Sunday, April 12, 2009

Easter Showers . . . For Some

As we've been saying, some have been seeing some Easter showers throughout the day today. Here's a quick capture of the radar.The areas I circled in yellow are where rain is actually hitting the ground - if you look close you can see those areas have a darker shade of green to them. This is also where rain has actually been measured.But not all the green areas in the first picture (radar capture) have rain actually hitting the ground, it may be falling but it doesn't all reach the ground. This is called virga. You can actually see virga when it's happening too - it looks a bit like this:When saturated clouds move through an area, rain will usually hit the ground. But if the layer of air near the ground is really dry, the rain falling from the cloud layer above will evaporate because that ground layer is so dry. Air pressure also increases the closer you get to the ground, which is another reason for evaporation. This evaporation also cools some of the air because now those cooler water droplets have been mixed into the air... dropping the temperature of the air. Virga will also saturate the drier layer of air - so if a system is persistant over an area, eventually rain will be the product there as well.

~KDLT Meteorologist Jesse Ritka

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