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Project Thread/New Construction/Photo du jour/Const. CAMs


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22 hours ago, Mr_Bond said:

The two of us have noticed that many storms split up and go around the Nashville bowl, or the rain lightens up a bit as it passes over the bowl.  I once watched a major storm front moving in from the north (quite rare) just split in two and go to the east and west of us.

I don't know the exact science behind this, but I believe it has to do with the "heat island" effect present in most cities. Rain occurs when water condenses out of the air when it encounters colder temperatures, so warmer temperatures within a city could certainly alter the otherwise expected forecast.

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10 hours ago, claya91 said:

Weather nerd here. People discuss this quite a bit, so I figure I'll chime in. Since there is about a 400 ft difference in elevation between outlying areas on the rim like Joelton and Downtown Nashville, orographics, or the "bowl" effect Mr. Bond elluded to occasionally have a slight influence on precipitation that falls in Nashville proper, however radar bias is the main culprit for this phenomenon.

Basically, the radar at the Nashville NWS in Old Hickory shoots a beam outward that detects precipitation/objects in a ~100 mile  fixed radius around Nashville. Because this beam has an upward trajectory as it travels, the further away from Nashville, the higher off the ground the radar samples the atmosphere. This means the rain/sleet/snow it depicts over Nashville is detected just above ground level but what it depicts at Clarksville or Bowling Green is actually detected thousands of feet above ground level. Since precipitation often evaporates as it falls towards the ground, the 'split' you often see as weather approaches the city is merely more accurate data being presented due to closer proximity to the radar site. It's a current limition of doppler radar technology that can only be remedied by increasing the density of radar sites.

Fascinating.  My friend who was discussing this with me measures rainfall in her yard and compares that to the official totals.  Since she lives near an area prone to flooding, she feels more informed by measuring rainfall herself.

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Tying in the original theme of this thread with the posts about rain: I'm impressed by how many of these construction crews stay on the job and work through the rain and downpours. I've passed several of the big construction sites and saw crews working outdoors through the rain. I'm guessing that the only time these guys really do take off is when there's lightning in the area.

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