The 05/15-05/16 TX Tornado Outbreak
The last two weeks have featured some rather remarkable weather that has ranged from morning lows around freezing, high temperatures soaring way above 100, and unfortunately, some deadly tornadoes. As part of the Satellite Proving Ground at the NOAA Center for Weather and Climate Prediction (NCWCP), we are currently demonstrating some products that will help with diagnosing and forecasting convection. The Overshooting Top Detection (OTD) is the first product that forecasters are evaluating and in the next few months, we will introduce a new lightning density product (see earlier post on the first spring MCC) that utilizes the Vaisala GLD-360 lightning feed to create a density plot of lightning strikes.
As many of you know, the evening of 05/15 brought some very severe weather to the Dallas-Fort Worth metro with at least one EF-4 and one EF-3 tornado in the southwest suburbs. These storms were part of a larger scale system that was rotating through Oklahoma and the two products mentioned above provided some very interesting and useful information about these storms.
The image above was taken approximately four minutes before the first report of this eventual EF-4 tornado touched down in Granbury, TX. The Overshooting Top Magnitude product adds more information to the overshooting top (OT) associated with this supercell thunderstorm than just the fact that it exists. The OT is approximately 9-11 degrees Celcius colder than the surrounding cirrus of the anvil. This could indicate the potential for large hail and in this case, a precursor to the tornado. Typically, the severe weather occurs between 5-30 minutes after the time of the OT detection.
This radar image compliments the satellite image above and is valid approximately 2 minutes before the tornado report was received. The two supercells highlighted are the tornado producing storms west-northwest of Fort Worth, TX. The southernmost supercell is responsible for the OT seen in the satellite image. Although I cannot say with absolute confidence that the OT Magnitude product would have given a strong indication of a potential EF-4 tornado, it did provide information on the most intense updrafts associated with these storms.
The new Vaisala GLD-360 Lightning Density product that has been developed as a coordinated effort with the Ocean Prediction Center (OPC), NESDIS STAR, and the Cooperative Institute for Climate and Satellites (CICS) did a great job of showing the highest concentration of cloud-to-ground (CG) lightning strikes associated with the thunderstorms about 9 minutes after the tornado report was received. Notice how the two lightning cores are as distinct in this image as the radar image above! This algorithm takes all of the individual CGs (positive and negative) and bins them into 2-minute, 15-minute, and 30-minute lightning density plots. The above image is a 30-minute accumulation of CGs, scaled. The purpose of this product is to simulate the capabilities of the upcoming Geostationary Lightning Mapper (GLM) that will be on GOES-R and is a compliment to the Pseudo-GLM product that is being developed and provided by NASA SPoRT and the University of Alabama-Huntsville.
Another interesting caveat of this severe weather event was this unusually strong OT Magnitude signal observed at 0232 UTC. The OT Magnitude exceeded the scale I created for the product with an OT that was greater than 18 C colder than the surrounding cirrus anvil! I’m sure there was significant hail in this area at this time!
*I created animations of the above mentioned products for this event which you can access at the bottom of this post. Just click on the images and the animation should run on a separate window.*
A Supercell Thunderstorm over the Gulf Stream?!
In the early morning hours of 05/16, another supercell formed nearly 1800 miles to the east-northeast over the Gulf Stream, east of the Mid-Atlantic. As a thunderstorm crossed the north wall of the Gulf Stream, it quickly intensified around 08 UTC into a supercell as it moved east over very warm waters. Although not a threat to anyone, the storm was located over shipping lanes and there was a ship located just northeast of the storm during maximum intensity. As you look at the images below, I want you to think about this question: If you observe similar structures and similar lightning patterns to the TX case, and have no radar, is it possible that this supercell was producing large hail, torrential rainfall, microbursts, or even a large waterspout?
The image above shows the OT Magnitude product indicating an OT that is approximately 16-17 C colder than the surrounding cirrus! This is very intense for a maritime thunderstorm and indicates this storm most likely exhibited a supercell structure. One of the OPC forecasters noted that this is the most intense thunderstorm he has witnessed over the Atlantic offshore zones in a long time.
Once again, the GLD-360 Lightning Density product shows a very intense core of CG lightning strikes co-located with the OT indicated above. It actually appears the lightning was more intense in this supercell than what was observed over TX a few hours earlier.
One of the OPC forecasters had this to say about using these product for his operations:
“I used the overshooting cooling product to help determine the intensity of the supercell, whether [it] was exhibiting a weakening or strengthening trend. In the afternoon I used the overshooting cooling product to support adding higher winds in thunderstorms to the offshore forecast in developing convection over this same offshore zone. The product also validated the very high lightning density data seen with these thunderstorms.”
Once again, I have created animations of this event below for your convenience. Think about the question above when you look at the animations and I encourage you to leave comments or questions as this could lead to interesting discussion. I think these two events provide an interesting comparison and it might be feasible to use these products for maritime convection to warn recreational boaters, military ships, and cargo vessels of potential severe maritime convection. The OPC and Tropical Analysis and Forecast Branch (TAFB) will continue to evaluate these products through the summer as part of the GOES-R Proving Ground activities.
Thank you for reading!