HAPPY METEOROLOGICAL FALL!
Alright, pumpkin spice kings and queens. This is your time to shine — the season of crisp mornings, falling leaves, corn mazes, shades of auburn and orange and all things pumpkin is upon us! Today is the first day of fall (meteorological fall, that is).
So you may be thinking, “But wait, why does my calendar say fall doesn’t start for a few more weeks?” The reason for that would be the seasons most calendars show. The dates correspond to the astronomical seasons, rather than meteorological.
ASTRONOMICAL SEASONS VS. METEOROLOGICAL SEASONS
The seasons you’re used to seeing are astronomical seasons. They are based on the position of the Earth on its journey around the sun and the location on the Earth’s surface where the most direct solar radiation is occurring.
Think back to your school days and science class. Remember learning about the equator? The imaginary line is more than just a circle drawn around the center of a globe. To understand what it shows, you need to understand how the location of most direct sunlight shifts throughout the year.
The Earth is in constant motion, on a 365-day orbit around the sun. The other important factor is the tilt of the Earth. When you look at a map, you often see it presented as a straight, up-and-down view. That is probably because it makes more sense to us to view it this way, but it should actually be tilted by 23.5°. The Earth’s axis, meaning the tilt angle from the North Pole to the South Pole, is actually 23.5°. As the Earth rotates around the sun, this tilt causes the position of the most direct solar radiation to rise and fall between the northern and southern hemispheres. That tilt is what causes us to have seasonal variations in weather. The astronomical seasons mark four key time-frames in that journey, two equinoxes and two solstices.
The equator marks the central point where the sun’s journey between the northern and southern hemisphere occurs. When the most direct rays from the sun are occurring directly overhead at the equator, it is called an equinox and we experience equal amounts of day and night at all latitudes. The equinoxes occur twice a year, the autumnal equinox occurs in September, or fall, and the vernal equinox occurs in March, or spring.
The solstices mark the date the sun’s most direct rays reach the northernmost or southernmost point traveled from the equator. Those points on the Earth are marked by the imaginary lines called the Tropic of Cancer and the Tropic of Capricorn. The northernmost point, at 23.5° north latitude, is referred to as the Tropic of Cancer. The southernmost point, at 23.5° south latitude, is the Tropic of Capricorn. When the sun’s rays are directly over the Tropic of Cancer in June, the summer solstice occurs in the northern hemisphere and the winter solstice occurs in the southern hemisphere. During this time, the northern hemisphere receives the majority of the solar radiation from the sun, resulting in warmer temperatures and longer days. Six months later, the opposite occurs. The winter solstice takes place in December in the northern hemisphere, resulting in the least amount of solar radiation, colder temperatures and the shortest days.
The time and date these milestones are reached can vary by a few days. They typically fall on the 19-23 of a calendar month. Each season usually lasts around 90 days.
ASTRONOMICAL SEASON BREAKDOWN
—Autumnal Equinox (Late September – Late December)
—Winter Solstice (Late December – Late March)
—Spring Equinox (Late March – Late June)
—Summer Solstice (Late June – Late September
METEOROLOGICAL SEASONS OFFER STEADY DATES AND FOLLOW CLIMATOLOGY
Meteorological seasons are a little less complicated to explain and understand. The meteorological definition of a season is based on the climate, and the dates are based on the calendar months. This results in a more precise data-set when calculating seasonal dermatological averages and monitoring seasonal extremes and records.
The seasons start on the first of a calendar month and end on the last day of a month. The only season that would vary in duration from year to year would be winter, happening every four years, when a leap year occurs and February has 29 days.
METEOROLOGICAL SEASONS BREAKDOWN
—Autumn (September 1 – November 30 — 91 days)
—Winter (December 1 – February 28 or 29 — 90-91 days)
—Spring (March 1 – May 31 — 92 days)
—Summer (June 1 – August 31 — 92 days)
The meteorological seasons can also be simplified by what occurs climatologically as well. Autumn is the timeframe we see the greatest drop in average temperatures from season start to season end. The average high for Youngstown on September 1 is 78°. By the end of meteorological fall, November 30, the average high falls to 42°, a drop of 36°. This is due to the retreating peak solar angle as the sun’s most direct rays shift south of the equator and the bulk of the solar energy begins shifting to the southern hemisphere. That transition causes a rapid loss in hours of daylight throughout the period.
Meteorological winter is when we experience the coldest average temperatures, the least amount of solar radiation and the shortest days. The three months of meteorological winter are the three coldest months on average. The average temperature for December is 30.3°, for January is 25.8° and for February is 28.4°. Youngstown’s lowest average temperatures occur in January when we bottom out at an average high of 32° and an average low of 19°. This is also when our coldest temperature ever recorded occurred, a low of -22° on January 19, 1994.
Meteorological spring marks the season where we see the highest gain in average temperature from season start to season end. We also see a rise in the total daylight through the season and an increase in total solar radiation. The average highs jump by a total of 33° from start to finish. The average high on March 1 for Youngstown is 40° and rises to 73° by May 31.
Lastly, meteorological summer is when we experience the warmest average temperatures, the most solar radiation and the longest days in a calendar year. The three months of meteorological summer are the three warmest on average. The average temperature for June is 66.4°, for July is 70.5° and for August is 69.1°. Youngstown’s highest average temperatures occur in July when we top out at an average high of 82° and an average low of 60°. This is also when our warmest temperature ever recorded occurred, a high of 103° on July 10, 1936.