Aug 172011
 
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Skew-T plots are graphs of environmental conditions with altitude over a site. The weather service launches weather balloons twice a day from various locations around the world. As they rise through the atmosphere they record temperature, dewpoint and wind speed and direction as they rise. To me, they seem very complex and full of important, nuanced information. The Flagstaff area is one of the sites for these twice daily balloon launches. Here is this morning’s Skew-T for Flagstaff.

Skew-T plot for Flagstaff, 8-17-2011, 1200Z (From NOAA's Storm Prediction Center)

Skew-T plot for Flagstaff, 8-17-2011, 1200Z (From NOAA's Storm Prediction Center)

You can see how complicated the plot is, let alone the complicate values calculated values from it in the chart surrounding it. The green line is dewpoint temperature. The red is actual temperature. The brown dotted line, mostly to the right of the red line, shows what would happen to a parcel of air as it rises in altitude. One of the simpler calculations is the area between the red and brown dotted line. Notice there is a sizable gap between most of the red and brown line. This is called the CAPE or Convective Available Potential Energy. It’s calculated in the chart below the graph. It is a good indicator of the potential for thunderstorms

The bottom two CAPE values are greater than zero, but not huge. Compare it to the SUnday morning plot.

Skew-T plot for Flagstaff, 8-14-2011, 1200Z (From NOAA's Storm Prediction Center)

Skew-T plot for Flagstaff, 8-14-2011, 1200Z (From NOAA's Storm Prediction Center)

At first, they might look similar, but only because the charts have the same colors and style. The CAPE values are different. The plot from Sunday has a higher forecasted CAPE and a lower MU (most unstable) CAPE. Also, PW, precipitable water, is a bit higher on Sunday.

As I mentioned, I am still baffled by these charts and how to read them. I figure that by posting and discussing a few, I might bet better.

What will today bring? A reasonable chance of thunderstorms, I think.

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