Dueling Springs: Meteorological vs. Astronomical
Wx and the City
* Slowly Cooling: Our Full Forecast | Later: The Moon & Hurricanes *
Similar to last March, this March has quickly transitioned from winter to spring-like conditions. Quite a few changes have taken place over the past week: a 50-degree difference in temperature over five days; the switch to daylight saving time; and the onset of meteorological spring.
According to meteorologists in the midlatitudes, spring begins March 1 (ironically, our biggest snow this winter also occurred on this day) and lasts through May 31. But according to astronomers, spring begins March 20 in the Northern Hemisphere and lasts until June 20 or 21.
Why the three-week lag between meteorologists and astronomers?
Keep reading for the answer...
March 20 -- the vernal equinox -- is the day on which the sun shines directly above the equator, making daylight and nighttime hours roughly equal in both hemispheres: about 12 hours (equinox means "equal night"). This phenomenon occurs again on the autumnal equinox in September. Check out the reason for the seasons to find out why.
Weather doesn't follow the astronomical calendar to the tee. Meteorologists have found it easier to classify seasons by changes in temperature and precipitation. Meteorological winter consists of the coldest, most wintry three months of the year, on average -- December, January and February -- and meteorological summer consists of the warmest months of the year -- June, July and August. Spring and fall are the transition months between the two.
Even though March usually brings variable weather for us here in the mid-Atlantic, at least it ends up spring-like. I suppose "spring" is a relative term for both meteorologists and astronomers in northern Maine...
| March 9, 2009; 10:45 AM ET
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