Summary of Upper-Air Analysis Rules

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Summary of Upper-Air Analysis Rules

The following list is by no means all inclusive, but it does provide a guide for avoiding some typical and often repeated errors made by inexperienced analysts.

1. Use history. Always check the previous analyzed map before starting the current analysis.

Figure 8-1-15.—Time differential chart.

2. Isoheights (contours) are drawn parallel to winds where possible. This is not always possible, because of observation errors and nongeostrophic and/or nongradient winds. Always check the plotted wind shaft for the number indicating direction.

3. Contours are drawn following down the wind; therefore, wind direction cannot change discontinuously along a contour.

4. Do not overemphasize cyclonic curvature at troughs in the form of kinks. This implies a trough is a front.

5. Continue analysis into areas of no data. Use wind scales, history, and common sense to get central heights of highs and lows when no data is available.

6. Use geostrophic wind scales to determine correct spacing of contours. The spacing will be less than the observed wind indicates in areas of cyclonic curvature and greater than the observed wind where anticyclonic curvature is occurring.

7. The isotherm-contour pattern at 500 mb is normally one of cold lows and warm highs. A closed isotherm will be nearly coincident with height centers. Long-wave troughs are cold, ridges warm. The opposite is true for short waves.

8. Marked changes in the configuration of troughs should be doubted.

9. Insure vertical consistency.

a. Troughs and lows must slope toward coldest air.

b. Ridges and highs must slope toward warmest air.

c. Cold lows have little or no slope.

d. Warm lows at lower levels become short-wave (warm) troughs aloft.

e. Frontal waves at sea level become short waves aloft.

f. Occluded lows become cold or cutoff lows aloft.

10. Strive for a professional-looking product.

Avoid jagged, ragged or nervous isolines.

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