Wednesday, April 16, 2008

The Joys of Severe Weather Forecasting

The weather has been rather tame lately, so there hasn't been too much to talk about. What follows are random thoughts about weather forecasting......

There have been a couple of "busts" over the past few weeks with regards to severe weather forecasts. I remember the night of the NCAA National Championship many forecasters thought we were in for a substantial outbreak of severe weather. I had bought into the forecast as well. Needless to say, it didn't pan out as expected. Yes, we had a storm with hail that moved through North OKC that night, but that was only one of a few severe storms in the state that day, and none were even close to producing tornadoes. Now for the reason why.....

Lack of moisture. That's it. That's all. Most of the computers had predicted the high-moisture, high-octane air that was sitting over south Texas to surge north into Oklahoma during the evening, providing the last ingredient needed for tornadoes. The more moisture that there is in the air, the closer to ground-level that clouds can form, and the easier it is for storms to rotate closer to the ground. I honestly believe that if more moisture HAD been in place that night, the results would have been different. The storm that moved through OKC had a well-defined hook echo, but this "hook" was located a few thousand feet above ground level, so it was never a threat to tornado. Had that circulation been at ground level, I believe the result COULD have been a large tornado.

The forecasters did the right thing. The potential was there for dangerous weather that night. When the elements are coming together for an outbreak, you better err on the side of caution, because failing to do so could produce some undesirable consequences.

Monday, April 7, 2008

Monday Update

Just got done studying for my Intermediate Accounting test tomorrow, but before I go to bed here are my thoughts for Monday......

We have ALMOST all ingredients in place for a fairly nasty severe weather event Monday night. The one thing that will be lacking the most is moisture. Even if moisture ends up being a little low, I expect a few supercells to form in western Oklahoma between 5 and 7PM. The storms will probably be along a line from Alva to Clinton to Altus. Wind shear will be more than adequate for the storms to acquire rotation. They will move in an easterly direction at about 25 to 30MPH, putting them at the Highway 81 corridor around 9PM and possibly the I-35 corridor between 10:00 and 11:00. The storms will be capable of very large hail and isolated tornadoes, especially in the 9:00 to 11:00 timeframe, which is when surface winds will increase out of the SE, feeding the storm's inflow.

I will add that we should be thankful that moisture isn't going to be any higher than it already is going to be on Monday. If that were the case, I would be talking about the potential for strong/possibly violent tornadoes Monday night.

Sunday, April 6, 2008

Monday Severe Weather

Looking at the latest info, it appears that Monday evening/night could be rough. Many storm chaser message boards are buzzing about the prospects of a regional tornado outbreak in western and central Oklahoma. Wind shear (changing of wind direction or wind speed with height) is forecasted to be strong. Temperatures are going to warm to near 80, and dewpoints should be in the low to mid 60's, which is definitely enough moisture for severe weather.

It seems like I had this exact same post last week, but the storm system didn't pan out as had been forecasted a few days in advance. That could definitely happen again this time, but if this active pattern continues this Spring we are bound to get hit eventually....

More posts to come as needed.

Thursday, April 3, 2008

Reader Question

Sorry, couldn't resist the title.

Someone recently asked me how it is that a tornado can damage one house but leave the house next to it with little, if any, damage. From what I know here are the 3 main reasons:

1) Path of the tornado

Often times a tornado is weak enough or small enough to inflict damage on only a very small path. The most intense winds may be only a few yards or even feet wide, leaving one neighbor unscathed and the other neighbor weighted with bad luck. Also, a tornado may not always be fully in contact with the ground, displaying a "hop and skip" pattern.

2) Structural integrity

Small subtleties in the construction of a house can make a big difference. How well is the frame anchored to the foundation? What kind and how good are the clips that are used to attach the roof to the house? One home may display significantly more damage than another because of a small difference in quality of construction. If one small corner of a roof fails and causes the roof to become detached, the rest of the home is left open for the tornado to damage. A house across the street is hit by the same tornado, but the roof remains intact, and thus no interior damage is done......maybe except for a few windows.

3) Multiple-vortex tornadoes

Sometimes several small "suction vortices" will be visible in a tornado (see above image). Sometimes what appears to be one large tornado is actually many smaller vortices, all rotating around each other (hence the name). Oftentimes these can be the most violent tornadoes, and they can also leave striking damage paths. Since the smaller vortices are all rotating every which way, total destruction can lay next to a few shingles peeled off, only a few hundred feet away. The picture below shows a field that was hit by a multiple-vortex tornado. Note all of the smaller paths where the smaller vortices passed.

I hope that answered the question well enough (or maybe too well for some of you!)