Dec. 20, 2012 Severe Weather Threat

18 12 2012

Welcome to our first severe weather forecast post on our blog.  We are looking at an event that is 2 days away and everything looks like it might line up for a severe weather event.  First, just to get a broad point of view on what we are looking at, here is the severe thunderstorm outlook posted from the Storm Prediction Center.  All of our viewers are in the Slight Risk area for severe weather and that entire Slight Risk area is under a 15% chance of seeing severe weather.  That doesn’t seem like much, but for this far in advance and this time of year it poses some paying attention to.

Now time to break it down.  We all know what the jet stream is right?  It’s basically a narrow band of fast moving air about 30,000 to 40,000 feet above us.  When we get in a certain area of the jet stream, we can either see clouds and thunderstorms or clear blue skies.  Thursday morning to noon hours is looking to have the area of clouds and thunderstorms right over our viewing area.  There is another thing we look for dealing with wind that is called a low-level jet.  That is basically a focused area of strong winds about 5,000 feet above us.  We can actually see this phenomenon when we see clouds that are low moving really fast.  When this focused area of strong winds moves over are area, as it is forecast to do, reaches and exceeds 46 MPH or 40 Knots we tend to get concerned with it because it is another sign of seeing clouds and thunderstorms.  The low-level jet is looking to be 45-70 MPH or about 40-60 Knots Thursday morning.  That really makes us concerned about the chances of severe weather.

Our next concern we look for are in the temperatures.  First of all, this is a strong cold front and what we mean by that is that there is some very cold air behind it and very warm air ahead of it.  Any time we see this it automatically sends up some red flags for us to watch it for the chance of severe weather.  The other thing we look for is the transport of warm air and we look at this in the same area as the low-level jet mentioned earlier.  Any time we get a South or Southwest wind it’s coming from warm, moist area over The Gulf and into cooler, drier area far inland.  This is always a sign of clouds and showers/thunderstorms.  However, when you add the strong winds mentioned earlier in the low-level jet to that it’s more going to help produce thunderstorms which is what we are expecting to happen Thursday.

After looking at all of this, we look into another factor that is a little harder to explain and that is the movement of energy.  Basically, cold fronts are a separation of a lot of energy behind it and little energy in front of it.  We look at about 18,000 feet above us to see where this energy is and the direction the wind is blowing it to.  When we see air moving from high energy to a lower amount of energy it throws up a sign for us to watch it because when this happens we will get clouds and if there is a big enough difference in the energy it could bring up showers and thunderstorms.  There is some disagreement in this area with the forecast models we use which is a problem because this could make the difference between thunderstorms and supercells capable of producing tornadoes with everything else added into it that we have mentioned so far.  We will continue to watch this, but as of right now it is looking like this transport of energy is strong enough for us to watch for a wind event and some isolated tornadoes.

The final thing we look for is the change in wind direction with height from the surface to about 18,000 feet.  The ideal setup for tornadoes is when we have a surface wind from the Southeast and the wind at about 18,000 feet is from the West which is greater than a 45 degree change in direction.  Luckily, this is not what we are expecting Thursday morning, but it will be close.  The surface winds are looking to be from the South and from the Southwest at about 18,000 feet.  Not ideal for a tornadic event, but still poses the threat that a few tornadoes could be seen from this with everything else on top of it.

So to sum it all up now, we are looking at a very good chance of strong thunderstorms Thursday morning with a decent chance of severe thunderstorms capable of producing strong damaging wind and even some isolated tornadoes.  Our biggest concern with all of this is the fact that it will be in the morning hours which is definitely not ideal for severe weather like this to occur because we, typically, will have just have gotten out of the coolest part of the day which is about 6:40 AM right now.  With this included, it will lessen the threat of severe weather some.  But, nonetheless, the threat will be there and since this is 2 days ahead things can change.

We will continue to heavily monitor this and keep you updated with the latest for Thursday.

-Michael Vasquez



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