and weather—develop a weather product in the right format, and deliver to the right person, at the exact right timeBe right more than you are wrong!
51 Own the WeatherUSAF adopted this, and applied to weather support to US Army, USAF, and Special Operations forces in the mid-90’sUSAF weather personnel taught to forecast early in careerMost experienced technicians and officers trained in the concepts, and assigned to tactical level to tailor weather products
53 “Garske Chart”Synchronizes all significant environmental data into an operational timeline
54 EmploymentOver past 10 years, there was a large demand for new meteorologists--currently about 10,000 BS-level or higher graduates employedGovernment (National Weather Service; military)Private companiesConsultingBroadcast weatherOther related fields (physical and earth science; environmental fields)
55 Key Points and Concepts Persistence forecast is a prediction that future wx will be the same as the present.The trend method is based on the assumption that systems continue presently movementThe analogue method (regimes) makes a wx prediction by comparing past wx maps and wx patterns to those of the present.Climatological forecasts are based on the climatology (average weather) of a particular regionNWP is a useful tool for forecasting, but has limitations
56 Con’tEnsemble forecasting is a technique based on running several forecast models, each beginning with slightly different weather information to reflect errors in the measurements. If they agree—forecaster can have a high confidence in the model forecast.For a forecast to show skill, it must be better than a persistence forecast or climatological forecastAfter a number of days, the atmosphere’s chaotic behavior, along with flaws in computer models and small errors in measurements, limits the accuracy of forecast modelsSurface lows tend to move in direction parallel to the isobars (in the warm sector), and toward the direction of greatest pressure fall (isoallobaric)
57 Con’tWeather conditions have a huge effect on commercial and civil aviationMost GA crashes occur in IMC conditionsThe majority of flight delays in the National Airspace System (NAS) are due to weatherWeather can have a significant impact on the economy—resulting in billions of dollars in lost revenues; and can kill thousandsCompanies are learning to “own the weather” to minimize losses and increase competitivenessThe US armed forces introduced “own the weather” concepts now in use throughout the meteorological community