The National Weather Service will allow the Winter Weather Advisory to expire at 9 AM. That’s probably not a bad plan considering that all reporting stations I can find are above freezing except for a few isolated cold pockets up in DeKalb County.
The wintry mix has changed mostly to rain, and even though temperatures are hovering in the mid-30s north of U.S. 278, any icy spots should begin to wash away with the onset of heavier rain.
All this messy weather is caused by a process called “overrunning,” and it’s not complicated at all. Basically, cold air is dense and hugs the ground, but cold air like we have today only occupies about the lowest 4,000 to 5,000 feet of the atmosphere. You can consider that air mass to be shaped like a dome with the sloped edge coming through Central Alabama today. An area of low pressure along a cold front to the southwest of us is pushing warm, moist air from the Gulf of Mexico northward, and instead of moving the heavy, dense cold air, it takes the path of least resistance and jumps over it. As the warm air rises, it causes clouds and rain; those two things are going to actually enhance the cold air down here at the ground since they will keep us from having any sunshine to warm things up!
Back to that whole cold air – warm air thing. If the cold air is deep enough, you can get rain, sleet, snow, or a mixture of all three. This morning, the overrunning warm air began to erode the depth of the cold air somewhat, causing more of the precipitation to fall as rain instead of ice or snow. You win some, you lose some, and sometimes you just get lucky in situations like this. Given the model interpretations that we had over the weekend, the forecast was actually pretty good. Sure, the snow accumulations didn’t happen, but if you could move the low pressure center south by 50 or 100 miles, we’d see a big difference!
Speaking of models, I know a lot of folks like looking at every run and have fun trying to see what we’re all looking at in the weather office. I found a great website that has a lot of good information about how models work, and while it’s a little technical, it may give you some insight as to why the 12Z will be so different from the 0Z.
Here’s the site! UCAR Model Module
The wintry mix has changed mostly to rain, and even though temperatures are hovering in the mid-30s north of U.S. 278, any icy spots should begin to wash away with the onset of heavier rain.
All this messy weather is caused by a process called “overrunning,” and it’s not complicated at all. Basically, cold air is dense and hugs the ground, but cold air like we have today only occupies about the lowest 4,000 to 5,000 feet of the atmosphere. You can consider that air mass to be shaped like a dome with the sloped edge coming through Central Alabama today. An area of low pressure along a cold front to the southwest of us is pushing warm, moist air from the Gulf of Mexico northward, and instead of moving the heavy, dense cold air, it takes the path of least resistance and jumps over it. As the warm air rises, it causes clouds and rain; those two things are going to actually enhance the cold air down here at the ground since they will keep us from having any sunshine to warm things up!
Back to that whole cold air – warm air thing. If the cold air is deep enough, you can get rain, sleet, snow, or a mixture of all three. This morning, the overrunning warm air began to erode the depth of the cold air somewhat, causing more of the precipitation to fall as rain instead of ice or snow. You win some, you lose some, and sometimes you just get lucky in situations like this. Given the model interpretations that we had over the weekend, the forecast was actually pretty good. Sure, the snow accumulations didn’t happen, but if you could move the low pressure center south by 50 or 100 miles, we’d see a big difference!
Speaking of models, I know a lot of folks like looking at every run and have fun trying to see what we’re all looking at in the weather office. I found a great website that has a lot of good information about how models work, and while it’s a little technical, it may give you some insight as to why the 12Z will be so different from the 0Z.
Here’s the site! UCAR Model Module
on February 6, 2006, 9:08 am
On another note, I saw in the paper yesterday where they are hiring a weekend meterologist and a morning anchor. Someone leaving?
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