The time-liner is simply a local area map that is covered with transparent plastic and constructed as follows:

1. Using a large-scale map of the local area, construct a series of concentric circles centered on your station, and equally spaced from 10 to 20 miles apart. This distance from the center to the outer circle depends on your location, but in most cases, 100 to 150 miles is sufficient.

2. Make small numbered or lettered station circles for stations located at varying distances and direction from your terminal. Stations likely to experience your future weather should be selected. In addition to the station circle indicators, significant topographical features, such as rivers or mountains, maybe indicated on the base diagram. (Aeronautical charts include these features.)

By inspection of the latest surface chart, and other information, you can determine a quadrant, semicircle, or section of the diagram and the panmeters to be plotted. This should be comprised of stations in the direction from which the weather is approaching your station. Then, plot the hourly weather SPECIALS for those stations of interest. Make sure to plot the time of each special observation.

Overlay the circular diagram with another piece of transparent plastic, and construct isochrones of the parameter being forecast; for example, the time of arrival of the leading or trailing edge of a cloud or precipitation shield. The spacing between isochrones can then be extrapolated to construct "forecast isochrones" for predicting the time of arrival of occurrence of the parameter at your terminal. Refer to figure 4-14 for an example.

Figure 4-14.-Large-scale sample time-liner (Isochrones show advance of precipitation field).

Use of Doppler Radar in Cloud and Precipitation Forecasting

Doppler radar is very useful in determining weather phenomena approaching your station and estimating the probability of precipitation at your station, Refer to chapter 12 of this manual and the Federal Meteorological Handbook No. 11, Part B, for information on analysis of weather conditions and Doppler radar theory.

CLOUD ANALYSIS AND FORECASTING

LEARNING OBJECTIVES: Recognize upper air data and its value in forecasting. Recognize moisture features aloft and their significance to the forecaster.

Forecasters are frequently called upon to make forecasts of clouds over areas where synoptic observations are not readily available, or over areas where clouds above the lowest layer are obscured by a lower cloud deck. This section is designed to acquaint the forecaster with the principles of detection and analysis of clouds from rawinsonde data. A complete discussion of this problem is beyond the scope of this training manual. Further information on this subject may be found in the practical training publication, Use of the Skew T Log P Diagram in Analysis and Forecasting, NAVAIR 50-1P-5.

IMPORTANCE OF RAWINSONDE OBSERVATIONS (RAOB) IN CLOUD ANALYSIS

Cloud observations regularly available to forecasters in surface synoptic reports leave much to be desired as a basis for cloud forecasting.

Rawinsondes, which penetrate cloud systems, reflect, to some extent (primarly in the humidity trace), the vertical distribution of clouds. If the humidity element were perfect, there would usually be no difficulties in locating cloud layers penetrated by the instrument. Because of the shortcomings in the instrument, however, the relationship between indicated humidity and cloud presence is far from definite, and art empirical interpretation is necessary. Nevertheless, rawinsonde reports give valuable evidence that, when compared with other data, aids greatly in determining a coherent picture of stratiform and frontal cloud distributions. Their value in judging air mass cumulus and cumulonimbus distribution is negligible.

This information is now available on CD in Adobe PDF Printable Format

Privacy Statement - Press Release - Copyright Information. - Contact Us - Support Integrated Publishing