“A gush of bird-song, a patter of dew, a cloud, and a rainbow’s warning. Suddenly sunshine and perfect blue – an April day in the morning.”

~ Harriet Elizabeth Prescott Spofford (April 3, 1835 – Aug. 14, 1921), American writer of novels, poems and detective stories

Spring weather teeter-totters between the two seasons, winter and summer. On Monday, the teeter-totter landed with a thud, grounded in summer. The temperature hit 92 degrees! As the week moved along, temperatures  returned to those more typical at this time, the mid-70s. Fall and spring are known to exhibit abrupt temperature changes from one day to the next. But what about temperature change within a day’s period?

All of nature – critters (humans included), plants and ocean tides – have daily patterns, evident as they change throughout the course of a day. The term used is diurnal cycle. It recurs every 24 hours as a result of one full rotation of the Earth on its own axis. In the fields of climatology and meteorology the most familiar pattern is the diurnal temperature variation. It refers to the change of temperature from the daytime high to the nighttime low within a 24-hour time period. Once you know of such a happening, it’s fascinating to take note.

On any given day, the average temperature variation ranges between 20 and 30 degrees*. Determining conditions may include: Day length. The greater the daylight hours, the more time the Earth is heated by the sun. Cloudiness. On cloudy days, the ground is shielded from incoming solar radiation, i.e. heat. On cloudy nights any existing heat is trapped near the ground. In both cases daytime and nighttime temperatures are similar. Elevation. Mountain areas are located farther from the sun-heated surface. They are warmed less and also cool more rapidly after sunset than do valleys. Humidity. Water vapor is good at both absorbing and giving off heat. These conditions allow humid areas to maintain cooler temperatures. On the other hand, dry desert regions experience high temperatures plus the most extreme day-to-night temperature fluctuations. Wind speed. Winds cause air at different levels of the atmosphere to mix. This mixing lessens the difference in temperature between warmer and cooler air, thus decreasing the diurnal temperature range.

*In the foothills it’s not unusual for June temperatures to stay in the 60s for a 24-hour period – an entire day.

The warm and windy weather of yesterday is expected to change today with a chance for showers in the mountains tonight into tomorrow morning. Friday will be breezy and a bit warmer. Looking ahead, Saturday looks to be the warmest day of the next seven. As we have a family wedding in the afternoon, a beautiful spring day is appreciated. May flowers are certain to follow …

Sue Kilpatrick is a Crescenta Valley resident and  Official Skywarn Spotter for the  National Weather Service. Reach her at  suelkilpatrick@gmail.com.

  Sue Kilpatrick