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Thanksgiving Week Severe Weather


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MESOSCALE DISCUSSION 2075

NWS STORM PREDICTION CENTER NORMAN OK

1224 PM CST WED NOV 24 2010

AREAS AFFECTED...CNTRL/NE OK...SE KS...SW MO

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 241824Z - 242000Z

A SEVERE THREAT WILL LIKELY DEVELOP THIS AFTERNOON AS STORMS

INITIATE AND INCREASE IN COVERAGE ACROSS CNTRL/NE OK...SE KS AND SW

MO. AN ISOLATED THREAT FOR TORNADOES...LARGE HAIL AND WIND DAMAGE

WILL BECOME INCREASINGLY LIKELY. A WW SHOULD BECOME NECESSARY ONCE

STORMS DEVELOP AND BEGIN TO INCREASE IN INTENSITY.

THE LATEST VISIBLE SATELLITE IMAGERY SHOWS PARTIAL CLEARING FROM OKC

NEWD TO TULSA WHERE THE CUMULUS IS AGITATED AND A FEW CELLS ARE

TRYING TO INITIATE. THE CAPPING INVERSION IS ALREADY GONE ON THE 18Z

NORMAN SOUNDING AND SFC ANALYSIS SHOWS SLIGHTLY CONVERGENCE FLOW

WHERE SFC TEMPS HAVE WARMED INTO THE UPPER 70S F. THIS TREND SHOULD

CONTINUE RESULTING IN MODERATE INSTABILITY ACROSS NE OK INTO SE KS

AND SW MO BY MID-AFTERNOON. SFC-BASED THUNDERSTORMS APPEAR LIKELY TO

INITIATE ACROSS THE MCD AREA BY 20Z AS IS SUGGESTED BY SEVERAL

SHORT-TERM MODELS. IN ADDITION...WSR-88D VWPS ALONG WITH THE 18Z

SOUNDINGS FROM NORMAN AND SPRINGFIELD SHOW 0-6 KM SHEAR OF 75 TO 80

KT POINTING TO A FAVORABLE SHEAR ENVIRONMENT FOR SEVERE STORMS. THE

GREATEST THREATS IN THE INITIAL STAGES OF STORM DEVELOPMENT SHOULD

BE HAIL AND ISOLATED WIND DAMAGE. HOWEVER...A TORNADO THREAT SHOULD

EVENTUALLY DEVELOP AS THE LOW-LEVEL JET BECOMES MORE FOCUSED AND THE

STORMS TAKE ON SUPERCELL CHARACTERISTICS LATE THIS AFTERNOON.

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What's this mean, then?

Very favorable low to mid level lapse rates like that are good for meso/tornadic development. Increased buoyancy in a low LCL environment tends to stretch vorticity vertically (picture a figure skater pulling her arms in), increasing it and resulting in a stronger rotation in updrafts.

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What's this mean, then?

The dry adiabatic lapse rate is the theoretical rate at which an unsaturated parcel would change temperature with height if forced upward or downward. In parcel theory, a parcel that is rising will cool at this rate (9.8C/km) until it reaches its LCL (lifted condensation level, the level at which the lifted parcel is saturated), at which point it will continue to cool at the moist adiabatic lapse rate, which is much less at the low-mid levels than the DALR because of the release of latent heat due to the process of condensation which occurs above the LCL. In today's case, because part of this layer that has a nearly-dry adiabatic lapse rate is above the LCL, the theoretical parcel will cool much less rapidly than the environment. When a parcel is warmer than its environment, it is unstable, and if lifted upward will continue to rise.

The implications are clear for the severe threat. To have this very steep low-level lapse rate is to promote a very, very unstable low-level environment. This leads to high low-level CAPE values like were discussed for Monday's event. These high low-level CAPE values lead to rapid updraft acceleration, which promote strong vorticity stretching in the lowest levels of the atmosphere. This is what enhanced the strong tornado potential on Monday, and what I think is likely to do so today.

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Very favorable low to mid level lapse rates like that are good for meso/tornadic development. Increased buoyancy in a low LCL environment tends to stretch vorticity vertically (picture a figure skater pulling her arms in), increasing it and resulting in a stronger rotation in updrafts.

The dry adiabatic lapse rate is the theoretical rate at which a completely dry parcel would change temperature with height if forced upward or downward. In parcel theory, a parcel that is rising will cool at this rate (9.8C/km) until it reaches its LCL (lifted condensation level, the level at which the lifted parcel is saturated), at which point it will continue to cool at the moist adiabatic lapse rate, which is much less at the low-mid levels than the DALR because of the release of latent heat due to the process of condensation which occurs above the LCL. In today's case, because part of this layer that has a nearly-dry adiabatic lapse rate is above the LCL, the theoretical parcel will cool much less rapidly than the environment. When a parcel is warmer than its environment, it is unstable, and if lifted upward will continue to rise.

The implications are clear for the severe threat. To have this very steep low-level lapse rate is to promote a very, very unstable low-level environment. This leads to high low-level CAPE values like were discussed for Monday's event. These high low-level CAPE values lead to rapid updraft acceleration, which promote strong vorticity stretching in the lowest levels of the atmosphere. This is what enhanced the strong tornado potential on Monday, and what I think is likely to do so today.

Thanks guys, so if that is the Norman sounding does that mean the balloon drifted towards the Tulsa area? Or, is there ripe somewhat unforeseen unstable juice over central Oklahoma?

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DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK

0151 PM CST WED NOV 24 2010

VALID 242000Z - 251200Z

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS ERN OK TO LOWER MO

VALLEY...

--- UPDATES ---

..ERN OK TO LOWER MO VALLEY

MINOR EWD SHIFT OF WRN PORTION OF SVR OUTLOOK RELATES TO EWD

MOVEMENT OF MAIN CONFLUENCE LINE ACROSS ERN OK. THIS RESULTS IN

SWLY SFC WINDS TO ITS W SUPPORTING WEAKER CONVERGENCE AND MORE

UNIDIRECTIONAL WIND PROFILES. VIS IMAGERY AND RADAR ANIMATIONS AS

OF 1930Z INDICATE GRADUAL DEEPENING OF CONVECTION OVER SERN KS AND

E-CENTRAL OK. THIS IS OCCURRING AS SFC TEMPS WARM INTO MID-UPPER

70S AND LOW 80S F...SW OF WARM FRONT THAT WAS ANALYZED NEAR

HRO-JLN-CNU LINE AT 19Z. ACCORDINGLY MODIFIED SOUNDINGS YIELD

MLCAPE 500-1000 J/KG IN ENVIRONMENT OF 60-70 KT EFFECTIVE SHEAR

MAGNITUDE. PROFILERS INDICATE 250-400 J/KG OF 0-1 KM SRH IN SAME

AIR MASS. SUSTAINED TSTM DEVELOPMENT MAY BE IMMINENT...EVOLVING

INTO SUPERCELLS. REF MESOSCALE DISCUSSION 2075 FOR ADDITIONAL

NEAR-TERM FCST GUIDANCE.

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URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 750

NWS STORM PREDICTION CENTER NORMAN OK

230 PM CST WED NOV 24 2010

THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF

SMALL PART OF NORTHWEST ARKANSAS

PARTS OF SOUTHEAST KANSAS

SOUTHWEST MISSOURI

PARTS OF NORTHEAST OKLAHOMA

EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 230 PM UNTIL

1000 PM CST.

TORNADOES...HAIL TO 1.5 INCHES IN DIAMETER...THUNDERSTORM WIND

GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE

AREAS.

DISCUSSION...THUNDERSTORMS EXPECTED TO INCREASE IN NUMBER AND

INTENSITY ACROSS THE WATCH AREA AS NWD MOVING WARM FRONT HAS ALLOWED

AN UNSEASONABLY WARM AND MDTLY UNSTABLE AIR MASS TO FLOW INTO AREA.

VERY STRONG SHEAR PROFILES IN PLACE AND WITH CINH NEARLY

GONE...STRONG UPDRAFTS COULD DEVELOP INTO SUPERCELLS THRU THE

AFTERNOON INTO THE EVENING. IN ADDITION TO DAMAGING

WINDS...TORNADOES WILL BE POSSIBLE WITH ANY SUPERCELL THAT FORMS.

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BULLETIN - EAS ACTIVATION REQUESTED

TORNADO WARNING

NATIONAL WEATHER SERVICE SPRINGFIELD MO

321 PM CST WED NOV 24 2010

THE NATIONAL WEATHER SERVICE IN SPRINGFIELD HAS ISSUED A

* TORNADO WARNING FOR...

EAST CENTRAL CEDAR COUNTY IN SOUTHWEST MISSOURI...

HICKORY COUNTY IN CENTRAL MISSOURI...

NORTHWESTERN POLK COUNTY IN SOUTHWEST MISSOURI...

SOUTHEASTERN ST. CLAIR COUNTY IN WEST CENTRAL MISSOURI...

* UNTIL 345 PM CST.

* AT 318 PM CST...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A

TORNADO 4 MILES NORTH OF ARNICA...OR 8 MILES NORTHEAST OF

STOCKTON...MOVING NORTHEAST AT 50 MPH.

* LOCATIONS IMPACTED INCLUDE ARNICA...CAPLINGER MILLS...COLLINS...

CROSS TIMBERS...ELKTON...FLEMINGTON...GERSTER...HERMITAGE...

HUMANSVILLE...NEMO...PRESTON...QUINCY...WEAUBLEAU AND WHEATLAND.

OTHER LOCATIONS IN THE WARNING INCLUDE POMME DE TERRE LAKE AND TRUMAN

LAKE.

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A bit further to the west now.

BULLETIN - EAS ACTIVATION REQUESTED

TORNADO WARNING

NATIONAL WEATHER SERVICE SPRINGFIELD MO

345 PM CST WED NOV 24 2010

THE NATIONAL WEATHER SERVICE IN SPRINGFIELD HAS ISSUED A

* TORNADO WARNING FOR...

HICKORY COUNTY IN CENTRAL MISSOURI...

NORTHWESTERN CAMDEN COUNTY IN CENTRAL MISSOURI...

SOUTHEASTERN BENTON COUNTY IN CENTRAL MISSOURI...

* UNTIL 430 PM CST.

* AT 341 PM CST...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A

TORNADO 3 MILES EAST OF WEAUBLEAU...OR 10 MILES SOUTHWEST OF

HERMITAGE...MOVING NORTHEAST AT 50 MPH.

* THE TORNADO WILL BE NEAR...

WHEATLAND BY 350 PM CST.

HERMITAGE BY 355 PM CST.

CROSS TIMBERS AND PRESTON BY 400 PM CST.

EDWARDS BY 410 PM CST.

CLIMAX SPRINGS AND KNOBBY BY 415 PM CST.

BARNUMTON BY 425 PM CST.

OTHER LOCATIONS IN THE WARNING INCLUDE LAKE OF THE OZARKS...POMME DE

TERRE LAKE AND TRUMAN LAKE.

IN ADDITION TO A TORNADO...THIS STORM IS CAPABLE OF PRODUCING

DESTRUCTIVE STRAIGHT LINE WINDS IN EXCESS OF 70 MPH.

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Not to rant here or anything but I wish SN would get rid of wall cloud reports, more like not rotating wall cloud reports. They really dont mean much and I have seen people call something a wall cloud when its a shelf cloud or some scud under a base. IMO what matters is the clear slot and thats the real tell of tornadogenesis. Or report wall clouds if there are things going for it that would make it a tornadic wall cloud and not a lowering under a base that serves no purpose to report. If it had sfc based inflow, rapid vertical motion into it or scud sucking, persistent rotation, and then the development of a clear slot. I know Paul Sirvatka and Tyler Allison (head of Spotter Network) have been talking about doing this. They should have a clear slot icon, thats more help to the NWS than a not rotating wall cloud report IMO.

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