The 4 Sep 2011 Tornado in Eastern New York: An Example for Updating Tornado Warning Strategies Brian J. Frugis NOAA/NWS Albany, NY NROW XIII 2-3 November 2011

CSTAR IV & Motivation for Study New Tornado Climatology was developed over the summer of 2010 for the Northeastern US with CSTAR work by undergrad UAlbany students A goal of CSTAR IV is to develop/update tornado warning strategies using the new 8 bit high resolution radar data – V-R shear relationship has been an effective method for predicting tornadic development, however, this is based off of 4-bit radar data

Updated Tornado Climatology by CWA Number of Tornadoes for 1981 – 2010 Normal Period

Number of tornadoes from =100 Average number per year is 3.33

Number of Tornadoes = % are weak (EF0/EF1), 16% are strong (EF2/EF3) and only 5% are violent(EF4/EF5)

Previous Work LaPenta (2000) led a COMET study on V-R shear relationship for Northeastern United States tornadoes – Collaborate project between UAlbany and NWS Albany This study created nomograms for operational use based on a linear relationship between gate-to-gate shear and the strength of the rotational velocity of the mesocyclone

V-R Shear Relationship Maximum observed gate-to-gate shear below 3 km was found to be useful in identifying tornadic storms (LaPenta et al. 2000) S=V r /(D*1800) Shear (S) is measured in units of s -1, rotational velocity (V r ) in knots and D is the diameter of which S is calculated in n mi.

Accounting for Varying Shear Values With 4-bit data, adjacent pixels are 0.5 n mi apart within 30 n mi from the radar. This distance becomes 1.0 n mi at 60 n mi away from the radar due to beam spreading Because of this, D is variable depending on range from radar and must be normalized In the LaPenta study, D was set to 0.5 n mi for areas within 30 n mi of radar and adjusted for areas further away (LaPenta et al, 2000)

Maximum Velocity Differential of Mesocyclone (V m ) Determine strength of large-scale mesocyclone Based off “Mesocyclone Recognition Guidelines” (Andra et al. 1994) – Uses a 3.5 nm mesocyclone width Image from 1998 Mechanicville, NY F3 Tornado, courtesy of LaPenta, et al. 2000

(LaPenta et al, 2000)

Legacy 4-bit V/SRM Products Resolution: 1 km (0.54 nm) by 1 degree Range: 124 nm 16 data levels: -64 kts to +64 kts An example of 4-bit reflectivity (Z) image from KENX from 2123z 4 Sept 2011

8 Bit V/SRM Products Introduced in late 2002/early 2003 with AWIPS build Resolution: 0.25 km (0.13 nm) by 1 degree Range: 124 nm (no change) 256 data levels (2 8 ): kts to +123 (using standard setup) An example of 8-bit reflectivity (Z) image from KENX from 2123z 4 Sept 2011

Super Resolution 8 bit V/SRM Products Introduced in Spring- Summer 2008 with RPA/RDA Build 10.0 Resolution: 0.25 km (0.13 nm) by ½ degree Range: 162 nm 256 data levels (2 8 ): kts to +123 (using standard setup) An example of 8-bit super resolution reflectivity (Z) image from KENX from 2123z 4 Sept 2011

Advantages of New High Res Data With the 8-bit high res data, we no longer have to adjust D for range when using the V-R shear technique – This is because going from the mid point to mid point of adjacent pixels is 0.5 n mi or less for up to 60 n mi from the radar The higher resolution data allows more subtle features to be resolved – Higher velocity values can be calculated (up to 128 kts in normal setup for 8 bit as compared to 64 kts for 4 bit)

Area within 60 n mi of KENX RDA

4 Sept 2011 Tornado Rated EF1 with top winds of 110 mph by NWS Albany Survey Team Formed at 2120z near Florida, NY Up to a half-mile wide through Cranesville, NY Dissipated at 2135z near Glenville, NY On the ground for 7 miles KENX 0.5° Z Loop from 4 Sept 2011 between 2109z and 2146z

4 Panel KENX SRM from 2119z (0.5°, 0.9°, 1.3°, 1.8°)

KENX VWP 2051z – 2137z 4 Sept 2011

KENX 0.5° Reflectivity Loop w/TVS KENX 0.5° Spectrum Width Loop Using Spectrum Width as an Indicator of Tornadic Development

Calculating Legacy V-R Shear 4 bit KENX SRM 4 Sept 2011 – 2123z Since distance from RDA=20 nm, shear can be measured with 0.5 n mi diameter V r = 43.0 kts S= s -1

Maximum Velocity Differential of Mesocyclone (V m ) Tornadic Circulation Mesocyclone Circulation SRM Cross-Section from KENX Radar 2123z 4 Sept 2011 – About 20 n mi from RDA Maximum Velocity of Mesocyclone (V m ) = 55 kts Image is from Vertical Slice Pane from AWIPS FSI

(LaPenta et al., 2000) 4 Sept 2011 Tornado S=.0450 s -1 V m =55 kts

4 Sep Z KENX SRM Legacy 4-bit: (1 km x 1 degree) Super Resolution 8 bit: (0.25 km x 0.5 degree) V r =43.0 kts, D=0.5 n mi, S= s -1 V r =53.9 kts, D=0.5 n mi, S= s -1

Comparing Storm Types LaPenta et al. (2000) found that supercells were responsible for producing tornadoes in about half (49%) of the storms examined 67% of the storms were associated with a bow echo and 19% had a boundary interaction – The 4 Sept 2011 storm is a good example of a boundary interaction and a bow echo as well

Future Work Higher resolution data will require a new nomogram to be created – Scale of shear values (S) will likely change With 8 bit data, gate-to-gate shear can be calculated without having to adjust for range from radar – Will allow for faster identification and quicker warnings Future work over the next year will study all tornadoes since start of 8-bit data – Also, null cases (non-verified TOR) will be examined as well Storm type will be examined as well to see if our trends fit what LaPenta et al. found in 2000

Limitations/Potential Issues Knowing what was really a tornado can be somewhat subjective – Weak tornadoes common to this area don’t always show much different damage than thunderstorm winds/microbursts – NCDC StormData doesn’t allow for “landspouts” Radar doesn’t always show rotation – Not all classified tornadoes show classic rotation couplet on radar Radar data can be limited or affected by terrain – Beam may overshoot low-level features farther away from RDA – Many parts of the Northeast are affected by beam blockage

Items to Track in Spreadsheet for Study Date/Time/Location of Tornado Radar Site Used/VCP/Range from Radar V r, S, V m Storm Type and Tornado Formation – Boundary Interaction? Supercell with hook echo? Meso/TVS Present? Other Unique/Curious Items – Large Hail, Strong LLJ, Max Reflectivity, etc.

Questions? Any questions or comments?