Thursday, March 11, 2010

Welcome Rainfall Overnight

Rain has overspread all of central Virginia, and will continue overnight. Most areas will receive between 0.25" and 0.50", which will be the most rain than we have seen in a 12-hour period in Richmond over about the past month. A strong upper-level low will take it's time moving this way, bringing several rounds of rain to the area through Saturday night. It will be interesting to see what happens as the cold core moves right over Virginia on Sunday. I've seen situations like this produce wet snowflakes mixing in with rain showers with surface temperatures in the upper 40s and low 50s. There will be a much better chance of that happening farther west in the higher terrain. It looks like we could see a cool snap in about 11 to 13 days from now, but it should be very brief.

Tuesday, March 9, 2010

Spring Things

With high temperatures this week running 5-10 degrees above average, Spring things are on many of our minds, from watching the first bulbs rise out of the previously snow-covered ground, to the pleasantly mild afternoons prompting Richmonders to seek leisure outdoors. Even with a high of only 61 degrees on Sunday, I saw plenty of ice cream shops packed (and I was one of them rebelling against the final days of Winter, too)! The first Spring thing to note is that Daylight Saving Time begins this weekend. "Spring Forward" your clocks one hour at 2 a.m. this Sunday morning.
Next is the "official" start of Spring, which begins at 1:32 p.m. Eastern Daylight Time on Saturday, March 20. The start of Spring is defined by the Vernal Equinox ("Ver" from Latin meaning "spring," and "aequus" and "nox" combined to mean "equal night"), which is when (from our perspective on Earth) the Sun's incident solar rays are most directed at the Equator.
Earth is tilted at 23.44 degrees relative to its orbital plane, which means that as our planet orbits around the Sun throughout the year, the Sun's incident rays hit different parts of the Earth more directly.
(Image: NASA)
Thus, the Earth has seasons! Here's the perspective from Earth:

Sunday, March 7, 2010

What Happened To Winter?

Each year you know spring is around the corner when you hear people out riding their motorcycles - today they were out in full force! It looks like the cold Canadian air will stay bottled up north through at least next weekend. The next three days will be mainly quiet, then it's looking like it will be a stormy end to the week. A powerful storm will park itself over the Midwest and draw in moisture from both the Gulf of Mexico and the Atlantic Ocean. You will definitely notice the changes by Thursday and Friday!


We should see two or three waves of rain between Thursday and Saturday. In addition, we could see isolated thunderstorms embedded in these showers. Although the threat for severe storms seems limited at the time, a few strong storms could develop on Friday. Surface dew points should reach the lower 50s:


I'm expecting surface temps to also climb to near 70 degrees in the afternoon, so there should be enough instability to support thunderstorm development.


Jet stream winds will be strong enough to provide speed shear (increasing winds with height). However, this shear might be too strong and limit thunderstorm development.


This is still a long way out, and there are a lot of factors to consider. Regardless, it will be something that we will monitor through the week and will keep you updated!