John Wheeler: Recent up-and-down temperatures have been tricky to forecast

FARGO — The up-and-down temperatures this week reveal a fascinating aspect of warm fronts in winter, particularly when there is snow on the ground. Air density (or weight) is closely related to its temperature. When snow is on the ground, its ability to reflect sunlight and also radiate heat from the ground out into space, causes a persistent layer of air in the lower few hundred feet near the ground to be colder than the air just above.

When a warm front passes through, the warm air tends to ride up and over this denser, heavier air. With a warm front, the temperature at the surface is often a very tricky forecast. Weather models are still not very good at accurately representing the intricate vertical layering of atmosphere, leaving the forecaster to rely on experience and careful analysis of the conditions.



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