Day 129: Location of Highest Severe Threat on Monday

Posted by pmarsh on 9 May 2010 | 16 comments

As I’ve been alluding to for several days, the stage is being set for a significant severe weather outbreak on Monday. In fact, the VORTEX II crew called off any operations today, Day 9, so that they could travel to be in position for operations tomorrow.

Although it is becoming increasingly apparent that a significant severe weather outbreak will unfold tomorrow, the exact location of the worst weather is not entirely obvious. It is true that a very powerful mid-level trough will be racing through the plains at the same time warm, moist air will be drawn northward, and hot, dry air will be surging eastward from the west. But it isn’t apparent where the intersection of all these ingredients will occur.

Below are forecast soundings from a couple of sites throughout the southern plains taken from four different numerical models that were initialized and run this morning. A sounding is essentially a vertical snapshot of the atmosphere’s temperature, moisture, and wind profiles.  They allow meteorologists to assess the atmosphere’s potential for producing a wide variety of phenomena ranging from ice storms to wind storms to severe thunderstorms and tornadoes.  Temperature and moisture profiles are plotted on a Skew-T (named because the temperature lines are “skewed” at angles), whereas the wind profile is typically displayed using a hodograph.

The image above is taken from the 12 UTC (7 AM CDT) run of the North American Model (NAM). It is the sounding and hodograph for Norman, OK at 01 UTC Tuesday (8 PM CDT Monday). The image below is taken from the same model run but is valid an hour earlier for Wichita, KS. Without going into a lot of interpretation (if enough people request it, I’ll do a future blog post or two about interpreting soundings and hodographs), both of these images are representative of what would be expected in a significant severe weather outbreak. These images alone would argue that the chance of significant severe weather would be quite high in central Oklahoma and southern Kansas.

But, it can’t be that simple, right?

The image above is once again valid for Norman, OK at 01 UTC Tuesday (8 PM CDT Monday), the difference is that it comes from the 15 UTC (10 AM CDT) run of the North American Model with the Kain-Fristch convective scheme (NAMKF). The image below is taken an hour earlier from Wichita, KS. Notice anything different about these two images and the two images above?

Although the hodographs (wind fields) still look conducive to severe thunderstorm development, the thermal and moisture profiles do not. In these runs the instability is considerably lacking and the moisture appears to have dried out. This would indicate that central Oklahoma and southern Kansas would not be in the axis of greatest threat for a severe weather outbreak tomorrow. So where did it go?

This would indicate that central Oklahoma and southern Kansas would not be in the axis of greatest threat for a severe weather outbreak tomorrow. So where did it go?

If we take a look (above) at the same kind of plot a farther east of the I35 corridor, in this case, Tulsa, OK, we can once again find temperature, moisture, and wind profiles that look similar to the first two I showed. This would seem to argue for the severe weather threat to be centered more in the northeast Oklahoma area than the I35 corridor in central Oklahoma and southern Kansas.

So which is it? Maybe looking at another model will help us determine where the highest risk will be…

These images are taken from today’s 12 UTC run of the Global Forecast System (GFS) model. The image above is valid for Norman, OK at 00 UTC Tuesday (7 PM CDT Monday) and the image below is valid at the same time for Wichita, KS.

Although not as impressive as the NAM forecast for Norman, OK that I posted initially, the GFS forecast for Norman is certainly indicative of a significant severe weather potential. Wichita, KS, on the other hand, still has very good wind profiles, but doesn’t have the temperature and moisture profile to support a widespread significant severe weather outbreak.

What about Tulsa, OK?

The forecast (below; valid at the same time as Norman, OK and Wichita, KS) for Tulsa, OK isn’t as impressive as Norman’s, but is a lot better than Wichita’s.

This set of temperature, moisture, and wind profiles would argue for a severe weather threat centered in central Oklahoma, extending northeastward through Tulsa, OK and not much in the way for south central Kansas.

Anything else to look at? You bet! Below is a set of forecast soundings from a model with a grid-spacing of 4 kilometers. This model doesn’t have to parameterize convection as it is capable of generating thunderstorms in the model natively. What does this model forecast?

Once again, this model was initialized at 12 UTC (7 AM CDT) and the plots are valid for 00 UTC Tuesday (7 PM CDT Monday). The image above is for Norman, OK and the image below is for Wichita, KS. Norman’s sounding is once again indicative of a potential major event whereas Wichita’s is considerably more marginal.

Examining the sounding for Tulsa, OK (below) indicates that severe thunderstorms would be possible, but the threat for tornadoes might not be as high as the other models would indicate.

So what does all this mean? Well, for one, all these plots did was show whether the temperature, moisture, and wind profiles would be sufficient for severe weather. I didn’t even discuss whether or not a thunderstorm would develop in an environment characterized by one of these soundings. In general, the farther north you go tomorrow (based on the domain laid out in the post of central OK, southern KS, and northeast OK) the better your chance of seeing a thunderstorm. Thus, while the environment may be supportive of a major tornado in central Oklahoma, we aren’t guaranteed that a thunderstorm will develop.

Keeping all this in mind, what would you forecast if you were working tonight at the Storm Prediction Center? What would you forecast if you were working on the VORTEX II project? In both cases your forecast will put into motion various plans that affect a lot of people and millions of dollars worth of equipment. Do you err on the side of caution and over warn with your forecast, knowing it’s better to be safe than sorry? Or do you take a chance by making a more specific forecast, trying to save some people money and stress, and risk being wrong?

It’s a tough decision that meteorologists are faced with all the time. What is the best way to convey this kind of uncertainty? I’m interested in hearing your thoughts…