On Sept. 22, fall will officially arrive across the Inland Northwest and the rest of the country. However, the “meteorological” fall season arrived on Sept. 1, compared to the “astronomical” fall.
There is a difference between the meteorological and astronomical seasons. On Sept. 22, the sun will be directly overhead along the equator. At that time, the Earth’s position relative to the sun provides 12 hours of daylight and darkness across the entire planet, which is the beginning of our astronomical fall season called the autumnal equinox. By contrast, the meteorological fall season, as well as the other seasons, are based on the annual temperature cycles.
The Earth’s seasons are determined by the planet’s tilt of approximately 23.5 degrees. In the Northern Hemisphere, the first day of summer, the summer solstice, is around June 21, where the sun is directly overhead at 23.5 degrees in the northern latitudes. On the first day of winter, the winter solstice, near Dec. 22, the sun is directly overhead in the Southern Hemisphere at 23.5 degrees. This is why our days in the winter are much shorter when compared to the longer days in the summer – the sun angle is lower.
The Earth’s elliptical orbit around the sun leads to the seasons varying between 89 and 93 days. Our planet is actually closest to the sun around Jan. 3 and farthest away on July 4 by approximately 3 million miles. It’s the 23.5 degree tilt that has the major effect for determining our four seasons.
Our meteorological fall season, as well as the other seasons, are broken down into groupings of three months based on temperature cycles and our calendar. This system was created for observing and forecasting purposes for the monthly civil calendar, which also makes it easier to calculate monthly statistics.
The meteorological summer season, which began on June 1, across the Inland Northwest was very warm, especially in July and August. June started out near normal with an average temperature of 61.7 degrees. July was very warm with an average reading of 75.7 degrees, which was 5.9 degrees above normal. The warm weather continued in August with an average temperature of 72.2 degrees, which was 2.9 degrees above normal.
For the meteorological summer of 2014, there were 27 days with high temperatures at or above 90 degrees with one 100-degree day. The average reading was 2.8 degrees above normal for the three-month period. Air-conditioning bills were much higher thanks to the warmer weather.
The high pressure ridge should continue to keep us drier than normal with pleasant afternoon temperatures for the next several weeks. Conditions should start to change to the wetter side by the end of the month or around early to mid-October.