When Really is the First Day of Spring? (Credit: National Centers for Environmental Information, NASA, SPACE)
DISCUSSION: As we transition into spring in the Northern Hemisphere, it is important to understand the difference between astronomical and meteorological seasons. The first day of spring falls on March 20th for the astronomical season, while for the meteorological season it falls almost three weeks earlier on March 1st. So which one should we follow?
The astronomical season of spring falls between March 20th to June 21st and refers to the position of the Earth’s orbit in relation to the sun. The Earth’s axis is an imaginary pole going through the center of Earth from the North Pole to the South Pole. Each day the Earth completes a full spin around its axis creating days and nights. But since the axis is not straight, this causes the Earth to have seasons. As the Earth travels around the sun, the axis always stays in the same position which allows different parts of the Earth to receive direct rays from the sun at different times of the year. In March and September, the sun shines equally on the Southern and Northern hemispheres, which marks the beginning of fall and spring. In the Southern Hemisphere, the seasons are reversed but fall on the same days as the Northern Hemisphere. Leap years cause the exact date to vary. Furthermore, this also makes the length of the seasons to range from 89 to 93 days, which makes comparing seasonal statistics year to year extremely difficult for climatologists.
The spring season falls between March 1st and May 31st for the meteorological seasons. Meteorologist split the four seasons into three months each based off of annual temperature cycles and the calendar. Winter is known to be the coldest months: December, January, and February; while summer is known to be the warmest months: June, July, and August. Fall and spring are known as transition seasons, March, April, and May get increasingly warmer, while September, October, and November get increasingly colder. Since these seasons follow the calendar, the days per season are more consistent, ranging from 90 to 92 days. This allows climatologists to easily calculate seasonal statistics for each month and season, which is helpful for commerce and agriculture.
Even though these aren’t the only two ways of categorizing the seasons, these are the most common. The National Weather Service prefers to follow the meteorological seasons as it is more practical to handle whole months of data rather than fractions of months. Before meteorological seasons were put into use, it was tedious for the NWS to make exact seasonal comparisons since the first day of each season had varying dates. Even though the NWS follows the meteorological seasons, not everyone does. For example, schools don’t let kids out for summer on the first day of June, but instead near 21st. So while there is no wrong season to follow, there are advantages and disadvantages to them.
(Citied: National Centers for Environmental Information, NASA, SPACE)
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© 2018 Weather Forecaster Allison Finch
The clock was ticking yesterday, figuratively and literally, as I finalized this article. The first Pi Day event had taken place some twelve hours earlier (3:14:15 a.m. on 3/14); the second occurred this past evening. With such a special day in progress, I made sure to get around to do something circular! Yes, I recycled (and updated) this Pi Day story. What goes around, comes around … To read the full story, click here - http://www.weatherworks.com/lifelong-learning-blog/?p=1461
While New England has been the target of three major nor’easters, it is important to look into what specifically in the atmosphere determines the type of precipitation that falls from the sky. Temperatures above the surface can have a significant impact on the precipitation type that falls to the ground. The temperature of the surface itself can also play a role, however it is not as significant.
First, let’s talk about snow. Snow is ice crystals in a variety of forms. These forms could either be plates, columns, or flakes. Snow can also be a conglomerate of ice crystals. Snow is likely to develop when the cloud layer, this is the layer of the atmosphere above the surface where clouds form, is less than -10°C. However, the optimal snow growth region is when the temperature of the cloud layer is from -12°C to -16°C. Anything that comes out of this layer will make dendrites. Dendrites are the best for snow growth, since these are bigger and will join with other snowflakes.
Next, let’s talk about sleet. Sleet are ice pellets that are composed of somewhat melted snowflakes, not frozen rain. Sleet bounces on contact with the surface and can have different appearances. Sleet can look clear, or it could look milky white. This all depends on how the snowflake melts. In order for sleet to occur, there has to be an area of warmer temperatures above the surface.
Freezing rain is an entirely melted snowflake. The melted snowflake is super-cooled. This freezes on contact with a surface. For freezing rain to occur, snowflakes fall through a layer of that atmosphere that is warm enough to melt them into liquid. Then the melted snowflakes will encounter near freezing temperatures above the surface. The surface itself is at or below freezing.
In conclusion, the story of an air parcel can have many different endings such as: rain, snow, freezing rain, or sleet. This all depends on the temperature of the atmosphere at a given time and height.
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© Weather Forecaster Jennifer Naillon