The 4 September 2011 Tornado in Eastern New York: An Example for Updating Tornado Warning Strategies

While not having the high frequency of occurrence experienced by other parts of the country, tornadoes occasionally affect portions of the Northeast. The latest climatology developed from the Collaborative Science, Technology, and Applied Research (CSTAR) IV program has shown that the Albany County Warning Area is affected, on average, by about 3 tornadoes per calendar year. Advancements over the past ten years have dramatically increased the resolution of base radar data. This presents an opportunity to improve tornado warning strategies developed from the original version of the WSR-88D during the mid-1990s.

One of the original tornado warning strategies utilized was the V-R shear relationship. A local COMET study (LaPenta et al. 2000) found that maximum gate-to-gate shear below 3 km was useful in identifying tornadic storms. A linear relationship was found between the gate-to-gate shear and the rotational velocity of the mesocyclone. Using this concept, nomograms for operational use were developed for local tornado warning guidance. However, this relationship was very sensitive to range from the radar, and also has limitations due to the resolution of the original 4-bit radar products. The warning meteorologist had to be sure to normalize the diameter of the potentially tornadic velocity couplet used for calculating the shear value depending on the range from the radar of the storm in question. This necessary manual adjustment could reduce valuable lead time for tornado warnings.

As a result, an ongoing CSTAR project is updating the nomograms of the original V-R shear study by examining tornadoes across the Northeast that occurred after the implementation of the 8-bit base radar data in 2003 by using the new high-resolution velocity products. In addition, the study is using the GR2Analyst software to view the values of normalized rotation (NROT) for several radar scans up to the touchdown time of the tornado, which could potentially also have value as a tornado warning indicator.

On 4 September 2011, an EF1 tornado affected a 7 mile path across portions of the Mohawk Valley of eastern New York. While this tornado could have been effectively warned for using the original V-R shear relationship, this would not have incorporated the highest resolution data available and manual normalization for range would be needed. A poster will be presented showing how this tornado falls within the preliminary results of the updated V-R shear study and how the NROT values prior to the tornado formation could be used as a warning indicator. In addition, avoiding having to make manual adjustments for range can provide for longer lead times, resulting in improved protection of life and property.