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Weather Forecasting

GEOL 1350: Introduction To Meteorology

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Overview

• Weather Forecasting Tools

• Weather Forecasting Methods

• Weather Forecasting Using Surface Charts

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Weather Forecasting Tools

To help forecasters handle all the available charts and maps, high-speed data modeling systems using computers are employed by the National Weather Service.

Advanced Weather Interactive Processing System (AWIPS) has data communications, storage, processing, and display capabilities to better help the individual forecaster extract and assimilate information from available data.

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Weather Forecasting Tools

AWIPS computer work station provides various weather maps and overlays on different screens.

AWIPS gathers data from Doppler radar system, satellite imagery, and the automated surface observing system that are operational at selected airports and other sites through out the United States.

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Weather Forecasting Tools •  Doppler radar detects

severe weather size, movement, and intensity

  A forecaster can project the movement of the storm and warn those areas in the path of severe weather.

Doppler radar data from Melbourne, Florida, on Mar 25, 1992, during the time of a severe hailstorm. The hail algorithm determined that there was 100% probability that the storm was producing hail. It also estimated that maximum size of the hailstones to be greater than 3 inches.

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Weather Forecasting Tools •  It is essential that the data can be easily accessible for the forecasters and in a format that allows several weather variables to be viewed at one time.

• Meteogram is a chart that shows how one or more weather variables has changed at a station over a given period of time.

• Meteogram may represent how air temperature, dew point, and pressure change over five days.

Meteogram illustrates predicted weather elements at Buffalo from 1 pm Jan 18 to 7 pm Jan 20.

At 7 am on Jan 19:

P = 1007 mb, Cloud height = 2000 ft, Visibility=10 miles, Wind=15 knots, T=33F, Dew Point=24F, Minimum T=30F.

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Weather Forecasting Tools •  Radiosonde instruments can be used to measure the vertical profiles of temperature, dew point, and winds.

•  Saturated air extends up to about 820 mb.

• Below-freezing temperatures only exist in a shallow layer near the surface and the freezing rain would continue or possibly change to rain, as cold easterly surface winds are swinging around to warmer southwesterly winds aloft.

A sounding of air temperature, dew point, and winds at Pittsburgh, PA on Jan 14, 1999.

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•  Another valuable tool utilized to forecast the weather is the satellite.

•  Satellites provide extremely valuable cloud images of areas where there are no ground-based observations.

•  Before weather satellites were in use, tropical storms often went undetected until they moved dangerously near inhabited areas.

Weather Forecasting Tools

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Weather Forecasting Tools

NASA Satellites

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Weather Forecasting Tools

Observation Geometry

•  Occultation Method

•  One of the most recent and promising atmospheric remote sensing technique is the Radio Occultation applied to GPS measurements.

•  Its importance has been increasing during the last decade, since the first related mission highlighted its possibilities.

•  It has better vertical resolution.

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Weather Forecasting Tools

•  Nadir observations allow to probe the global tropospheric composition, in particular boundary layer:

•  Location of most sources and sinks of greenhouse gases and air pollutants

•  Nadir observation satellites include SBUV, TOMS, GOME, MISR, MODIS, TES, AIRS, SCIAMACHY, OMI

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Weather Forecasting Methods •  Probability Forecasts •  Climate records, often 30 years of data, are used to generate

probability forecasts for a given event. •  In this case, most of Texas has a less than 5% chance of snow on

Dec 25, while northern Minnesota has more than 90% chance of snow on Dec 25.

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Weather Forecasting Methods •  Several methods are used to forecast weather

•  Persistence Forecast: a prediction that future weather will be the same as present weather.

•  Trend Forecast: Surface weather systems tend to move in the same direction and at approximately the same speed as they have been moving.

•  Analogue Forecast: The future will be like weather that historically occurred when similar conditions were present.

•  Statistical Forecast: Made routinely of weather elements based on the past performance of computer models.

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Weather Forecasting Methods •  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.

The 90-day outlook for (a) precipitation and (b) temperature for Feb, Mar, and Apr, 1999. For precipitation (a), the darker the green color the greater the probability of precipitation being above normal, whereas the deeper the red color the greater the probability of precipitation being below normal. For temperature (b), the darker the orange/red colors the greater the probability of temperatures being above normal, whereas the darker the blue color, the greater the probability of temperatures being below normal.

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Weather Forecasting Methods •  Short-time Forecasting with Surface Charts •  Simplified 6 AM Tuesday surface weather map is useful for short

time interval predictions of fronts and associated weather.

Surface weather map for 6 AM. Dashed lines indicate positions of weather features six hours ago. Areas shaded green are receiving rain, while areas shaded white are receiving snow, and those shaded pink, freezing rain or sleet.

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Weather Forecasting Methods •  Short-time Forecasting with Surface Charts •  Simplified 6 AM Tuesday surface weather map is useful for short time interval

predictions of fronts and associated weather. •  For short-time intervals, mid-latitude cyclonic storms and fronts tend to move

in the same direction and at approximately the same speed as they did during the pervious six hours.

Surface weather map for 6 AM. Dashed lines indicate positions of weather features six hours ago. Areas shaded green are receiving rain, while areas shaded white are receiving snow, and those shaded pink, freezing rain or sleet.

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Weather Forecasting Methods •  Surface Chart Predictions •  3-hour pressure tendencies plotted on isobar maps help predict the movement

of highs and lows and indicate how rapidly pressure systems are changing. •  Lows tend to move toward the region of greatest pressure fall, while highs

move toward the region of greatest rise. •  The low from the previous map will likely move to the NE, while the high will

move to the SE.

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Weather Forecasting Methods •  Upper Level Charts •  Upper level winds, particularly those at 5500 m, which is a common elevation

for the 500 mb surface, often guide the path of surface pressure systems. •  These upper level winds, however, travel at nearly twice the speed as the

surface systems. •  Low will head to the NE, while the high will head SE.

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Weather Forecasting Methods •  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.

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Weather Forecasting Methods •  Observed Movement of Fronts •  Surface weather observations for 6 AM Wednesday

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Weather Forecasting Methods •  Surface Weather Map for 4 PM Monday

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Weather Forecasting Methods •  Visible Satellite Image for 9 AM Tuesday