It's already meteorological spring, but the vernal equinox arrives tomorrow, Wednesday, morning at 7:02am. Now this time last year, it definitely felt like spring with 8 days at 70° or higher. Three of those days were 80° or above. This March has been quite a different story! The highest temperature this month was 63° on the 10th. The month is a bit below average and snow fell in parts of the area yesterday morning. Check out these poor daffodils that can't tell what season it is!
- M. Joyce - Fredericksburg, VA
Since the vernal equinox, or first day of astronomical spring, arrives tomorrow morning, it should start to warm up, right? Well, it's not that simple, but the general trend will be for warmer temperatures over the next few months. The equinox occurs at the point when the sun crosses the celestial equator from South to North. Here's a way to visualize this:
At the equinox, the geometric center of the Sun crosses the equator and this point is above the horizon for 12 hours everywhere on Earth. Now when we think about the equinox, we often think about equal hours of daylight and darkness. The word equinox comes from the Latin word "aequus" meaning "equal" and "nox" meaning "night". Although it's close, there are actually a few more minutes of daylight on the equinox than darkness. Sunday we had 12 hours of daylight and 12 hours of darkness. Sunrise on March 17, 2012 was 7:16 AM and sunset was at 7:17 PM. So you may be asking, why wasn't Sunday the equinox?
Well, it all comes down to that exact point when the center of the sun crosses the equator. Sunrise and sunset occur when the top of the sun, not the center, is on the horizon. That's why there are actually a few more minutes of daylight on the equinox. Also, the earth's atmosphere refracts, or bends, light from the sun. So, the top of the sun appears to be above the horizon when it is actually below the horizon.
Tomorrow, on the equinox, we'll have a little over 12 hours of daylight and darkness. From here on out, up until the summer solstice, we'll gain daylight. Check out some of the sunrise and sunset times through the summer solstice.
The growing daylight and higher sun angle help promote warmer days. Unfortunately, it can sometimes be a slow process in these transition months. Case in point, this March. The next 7 days will be below average. The average high for the middle of March is about 55°. By the end of the month, the average high will be 61°. No 60s in this extended outlook.