|WINTER CLOUDS IN MID LATITUDES
METEOROLOGIST JEFF HABY
Clouds are often more common in the winter than any other season, especially overcast cloudiness. Why can it get so cloudy in the winter
and sometimes cloudy for days on end?
One reason is due to the cooler temperatures in winter. When temperatures are cooler, the temperature is more likely to be closer to
the dewpoint temperature. A temperature equal to the dewpoint produces saturated conditions and thus clouds are more likely.
Another reason is due to an active jet stream. Low pressure systems are associated with an active jet stream with troughs. These
low pressure systems drive in fronts and bring in lifting mechanisms that make clouds more common.
A third reason is upslope flow. Since the air is cooler, it is easier to lift the air to the point of saturation. An upslope flow
can produce clouds for significant time periods.
Additionally, the sun angle is lower in winter and the days are shorter. This produces less warming of the Earth’s surface. With
decreased warming, it is more likely clouds can stay in place. Significant warming will cause the air to become drier and this
makes it easier for clouds to dissipate. With less warming, clouds can hang around throughout the day.
Finally, the ground surface is often high in moisture content in winter. This can occur from the snow on the ground and snow
melting which saturates the soil. With the cool temperatures outside, it is easy for this moisture to evaporate and saturate
the air above. Any lifting will help produce clouds. Snow on the ground also reflects solar radiation which keeps temperatures cooler.