QTP TW 1W0X1 passes over the Great Lakes in the spring. When the cold air behind the cold front moves over the Great Lakes, the air is cooled from below and the cold front can undergo a small amount of frontogenesis. •
If a surface front moves into a deep pressure trough frontogenesis can occur. For example: a cold front moving into a lee side trough.
5.3.2. Frontolysis •
Occurs when the relationship between the isotherms and the axis of dilatation is more than 45°. Figure 5.2 shows how isotherms are being spread apart. The spreading apart of isotherms causes frontolysis.
Figure 5-2. Isotherm Spreading Leading to Frontolysis •
Convergence aloft over the frontal boundary with low-level divergence.
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Decreased cyclonic flow around the low when it is filling will decreases low-level convergence.
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Diabatic Effects: •
A cold front moving over a warm surface or a warm front moving over a cold surface will decrease the temperature contrast, and frontolysis occurs.
5.3.3. Movement •
Fronts move in the direction of the second standard level winds (925 mb). You may use the 850 mb or 700 mb level winds when the front is moving over mountainous terrain.
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