As with cold fronts, the use of constant pressure charts in conjunction with the surface synoptic situation is helpful in forecasting warm-frontal cloudiness and precipitation.

Cloudiness and precipitation occur where the 700- hPa flow across the warm front is from the warm air to the cold air, and is moving in a cyclonic path or in a straight line. This implies convergence associated with the cyclonic curvature. Warm fronts are accompanied by no weather and few clouds if the 700- hPa flow above them is anticyclonic. This is due to horizontal divergence associated with anticyclonic curvature.

The 700-hPa ridge line ahead of a warm front may be considered the forward limit of the prewarm frontal cloudiness. The sharper the ridge line, the more accurate the rule.

When the slope of the warm front is gentle near the surface position, and is steep several hundred miles to the north, the area of precipitation is situated in the region where the slope is steep. There may be no precipitation just ahead of the surface frontal position.

Warm fronts are difficult to locate on satellite imagery. An active warm front maybe associated with a well organized cloud band, but the frontal zone is difficult to locate. An active warm front maybe placed somewhere under the bulge of clouds that are associated with the peak of the warm sector of a frontal system. The clouds are a combination of stratiform and cumuliform beneath a cirriform covering. See figure 4-7.

You must remember that no one condition represents what could be called typical, as each front presents a different situation with respect to the air masses involved. Therefore, each front must be treated as a separate case, by using present indications, geographical location, stability of the air masses, moisture content, and intensity of the front to determine its precipitation characteristics.

Figure 4-6.-Inactive and active cold front satellite imagery.

Figure 4-7.-Warm front satellite cloud imagery.

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