Monthly Archives: February 2012

For complete details on tomorrow‘s severe weather setup, please view our video briefing on YouTube.

[caption id="attachment_6120" align="aligncenter" width="600" caption="Day 2 Convective Outlook"][/caption]

Let’s start out by detailing the latest severe weather outlook from the Storm Prediction Center. This outlook was issued just before noon today and we will have a new outlook out by midnight, which we will bring to you. As of this outlook, the standard 15% probabilities have been removed from much of North and Northeast Texas. Right now, the 15% probabilities are limited to extreme Northeast Texas, extending from Texarkana northwest to Paris, Texas. The elevated severe weather probabilities, shown in the 30% region, are placed over Eastern Oklahoma and Arkansas. That’s where the most concentrated severe weather is expected to be located. Low-end 5 percent probabilities extend from Shreveport to Mabank, northwest to Weatherford and Wichita Falls. Conditions are actually pretty favorable for severe weather across all of North Texas, but a strong cap is going to be in place which will limit thunderstorms. In fact, we may not have any thunderstorms develop at all. Mesoscale factors (differential heating boundaries, gravity waves, outflow boundaries from morning convection, etc) can’t be determined until we actually start seeing them tomorrow morning and afternoon. Weather models can’t pick up on those and they’re often only noticed hours before an event.

[caption id="" align="aligncenter" width="600" caption="0Z NAM: Most Unstable Instability Values at 12 AM WednesdayIf you watched the weather video I published at 8 PM, you saw this graphic from the 18Z North American Model. This graphic shows the most unstable instability amounts at 12 Am Wednesday. The reason I'm showing values from 12 AM verses 6 PM on Tuesday is that I don't think it's likely we're going to have any storms in progress at that point. It's more likely we're going to have to wait a few hours until the cold front arrives and brings that forcing needed to break the cap. Compared to earlier model runs, the 0Z NAM has come in with higher instability amounts. It looks like much of North Texas and East Oklahoma will have instability values between 1,500 and 2,000 joules per kilogram. When looking for the possibility of severe weather during the winter/early spring months, I like to use instability amounts at or above 750 joules. Severe weather can happen with instability values below that, but I like using 750 J/Kg as a mean. Obviously we're going to have more then enough instability to support organized thunderstorms tomorrow night, but instability isn't the only ingredient you need for thunderstorms, and their associated severe weather.0Z NAM: 3 KM Helicity Values for 12 AM Wednesday"][/caption]

This graphic is basically a combination of multiple severe weather products. This takes into account wind shear at multiple levels of the atmosphere. Basically, this tells us how much spin is available for storms. The highest values are located over Arkansas, closer to the upper level storm system. However, enough wind shear will be present across Northeast Texas to support the possibility of organized thunderstorms.

Basically, if we had a weaker cap tomorrow, we would be dealing with a widespread severe weather outbreak in North Texas. That isn’t likely to happen because the cap is strong and the storm system will be passing to our north. We’re going to get scraped by that storm system tomorrow night, which is when we may have a few storms develop. The most likely time for thunderstorm development will be along the cold front from 9 PM to 3 AM in Northeast Texas. IF storms do develop, they’ll likely be in the form of a linear squall line or line segments. The storm mode and the southwest winds at the surface suggest the tornado threat will be limited, but there will be a threat for large hail and damaging straight-line winds.

I’ll be honest with all of you right now. This is a low confidence forecast. It would only take a few things to change slightly to change this from a marginal storm setup to something more potent. If there are only a few storms tomorrow, it won’t matter how significant the overall event is, because if one hits your house you will think it was a big event. That being said, I encourage you to stay tuned tonight and tomorrow. We’re going to be around posting numerous updates on the event. If we see anything change, we’ll let you know ASAP. There is no reason to be worried or scared of storms tomorrow. This does not look like a major event! In fact, you shouldn’t be scared even if this was a major tornado outbreak. Knowledge is Power! Just stay tuned and have a way to receive weather warnings. If you go under a severe thunderstorm or tornado warning, just go ahead and take protective action. That applies to any severe weather setup, whether it be big or small.