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Significant Severe Events: June 14th-19th


andyhb

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Supercell "L" from Dr. Fujita's survey of Palm Sunday 1965 spawned six F4s, including the Strongsville tornado (which may have been F5). The supercell tracked from SE of Lafayette, IN, to the Cleveland metro area.

 

Impressive, thanks. I figured there would be at least a couple that dropped more from a very high end outbreak, but that supercell is certainly in elite company. As far as I can tell, there have only been ten entire tornado days since 1950 that have dropped more violent tornadoes than this single supercell!

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very good analysis. if more convection had been able to fire anywhere close to E Nebraska today, it would've been a pretty memorable day (as if it wasn't already given the dual-wedges. And devastation in Pilger) Am pretty interested as to why that supercell lost a lot of its intensity as it crossed the NE/IA border, it's not like it crossed a boundary and moved into a far inferior environment or something like that. I've kinda noticed a bit of a trend with supercells like this one--that put down a significant long-lived tornado-- after the main tornado dissipates, the storm disappates as well within an hour or two, and fails to produce anymore noteworthy tornadoes. Esp across the plains. (Moore '99/'13, wichita '12, SE NEB a few weeks ago, And several other examples) correct me if I'm wrong, but it just seems to happen a lot, and yes there are numerous other instances where this did not happen and it continues to put down sig tor's for an extended amount of time afterward. But it certainly seems to happen at least semi-frequently.

 

 

I thought it might have crossed into rain cooled air and/or subsidence from the previous convection, but I'd have to look at analysis from earlier (and also the s/w trough was passed it by that time meaning weaker deep layer shear). The storm merger might have also had an effect and it appeared that the storm was cut off from inflow as it approached the Sioux City area. The storm almost took on a NW flow type look as it was dying out.

This was when the Sig. TOR parameter dropped from 15 or so down to 6-8 (I can't remember which). If I recall correctly, the environment had already recovered and little rain-induced cooling had occurred by the time the supercell neared Sioux City. Does anyone have a judgment as to why the supercell weakened? I would be very interested in understanding why.

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50/50 tor probs.

URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 327

NWS STORM PREDICTION CENTER NORMAN OK

625 PM CDT WED JUN 18 2014

THE NWS STORM PREDICTION CENTER HAS ISSUED A

* TORNADO WATCH FOR PORTIONS OF

EXTREME NORTHWESTERN IOWA

EXTREME SOUTHWESTERN MINNESOTA

NORTHEASTERN NEBRASKA

SOUTHEASTERN SOUTH DAKOTA

* EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 625 PM

UNTIL 200 AM CDT.

* PRIMARY THREATS INCLUDE...

A FEW TORNADOES AND A COUPLE INTENSE TORNADOES POSSIBLE

SCATTERED LARGE HAIL AND ISOLATED VERY LARGE HAIL EVENTS TO 3

INCHES IN DIAMETER POSSIBLE

ISOLATED SIGNIFICANT DAMAGING WIND GUSTS TO 75 MPH POSSIBLE

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 80 STATUTE

MILES NORTH AND SOUTH OF A LINE FROM 60 MILES WEST SOUTHWEST OF

MITCHELL SOUTH DAKOTA TO 35 MILES EAST SOUTHEAST OF SIOUX FALLS

SOUTH DAKOTA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU7).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR

TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH

AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR

THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS

AND POSSIBLE WARNINGS.

&&

OTHER WATCH INFORMATION...CONTINUE...WW 321...WW 322...WW

323...WW 324...WW 325...WW 326...

DISCUSSION...TORNADIC SUPERCELL IS EXPECTED TO MOVE EWD OUT OF WW

322 SOON INTO NWRN PART OF THIS WW...WHILE ADDITIONAL DVLPMT IS PSBL

BETWEEN THAT AND HIGHER-BASED ACTIVITY NOW STRENGTHENING RAPIDLY

OVER ONL AREA S OF WARM/COLD FRONTAL TRIPLE POINT. ANY SUPERCELLS

INTERACTING WITH VORTICITY-LADEN WARM FRONTAL ZONE MAY PRODUCE

SIGNIFICANT TORNADOES...BUT ALSO EVOLVE INTO HEAVY-PRECIP MODE

RATHER QUICKLY GIVEN WEAK STORM-RELATIVE MID-UPPER WINDS. LOW-LEVEL

HODOGRAPHS ARE FCST TO REMAIN LARGE...ESPECIALLY ALG/N OF WARM FRONT

NEAR NEB/SD BORDER. UPSCALE GROWTH INTO MCS IS PSBL AS WELL.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL

SURFACE AND ALOFT TO 3 INCHES. EXTREME TURBULENCE AND SURFACE

WIND GUSTS TO 65 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO

650. MEAN STORM MOTION VECTOR 24020.

...EDWARDS

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