Effects of Eastern Pacific Cyclone Moisture on a Heavy Rain and Flood Event in Texas and Oklahoma

National Weather Diges t EFFECTS OF EASTERN PACIFIC CYCLONE MOISTURE ON A HEAVY RAIN AND FLOOD EVENT IN TEXAS AND OKLAHOMA

by G. Alan Johnson (1) and Edward B. Mortimer (2) National Weather Service Forecast Office New Orleans Area 1120 Old Spani1;h Trail Slidell, LA 70458

ABS TRACT of Texas into southeastern Oklahoma. There were several 380 mm centers with maximum A series of heavy rain events caused deva rainfall amounts in excess of 500 mm (Fig stating floods across portions of north ure 1) (11, 12). These rains caused deva central and southwest Te x as into southeast stating floods with extensive damage, esti Oklahoma from October 11-14, 1981. The mated in excess of 175 million dollars . Ten occurrence of both a f rontal and mesoscale flood-related deaths were also recorded, flash flood pattern and the entrainment of eight in Texas and two in Oklahoma (13). tropical moisture from eastern Pacific Hur ricane Norma combined to produce the heavy In October 1983, eastern Pacif ic Hurricane rainfall. Al though the episode persisted Tico followed a similar pattern to NORMA. over a three day period, the heaviest con This produced heavy rains and flooding from vective activity was nocturnal in nature . north central and west Texas into central An ex tensive area with storm totals of 254 Oklahoma. Maximum rainfall amounts across to 508 mm stretched from southwest Te x as central Oklahoma were 356 to 432 mm . into south cen tral Oklahoma. There were isolated pockets with storm totals in ex This paper is a case study examining the cess of 508 mm. This is a case study ex am various meteorological and hydrologic para ining the meso-scale, upper air and hydro meters which helped trigger the heavy rain logic aspects which led to the prolonged event associated with tropical cyclone heavy rain and flood episode. NORMA during mid October 1981.

1. INTRODUCTION 2. SYNOPTIC SCALE

Heavy rains produced by tropical systems 2. 1 Upper Air moving from the Gulf of Me x ico into Texas have been well documented in the past seve A high latitude blocking pattern became ral years (3,4,5,6) . Hale (7) discussed well established over the Davis Straits in the effects of tropical moisture from the eastern Canada during the first half of the eastern Pacif ic into the southwestern U.s. month, but began to break down toward mid However, little has been written regarding month (Figure 2) (9,10). Nevertheless, a the entrainment of eastern Pacific tropical strong eastern U. S. ridge coupled with a moisture across the Sierra Madre Mountains Great Basin trough allowed for southwester of Me x ico into Texas and Oklahoma (8). ly flow to persist from the Gulf of Cali fornia into the central plains throughout During October 1981, the remnants of three the period under study. This flow acted as eastern Pacific hurricanes (Lidia, Norma the steering mechanism for the entrainment and Oti s) moved across the Mex ican high of middle and upper level moisture from lands into Texas. These three storms both eastern pacific Hurricanes Lidia interacted with synoptic scale systems as (LIDIA) (October 6-8) and NORMA (Figure 3) they moved across Texas . Each produced across northern Mex ico into Texas. rains in excess of 250 mm (9) and flooding across portions of Texas and/or southeast In the lower troposphere, weak 850 mb and ern Oklahoma. Monthly rainfall totals in 700 mb warm air advection (Figure 4) was excess of 300 percent of normal were re indicated on the analysis beginning at 1200 corded from the Texas Big Bend region into GMT on the 11th and continued through 0000 southeastern Oklahoma (9,10) . But nearly GMT on the 14th. A low level high pressure half the monthly total fell during the system in the central Gulf of Mexico main three-day period from about 0900 GMT 11 tained a strong moist south to southeast October to about 0600 GMT 14 October . This flow into Texas . Local studies have shown was when the remnants of eastern pacific that warm air located to the west of the Hurricane Norma (NORMA) affected the area. m6ist ax is is an important criteria for heavy rains in the Texas/Oklahoma area. Tropical moisture from NORMA combined with several other synoptic features to produce In the mid-levels of the troposphere, seve rainfall amounts of 125 to 250 mm across ral short-wave troughs (S/W) and posi ti ve much of the area from the Edward's plateau vorticity advection (PVA) lobes rotated

16 Volume 9 Number 4 through the long-wave trough and aided the 2.2 Surface Pattern development of thunderstorm activity. The first weak PVA lobe moved across the Pecos A cold front had moved southward across valley during the morning and afternoon west and north Texas on October 9th, hours of the 11th (per Kansas city satel becoming quasi-stationary along the upper lite Interpretation Message). This trig Texas coast by 1200 GMT on the 11th. Be gered thunderstorms across the Edward's hind the front, dew points remained in the Plateau during the day. Another S/W moved upper 50s to mid 60s. The front moved across central Texas on the evening of the sl-owly northward as a warm front on the 11 th and aided thunderstorms in that area lLth (Figure 7). The warm front continued throughout the night. At 0900 GMT on the to fuove northward into Oklahoma on the 12th 12th, satellite imagery indicated the heav before dissipating. south of the front, iest thunderstorms associated with this S/W dew points were in the upper 60 s to lower were in north Texas, northwest of Fort 70s through the 13th. Worth (F igure 5). On the evening of the 12th, a vorticity maximum associated with Warm, moist air from the Gulf of Mexico was NORMA moved northeastward from Mexico into lifted over the warm front as it moved the Edward's plateau and then turned east northward and combined with an upper level ward during the morning hours of the 13th. S/W (discussed above) to produce rains (Figures of the S/W and PVA lobes are not across the Edward's plateau during the day shown) . of the 11th. The rains moved northward and fell between Abilene and southeast Oklahoma In the upper levels of the atmosphere, the during the nighttime hours of the 11th and subtropical jet (STJ) was a major factor in early morning of the 12th. This was a this heavy rain event. It was generally classic example of a frontal flash flood located from southwestern New Mexico/far pattern (17). west Texas into central Kansas then anti cyclonically into Missouri. Several speed 3. DISCUSSION OF MESOSCALE FEATURES maxima rotated through this flow, one dur ing the late nighttime hours of the 11th There were several mesoscale features, such (F igure 5), and another dur i ng the day of as rain-cooled boundar ies, mesohighs, and the 13th. Central Texas and southeast thunderstorm outflow boundaries, evident Oklahoma were in the right rear quadrant of during the heavy rain episode. Since many these wind maximas, which is a region of of these features were subtle, only two of upward vertical veloci ty (UVV). A weak the predominant ones will be discussed. diffl uent region was also apparent across this same area during the period. (Figures 3.1 Outflow Boundary Features of the diffluent region are not shown). Both uvv and diffluence have been found to Scattered thunderstorms which occurred over be favorable areas for thunderstorm devel southern Oklahoma and the extreme northern opment (14,15). portion of north Texas during the early part of October 12th had dissipated but The winds were south and southeast in the produced an outflow boundary. A classic lower atmosphere veering to a more westerly "arc cloud" associated with this boundary direction with height on the 11th and early was easily recognized in satellite imagery on the 12th (16). This was indicative of (Figure 8). Scattered thunderstorms rede the warm advection pattern mentioned ear veloped about 1700 GMT along the intersec lier. During the afternoon and evening of tion of the western flank of this outflow the 12th, the winds became more southerly boundary and a low level convergence line at all levels. southwest of Abilene. By 2100 GMT, the thunderstorms were intensifying rapidly This was during the rain event itself. along the western flank of the arc cloud. Southerly wind flow in the lower atmos This is often a favored location for heavy phere, combined with veering winds in the rainfall (18). Figure 9 illustrates the mid and upper troposphere, has been observ intersection of the arc cloud, as depicted ed with many significant rain events (3) . by satellite imagery and also defined in The atmosphere over Texas became increas the surface analysis and by the surface ingly moist and unstable between 0000 GMT moist axis . on the 11th and 0000 GMT on the 12th. 3.2 Meso-High Feature Thi s was reflected by a doubling in both the mean relative humidity and the precipi A cluster of thunderstorms associated with table water values between 0000 GMT and the center of NORMA'S circulation redevel 1200 GMT on the 11th at Stephenville, TX oped in the western portion of the Edward's (about 50 miles southwest of Fort Worth), plateau during the evening hours of the as illustrated in Figure 6a. The lifted 12th. During the early nighttime hours, index also destablized; the K-index thunderstorms increased in areal coverage increased rapidly during the same period and intensity. By 0800 GMT on the 13th, a (Figure 6b) and remained nearly. constant small meso-high became discernible at the throughout the heavy rain event.

17 National Weather Digest surface in the vicinity of San Angelo, TX homes, businesses and agricultural inter (Figure 10). During the early morning ests also occurred during the episode. hours of the 13th, the thunderstorm cluster Record stages were reported at numerous evolved into the "core rain" regime (19). locations across this area. These incl ud The meso-high acted as the focusing mechan ed: the mainstream of the Red River from ism for flood- producing rains during the Thackerville, OK to near De Kalb; Clear late nighttime and early morning hours Boggy Creek near Caney, OK; the Trinity (16). This high persisted as it drifted River at Boyd, TX; and the Brazos River eastward during the morning of the 13th near Dennis, TX. The Deep Creek in Shack under the influence of NORMA. This was leford County of Texas reached its highest another classic "nocturnal" flash flood crest in 100 years. event (20). The heavy rains and flash flood waters 4. HURRICANE NORMA across the region filled many reservoirs and lakes. Several of the dams were NORMA was the third of four eastern Pacific breached during the event. Texoma, Atoka hurricanes (LIDIA, Oct. 2-8; MAX, Oct. and Coalgate Reservoirs in Oklahoma were 8-10; NORMA; and OTIS, Oct. 25-30) to de filled during the event. velop during the month of October 1981. Of these, only MAX did not strike the Mexican Heavy rains across the Edward's plateau of coast; however, mid and upper level mois Texas also produced flash flooding/flooding ture from all the storms was transported along the Devil' s River on the 11th and into Texas. Tropical Depression NORMA along many other streams and rivers on the developed near 14.5N 104.4W around 1800 GMT 12th and 13th. October 8th and by 1800 GMT on the 9th NORMA was classified as a hurricane. NORMA The nocturnal nature of the heavy rains moved northwestward to near 18.6N 108.5W at made rescue and evacuation operations more 0600 GMT on the 11th before curving north difficult and hazardous. As an example, a eastward and striking the Mexican coast nursing home in Breckenridge, TX had to be near Mezatlan around 1100 GMT on the 12th evacuated on three consecutive nights, (Figure 11). The upper circulation from while in Oklahoma, one nursing home had to NORMA remained well defined on satellite be evacuated for two days due to high imagery through much of the 12th. By 0000 water. GMT on the 13 th, the center was located about 160 Km south of the Texas Big Bend. 6. SUMMARY OF SEQUENCE OF EVENTS By 1200 GMT, NORMA had moved northeastward to near San Angelo. a. The heavy rains across portions of Texas and Oklahoma on 11-14 October 1981 Mid and upper level moisture from the rem were the combined effects of several synop nants of MAX became entrained in the south tic and mesoscale features. As observed in westerly flow and spread across Arizona and other heavy rain events (21), this event New Mexico into west Texas around 1200 GMT was preceded by heavy rains associated with on the 10th. By 0600 GMT on the 11th, the LIDIA the previous week, saturating the moisture from MAX and the outflow from ground and swelling many rivers and NORMA merged and spread into western and streams. Thus, the additional 250 to 500 northern Texas (Figure 12). Satellite pho mm rains (second event) of 11-14 October tos showed this entrainment of moisture were reflected mainly as runoff and in continued across the highlands of Mexico creased the seriousness of the flood situa into Texas until the remnants of NORMA's tion. upper level circulation moved across Texas on the night of the 12th and the day of the b. Early on the 11th, heavy rains develop 13th. NORMA demonstrated oscillations be ed over the Edward's plateau in association tweeridaytime "pheripheral showers" and wi th a warm front dr ifting northward nighttime "core rains" on both the 12th and through central Texas and an upper level the 13th (Figure 13) (19). This system S/W. Total rains from this episode ranged produced the third significant rainfall from 250 to 380 mm. event within a three-day period. c. During the evening hours of the 11th, 5. HYDROLOGICAL CONSIDERATIONS heavy rains developed from the Abilene area of north central Texas into southeastern Flash flooding and river flooding of record Oklahoma. These thunderstorms developed or near record magnitude occurred over por along the warm front as it moved across the tions of north central Texas and south cen same area. The heavy rainfall was enhanced tral Oklahoma, generally bounded by an Abi by the entrainment of moisture from NORMA lene-Wichita Falls-Sulphur OK-Clayton OK which was located near the west coast of (about 40 miles southeast of McAlster) Mexico (Figure 5). This resembled Maddox's Dallas-Abilene line (Figure 1). County, (16) frontal flash flood pattern and was state and federal roads and bridges were nocturnal in nature (20). Rains of 50 to blocked, washed out or destroyed at hun 175 mm were received across north central dreds of locations. Extensive damage to Texas during the night. This pattern con- 18 Vol ume 9 Number 4 tinued across south central Oklahoma on the across the Mexican highlands into Texas and 12th, with rainfall amounts in excess of Oklahoma. The intrusion of low level mois 450 mm reported. ture from the Gulf of Mexico combined with mid and upper level moisture to produce d. Heavy thunderstorms developed on the precipitable water values in excess of 200 afternoon of the 12th over the western por percent of normal. K-indices of 36 to 41 tion of north central Texas. This thunder and lifted indices of minus 4 to minus 6 storm activity was associated with an out r e.~ lected the highly unstable air mass in flow boundary, as discussed in the section the area. on mesoscale features. '",- Both the frontal and meso-high flash flood e. Finally, the upper level circulation of pattern of Maddox were evident during the NORMA moved northeastward from Mexico into event. Several other mesoscale features Texas. By midnight on the 13th, the rem helped to focus the excessive rains. These nants of NORMA were just to the southwest included rain-cooled boundaries and thun of Del Rio. Convection redeveloped from derstorm outflow boundaries. Detailed the western portions of the Edward's pla mesoscale analyses and satellite imagery teau into north central Texas during the were a tremendous aid to forecasters in nighttime hours. Thunderstorms intensified identifying these potentially dangerous during the late nighttime hours as NORMA areas for severe flooding. The first neared the Edward's Plateau. Heavy thun heavy rain spell saturated the ground in derstorms gradually moved eastward into early October and set the stage for the north central Texas and southeastern Okla second event of 11-14 October 1981. Thus, homa during the daytime hours of the 13th. the additional 250 to 500 mm rains were Heavy rains continued into the evening reflected as mainly runoff and intensified hours and ended around midnight on the 14th the flood situation. (Figure 14). Twenty-four hour rainfall amounts ending at 1200 GMT on the 14th The heaviest rains and much of the flash ranged from 50 to 250 mm. flooding were "nocturnal" during the event, occurring mainly after midnight. In some f. These combined systems produced wide cases, radar and satellite showed that spread rainfall totals of 125 to 250 mm. thunderstorms repeatedly moved across the There were several 8 to 10 square kID areas same area. wi th rainfall totals in excess of 500 mm (Figure 1). 8. ACKNOWLEDGMENTS

7. CONCLUSIONS The authors express their thanks to Dr. Robert Maddox for providing photographs, Several synoptic and mesoscale features San Francisco NESS for information on interacted to produce this excessive rain NORMA, O. D. Mccalip (23) for hydrological fall event from the Edward's plateau of information, Jim Lynch, New Orleans NESS Texas into southeastern Oklahoma. One of unit and Mike Mogil, SSD, SRH, Fort Worth, the primary factors was the prolonged en for reviewing the paper. trainment of mid and upper level tropical moisture from the eastern Pacific (NORMA)

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OLD ADDRESS:

NEW ADDRESS:

19 National Weather Digest

11 I

.~- ,

. T.. -.. · ",n, (; ... " .t ..

/ L-______~------~

Figure 1 Isohyets of storm totals 11-14 October 1981 . Dark areas indicated storm totals in e xcess of 508 rum. Greatest storm totals were 665 . 5 rom at Linn, Ok (south east of Ardmore) and 584 . 2 wm at Cly de 5n, Tx. (east of Abilene) . The insert map shows the geographical regions discussed in the paper . (Note: ADH - Ardm.ore, ABI - Abilene , FTW - Fort Worth)

20 Vol ume 9 Number 4

Figure 2 500 HB analysis 0000 GMT 13 October 1981 .

Figure 3 Infrared satellite imagery 0200 Q1T 12 October 1981 showing entrainment of tropical rroisture from NORMA northward into Texas.

21 National Weather Digest

A) 850 MB analysis 0000 GMT 12 October 1981; B) 850 MB analysis 0000 GMT 13 October 1981;

Figure 4

Stipled area indiates low and mid- level moisture.

C) 700 MB analysis 0000 GMT 12 October 1981; L

12. - D) 700 MB analysis 0000 GMT 13 October 1981.

22 Volume 9 Number 4

Figure 5 Infrared satellite imagery 0800 GMT 12 October 1981. Note: Bulge in cirrus clouds over southeast New Mexico suggests a speed maximum in the general jet-stream pattern. NORNA was approaching the western Mexican coast. Heavy thunderstorms can be seen south of the Big Bend National Park and over north Texas.

10~------,

90 50

(-4) (-5) (-3) 80 4 ( -4)

RH K (1) 60

50 (b) .84 (91%) ( 1) 40 O~--+---~---+--~--~r---r-~ OOZ/11 00Z/12 OOZ/13 00Z/14 OOZ/11 00Z/12 OOZ/13 00z/14 Time/Date Time/Date

Figure 6 a) Mean relative humidity and precipitable water amounts with percent of normal in parentheses for Stephenville, TX during the heavy rain episode.

b) K-index with lifted index in parenthesis for Stephenville, TX for the same period.

2J National Weather Digest f

o AHA

o LBB

o IW" o SJT

'\ Figure 7 Sequence of frontal positions.

Figure 8 Visible satellite imagery 1900 GMT 12 October 1981 . NOTE: Arc cloud (a-b) in north central Tex as.

24 Vol ume 9 Number 4

Figure 9 Mesoscale surface analysis 1900 GMT 12 October 1981. Dots are isodrosotherms.

Figure 10 Mesoscale surface analysis 0800 GMT 13 October 1981.

25 National Weather Digest

, /

. , -- -,- -- 20N LIDIA , ,,\11 -29 °'_10 I ) ° MAX - ~ - - - ! ----_., ""-_ is '·Z,,- "'---..:--- NORMA 07.,27

( _26 ~ : • 25 115, - ----.--...1.I '- ' ",---.. 24 i OTI S 105 95

Figure 11 Track of eastern Pacific Tropical Cyclones affecting the U. s. during October 19 8'i.

Figure 12 Infrared satellite imagery 0630 GMT 11 October 1981. Cloudiness over southeast Arizona and New Mexico is remnants of MAX_

26 Vol ume 9 Number 4

Figure 13a Infrared satellite imagery 2300 GHT 12 October 1981. Peripheral showers associated with NORl1A.

Figure 13b Infrared satellite imagery 0800 GMT 13 October 1981. Nighttime core rains associated with NORMA .

l National Weather Digest

Figure 14 Infrared satellite imagery 1700 GHT l3 October 1981.

FOOTNOTES AND REFERENCES

1. G. Alan Johnson, Forecaster-in-charge 10 . Erickson, C. 0., 1982: Wea ther and (F IC), WSFO New Or leans area, formerly a circulation of October 1981 - A month with FIC at WSFO Lubbock, TX. strong high-latitude blocking. Mon. Wea. Rev., Vol. 110, 46-54. 2. Edward B. Mor timer, forecaster, WSFO New Orleans area, formerly a forecaster at 11. Dept. of Commerce, NOAA: Oklahoma Cli WSFO Lubbock, TX. matologica1 Data, Oct. 1981, Vol. 90, No. 10, 26 pp. 3. Grice, G. K. and Maddox, R. A., 1982: Synoptic aspects of hea vy rain e vents in 12. Dept. of Commerce: Texas Climatologi south Texas associated with the westerlies. cal Data, Oct. 1981, Vol. 86, No. 10,75 NOAA Tech Memo, NWS SR-106, 21 pp. pp.

4. Korty, B., 1980: Excessi ve rainfall 13. Dept. of Commerce: Storm Data, Oct. across east Texas and the lower Mississippi 1981, Vol. 23, No. 10, 75 pp. Valley. Preprints, Second Conf. on Flash Floods (Atlanta), AMS, Boston, 11-17. 14. Grice, G. K. and Ward, J. D., 1983: Synoptic conditions of heavy rains and non 5. Chin, E. D. and Marshall, H. E., 1980: hea vy rain e vents a ver south Texas associ Meteorological settings of central Texas ated with tropical cyclones. Preprints, floods, August 1978. Prepr ints, Second Fifth Conf. on Hydrometeorology (Tulsa), Conf. on Flash Flood (Atlanta), AMS, Bos- AMS, Boston, 130-137. ton, 38-44. 15. Uccel1ini, L. W. and Johnson, D. R., 6. Clark, J. D., 1980: An evaluation of 1979: The coupling of upper and lower tro satellite precipitation estimates for a pospheric jet streaks and implications for record breaking rainfall. Prepr ints, the de velopment of se vere can vecti ve Second Conf. on F lash Floods (A tlanta), storms. Mon. Wea. Rev., Vol. 107, 682-703. AMS, Boston, 123-129. 16. Maddox, R. A., 1979: A methodology for 7. Hales, J. E., Jr., 1974: Southwestern forecasting hea vy con vecti ve precipi tation United States summer monsoon source - Gulf and flash flooding. Nat. Wea. Digest, Vol. of Mexico or Pacific Ocean? J. Appl. 4, No.4, 30-42. Meteor., Vol. 13, 331-342. 17. Maddox, R. A., Chappell, C. F. and 8. Christmas, Stan, 1982: Case study - Hoxit, L. R., 1979: Synoptic and mesoscale F lash flooding 0 ver north Texas, Oct. aspects of flash flood events. Bull. of 11-14, 1981. Unpublished, 36 pp. Am. Meteor. Soc., Vol. 60, 115-123.

9. Ludlum, D. M., 1981: Weather watch - October 1981. Weatherwise, Vol. 34, No.6, 280-283.

= Volume 9 Number 4 18. Mogil, H. M. and Groper, H. S., 1976: mum of flash floods in the central and Short-range prediction of localized exces eastern U. S. Preprints, Conf. on Weather sive convective rainfall. preprints, Conf. Forecasting and Analysis and Aviation of Hydrometeorology (Fort Worth), AMS, Bos Meteorology (Silver Spring), AMS, Boston, ton, 9-12. 52-57.

19. Ward, J. D., 1981: Spatial and tem 21. Hales, J. E., 1977: The Kansas City poral heavy rainfall patterns over land flash flood of September 12th, 1977. Prep- associa ted wi th weakening tropical cy r i Frt s, Fir s t Con f . 0 n F las h Flood: Hy d ro - clones. Preprints, Fourth Conf. of Hydro met §.,orological Aspects (Los Angeles), AMS, meteorology (Reno), AMS, Boston, l74-~ Boston, 158-162.

20. Hoxit, L. R., Maddox, R. A. and Chap 22. McCalip, O. D., Hydrologist, WSFO, Fort pell, C. F., 1978: On the nocturnal maxi- Worth, TX (deceased).

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