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

At approximately 1:00 PM November 22, 1996

Tornado!

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

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

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

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

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

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

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)

Visible Satellite Image 12 PM Cloud-free area

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

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

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

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

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)

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

Visible Satellite Image 12:30 PM

12 PM November 22 2 PM November 22

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.