Tornadic  Thunderstorm Types in the Northeastern United States

Issuing (or not issuing) Tornado Warnings for Wind Max Tornadoes

Tornadic Thunderstorm Types in the Northeastern United States

Introduction

Supercells

Appendages

Bow Echoes

Boundary Interaction

Miscellaneous Types

 Summary Table

References

Issuing Tornado Warnings based only on the presence of a wind maxima can be a risky proposition, and would likely  yield an unacceptably high false alarm ratio.  In most cases these tornadoes are F0 (40-72 mph) and F1 (73-112 mph).  Often damage associated with these tornadoes is embedded in large areas of damage caused by straight line winds.  Especially in cases of F0 tornadoes, damage from thunderstorm winds is as severe and more extensive than the tornadic damage.  Given the false alarm problem and the damage involved, Severe Thunderstorm Warnings for these events are probably adequate in many cases.  However, for the stronger F1 tornadoes and F2 tornadoes associated with wind maxima, a Tornado Warning is desirable. While warning for these storms will be difficult, look for the following storm characteristics:

• A very strong low level wind Max.  Using PUP/AWIPS data 64+ kt is the maximum displayable. WDSS systems (archive Level II type data) will display actual velocity maxima greater than 64 kt.
  

•  Very large shear associated with the leading edge of a wind maximum
  

• A notch in the reflectivity pattern on the leading edge of a bowing portion of an intense line of storms.

The WSR-88D detected a concentrated low-level radial velocity maximum of over 80 kt  with this intense bow echo (above).  A well defined notch is observed in the reflectivity pattern near the apex of the bow.  The shear at the leading edge of the wind max measured 0.029 s^-1.  A Tornado Warning was justified in this case, especially since significant straight line wind damage was likely, even if a tornado wasn't identified.  An F2 tornado was observed in this case.

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