1. Documentation of a Tornadic Supercell Thunderstorm in the San Joaquin Valley, California
Ted B. Schlaepfer
Department of Geosciences
San Francisco State University

2. At approximately 1:00 PM
November 22, 1996

3. Tornado!

4. Purpose of this study* Provide complete case study of this storm
Study the evolution of the storm structure on basis of analyses of satellite & Doppler radar imagery
Compare buoyancy and shear values to those observed for other tornadic supercell storms
Compare the synoptic/subsynoptic pattern to that observed with past Central Valley tornadoes
*Omitted some meteorological details from this presentation for simplicity

5. What is a supercell? A thunderstorm Persistent (~15 min.) updraft core
Rotation through a third of the depth of the storm
Summarized : A Supercell is a convective storm that possesses a deep, persistent mesocyclone

6. Why is the Lemoore Storm Unique?
First documentation of a right-moving supercell in CA using photographic, satellite and WSR-88D radar information
Tornado occurred in close proximity to WSR-88D radar at Hanford (KHNX)
High-quality low-elevation (0.5 degree) radar imagery of storm

7. November 21, 1996, The previous day Progressive frontal system
Two post-frontal troughs
Second trough associated with comma-cloud
Trough along CA coastline at 4 AM November 22

8. Broad Area of Upward Vertical Motion over CA
Stronger field of UVM centered over Central CA

9. 11 AM November 22 Meso-low in the Sacramento Valley
Lee-side trough in Central Valley
Southeast winds east of the lee-side trough axis
STRONGER low-level & deep-layer shear east of trough axis
H20 convergence along trough axis

10. Schematic Showing Pattern Associated w/ Valley Tornadoes
Nov. 22 pattern had similar synoptic features
Focus was south in S.J.V. (stronger 0–6-km shear)

11. Visible Satellite Image 12 PM
Cloud-free area

12. Convective Available Potential Energy
Definition: The maximum energy available to an ascending parcel
“Bull-eyes” region near Lemoore Naval Air Station

13. Lemoore Naval Air Station Sounding
Increased CAPE due to sensible heating and moisture convergence.

14. Deep-layer Shear (0–6-km)
Moderate over entire valley
Strong over the Central San Joaquin Valley
“Bulls-eye” between Lemoore and Fresno

15. Focus Area (Shear and CAPE)
Combined shear and CAPE was strongest over Central San Joaquin Valley
“Bulls-eye” at Lemoore

16. Lemoore (KNLC) Hodograph
Created from VAD wind profile from from KHNX at tornado genesis
Long length hodograph
Strong low-level shear (leads to the development of the low-level mesocyclone and possibly a tornado)

17. How does the Lemoore Storm Compare?
Positive Shear
Level
0–1-km 14
0–2-km
8.6
0–3-km
7.8
0–6-km
4.3
Strong shear in the lowest levels
0–2-km and 0–3-km pos. shear within F1/F2 shear category
Shear at all levels at least F0 strength

18. Visible Satellite Image 12:30 PM

19. 12 PM November 22
2 PM November 22

20. 2:30 PM November 22 3 PM November 22 2 PM November 22 1 PM November 22
Convergence zone near Lemoore
Expanding outflow in forward and rear flanks

21. 1:37 PM November 22 Supercell structure Hook Echo 68 dBZ updraft core
WSR-88D Mesocyclone algorithm detected rotation
Weak low-level velocity couplet
No Rear Flank Downdraft (RFD) yet

22. 2:00 PM November 22
Reformation stage
New Hook Echo
New updraft core
Old Core move into the Rear Flank
No Rear Flank Downdraft (RFD) yet

23. 2:00 PM November 22
Cross-Section
2 areas of strong returns (>65 dBZ)
Lower region is updraft core
Upper region is suspended large hail
Elevated returns indicate wrap-around flow around hook-echo

24. 2:06 PM November 22
Large hail falling through updraft
New Updraft core
Mesocyclone indicated by algorithm
Bounded Weak Echo Region (BWER)Evident adjacent to updraft

25. 2:23 PM November 22 Knob-shaped hook echo of strong returns
Inbound return in vicinity of hook echo
Rear Flank Downdraft (RFD) initiated
Weak low-level velocity couplet

26. 2:29 PM November 22
Inbound velocities increase in vicinity of hook echo
Simultaneous strengthening of the low-level mesocyclone
A Tornado Cyclone Signature detected on Relative Velocity Scan
F0 Tornado on ground

27. 2:34 PM November 22 F0 Tornado dissipating
Mesocyclone detected by the WSR-88D
TCS weakened on velocity scan
New Core Updraft in center of storm
Very strong returns in hook echo region

28. 2:40 PM November 22 Reflectivities decrease within hook echo
New RFD initiated (storm-scale occlusion downdraft)
Inbound velocities increase in hook region
Weak Echo Region (WER) adjacent to hook echo

29. 2:46 PM November 22 Core updraft moved into rear flank
BWER develops adjacent to updraft
Low-level mesocyclone strengthens again
Mid-level mesocyclone detected by WSR-88D
Cell developing on right flank of storm

30. 2:52 PM November 22 F1 Tornado in Lemoore Naval Station grounds
BWER associated with very sharp hook echo
Strong Low-level mesocyclone
Mid-level mesocyclone weakened
Strong TCS detected

31. 2:58 PM November 22 F1 Tornado about to dissipate near Hwy 198
Low-level mesocyclone weakened
TCS weakened
Adjacent cell merged with hook echo region of Lemoore Storm
Lemoore Storm begins to dissipate

32. How strong was the storm rotation?
F1T
How strong was the storm rotation?
Storm Rotation = 2 Vr / D
where
Vr = |Vi| + |Vo| / 2
F0T
Meso
TCS
Event
Lemoore Storm Rotation
F1M F0
11.5
23.2 F1
14.6
51.4
F0M
Mesocyclone rotational shear within range for tornadoes
F1 TCS in the range of strong/violent mesocyclones outside CA

33. Summary and Conclusions
Buoyancy and Shear were within ranges observed with other tornadic storms in CA and elsewhere
November 22 weather pattern generally fit the synoptic/subsynoptic schematic assoc. with a typical C.V. severe weather outbreak
An example of topographically induced stronger wind shear F1 tornado event
First documentation of a TCS in CA

34. What Can Be Gained from this Study?
Damaging tornadoes do happen in CA
Usefulness of WSR-88D in identifying and analyzing severe storms in CA
Heightened awareness of weather patterns that can lead to severe weather and tornadoes in CA

35. Documentation of a Tornadic Supercell Thunderstorm in the San Joaquin Valley, California
I gratefully acknowledge Steven Mendenhall, MIC and Dan Gudgel, WCM, WFO Hanford for their support and help.
All of the radar plots, photographs of the tornado and parent cumulonimbus, damage track, and official storm reports obtained for this study were provided by Mr. Gudgel.
I also thank SOO Larry Greiss and all of the Lead Forecasters at WFO Hanford for their encouragement and help in this endeavor.