The past few days have seen mostly cloudy conditions here in Iowa. The noticeable visual effect for us is a lack of sunshine during the day and not seeing stars at night! Besides visual effects, clouds are an important component of the surface energy budget (which drives weather variables like near surface temperature). During the daylight, clouds reflect energy from the sun back out into space and act like a mirror. For all 24 hours of the day, clouds are absorbing and re-emitting energy from the ground back down to us, acting like a blanket. The featured image illustrates the effect of significant cloud cover by comparing hours with clouds against all available hours of observations from the Des Moines Airport sensor. The plot shows the primary effect of keeping temperatures cooler during the daytime and keeping temperatures comparatively warmer during the nighttime. The strongest effects are when solar heating of the ground is most efficient in the late summer / early fall season (drier/warmer soils, plenty of potential sunshine for surface heating) and during the early morning hours in spring and fall (peak radiational cooling due to lower humidities). Restating, these times are when clouds have the most influence. So while clouds have been helping to keep us recently cool during the daytime, they have kept overnight temperatures higher than they would be with clear skies at night.

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Tags:   clouds