It’s
spring!
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| The vernal equinox on March 20, 2013. It is that time of year again (it happens twice) when the relative angle of Earth is perpendicular to the Sun, causing equal incoming solar energy to the Northern and Southern hemispheres - as well as equal day and nighttime. At 7:02 ET on March 20, 2013, Earth was at its equinox. At 7:45 ET, the GOES-13 satellite captured this full disk image of Earth. Click on the image for a larger view. Image Credit: NOAA. |
Both
meteorological and astronomical springs have arrived. The vernal equinox marks the beginning of
spring in the Northern Hemisphere. This
is when the vertical rays of the sun are directly over the earth’s equator and
crosses the equator on its northward journey.
Funny,
it doesn’t feel like spring. Let me check
the forecast:
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| The 5-day forecast for March 20, 2013 for Columbia, SC. Image Credit: WLTX-TV. |
Remember
those groundhog forecasts from six weeks
ago. A couple of them got it right, but
most got is wrong. Not only did spring
not come early, it does not appear to be in sight.
 |
| The 6-10 day outlook prepared on March 19, 2013 for the period of March 25-29. Notice the unseasonably cold weather in the East. Click on the image for a larger view. Image Credit: NOAA/CPC. |
March
is running almost 2 degrees F below normal in Columbia, South Carolina. This is in stark contrast to last year when
March was almost 10 degrees F above normal.
It was the warmest March on record.
 |
| A comparison of March 2012 with March 2013. Click on the image for a larger view. Image Credit: Climate Central. |
So
what is going on?
It
relates to a phenomenon in the Arctic known as the Arctic Oscillation. I have mentioned this before in writing about
the winter outlook. The oscillation has
two phases; a warm phase (positive) and a cold phase (negative). An index has been developed to distinguish
between the two phases.
When
the Arctic Oscillation is positive the jet stream is stronger and tends to keep
the cold Arctic air bottled up over the Polar Regions. This is what happened last year resulting in
the record warm March. However, in the
negative phase the jet stream is weaker and meanders more often. This allows for outbreaks of very cold air
into the mid-latitudes.
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| Observations of the Arctic Oscillation Index through the winter of 2012-13 and into early spring. Note the extreme negative numbers recently. Click on the image for a larger view. Image Credit: NOAA/CPC. |
This
month the index has been near record levels on the negative side. There has been a steady push of cold Arctic
air into the Upper-Midwest and into the eastern U.S. The forecast is for the index to retreat
toward neutral over the next two weeks, but the effects may linger through the
end of March. Andrew Freedman of Climate
Central has an interesting piece comparing last March and this month.
It
is best not to plant anything sensitive to cold until April (after
Easter). There will be another shot at
freezing temperatures before the end of March.
The month is likely to be below normal.
You can reassess you planting times at the beginning of April.
