NOAA Technical Memorandum NWS WR-221
UTILIZATION OF THE BULK RICHARDSON NUMBER, HELICITY AND SOUNDING MODIFICATION IN THE ASSESSMENT OF THE SEVERE CONVECTIVE STORMS OF 3 AUGUST 1992
~ \
Eric C. Evenson Weather Service Forecast Office Great Falls, Montana
November 1993
u.s. DEPARTMENT OF I National Oceanic and National Weather COMMERCE Atmospheric Administration I Service 75 A Study of the Low Level Jet Stream of the San Joaqnin Valley. Ronald A Wlllis and NOAA TECHNICAL MEMORANDA Philip Williams, Jr., May 1972. (COM 72 10707) National Weather Service, Western Region Subseries 76 Monthly Climatological Charta of the Behavior of Fog and Low Stratus at Los Angeles International Airport. Donald M. Gales, July 1972. (COM 72 11140) The National Weather Service (NWS) Western Region (WR) Subseries provi~es an informal 77 A Study of Radar Echo Distribution in Arizona During July and August. John E. Hales, Jr.. medium for the documentation and quick dissemination of results not. appropnate, or not ~et July 1972. (COM 72 11136) ready, for formal publication. The series is used to report. o'! work '-? progreas, to des~ 78 Forecasting Precipitation at Bakersfield, California, Using Preasure Gradient Vectors. Earl technical procedures and practices, or. to relate progre_as ~ a limited. audience. These Techrucal T. Riddiough, July 1972. (COM 72 11146) Memoranda will report on investigations devoted primarily to regtonal and local problems of 79 Climate of Stockton, California. Robert C. Nelson, July 1972. (COM 72 10920) interest mainly to penionnel, and hence will not be widely distributed. 60 Estimation of Number of Days Above or Below Selected Temperatures. Clarence M. Sakamoto, October 1972. (COM 72 10021) Papers 1 to 25 are in the former series, ESSA Technical Mem~randa, Western ~egion Technical 81 An Aid for Forecasting Summer Maximum Temperatures at Seattle, Washington. Edgar G. Memoranda (WRTM); papers 24 to 59 are in the fo'"!"e~ sen.es, ESSA Technical Memoranda, JohiiSon, November 1972. (COM 73 10150) Weather Bureau Technical Memoranda (WBTM). Begtnrung With 60, the pape~ are part of the 82 Flash Flood Forecasting and Warning Program In the Western Region. Philip Williams, Jr., series, NOAA Technical Memoranda NWS. Out-of-print memoranda are not listed. Chester L. Gle1111, and Roland L. Raetz, December 1972, (Revised March 1978). (COM 73 10251) Papers 2 to 22, ex~pt for 5 (~d _e<;U?on), are available from the Na?o?B~ Weather Service 83 A comparison of Manual and Semiautomatic Methods of Digitizing Analog Wind Records. Western Region, SCientific Semces DIVls!On, P.O.. Box 1~1!!8, Federal Building, ~5 ~outh. State Gle1111 E. Rasch, March 1973. (COM 73 10669) Street, Salt Lake City, Utah 84147. P~per 5 (reVI~d editio':'), and all others begmnmg Wlth 25 86 Conditional Probabilities for Sequences of Wet DII,YB at Phoenix, Arizona. Paul C. Kangieser, are available from the National Technical Information Semce, U.S. Department of Comme~ce, June 1973. (COM 73 11284) Sills Building 5265 Port Royal Road, Springfield, Virginia 22161. Prices vary for all paper cop1es; 87 A Refinement of the Use of K-Values in Forecasting Thunderstorms In Washington and microfiche ar~ $3.50. Order by acceasion number shown in parentheses at end of each entry. Oregon. Robert Y.G. Lee, June 1973. (COM 73 11276) 89 Objective Forecast Precipitation Over the Western Region of the United States. Julia N. ESSA Technical Memoranda (WRTM) Paegle and Larry P. Kierui1T, September 1973. (COM 73 11946/SAS) 91 Arizona 'Eddy" Tornadoes. Robert S. Ingram. October 19.73. (COM 73 10465) 2 Climstological Precipitation Probahilities. Compiled by Lucianna Miller, December 1965. 92 Smoke Management in the Willamette Valley. Earl M. Bates, May 1974. (COM 74 3 Western Region Pre- and Post-FP-3 Program, December 1, 1965, to February 20, 1966. 11277/AS) Edward D. Diemer, March 1966...... 93 An Operational Evaluation of 500-mb 'JYpe Regression EquatioiiS. Alexander E. MacDonald, 5 Station Descriptions of Local Effects on Synoptic Weather Patterns. Philip Williams, Jr., June 1974. (COM 74 11407/AS) April 1966 (Revised November 1967, October 1969). (PB-17600) 94 Conditional Probability of VIsibility Less than One-Half Mile in Radiation Fog at Fresno, 8 Interpreting the RAREP. Herbert P. Benner, May 1966 (Revised January 1967). California. John D. Thomas, August 1974. (COM 74 11555/AS) 11 Some Electrical Proceases in the Atmosphere. J. Latham, June 1966. 95 Climste of Flagstaff, Arizona. Paul W. SoreiiSOn, and updated by Reginald W. Preston, 17 A Digitalized Summary of Radar Echoes within 100 Miles of Sacramento, Califomis. J. A January 1987. (PB87 143160/AS) Youngberg and L. B. Overaas, December 1966. 96 Map type Precipitation Probabilities for the Western Region. Glenn E. Rasch and Alexander 21 An Objective Aid for Forecasting the End of East Winds in the Columbia Gorge, .July E. MacDonald, February 1975. (COM 75 10428/AS) through October. D. John Coparanis, April 1967. 97 Eastern Pacific Cut-Off Low of April 21-28, 1974. William J. Alder and George R. Miller, 22 Derivation of Radar Horizons in Mountainous Terrain. Roger G. Pappas, April 1967. January 1976. (PB 250 711/AS) 98 Study on a Significant Precipitation Episode in Western United States. Ira S. Brenner, April ESSA Technical Memoranda, Weather Bureau Technical Memoranda UTILIZATION OF THE BULK RICHARDSON NUMBER, HELICITY AND SOUNDING MODIFICATION IN THE ASSESSMENT OF THE SEVERE CONVECTIVE STORMS OF 3 AUGUST 1992 Eric C. Evenson Weather Service Forecast Office Great Falls, Montana November 1993 UNITED STATES National Oceanic and National Weather Service DEPARTMENT OF COMMERCE Atmospheric Administration Elbert W. Friday, Jr., Assistant Ronald H. Brown, Secretary (Vacant), Under Secretary Administrator for Weather Services and Administrator This publication has been reviewed and is approved for publication by Scientific Services Division, Western Region Kenneth B. Mielke, Chief Scientific Services Division Salt Lake City, Utah / ' TABLE OF CONTENTS I. INTRODUCTION ...... 1 II. COMPOSITE ANALYSIS ...... 1 III. SURFACE ANALYSIS ...... 2 IV. THETA-E ANALYSES ...... 3 V. SOUNDING AND HODOGRAPH DATA ...... 3 VI. BULK RICHARDSON NUMBER ...... 3 VII. HELICITY ...... 5 VIII. CONCLUSIONS .._ ...... 5 \, -· IX. ACKNOWLEDGEMENTS ...... 6 X. REFERENCES ...... 6 iv TABLE OF FIGURES Figure 1: Lot of known severe weather events across Hill county in north-central Montana on 3 August 1992. (Reports from Storm Data and local storm reports.) T =tornado W =wind damage A= hail greater than 3/4 inch diameter...... 8 Figure 2: Composite analysis at 1200 UTC on 3 August 1992. Arrow represent jet maxima at various levels. Dotted line represents the 850 mb thermal ridge. Large dashed line denotes 700mb short-wave trough. Triangular line indicates thermal trough at 500 mb. Jagged dot-dashed line represents diffluence at the 500 mb level. Thin dashed lines represent surface isodrosotherms analyzed every 5°F ( >50°F). Stippled area denotes Lifted Indices less than or equal to zero...... 9 Figure 3: Same as Figure 2 except at 0000 UTC on 4 August 1992...... 10 Figure 4: 1800 UTC surface analysis on 3 August 1992. Solid lines represent isodrosotherms analyzed every 5°F...... 11 Figure 5: 0000 UTC surface analysis on 4 August 1992. Solid lines represent isodrosotherms analyzed every 5°F...... 12 Figure 6: 1200 UTC 700 mb equivalent potential temperature analysis on 3 August 1992. Solid lines represent equivalent isentropes analyzed every 5K...... 13 v Figure 7: 0000 UTC 700mb equivalent potential temperature analysis on 4 August 1992. Solid lines represent equivalent isentropes analyzed every 5K ...... 14 Figure 8: 1200 UTC Great Falls, Montana (GTF) SkewT- logP sounding on 3 August 1992...... 15 Figure 9: 1200 UTC Great Falls, Montana (GTF) hodograph 1 on 3 August 1992 in ms· . Points along the hodograph indicate thousands of feet above mean sea-level...... 16 Figure 10: Same as Figure 8 except at 0000 UTC on 4 August 1992...... 17 Figure 11: Same as Figure 9 except at 0000 UTC on 4 August 1992...... 18 Figure 12: 0000 UTC 4 August 1992 modified SkewT-logP sounding for Havre, Montana (HVR) via the SHARP Workstation...... 19 Figure 13: 0000 UTC 4 August 1992 modified hodograph for Havre, Montana (HVR) via the SHARP Workstation using the default storm motion (70% of the magnitude and 30 o to the right of the 0-6 km mean wind)...... 20 Figure 14: 0000 UTC 4 August 1992 modified Havre, Montana (HVR) hodograph using the observed storm motion from radar data...... 21 VI Utilization of the Bulk Richardson Number, Helicity and Sounding Modification in the Assessment of the Severe Convective Storms of 3 August 1992 Eric C. Evenson WSFO Great Falls I. INTRODUCTION Storms Forecast Center (NSSFC), are a useful technique in observing those On August 3, 1992, a severe meteorological parameters necessary for thunderstorm developed during the early the development of severe local storms. . evening hours over north-central From the composite chart, wind, Montana (Fig. 1). The severe moisture, and temperature patterns at thunderstorm dropped baseball-size hail, various levels in the atmosphere can be causing extensive damage to homes, visualized. Also, these patterns can be vehicles, and crops. An FO tornado and compared to the orientation of the static one report of wind damage was also stability fields at a given time. The SELS reported. forecaster uses the chart to help define and delineate areas in which severe When assessing the threat of severe thunderstorm development is most likely. weather, forecasters typically ask the question, "What type of storm structure The composite analysis (Fig. 2) valid at can be expected"? One way to forecast 1200 UTC on 3 August showed several storm type is through the use of the Bulk features conducive to the generation of Richardson Number (BRN) as defmed by severe thunderstorms. A north-south Weisman and Klemp (1982, 1984). The oriented stationary surface front BRN involves a relationship between extended from east of Cut Bank, Montana storm type, wind shear, and buoyancy and (CTB), through Great Falls (GTF) and is especially useful in determining southeast through Billings (BIL). Surface isolated supercell development. This dew points were 50° F or greater over study examines the conditions that led to much of Montana east of the Continental the initiation of the severe convection, Divide. At 850mb, southeasterly low forecasting the location of severe level winds of 25 knots prevailed across weather, and assessing the type of storm eastern Montana. Also at the 850 mb structure using the BRN. The role of level, a thermal ridge extended from helicity and sounding modification is also southern Alberta through western examined. Montana and continued south into western Utah. Progressing upward to the 700 mb level, a positively tilted short IT. COMPOSITE ANALYSIS wave trough was located across southern Alberta and into the northeast portion of Johns and Doswell (1992) note that Washington state. At 500mb, a low composite analyses, prepared daily by the pressure trough and associated cold pool forecasters at the SEvere Local Storms of air was situated over southeast British (SELS) unit of the National Severe Columbia. Across eastern Washington 1 state, northern Idaho, and western maximum at 300 mb, previously located Montana, a mid-level wind maximum (500 over eastern Washington state, was now mb) of 35 knots was observed. Diffluence over western Montana (the 0000 UTC 4 was also noted at 500 mb over northwest August GTF sounding indicated a 79 knot Montana. The 300 mb upper-air chart wind at the 300 mb level). The jet showed a strong jet maximum located maximum helped to create favorable over eastern Washington state illustrated speed shear north of the jet axis, and the by the observed 95 knot wind at Spokane left front quadrant of the jet maximum (GEG). Lifted Indices (LI) of zero or less was placed across north-central Montana. were observed from west-central Montana McGinley (1986) and others note that southwest into Idaho. Specifically, the this region is favorable for enhancing 1200 UTC sounding at GTF indicated an upward motion through the ageostrophic LI of -1. secondary circulation. By 0000 UTC on 4 August, conditions had Through the use of the composite charts become more favorable for severe (Figs. 2 and 3), the forecaster is now convection across Montana. The aided in visualizing the changing dynamic composite analysis (Fig. 3) at 0000 UTC and thermodynamic structure of the showed several parameters converging atmosphere. This can help in narrowing across southern Alberta and north-central down a region favorable for strong or Montana. The surface frontal boundary severe thunderstorm development. In was located east of a line from this particular case, the composite charts Lethbridge, Alberta (YQL) to GTF and indicated north-central Montana as the extended south to Bozeman, Montana area most conducive to severe weather. (BZN). Surface dew points remained above 50° F across portions of central and eastern Montana with dew points greater Ill. SURFACE ANALYSIS than 55°F across north-central Montana. The southeasterly jet maximum of 25 The 1800 UTC 3 August surface analysis knots at 850 mb remained across eastern (Fig. 4) showed dew points greater than Montana, as did the thermal ridge over 50°F extending from southern Alberta southern Alberta, western Montana, and across central Montana with a 6rF dew into western Utah. The positively tilted point noted at YQL. A frontal boundary, short-wave trough at 700 mb was east of the Continental Divide, extended propagating east across western Manitoba from north-central to south-central and north-central Montana. Warming Montana. By 0000 UTC, the front had temperatures in the lower layers of the moved east and was located just east of a atmosphere combined with cooling aloft line from YQL to GTF and south to BZN. associated with the thermal trough at 500 This frontal boundary had similar mb advecting eastward, resulted in characteristics associated with those of a steepening lapse rates across north Southern Plains dry line. Warm, dry air central Montana. This contributed to a existed west of the surface boundary more favorable environment for severe while a relatively cool, moist air mass convection by increasing potential prevailed east of the boundary. Dry air instability. A 50 knot mid-level jet was aloft and steep lapse rates aided in also apparent moving across the central transferring momentum to the lower portions of Montana. The upper-level jet layers of the atmosphere which 2 contributed to the eastward progression Convective Available Potential Energy of this boundary, as well as strengthening (CAPE). A favored area for the formation the moisture gradient found along it. of severe convective development, as The dew point at GTF decreased 18°F noted by Campbell (1991), is along a during the six-hour period from 1800 theta-e axis. The 0000 UTC 4 August UTC to 0000 UTC as dry northwesterly 700 mb theta-e analysis (Fig. 7) indicated winds began to advance south along the the theta-e ridge axis had now shifted east slopes of the Rocky Mountains. into eastern Montana, enhancing the Between 1800 UTC and 0000 UTC, potential for severe thunderstorms. moisture pooled over north-central Montana and southern Alberta, as illustrated by the position of the 55°F V. SOUNDING AND isodrosotherm. As noted by Johns and HODOGRAPH DATA Hirt (1987), increased low-level moisture contributes to greater positive buoyancy The 1200 UTC 3 August GTF sounding for a lifted parcel and lowers the level of (Fig. 8) showed marginal instability with free convection (LFC). This decreases the Showalter and Lifted Indices both the amount of dynamically induced lift indicating values of -1. Mielke's (1979) necessary to initiate and sustain deep local program for measuring CAPE, convection. The moisture gradient east computed 1,920 J /kg of buoyant energy of the Rocky Mountains continued to in the sounding. The GTF hodograph increase as noted on the 0000 UTC 4 (Fig. 9) showed significant veering in the August surface analysis (Fig. 5). A dew wind field and increasing speeds from the point difference of 16°F existed between surface through 9,000 feet (MSL). This GTF and HVR as the drier, low-level air type of hodograph favors the continued to filter southeast along the development of cyclonically rotating, Continental Divide. right-moving supercells (Doswell 1990). The intrusion of drier air along the east The 0000 UTC GTF sounding on 4 slopes of the Rocky Mountains alerts the August (Fig. 10) showed the atmosphere forecaster that this area has a decreased had stabilized in the past 12 hours as the threat for the development of severe lowest layers had dried considerably. convection. Thus, the focal point of the This corresponded to the drier air found operational meteorologist shifts to the west of the frontal boundary. The area where the higher concentration of Showalter and Lifted Indices were now low-level moisture exists. + 1 and + 2, respectively. The threat for severe weather had now shifted east where the sharp dew-point gradient IV. THETA-E ANALYSES existed. The 0000 UTC GTF hodograph on 4 August (Fig. 11) showed a noticeable A 700 mb theta-e ridge (Fig. 6) at 1200 change in the structure of the wind field. UTC on 3 August extended from Winds from the surface to about 8,000 Edmonton, Alberta (WEG) to GTF and feet (MSL) prevailed from the northwest south to Lander, Wyoming (LND). Last compared to the previous 12 hours where (1992) pointed out that equivalent a southerly component to the winds potential temperature (theta-e) analyses existed. are useful in locating areas of high 3 VI. BULK RICHARDSON NUMBER moderate 0-6 km wind shear (4 x 10 -3 s- 2). The value of R may be well within the Severe weather can result from any type range for supercell development, and a of convective storm, however certain forecaster would then expect some of the storm types are more likely to produce convective storms to have the steadiness severe weather than others. Being able and propagation characteristics of to determine what type of convective supercell storms. However, since other storm may result from a given factors are also important for severe environment can be a valuable tool in this convective development, one cannot be assessment. One such tool, the Bulk assured that given the existence of a Richardson Number (BRN), is a supercell, severe weather will occur relationship between wind shear and (Johns and Doswell1992). Also, an buoyancy. Observations and research environment with large buoyant energy 2 2 from Weisman and Klemp (1986) suggest (B > 3500 m / s ) and moderate 0-6 km the BRN can be related to a preferred wind shear may be characterized by a storm type. The BRN (R) is expressed relatively large value of R, yet produce by: tornadoes or large hail with a relatively unsteady, or cyclic storm. R = B 1/2U2 In the case on 3 August, the 1200 UTC hodograph at GTF (Fig. 9) had an where B is the buoyant energy in the observed BRN value of 28 which is in the storm's environment (CAPE) and U is a range determined by Weisman and density weighted mean measure of the Klemp for isolated supercell storm vertical wind shear through a relatively structure. As mentioned earlier, the deep layer (0-6 km AGL). Lazarus and buoyant energy at GTF was 1,920 J /kg Droegemeier (1990) point out that the and considerable wind shear was evident BRN is a bulk measure of the ambient from the hodograph. This diagnosis can shear and does not account for detailed aid the forecaster in assessing not only if aspects of the wind proflle, particularly the threat of severe weather exists, but low-level veering. The results obtained what type of storm structure will or by Weisman and Klemp, in their should occur. numerical studies of convective storms, noted that for unsteady, multicellular The 0000 UTC 4 August GTF hodograph storm growth, values of R were greater (Fig. 11) indicated a BRN value of 2, than 30. For isolated supercellular storm which did not fit into either category of growth, values of R ranged between 10 multicellular or isolated supercell storm and 40. type. The influence of the dry, low-level northwesterly winds along the east slopes Weisman and Klemp (1986) note that of the Rocky Mountains significantly although the magnitude of R may altered the buoyancy and wind shear indicate a preferred cell type to be terms of the BRN equation. favored in a given region, it does not necessarily provide an indication to the However, by modifying the low-level severity of that convection. An example conditions (e.g., surface to 700 mb) of the of this is an environment with small GTF sounding to those near HVR in 2 2 buoyant energy (B < 1000 m /s ) and north-central Montana, a proximity 4 sounding representing conditions near through the storm inflow layer and the area of possible severe weather can indicates the rotation potential of a be constructed. This is achieved by thunderstorm updraft. In other words, substituting the surface data from HVR air parcels flowing toward the updraft for GTF, and then interpolating values region of a thunderstorm spin about a from the upper-air data at 850 mb and horizontal vorticity axis. When lifted into 700mb. Through the substitution of the updraft, this axis is tilted and these data, a modified HVR sounding and stretched into the vertical and develops a hodograph was constructed using the cyclonic rotation. SHARP Workstation (Hart and Korotky 1991). The 0000 UTC 4 August modified SRH is calculated on the SHARP sounding for HVR indicated a positive Workstation as twice the area bounded by buoyant energy of 2170 m2 /s2 (Fig. 12). the hodograph between the storm inflow The modified HVR hodograph (Fig. 13) vectors at the top and bottom of the produced a BRN of 24, which indicated measured layer. SHARP uses an initial an environment conducive for isolated storm motion of 30 degrees to the right supercell storm structure and of the 0-6 km mean wind, and 7 5 percent development. Satellite photos (not of its magnitude (after Leftwich 1990) to shown) indicated that an isolated get an estimate of the SRH. This would supercell developed over north-central allow the forecaster an initial first guess Montana and moved south-southeast as to the amount of SRH available in a (330° ). This movement was noticeably to given environment before the storms the right of the 0-6 km mean wind develop. Then, storm motion can easily (252° ). This cell was responsible for the be updated on the SHARP Workstation production of large hail and an FO with the use of radar data, for example. tornado. In a study of 28 tornado cases, Davies Jones (1990) found approximate ranges of 0-3 km (AGL) SRH corresponding to Vll. HELICITY tornado intensity. For weak tornadoes (FO-F1), helicity values were between Although the BRN is a useful parameter, 150-299 m2 /s2 while for strong tornadoes it is not as detailed of a predictor of (F2-F3), helicity values ranged from 300- 2 2 storm rotation because it is a bulk 449 m js • Violent tornadoes (F4-F5) measure and does not take into account produced helicity values greater than 450 details of the vertical wind profile. In mz;sz. recent years, special emphasis has been placed on the lowest 2 or 3 km of the Calculations of SRH were made by using atmosphere, usually below the level of the modified hodograph in section 6 and free convection (LFC), which is modifying the observed storm motion. considered the inflow layer into a Storm motion, initially calculated by the convective storm. Storm relative helicity SHARP Workstation, indicated a storm (Davies-Jones 1990) is an important motion of 286 degrees at 14 knots and a parameter used to measure the potential SRH of 157 m2 js2 (Fig. 13). Using the storm rotation obtainable for a given observed radar data, a storm motion of environmental low-level wind field. 330 degrees at 15 knots was substituted Storm relative helicity (SRH) is the for the SHARP Workstation storm summation of the streamwise vorticity motion. Given these modifications, the 0- 5 3 km SRH was 221m2 /s2 (Fig. 14) which data features in close proximity to the is a considerable increase over the initial severe weather threat area to derive a calculation of SRH. The increased SRH better representation of the near storm shows a greater rotation potential of the environment. AB in the above case, this thunderstorm updraft. can be a very valuable tool to forecasters. vm. CONCLUSIONS IX. ACKNOWLEDGMENTS Severe convection initiated as a result of I would like to thank John Mecikalski several key parameters: low-level (University of Wisconsin) and Bob Johns moisture ahead of a sharpening moisture (NSSFC) for their valuable insight into gradient as a front moved east into the this project as well as Jeff Last (WSFO HVR area; low-level convergence and a MKX) for his assistance with some of the 700 mb short-wave trough were present modifications made on the SHARP to provide dynamical forcing of the moist Workstation. air; a thermal trough at 500 mb aided in destabilizing the atmosphere as mid-level cold air advection advanced into north X. REFERENCES central Montana; the left front quadrant of a 300 mb jet maximum supported Campbell, M., 1991: Equivalent potential upward motion; and moderate values of temperature (theta-e) applications. buoyant energy existed. Composite Western Region Technical Attachment 91- analysis proved 'useful to graphically show 37, NWS Western Region, Scientific · all of the above features. This aided the Services Division, Salt Lake City, Utah. forecaster in isolating north-central Montana as the area most favored for Davies-Jones, R., D. Burgess, and M. severe weather. Foster, 1990: Test of helicity as a tornado forecast parameter. Preprints, 16th The Bulk Richardson Number was Conference on Severe Local Storms, utilized to assess the predicted type of Kananaskis Park, Alberta, Amer. Meteor. storm structure for this particular Soc. 588-592. environment. Modifications made to the sounding and hodograph data using the Doswell, C. A. ill, 1990: On the use of HVR surface and low-level observations, hodographs: vertical wind profile via the SHARP Workstation, led to a information applied to forecasting severe more accurate assessment of potential thunderstorms. Training Notes, NWS buoyant energy and vertical wind shear in Southern Region Headquarters, 37 pp. the convective area. Storm relative helicity provided even further Hart, J. A., and W. Korotky, 1991: The information about the low-level inflow (0- SHARP Workstation v1.50. A SkewT- . · 3 km AGL) into a convective storm and hodograph research program for the IBM its potential to generate cyclonic rotation and compatible PC. NOAA/NWS, and long-lived supercell thunderstorms. Charleston, West Virginia, 30 pp. The forecaster may want to consider modification of the surface and upper-air 6 Johns, R. H., and W. D. Hirt, 1987: Weisman, M. L., and J. B. Klemp, 1986: Derechos: widespread convectively Characteristics of isolated convective induced windstorms. Wea. Fest., 2, 32-49. storms. Mesoscale Meteorology and Forecasting, (P. S. Ray, ed.), Amer. Johns, R. H., and C. A. Doswell ill, 1992: Meteor. Soc., 331-358. Severe local storm forecasting. Preprints, Symposium on Weather Forecasting, Atlanta, Georgia, American Meteorological Society, 225-236. Last, J. K., 1992: Examples of significant thunderstorm initiation in identifiable low level theta-e patterns. Central Region Technical Attachment, NWS Central Region, Scientific Services Division, Kansas City, Missouri. Lazarus, S.M., and K. K. Droegemeier, 1990: The influence of helicity on the stability and morphology of numerically simulated storms. Preprints, 16th Conference on Severe Local Storms, Kananaskis Park, Alberta, Amer. Meteor. Soc., 269-274. McGinley, J., 1986: Nowcasting Mesoscale Phenomena. Mesoscale Meteorology and Forecasting, (P. S. Ray, ed.), Amer. Meteor. Soc., 657-688. Mielke, K. B., 1979: A computer program for convective parameters. Natl. Wea. Dig., Volume 4, Number 3, 10-18. Weisman, M. L., and J. B. Klemp, 1982: The dependence of numerically simulated convective storms on vertical wind shear and buoyancy. Mon. Wea. Rev., 110, 504- 520. Weisman, M. L., and J. B. Klemp, 1984: The structure and classification of numerically simulated convective storms in directionally varying wind shears. Mon. Wea. Rev., 112, 2479-2498. 7 ------,--1------····- -- I ' ,_.. ------z-·------~----~~~~~~~~~~~~~-~~~~~~ I,_J·;l~::~[) Ka~~::l~~ \~, ' .1 ...... ~~A I ') ··-t { ~ Chote.a'u-·- ~~~\ ~-~r1 -- -- Jordan • £ ~·7is~;~. \.He\e~~ • l)-- Bak~ Tw A CD k, ..- 1__, \;-/~ --.'.,_But\te ~~- _ !.) J ' ~ \_/~ s:__" Boze an 0 \ t_, ~--1 • - A A \ ·-.. l . ~ I . * ~ "\ ~ Gilford \ -J----- ~r·------~I Figure 1: Plot of known severe weather events across Hill county in north-central Montana on 3 August 1992. (Reports from Storm Data and local storm reports.) T = tornado W; = wind damage A = hail greater than 3/4 inch diameter. /---- ~ 50F 5~F .fiF & ] ·..•...... · *HVR ·. · GTF· \0 .·-::::-:: ::-.-:;:~:~:~:~:~:~ .... &. &. • • FIGURE 2 Figure 2: Composite analysis at 1200 UTC on 3 August 1992. Arrow represent jet maxima at various levels. Dotted line represents the 850 mb thermal ridge. Large dashed line denotes 700 mb shott wave trough. Triangular line indicates thermal trough at 500 mb. Jagged dot-dashed line represents diffluence at the 500 mb level. Thin dashed lines represent surface isodrosotherms analyzed every 5o F ( >50 oF). Stippled area denotes Lifted Indices less than or equal to zero. 50F • 50F • : 55F 5#.: ······.. ./~140 • ··~. ..... 0 / ~ .. ···'.k.BIL : •• I • ~F ~5F 55F 50: • FIGURE 3 ~ Figure 3: Same as Figure 2 except at 0000 UTC on 4 August 1992. 0 YCT 64 159 55 F.~ 50F 0 '"""P \ YKY 60F-t) 64,} lojag ~ YXI 61 YQL ...... 80 135 a---' MSO 72 127 54~ 0 COD Figure 4 Figure 4: 1800 UTC surface analysis on 3 August 1992. Solid lines represent isodrosotherms analyzed every s•F. 0 YRV 55F ~\: 0 YYN ~144 75 1 59 YQL ..... "' Figure 5 Figure 5: 0000 UTC surface analysis on 4 August 1992. Solid lines represent isodrosotherms analyzed every 5•F. ~0 -0~308 1 +05 7184• +12 33 Cl- P-01 W36 . +11 :t3.. 7625 13 "; Figure 6: 1200 UTC 700 mb equivalent potential temperature analysis on 3 August 1992. Solid lines represent equivalent isentropes analyzed every 5K. Figure 7: 0000 UTC 700 mb equivalent potential temperature analysis on 4 August 1992. Solid lines represent equivalent isentropes analyzed every 5K. +00 ~+00~6 7186 +13 337 ~-02 7237 14 ' ---, l Figure 8: 1200 UTC Great Falls, Montana. ",F) SkewT-logP sounding on 3 August 1992. -100 \.h. + 310/ 30 50 '4.....: 300/ 42 t\\ 280/ 61 ~+ 280/ 50 40 L_ 275/ 48 ~ E?~( §Z +·270/ 54 I 7 / \.\:7. . / . ')( . 1 C\\:.7 c . ",( . Jl';..'(. -7'. ''-0.4. . iX: r J[>.''- 7/ . - ')(- 72>< 7/ "--.../ .:6.:J+- 30 ~·270/ 51 1-' U1 + 275/ 53 ~'27~; ~8 20 \lll_ 270/ 34 + 265/ 36 ~ 255/ 29 + 255/ 28 \\._ 270/ 22 + 280/ 12 \.-- 255/ 09 10 + 250/ 14 240/ 13 ~ 210/ 11 120/ 05 "").. D I R/KTS D I R/KTS ~ ·50 ·60 70 -~ 90 100 110 1c:Z/AU/ 03/ ::::t2 KM/KFT GTF 12Z 3 AUG 92 B R N = 28 UNITS KNOTS, LVLS : THSD FT CMSL) B+ = 161 CM/SEC>**2 X 10 B- = 0 CM/SEC>**2 X 10 SHR = 58 (M/SEC>**2 WMAX = 57 M/SEC EL = 197 MB, 402 HND FT MPL = 489 HND FT vss = 7 CM/SEC>**2 SS15 = 68 10-4 SEC-1 PARCEL FROM PMAX ENTRAINMENT = 60 PERCENT P0 = 888 MB PMAX = 771 MB I 180 7 LCL = 679 MB LFC = 511 MB EI = -2 J/KG X 10 EI+ = 6 C+ PART) EI- = -7 C- PART) ENERGY CHANGE IN LAVERS 1090 P1 P2 771 511 -7 J/KG X 10 511 236 15 ... 236 100 -472 I 360 LI = 0 Figure 9: 1200 UTG Great Falls, Montana (GTF) hodograph on 3 August 1992 in ms·•. Points along KI = 31 the hodograph indicate thousands of feet (MSL). SWI = -1 1t:; CCL = MB ., -40 '&._.. 270/ 28 + 270/ 29 \\.\\._ 285/ 39 40 ~ 275/60 lfVU .LV '-.I..L.. ~.l. .... "'lo .I.U ~u· ...... 1-L.. .I v ...... , '-L..U.. ·L..o """' F..JL.. r r J r r 1i~~ - 3 ~ /\'-YE;RT.I CA.L TOTALS =: 1',. ~~ X '\.V '\ }(\ A ><'/.Y V X Tf'IT.OI Tf'IT.OI ~ - .~g /~ ~ t\\\\, 'T ~?~) §~ ~~~l 270/ 84 + 270/ 82 30 f\\\\ 270/ 79 + 270/ 54 ~ ~~~~ §1 ~ 275/ 50 20 ~ 275/ 47 270/ 48 + 280/ 31 ~ 245/ 22 + 245/ 16 10 ~ ~~~~ l'f ..l- 265/ 07 ~ 305/ 05 340/ 07 t 350/ 09 ~~~::::~5 / ~0~' D I R/KTS D I R/KTS -30 30 040z)Au)0 04°/ KM/KFT 17 GTF 002 4 AUG 92 B R N = 2 UNITS : KNOTS, LVLS : THSD FT CMSL) B+ = 12 CM/SEC)**2 X 10 B- = 0 CM/SEC)**2 X 10 SHR = 67 (M/SEC)**2 WMAX = 16 M/SEC EL = 304 MB, 308 HND FT MPL = 365 HND FT VS5 = 0 (M/SEC)**2 SS15 = 72 10-4 SEC-1 PARCEL FROM PMAX ENTRAINMENT = 60 PERCENT P0 = 886 MB PMAX = 869 MB 180 14 LCL = 595 MB LFC = -999 MB EI = -30 .J/KG X 10 EI+ = 0 C+ PART) EI- -30 (- PART) 1 k ~ 1 1 1 1 1 1 1 ~~~. 25 '270 = 090 4 ""' 4 r::: ';)Qt ';)1:: ':I"" '::11:: .A""' A~ r:::..,t ENERGY CHANGE IN LAYERS P1 P2 869 100 -679 .J/KG X 10 360 LI = 1 KI = 22 SWI = 1 Figure 11: Same as Figure 9 except at 0000 UTC on 4 August 1992. CCL = 579 MB C TMP = 30 c. 86 F WAVG = /~ G/KG X 10-1 018 SFC ELV CFT) = 3655 = 16 Ii ul,,,,,.T . -7 !16 TT ...... 51 I ,/ TEl ..... 25 .21 I K... I I. I 30 i I SIJEAT ••• 283 I C~P~ .... 1.6 CURSOR MTA 3941th 645918 21192' &=352 !s=103F 26 w= 7~5 -3 ~7C 25F RAOB DATA P.• II I 488 T.... I -24.3 Td .... -38 ~3 Tdd~.. 14~0 Uind~ ~278151 t------140 PARCEL DATA 50 B+ .... 2170 B- ... , 45 LPL~. 8861tb EL~ I .35eoort MPL •• 46308Ft 78 LCL •• 5294rt F2L. • 9945rt 85 UBZ •• 8388ft PU. .. 8 ~66 in 1051~~~----~--~----~~~~----~----~--~ ~~:...-_ __._~--"----~---'----'--:;,...___..:..._ ___ -10 8 18 28 38 48 58 68 Lm -ED IT LEUEL RIGHT-RE-DRAU CHART IRIGHT FOR MENUBUTTON I Figure 12: 0000 UTC 4 August 1992 modified SkewT-logP sounding for Havre, Montana (HVR) via the SHARP Workstation. 19 1SG I . I 09G--+--273 I I 369 I I 15 f5 - Hel/S}Ira src - 7330 M F6 - Res~t F7 - Help rs - LEFT - EDIT MOTION - RE-DRAW F9 - Figure 13: 0000 UTC 4 August 1992 modified hodograph for Havre, Montana (HVR) via the SHARP Workstation using the default storm motion (70% of the magnitude and 30 o to the right of the 0-6 km mean wind). 20 GTF I QS/04/92 I QSZ 180 Mean Wind MODIFIED I I 0-3kM •• 1951 9 - 90--+--279 0-6kM •• 252118C• 60 I I Positive Shear 360 &-21-~ •. 3.8 11 c - e-3k."'i .• 40 .J 45 SR Helici tq I Q-2Jr..M.. 172 Q-3kM .. 221 I - 3@ StorM Motion 33@/ 15$ -·- ,~ ~~ J l,:.t 1 15 OPTIONS - 15 • F1 - Zool!i F2 - Edit Wind - 30 F3 - Hel Contours F4 - StorM Inflow - 45 F5 - Hel/Slli' F6 - Reset - 69 SFC - 7990 M F7 - Help jl F8 - Save LEfT - EDIT MOTION RIGHT - RE-DPJIW II F9 - EXIT ! Figure 14: 0000 UTC 4 August 1992 modified Havre, Montana (HVR) hodograph using the observed storm motion from radar data. 21 142 The Usefulness of Data from Mountaintop Fire Lookout Stations in Determining 200 Annual Data and Verification Tabulation Eastern North Pacific Tropical Storms and Atmospheric Stability. Jo:nathan W. Corey, April 1979. (PB298899/AS) Hurricanes 1988. Roger L. Cross and Kenneth B. Mielke, September 1987. (PB88110895/ASl 143 The Depth of the Marine Layer at San Diego as Related to Subsequent Cool Season 201 An Inexpensive Solution for the Mass Distribution of Satellite Images, Glen W. Sampson and Precipitation Episodes in Arizo11a. Ira S. Brenner, May 1979. (PB298817/AS) George Clark, September 1987. (PB88 114038/AS) 144 Arizons Cool Season Climatologicsl Surface Wind and Pressure Gradient Study. Ira S. 202 Annual Data and Verification Tabulation Eastern North Pacific Tropical Storms and Brenner, May 1979. (PB298900/AS) Hurricanes 1987. Roger L. Croas and Kenneth B. Mielke, September 1988. 146 The BART Experiment. Morris S. Webb, October 1979. (PB80 155112) . . (PB88 101935/AS) 147 Occurrence and Distribution of Flash Floods m the Western Reg:10n. Thomas L. Dietnch, An Investigation of the 24 September 1986 "Cold Sector• Tornado Outbreak in Northern December 1979. (PB80 160344) 203 ,, 149 Misinterpretations of Precipitation Probability Forecasts. Allan H. Murphy, Sarah California. John P. Monteverdi and Scott A Braun, October 1988. (PB89 121297 /AS) Lichtenstein, Baruch Fischhoff, and Robert L. Wmkler, February 1980. (PB80 174576) 204 Preliminmy Analysis of Cloud-To-Ground Lightning in the Vicinity of the Nevada Test Site. 150 Annusl Data and Verification Tabulation - Eastern and Central North Pacific Tropicsl Cerven Scott, November 1988. (PB89 128649/AS) Storms and Hurricanes 1979. Emil B. Gunther and Staff, EPHC, Apri11980. (PB80 220486) 205 Forecast Guidelines For Fire Weather and Forecasters - How Nighttime Humidity Affects 151 NMC Model Performance in the Northeast Pacific. James E. Overland, PMEL-ERL, April Wildland Fuels. David W. Goens, February 1989. (PB89 162549/AS) 1980. (PB80 196033) 206 A Collection of Papers Related to Heavy Precipitation Forecasting. Western Region 152 Climate of Salt Lake City, Utah. Wilbur E. Figgins The National Oceanic and Atmospheric Administration was established as part of the Department of Com merce on October 3, 1970. The mission responsibilities of NOAA are to assess the socioeconomic impact of natural and technological changes in the environment and to monitor and predict the state of the solid Earth, the oceans and their living resources, the atmosphere, and the space environment of the Earth. The major components of NOAA regularly produce various types of scientific and technical information in the following kinds of publications. 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