Another Day; Another Risk of Severe Weather

06 May 2012 David Reimer 0 Comments

This graphic shows the probability of experiencing a severe thunderstorm within 25 miles of your location today and tonight. The brown shaded zones are what we consider a low risk, or a 5 percent chance. Within the yellow zone, the Storm Prediction Center has issued a standard risk of severe weather which means there is a 15 percent chance of experiencing severe weather within 25 miles of any given point. Thunderstorm coverage will be isolated across South Texas with a slightly higher coverage expected across North Texas.

The strongest storms will be capable of producing golfball size hail and damaging winds in excess of 60 MPH. However, all storms will be capable of producing cloud to ground lightning. As it is a Sunday and numerous outdoor events are planned, please keep that in mind. Thunderstorms should begin firing by 4 to 5 PM to the west of Interstate 35 and begin approaching Interstate 35 by 6 to 9 PM. Remember, expect the unexpected when it comes to thunderstorms and have a way to receive weather warnings later this afternoon, especially if you’re planning to be outdoors. When thunder roars, go indoors!

We’ll be chasing northwest of Fort Worth this afternoon and plan on following the storms back into the metroplex. We’ll have live video available after 1 PM.

7 AM Severe Weather Update for later Today

02 April 2012 David Reimer 0 Comments

Good Morning!

I wanted to provide a brief update early this morning. This graphic shows the probability of receiving severe hail (Larger then 1 inch) within 25 miles of any given point today. The standard 15% probability extends all the way from Southern Kansas south into Texas, and then eastward along Interstate 20 into East Texas. The enhanced probabilities, where we expect the highest concentration of severe storms, runs along and east of from Woodward, Oklahoma south to Vernon and Abilene. This enhanced zone does approach Interstate 35. Within this enhanced zone, there is nearly a 1 in 3 chance that you may experience severe weather this afternoon. In addition, conditions are very favorable for very large hail, which could be larger then baseballs and capable of producing property damage. In addition, a few brief tornadoes cannot be ruled out. These storms will form west of Fort Worth, but could approach the western sections of the Dallas – Fort Worth Metroplex by 10 PM. Please keep that in mind if you see storms off to the west later tonight…

March 30, 2012 Chase Recap

30 March 2012 David Reimer 0 Comments

Sadly, days that end up busting are usually the easiest logs to write since they’re short and to the point. Jenny and I left her house just southeast of Denton around 12:45 PM. We took the brief jog northbound on Interstate 35E before turning west onto Highway 380. We debated about continuing west or going more to the north on Highway 287. We ended up choosing Highway 287. It took us just over an hour to reach Wichita Falls, where we ended up staying for 30 minutes before deciding we needed to move back south. After an hour drive south on Highway 281, we arrived in Jacksboro where we met up with several other chasers. We sat around at a local gas station for about two hours until it became obvious that the cap was going to win and that no thunderstorms would be able to develop. We called the chase at 6:30 PM and headed back to town for dinner.

March 30, 2012 7 PM Fort Worth Sounding

A weather balloon launched from the National Weather Service in Fort Worth clearly shows why we did not have any thunderstorms this afternoon. While instability amounts were quite high and wind shear sufficient to support severe storms, a strong cap remained in place. You can see the inversion layer encased by a black line on the Skew-T while I’ve highlighted the convective temperature below. According to the data measured by the weather balloon, the surface temperature needed to reach 89°F for the cap to break and to support thunderstorms. We generally saw high temperatures of around 82°F to 84°F. We were close to having a few severe storms, but no cigar today.

What happened to Monday’s Severe Weather?

20 March 2012 David Reimer 2 Comments

Monday's Severe Weather Outlooks with Storm Reports

This graphic shows the severe weather outlook from the Storm Prediction Center for Monday, March 20. A standard risk of severe weather was in effect from Wichita Falls southwest to Langtry and points east. An enhanced, significant risk of severe weather was in effect from Southeast Oklahoma southwest into North and Central Texas. Overlaid on the outlook are official storm reports which show hail larger then one inch, winds over 58 MPH, and tornadoes. We see several reports of large hail, damaging winds, and even a few tornadoes in the southern portion of that significant risk area, but what happened in North Texas and Southeast Oklahoma? There are only a few reports of marginally severe hail and damaging downburst winds. The sun was out and instability was there, wind shear was very favorable for a severe weather outbreak, yet most folks only received garden variety thunderstorms with heavy rainfall. In terms of severe weather for the northern half of the significant risk area, our forecast was a bust. I want to explain what came together to cause the severe weather not to occur. We were always saying the highest tornado risk was in South Texas, where tornadoes did occur, but we expected large hail and damaging winds up north. We still got a few reports of those events, but the coverage was expected to be much greater. Lets go ahead and dive into some details and explain what factors came together to prevent widespread severe weather.

North Texas Radar - 4:04 PM CDT

I saved this reflectivity image at 4:04 PM on Monday for North Texas. The white line on the screen is an outflow boundary, which is essentially the leading edge of rain-cooled air. To the west of this line, thunderstorms are elevated above the surface and temperatures were in the upper 50s. To the east of this outflow boundary, temperatures were in the upper 70s with dewpoint values between 63°F and 67°F. Those living in those areas know how humid and muggy it was on Monday. The airmass ahead of the outflow boundary was very unstable and as many of you could tell yesterday from the surface winds, we did have a lot of wind shear in place. So why did we not receive severe weather in North Texas? Take a look at that radar image again and notice where all the rain/thunderstorms are located in relation to the outflow boundary. All the rain and thunderstorms at the time of this radar image were behind, or west, of the outflow boundary. That means those storms were ingesting rain-cooled air and were elevated above the surface, meaning they were not rooted in the boundary layer of rich, unstable air. If that outflow boundary had not pushed out ahead of the thunderstorms, it’s likely they would have been quite strong to severe as they pushed eastward across North Texas. So why did nothing form out ahead of this line in the warm, humid air mass?

Weather Balloon Data - 1 PM Fort Worth

The National Weather Service in Fort Worth launched a weather balloon at 1 PM on Monday. This allows us to actually see what is going on in the atmosphere. I know there is a lot of data on this graphic, but I want to focus your attention on the black circle I’ve placed on the screen. Do you see how the red line quickly rises? That red line actually shows the temperature around 6,000 feet above sea level and that rise in temperature is indicative of a strong inversion, or cap, in the atmosphere. That cap prevented thunderstorms from developing ahead of that line. Based on the data this weather balloon provided, it appears temperatures would have needed to be near 90°F in order for thunderstorms to break the cap. Obviously we didn’t get near that yesterday.

Further south in areas south and west of San Antonio, they were warmer and the upper level forcing associated with the storm system was closer to them, thus the cap was weaker and discrete thunderstorms were able to form out ahead of the line of thunderstorms. These storms quickly became supercellular and produced giant hail and tornadoes, one of which did appear to be rather significant. Luckily, these occurred outside major metropolitan areas, but did approach San Antonio. Yesterday goes to show that no matter how well you think you understand a weather setup, mother nature will always throw something unexpected into the mix. Don’t think just because yesterday didn’t end up being a major severe weather day that future forecasts will be so lucky.

Significant Severe Weather Outbreak still expected later Today!

19 March 2012 David Reimer 4 Comments

Visible Satellite at 9:40 AM

If you see sunshine today, that is NOT a good sign! The more sun we get, the more instability is able to build in. As you can see off this satellite image, there are breaks in the cloud cover that will allow instability to build…

Chance of severe weather within 25 miles of any given point

This graphic shows the probability of experiencing severe weather within 25 miles of any given point (such as a house) this afternoon and tonight. The highest risk is shown by the red line, which means locations in that risk have a nearly 1 in 2 chance of having severe weather within close proximity to their location tonight. This graphic has the probability numbers listed on the lines. We’re getting ready to head out to chase, so no long blog post this morning. I’ll summarize it real fast.

Threats: Tornadoes, Very Large Hail, Damaging Winds, Flooding

Timing: 11 AM Monday – 7 AM Tuesday

Risk: Significant

Risk Areas: Central Texas, North Texas (Includes San Antonio, Austin, Waco, D/FW)

Please have a way to receive weather warnings this afternoon!!!