the situation…

A Case Study of Two Left-Moving A Case Study of Two Left-Moving Mesoanticyclonic Supercells on 24 Mesoanticyclonic Supercells on 24

April 2006April 2006Chris BowmanChris Bowman

National Weather Service – Wichita, KSNational Weather Service – Wichita, KS

The Situation…The Situation… Synoptic environment favored Synoptic environment favored

supercells.supercells. Tornado Watch 244 already issued.Tornado Watch 244 already issued. As the event is unfolding, storms are As the event is unfolding, storms are

not taking on classic supercell not taking on classic supercell characteristics.characteristics.

Two cells and especially one in Two cells and especially one in particular begin to exhibit unusual particular begin to exhibit unusual radar signatures.radar signatures.

RUC Model 22Z Forecast RUC Model 22Z Forecast SoundingSounding

22Z RUC Forecast Hodograph22Z RUC Forecast Hodograph

KICT Reflectivity and SRM KICT Reflectivity and SRM 0.50.5° ° EvolutionEvolution

21:38Z – 22:13Z Animation21:38Z – 22:13Z Animation

KICT Reflectivity and SRM All-TiltsKICT Reflectivity and SRM All-Tilts

22:13Z 0.5° -19.5° Animation22:13Z 0.5° -19.5° Animation

KVNX Reflectivity and SRM KVNX Reflectivity and SRM 0.50.5° ° EvolutionEvolution


KICT and KVNX SummaryKICT and KVNX SummaryObserved Items of InterestObserved Items of Interest

Boundary interaction or cell merger Boundary interaction or cell merger (BICM).(BICM).

Rapid strengthening of storm after BICM.Rapid strengthening of storm after BICM. Persistent and strengthening low-level Persistent and strengthening low-level

(0.5°) rotation.(0.5°) rotation. KICT indicates cyclonic (≈1,000 ft), KVNX KICT indicates cyclonic (≈1,000 ft), KVNX

indicates anticyclonic (≈4,750 ft).indicates anticyclonic (≈4,750 ft). KICT indicates a transition from low-level KICT indicates a transition from low-level

cyclonic rotation (≈900 – 2,700 ft) to a cyclonic rotation (≈900 – 2,700 ft) to a convergent signature (≈3,000 – 10,000 ft) convergent signature (≈3,000 – 10,000 ft) to a mesoanticyclone (≈12,000 ft – 25,000 to a mesoanticyclone (≈12,000 ft – 25,000 ft).ft).

What’s the decision?What’s the decision?Tornado? Severe? No warning?Tornado? Severe? No warning?

You’re in the warning chair under a You’re in the warning chair under a tornado watch. tornado watch.

Storms have not exhibited typical Storms have not exhibited typical supercell characteristics.supercell characteristics.

A storm develops rapidly with A storm develops rapidly with strengthening cyclonic rotation strengthening cyclonic rotation corroborated by another radar.corroborated by another radar.

Storm appears to be supercellular but Storm appears to be supercellular but opposite of what was anticipated.opposite of what was anticipated.

The storm is moving into the Wichita The storm is moving into the Wichita Metro.Metro.

What Actually HappenedWhat Actually Happened

Tornado warning issued at 22:15Z for SW Tornado warning issued at 22:15Z for SW Sedgwick and NW Sumner Counties but Sedgwick and NW Sumner Counties but polygon kept Wichita out of the warning.polygon kept Wichita out of the warning.

Two off-duty NWS mets as well as private Two off-duty NWS mets as well as private mets observe a wall cloud with the storm. mets observe a wall cloud with the storm. Only live report came from an off-duty NWS Only live report came from an off-duty NWS met as the storm and “ill-defined wall cloud” met as the storm and “ill-defined wall cloud” moved over his house.moved over his house.

No tornado was reported but several severe No tornado was reported but several severe hail reports were received. hail reports were received.

The storm, as viewed from KVNX, maintained The storm, as viewed from KVNX, maintained its supercellular characteristics as it moved its supercellular characteristics as it moved over Wichita, producing only hail reports.over Wichita, producing only hail reports.

KICT and KVNX SummaryKICT and KVNX SummaryThe UnexplainedThe Unexplained

Although the environment favored left-Although the environment favored left-moving, mesoanticyclonic storms (more on moving, mesoanticyclonic storms (more on this later), there is no clear explanation for this later), there is no clear explanation for KICT’s vertical SRM transition from low-KICT’s vertical SRM transition from low-level cyclonic rotation to mid/upper-level level cyclonic rotation to mid/upper-level anticyclonic rotation anticyclonic rotation

The low-level velocity signature from both The low-level velocity signature from both KICT and KVNX are ≈3 miles north-KICT and KVNX are ≈3 miles north-northeast of the reflectivity signature.northeast of the reflectivity signature.

Reflectivity aloft is almost on top of low-Reflectivity aloft is almost on top of low-level SRM signature.level SRM signature.

Possibly a boundary being ingested and Possibly a boundary being ingested and stretched or even thunderstorm outflow.stretched or even thunderstorm outflow.

Storm #2Storm #2

Actually occurred before the tornado Actually occurred before the tornado warned storm.warned storm.

Exhibited similar characteristics Exhibited similar characteristics (including velocity signature ≈3 (including velocity signature ≈3 miles north-northeast of reflectivity miles north-northeast of reflectivity signature) but only observed from signature) but only observed from KVNX.KVNX.

Storm not as persistent and not as Storm not as persistent and not as strong.strong.

KVNX Storm #2 0.5° Reflectivity and KVNX Storm #2 0.5° Reflectivity and SRMSRM


Storms #1 and #2 SummaryStorms #1 and #2 Summary

Two storms in the same county within Two storms in the same county within several volume scans of each other both several volume scans of each other both develop low-level anticyclonic rotation develop low-level anticyclonic rotation displaced by about 3 miles to the north of displaced by about 3 miles to the north of the reflectivity signature.the reflectivity signature.

Both have a boundary interaction or cell Both have a boundary interaction or cell merger and strengthen rapidly merger and strengthen rapidly afterward.afterward.

Both storms are in the same environment Both storms are in the same environment and this is the key.and this is the key.

Environmental DataEnvironmental Data


Parameters derived Parameters derived from surface T/Td of from surface T/Td of 76/66.76/66.

Near storm Near storm environment was environment was actually ≈ 74/64.actually ≈ 74/64.

Not a huge difference Not a huge difference right? In this case it right? In this case it actually makes a big actually makes a big difference.difference.

Need to modify Need to modify sounding as a result.sounding as a result.


Modified sounding Modified sounding drops CAPE from drops CAPE from 2,038 J/Kg to 1,324 2,038 J/Kg to 1,324 J/Kg.J/Kg.

Increases CIN from -Increases CIN from -10 J/Kg to -68 J/Kg.10 J/Kg to -68 J/Kg.

Results in an Results in an environment that is environment that is elevated.elevated.

As a result, a modified As a result, a modified hodograph needs to be hodograph needs to be used.used.


Unmodified hodograph with derived parameters.

V(obs) SRH values are positive.

Storm motion = 255 @ 21 kts.


Modified hodograph with derived parameters using an elevated depth of 1 km and actual storm motion of 200 @ 29 kts. V(obs) SRH values have become negative.

Case SummaryCase Summary Two storms occurred in the same county and Two storms occurred in the same county and

within several volume scans of each other that within several volume scans of each other that exhibited unusual radar characteristics including:exhibited unusual radar characteristics including:

Persistent and strengthening low-level (0.5°) Persistent and strengthening low-level (0.5°) rotation. Cycolnic with KICT and anticyclonic with rotation. Cycolnic with KICT and anticyclonic with KVNX. KVNX.

The rotation (from KICT and KVNX) is displaced The rotation (from KICT and KVNX) is displaced ≈3 miles north-northeast of reflectivity.≈3 miles north-northeast of reflectivity.

KICT indicates a transition from low-level cyclonic KICT indicates a transition from low-level cyclonic rotation to a mid/upper-level mesoanticyclone. rotation to a mid/upper-level mesoanticyclone.

Case SummaryCase Summary Model data indicated a surface based Model data indicated a surface based

environment when the near storm environment when the near storm environment was actually elevated.environment was actually elevated.

Model forecast storm motion was not Model forecast storm motion was not correct.correct.

Modified hodograph, taking into account Modified hodograph, taking into account the elevated nature and actual storm the elevated nature and actual storm motion, reveals an environment motion, reveals an environment favorable for left-moving, favorable for left-moving, mesoanticyclonic supercells.mesoanticyclonic supercells.

AcknowledgementsAcknowledgements

Matt Bunkers, SOO, WFO Rapid CityMatt Bunkers, SOO, WFO Rapid City

For his help and expert opinions as For his help and expert opinions as well as his hodograph spreadsheet.well as his hodograph spreadsheet.

Ken Cook, SOO, WFO WichitaKen Cook, SOO, WFO Wichita

the situation…

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