Monday, December 19, 2011

Severe Weather Discussion- Dec. 19

There is a severe weather risk in Texas, including a tornado, damaging wind and hail risk. We will explain it based on the graphic above. As a pre-warning, don't let it overwhelm you.
We will explain everything that needs to be explained on this image.
Sounding from Corpus Christi, TX
Let's start on the top. There is a vertically positioned bar graph showing colors and bars. These are wind speeds with heights. Basically, the more difference there is between these bars indicates a better environment for tornadoes. We can see some difference, but nothing that really alarms me for this specific graph. Moving to the right we see a square box with what looks like a target. This is a hodograph. A hodograph, in simple terms, monitors which direction the weather balloon travels (because all this information can only be detected when sent up by a weather balloon). The direction of travel is then graphed on this target-like image to produce a squiggly line. If the line goes in a fairly circular direction, that means that there is rotation in the atmosphere and tornadoes may occur. Luckily, the only somewhat circular motion we see is very near the surface, and we need some more rotation in upper levels of the atmosphere for tornadoes.
Okay, now we get into the statistics on the bottom left. Surface CAPE (instability) is fairly low this morning, which is good, because tornadoes need high CAPE values. Forecast Surface CAPE only amounts to just over 1300 j/kg CAPE, which is still somewhat low. CINH (stability) is low, meaning that storms should be able to form somewhat easily.
PWAT values indicate the amount of water that would be present if a column of air in the atmosphere was condensed into a small space. This morning's PWAT values are at 1.5 inches, indicating a very wet atmosphere prime for wet thunderstorms.
In the small box still on the bottom left we see 'Supercell' at 6.4 units. That means that super cells have a potential to happen, especially seeing that 6.4 is a pretty substantial value. Significant Tornado (SIG TOR) values are at 0.5, which is an interesting value for December.
Something not especially noted on here is the Significant Tornado Parameter. The NAM is indicating that the Significant Tornado Parameter values may reach at 5 out of 10, which is about the same as the SIG TOR index.
The Significant Hail parameter is at 0.4, which indicates some hail could fall today.
The last thing is the box on the lower right hand corner. In small pink text below the word 'supercell', there is '9 loose matches' and then 'SARS: 67% TOR'. This means that this sounding generally matched up with 9 soundings in recent history, and out of those 9, 67% produced tornadoes. We are not entirely sure about that as information concerning this topic is somewhat scare, but this is what we have come up with.

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