comet faculty course — june 2000

COMET FACULTY COURSE — JUNE 2000COMET FACULTY COURSE — JUNE 2000

The Dallas and Fort WorthThe Dallas and Fort Worth Storms of May 5, 1995Storms of May 5, 1995

FROM: The University of Oklahoma, Dr. Ken Crawford andFROM: The University of Oklahoma, Dr. Ken Crawford and7 Senior-Level Students in Meteorology [Fall 1999]7 Senior-Level Students in Meteorology [Fall 1999]

Synoptic Overview of theSynoptic Overview of the

Dallas and Fort WorthDallas and Fort Worth

Storms of May 5, 1995Storms of May 5, 1995

850 mb Heights and Observations850 mb Heights and Observations

850 mb Heights and Observations850 mb Heights and Observations

Strong Flow from the Gulf, Bringing in Moistureat 850mb

850 mb Dew point Temperatures850 mb Dew point Temperatures

10°-16°C Dew Points10°-16°C Dew Pointsat 850mbat 850mb

5:00 p.m. Surface Analysis5:00 p.m. Surface Analysis

LL

Soundings from DFWSoundings from DFW

12Z May 512Z May 5 00Z May 600Z May 6

Lifted Indices at 00Z May 6Lifted Indices at 00Z May 6

Precipitable Water at 00Z May 6Precipitable Water at 00Z May 6

Composite MapComposite Map

• • 250 mb diffluent 250 mb diffluent flowflow



• • 500 mb shortwave500 mb shortwave




• • 850 mb dew point850 mb dew point temperatures 10° -temperatures 10° - 16° C16° C




• • 850 mb dew point850 mb dew point temperaturestemperatures

• • low-level jet low-level jet





• • low-level jetlow-level jet

• • stationary frontstationary front





• • low-level jetlow-level jet

• • stationary frontstationary front

• • precipitable waterprecipitable water values from 1.5-2.0values from 1.5-2.0 inchesinches

Radar Summary of theRadar Summary of the

Dallas and Fort WorthDallas and Fort Worth

Storms of May 5, 1995Storms of May 5, 1995

Base Reflectivity Loop from 6:04 p.m. to 8:59 p.m.Base Reflectivity Loop from 6:04 p.m. to 8:59 p.m.

Dallas Co.Dallas Co.Tarrant Co.Tarrant Co.Parker Co.Parker Co.

• • 6:00 p.m DFW RADAR6:00 p.m DFW RADAR

• • Supercell located in SW Supercell located in SW Parker CountyParker County

• • Squall line extends fromSquall line extends from Young to Eastern CountyYoung to Eastern County

• • Reflectivity max at Reflectivity max at 60 dBz’s60 dBz’s

• • Golfball sized hail nowGolfball sized hail now 18” deep in southern18” deep in southern Parker CountyParker County

Base Reflectivity Cross SectionBase Reflectivity Cross Section

• • 6:00 p.m. DFW6:00 p.m. DFW radarradar

• • South to North South to North cross sectioncross section

• • Bounded Weak Bounded Weak Echo RegionEcho Region

• • Hail CoreHail Core


• • 6:45 p.m. DFW radar6:45 p.m. DFW radar

• • Supercell located in SE Supercell located in SE Parker County about to Parker County about to enter FTW metroenter FTW metro

• • Squall line beginning toSquall line beginning to bow west of the bow west of the supercellsupercell

• • Max Reflectivity ofMax Reflectivity of 75 dBz’s75 dBz’s

• • Grapefruit-sized hailGrapefruit-sized hail about to occur inabout to occur in Tarrant CountyTarrant County



• • South to NorthSouth to North cross sectioncross section

• • More pronouncedMore pronounced Bounded Weak Bounded Weak Echo RegionEcho Region

• • Hail CoreHail Core



• • Base Velocity Base Velocity productproduct

• • Strongest mesoStrongest meso WNW of radar siteWNW of radar site

strong mesostrong meso

Base Velocity Cross SectionBase Velocity Cross Section


• • West to EastWest to East cross sectioncross section

• • Meso evidentMeso evident within the Super-within the Super- cellcell

• • Isentropic liftIsentropic lift


• • Supercell located inSupercell located in Tarrant CountyTarrant County

• • Time of largest hail Time of largest hail [grapefruit sized][grapefruit sized]

• • Supercell is caught bySupercell is caught by the squall linethe squall line

• • Max Reflectivity ofMax Reflectivity of 67 dBz’s67 dBz’s




• • Hail Core lesseningHail Core lessening

• • Lower dBz’s aloftLower dBz’s aloft


• • 17 people about to17 people about to drown in Dallasdrown in Dallas


• • Heavy precip threatHeavy precip threat beginningbeginning

• • Supercell is consumedSupercell is consumed by the squall lineby the squall line

• • Large area of reflectivity Large area of reflectivity greater than 50 dBzgreater than 50 dBz


• • West to EastWest to East cross sectioncross section

• • Strong upliftingStrong uplifting within the squall-within the squall- line.line.

Base Velocity Cross SectionBase Velocity Cross Section

One Hour Precip from 8:00 to 9:00 p.m.One Hour Precip from 8:00 to 9:00 p.m.

Approx. 3 inchesApprox. 3 inchesof rain in one hourof rain in one hour

One Hour Precip Loop from 8:04 to 8:50 p.m.One Hour Precip Loop from 8:04 to 8:50 p.m.




• • Very low dBz’s aloftVery low dBz’s aloft


• • 9:00 p.m. total precip9:00 p.m. total precip imageimage

• • Areas received overAreas received over 3.5 inches of rain3.5 inches of rain

3.5 + inches 3.5 + inches of rainof rain

• • 7:30 p.m radar image 7:30 p.m radar image

• • Time of largest hailTime of largest hail [grapeftuit sized][grapeftuit sized]

• • Strong bow in squall lineStrong bow in squall line approaching supercellapproaching supercell

Inflow NotchInflow Notch Heavy Heavy RainsRains

9:10 p.m. Reflectivity Image9:10 p.m. Reflectivity Image

OFFICIAL HAIL DAMAGEOFFICIAL HAIL DAMAGE

• 80+ REPORTS OF 1” OR SMALLER 80+ REPORTS OF 1” OR SMALLER HAILHAIL

• 8 REPORTS OF 2” - 3” HAIL8 REPORTS OF 2” - 3” HAIL

• 3 REPORTS OF 3 REPORTS OF 4” HAIL4” HAIL

• 90 INJURIES ASSOCIATED WITH HAIL90 INJURIES ASSOCIATED WITH HAIL

• DAMAGE TO BUILDINGS.DAMAGE TO BUILDINGS.

FLASH FLOODINGFLASH FLOODING

• LARGEST CONTRIBUTOR TO LARGEST CONTRIBUTOR TO FATALITIESFATALITIES

• 15 MINUTE RAINFALL AMOUNTS 15 MINUTE RAINFALL AMOUNTS VARYING FROM 1.58” TO 2.24” IN VARYING FROM 1.58” TO 2.24” IN DALLAS METRO AREADALLAS METRO AREA

• INSUFFICIENT DRAINAGE FOR INSUFFICIENT DRAINAGE FOR RAINFALL RATERAINFALL RATE

WIND DAMAGEWIND DAMAGE

• SEVERAL REPORTS IN EXCESS OF 70 SEVERAL REPORTS IN EXCESS OF 70 MPHMPH

• WALL OF LOCAL WAREHOUSE WALL OF LOCAL WAREHOUSE BLOWN INBLOWN IN

MAY 5 - 6 FATALITIESMAY 5 - 6 FATALITIES

• 20 DEATHS TOTAL20 DEATHS TOTAL

• 4 FATALITIES FROM VICTIMS DRIVING 4 FATALITIES FROM VICTIMS DRIVING INTO HIGH WATERINTO HIGH WATER

• 2 FATALITIES WHEN ROOF COLLAPSES2 FATALITIES WHEN ROOF COLLAPSES

• 1 VICTIM STRUCK BY LIGHTNING1 VICTIM STRUCK BY LIGHTNING

• 3 VICTIMS PULLED INTO DRAINAGE 3 VICTIMS PULLED INTO DRAINAGE SYSTEMSYSTEM

AN OUNCE OF PREVENTIONAN OUNCE OF PREVENTION

• 60 - 70 OF HAIL INJURIES OCCURRED 60 - 70 OF HAIL INJURIES OCCURRED AT MAYFESTAT MAYFEST

• MAYFEST OFFICIALS DID NOT MAYFEST OFFICIALS DID NOT CONTACT NWS FOR WEATHER CONTACT NWS FOR WEATHER REPORT PRIOR TO EVENTREPORT PRIOR TO EVENT

• ““WARNINGS WERE ISSUED NEARLY WARNINGS WERE ISSUED NEARLY 25 TO 30 MINUTES” PRIOR TO STORM 25 TO 30 MINUTES” PRIOR TO STORM HITTING MAYFESTHITTING MAYFEST

Questions?Questions?

You’re not the only one!You’re not the only one!

A Few Bullets Related to the Learning Objectives:A Few Bullets Related to the Learning Objectives:

This event had the synoptic scale appearance of a severe weatheroutbreak with relatively fast moving storms. However, the strongdigging trough into a negatively tilted ridge in the upper levels, and a very notable northward transport of moisture in the lower levelssuggested the potential for heavy precipitation.

Large scale jet dynamics [divergence/diffluence over Texas]supported upward motion. In the low levels, surface boundariesassociated with a warm front and with a mesohigh that developedbecame the focus of low-level convergence and enhanced upwardmotion. This was especially true of the east-west warm frontalboundary that was roughly perpendicular to the 850 mb flow. Sucha configuration lead to a common generation point.


By the beginning of this event, conditions suggested enhancedduration was possible where the low-level flow intersected surfaceboundaries.

But rainfall intensity and hydrologic character of the basin were more important in this event. Although large amounts of hail occurred throughout much of the storm history, a transformation into a more intense rainstorm occurred in Dallas County. Thisevolution can be seen in the change of characteristics of the radarecho. The low-level moisture transport was very strong, and whencoupled with vertical motion, may have increased the height of the freezing level. The result was a deeper warm cloud layer and thus more efficient precipitation processes.


The hydrologic response in this highly urbanized area was very rapiddue to the impermeable surfaces and constricted waterways.

Even though a second heavy accumulation band can be noted south of the Dallas rainfall footprint, serious flooding did not occur there [primarily] because the rainfall intensity and urban runoff characteristics were so different from that in Dallas.

The final rainfall amounts were not very impressive by Texasstandards. The intensity of the precipitation and the hydrologic response of the urbanized environment contributed greatly to this deadly flash flood event. Rainfall amounts up to 4.75 inches were reported in Dallas, but rainfall rates for short periods approached 10 inches per hour.

The Financial Toll:The Financial Toll:

Estimated damages across Parker, TarrantEstimated damages across Parker, Tarrantand Dallas counties — from this storm — was and Dallas counties — from this storm — was estimated at over $1.2 Billion — the costliestestimated at over $1.2 Billion — the costliestthunderstorm event in the history of the USA.thunderstorm event in the history of the USA.

comet faculty course — june 2000

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