Chapter 12Weather Analysis & ForecastingPower Point by Michael C. LoPresto. Revised by J. Karnath
The Weather Business: A Brief Overview• Public Sector:– In the US, the governmental agency responsible forgathering and disseminating weather-relatedinformation is the National Weather Service (NWS), abranch of the National Oceanic and AtmosphericAdministration (NOAA).• Private Sector:– In the US, there are many private companies thatprovide forecasts to the general public, sports teams,airlines, media outlets, oil companies and countlessother avenues.– Examples are, CNN, The Weather Channel,Accuweather, USA Today, and subsidiaries ofcollegiate institutions.
Forecasting MethodsSkilledSynoptic-Analog-Numerical-StatisticalUnskilled-Persistence-Trend-Nowcasting-Climate (Long-term forecasting)
Synoptic Weather Forecasting• Until the late 1950’s, synoptic weather forecasting wasthe primary means for making weather predictions.– Synopsis weather maps display a synopsis, outline orsummary, of the status of the atmosphere at any given time.– Therefore, synoptic forecasting involves the study andprediction of weather patterns as gathered and displayed on asynoptic map using different techniques.• Analog Method• Persistence Forecasting• Trend Forecasting
Synoptic Weather Charts
Numerical Method• Modern weather forecasting relies heavily on numerical weatherprediction.• Ironically, the word “numerical” is somewhat misleading becauseall types of weather forecasting relies on some quantitative(numbers) data.• Although complicated, this method employs a number of highlyrefined computer models that attempt to mimic the behavior of thephysical laws of the fluidity of the atmosphere.– Although computers have been refined to tabulate trillions of calculations,slight variations in conditions can produce very different forecasts over time.– Therefore, several runs of the same program are usually performed.– Interested in more, learn about Chaos Theory and the “butterfly effect”!
Numerical Forecasting Computer Runs
Statistical Method• Statistical methods are used in conjunction with numericalweather predictions.• Past weather data are carefully examined to determineweather patterns that are good predictors of future events.• This is most often used to determine a single aspect ofweather; Like daily maximum or minimum temperatures,or daily precipitation totals.
Statistical Forecasting Maps
Persistence Method• Perhaps the simplest forecasting technique is based onthe tendency of the weather at a given site to remainunchanged for several hours, or even a day or so.• Persistence forecasts predict that the future weather willbe the same at the present conditions. (i.e. rain now =probable rain in the next few hours.)– These forecasts do not account for changes in a weathersystem, or the creation or dissipation in a cyclone.– Therefore, for most area (not Southern California) this is onlyvalid for six to 12 hours, at most 1 day.
Trend Method• Trend forecasting assumes that weatheroccurring upstream will persist and move on toaffect the area in its path.– For example, Western New York usually has weather systemsmove in from the southwest or west. Therefore, look atweather to the west, calculate it rate of movement, and predictwhen it will “hit” us.
Nowcasting Method• Nowcasting is just what it states; a forecast forright now!• It is necessary for severe weather (tornadoes,thunderstorms, and hail) and many other shortlivedor small scaled phenomena (lake effectsnow) that are too-small to predict accurately inadvance.• This technique relies heavily on weather radarand geostationary satellites.
Long-Range Forecasts• Long-range forecasting is an area that relies heavily onstatistical averages obtained from past weather data, alsoreferred to as climactic data.• They are usually estimates of the precipitation andtemperatures that can be expected during long-term periods.• In general, monthly extended forecasts are produced by thefollowing procedures:– 1 st , a mean 700-mb contour chart is constructed for the comingmonth.• This is complied by examining the statistical data for the season of the year,and then modifying the data based on the known effects of oceantemperatures (or lake temps in our case), snow cover, and other factors.– 2 nd , Once this map is finished, relations between the flow aloft andand the development and movement of surface weather patternsare considered.
Were They Right About WNY’s December?Average Monthly: 29.7 ºFDeparture from normal: -0.1 ºFPrecip. Total for Month: 4.99 inchesDeparture from normal: 1.19 inchesSource: http://www.erh.noaa.gov/buf/climate/bufprecli1204.htm
Forecasting Accuracy• “I’d like to be a weather man. You can be right30% of the time, and still keep your job!”– My father In-law• Many argue that meteorologists are often wrong.NWS forecasts have been documented to becorrect 80% of the time in predicting theoccurrence of precipitation.• However, skill of its forecasts are acquired overan extended, continuous time, and often take yearsin one area to be “perfected”.
Station Model Data
Forecasting Tools - Satellites
GOES = Geostationary Operational Environmental Satellite
• Normal is simply anaverage of a climateelement over a 30-yearperiod.• So, a departure fromnormal is the differencebetween currentlyobserved values and the30-year average.• Ironically, experiencing avalue that equals thenormal is actually theexception and not the rule!• “Normals” are calculatedevery decade in an attemptto keep up with anyclimactic changes.What is Normal?