AS-201 Weather Forecasting. This section discusses: Various weather forecasting methods, their tools, and forecasting accuracy and skill Images for the forecasting of 6 cities Applications of weather forecasting. Four forecasting steps:.
The 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.
Climate 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.
NWP is the 2nd largest user of super computers in the worldNumerical Weather Prediction (NWP)
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.
Gives forecaster a good estimate of the possible range of weather conditions at a future timesEnsemble Modeling
Two 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
Viewing 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.
Weather Surveillance Radar - 1988 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.
Predicted 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.
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 occurNWS Probability of Precipitation
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.
Vertical soundings are also used for strength and timing of convective wx, cloud types and heights, turbulence and icing, etc.
Upper level winds guide the path of surface pressure systems.
Surface weather observations from 6 PM Tuesday and 6 AM Wednesday show how the fronts, pressure systems, and precipitation have moved as predicted.
Look at 500mb chart for clues:
564 line across the area (local ROT); Omega High present…but cold advection and shortwave may change the stagnant upper pattern; upper-level divergence??
Forecaster has access to several forecast models
-Which one is best?
-- Choice is based on initialization and experience….
83% of fatal crashes involved FAR Part 91 (General Aviation) aircraftWeather Impacts on Aviation Mishaps
Synchronizes all significant environmental data into an operational timeline