Chesapeake and Ohio Express: The Derecho of June 2012

Chesapeake and Ohio Express: The Derecho of 29-30 June 2012 Richard H. Grumm, Charles Ross And Contributors from the Albany MAP and the Storm Prediction Center National Weather Service Office State College, PA 16803 1. Overview An area of convection developed south of Chicago around 1600 UTC on 29 June 2012. This bow-echo like structure evolved out of convection which had moved across Iowa and western Illinois overnight and during the morning hours of 29 July 2012. The convection quickly developed a large lineecho wave like pattern and accelerated southeastward (Fig. 1). The developing derecho produced wide spread wind damage (Fig. 2). The strong winds downed trees and power lines (AP 2012a) and killed at least 13 people. The death toll would rise as Figure 1. Discrete images of composite reflectivity in hourly segments with annotation as to the storms path and observed wind gusts. Data was produced the National Weather Service Storm Prediction Center. Annotations by Greg Carbin of the SPC and image courtesy of Greg Carbin. Return to text. accidents related to clean up were added to the tally (AP 2012b). The massive swath of wind damage cut power to over 3 million customers (AP 2012a) in a region suffering from a massive heat wave. This line of thunderstorms became a mesoscale convective complex (MCS: Maddox 1979). This particular MCS met the definition of a derecho (Johns and Hirt 1987) in that it was a widespread convective windstorm with a concentrated area with winds over 50kt spanning at least 240 miles (400km) which includes wind gusts in excess of 58 kts (SPC website). Based on wind shear and storm progression, this derecho would further be defined

Figure 2. Storm reports from the Storm Prediction Center for the 24 hour period ending at 1200 UTC 30 June 2012. Return to text as a progressive derecho. Based the known derecho climatologies (Bentley and Mote 1998; Bentley and Mote 2000; Bentley et al 2003), this derecho developed within an area which averages one derecho per year. But as it moved eastward, it entered a region that experiences on average about 1 derecho every 3-4 years. Thus in Virginia and Maryland, this was a relatively rare event. The flow over large ridges during the warm season is a favored location for MCS development and in some instances derecho development. A strong derecho affected northern New York and New England on 15 July 1995 (Bosart et al. 1998; Cannon et al. 1998). Bentley (1997) described the conditions associated with the derecho of July 1995. The tendency of these systems to move over the top of larger ridges produced the evolution of the term ridge-roller (Galarneau and Bosart 2006; Galarneau et al. 2008). Ridge-rollers, as the name implies come over the top of strong ridges during the warm season. The ring-of-fire affect with large ridges, in which MCSs activity can and often is enhanced is well known. But stronger ridges, which often occur with heat waves, often produce some of the more active periods of MCS and derecho activity. The northern New York and New England event was one in a series of derechoes in the eastern United States during the mid-july heat wave of 1995. Congilio et al (2011) documented the derecho of 8 May 2009. They provided an overview of the conditions associated with this early season event and an excellent summary of derecho climatology and formation. High precipitable water (PW), CAPE, and a strong low-level jet were all important in the evolution of 8 May 2009 derecho. The strong updrafts

and factors confining the downdrafts may help generate the strong surface outflow. The 8 May derecho developed over northeastern Kansas and produced severe weather from Kansas to eastern Tennessee and Kentucky (see Fig 1 Coniglio et al 2011). Coniglio (2011) used the term derecho-producing convective system to tie in the concept of this special type of MCS. This case study will document the derecho event of 29-30 June 2012. The focus here is on the pattern associated with this system and the value of standardized anomalies in identifying such systems. Some examination of forecast products is shown. However, explicit forecasts of such mesoscale systems are beyond the capabilities of most operational numerical forecast systems and ensemble forecast systems. 2. Data and Methods Satellite and radar data were obtained using AWIPS. All data shown were produced from AWIPS. Model data and standardized anomalies were produced using GrADS (Doty and Kinter 1995). Storm reports were taken locally and the Storm Prediction Center plots are displayed herein. The definition of a derecho was met here but this term and MCS are used interchangeably. 3. The large scale pattern The large scale pattern over the United States from 0000 UTC 28 June through 1200 UTC 30 June 2012 showed a strong ridge over the central United States (Fig. 3) with a deep trough off the coast of New England. This created a pattern with fast northwesterly flow over the ridge from the Great Lakes into the Mid-Atlantic region. This pattern is similar to the pattern of 12-15 July 1995 when a series of derechoes impacted the eastern United States. During the derecho event of 15 July 1995, a closed 5940 m high was over the Midwest and the fast flow in the northeast quadrant of the ridge was over New England (Fig. 4). The regional pattern of 12 June shows the surge of high PW air over the ridge (Fig. 5). Clearly, the surge of high PW air over Pennsylvania at 0600 UTC 29 June was stronger than the surge at 1800 UTC 29 June and 0000 UTC 30 June. A strong 700 hpa jet was present at both times (Fig. 6). There was a weaker and less destructive MCS which crossed Pennsylvania and New Jersey between about 0400 and 1000 UTC 29 June. In addition to the strong winds at 700 hpa, in the enhanced 500 hpa gradient there was an enhanced 500 hpa jet (Fig. 7). Strong winds were present at 850 hpa (not shown) and the 850 hpa moisture flux shows the strong moisture flux (Fig. 8) which was associated with two ridgerolling MCSs of 29 June 2012. The forcing from a wind and moisture perspective appeared more impressive around 0600 UTC 29 June; however the CAPE over the region where the MCS tracked from 1800 UTC 29 June through 0600 UTC 30 June was higher (Fig. 9) based on the GFS analyzed CAPE. Both events had extremely high CAPE. Around 0000 UTC 30 June 2012 the CAPE was over 3600 to 4200 JKg-1 in the Washington Metropolitan area as the ridge-rolling MCS/derecho blew through.

4. Satellite The IR satellite image at 1402 UTC (Fig. 10a) shows the convection associated with an MCS moving out of Iowa (Fig. 10). This systems character would change dramatically on radar (next section) as it moved just south of Chicago at 1702 UTC (Fig. 10b). The system tracked across Indiana and split (Fig. 10c) as it took a sharp turn to the right (Fig 10d) taking on a distinct bow shaped pattern. The massive cold cloud shield and lightning was racing into WV by 0115 UTC (Fig. 11a). The MCS raced across West Virginia (Fig. 11a) and across the Washington-Baltimore region (Fig. 11b-c) then off the coast of New Jersey by 0715 UTC. The lightning data implied a sharpening of the line with a more north-south oriented line of storms after 0115 UTC and a sharp north-south line was evident in these data at 0315 and 0415 UTC. After making the sharp right in Indiana it made another directional change in Maryland and Virginia. 5. Radar The composite reflectivity (Fig. 12) shows the initial re-developing bow over Illinois around 1600 UTC and then its right turn around 1900 UTC, note the split in the convection which matches the lightning split (Fig. 10). The system then raced southeastward across Ohio (Fig. 12 bottom) as shown at 2100 UTC. By 2200 UTC (Fig. 13) a region of 35 to 45 dbz echoes developed over the expansive evolving rear inflow jet (RIJ). The more stable looking echoes behind the line are common features with self-sustaining MCS s and derechoes (Houze et al. 1989). Note the reflectivity data weakened in the Mountains of West Virginia. However, velocity data (not shown) and the more stable appearing echoes in the stratiform rainfall area continued to imply the strong RIJ behind the line. KLWX radar showing the velocity and reflectivity data at 0114 UTC (Fig. 14) shows the line of storms form Fig. 13 west of Washington, DC. The velocity data shows winds in excess of -60kts (inbounds) with blue colors showing winds over 70 kts. Base velocity data is often idea to base warning decisions on with multi-cellular lines. This concept is made clearer at 0144 UTC where the multi-cellular line storms looks relatively weak in a region where the velocity data show deep blue colors implying winds in excess of 80 kts. The effect was even more apparent as the gust front blew through the KLWX RDA and the cells appeared very weak (Fig. 15) though outbound winds of 60 to 86kts were present all along the line at 0231 UTC. The relatively weak echoes still plague the radar at 0252 UTC though outbound velocity data show winds of 50 to 86 kts east of the radar over Maryland. There were some interesting waves, likely of no consequence in the KLWX velocity data. The system moved on to the east producing damage on its trek to the coast and coastal waters. The evolution of the stratiform rainfall area requires the development of a large cold-pool. Once this structure develops it can persist of 5-10 hours (Houze 1989;Rotunno et al. 1988;Weisman 1988).

6. Summary A cluster of thunderstorms developed in part from the remnants of an MCS which moved out of Iowa and western Illinois on 29 June 2012. A bow echo developed south of Chicago and accelerated to the east and south. This system developed a cold pool and made a sharp right turn over Indiana and raced southward across Ohio. Over Ohio, this derecho clearly developed a stratiform rain region (House et al 1989) indicating the development of a strong rear-in-flow jet. The system continued to race southeastward into West Virginia before turning to the left and racing through Washington-Baltimore corridor leaving a wake of downed trees, damaged, homes, leaving over 3 million people without power and causing perhaps 22 fatalities (AP 2012C). Some of the strong events of this nature have been term ridge roller (Galarneau and Bosart 2006). The 15 July event had a similar pattern. The strong ridge was displaced to the north of the ridge of June 2012. In both cases there was a surge of high PW over the ridge into the affected region and there was enhanced northwest low-level jet. Clearly, the pattern with these derechoes implies some impulse in the flow which triggers the deep warm air mass to realize the instability. The 15 July derecho caused over 500 million dollars in damages.this event, affecting a denser population area will likely surpass this event. The pattern during the height of the July 1995 event (Fig. 1) showed the enhanced 250 hpa jet over the ridge (Fig. 4a), in this example the 500 hpa ridge is shown, with a 5940 m closed contour over the Midwest. Strong winds were present at 500 hpa (not shown) and 700 hpa (Fig. 4c) in close proximity with the flow deep moisture over the ridge (Fig. 4d). The PW values were in the 50mm range over the ridge which was 2-3σ above normal. The high PW air implied relatively high CAPE. The June 2012 was similar though the ridge and thus fast flow was suppressed to the south and west. Thus the plume of moisture, coming over the ridge (Fig. 5) a favored a trajectory from Illinois to the coast. The data in Figures 3 & 5 show strong flow and a strong PW and wind surge between 0000 UTC 0600 UTC 29 June when a smaller derecho tracked across Pennsylvania and New Jersey. As in the 1995 event, the strong ridge of June 2012 had several ridge-rolling MCS which classified as derechoes. The radar data with this derecho suggest that the system evolved from a previous MCS which had moved out of Iowa into Illinois. The new convection began to bow as it moved south of Chicago and into Indiana. On satellite and radar, the derecho made a sharp right turn over Indiana and then raced southward across eastern Indiana and Ohio. In southern Ohio the reflectivity data showed an area of 30-45 dbz cores behind the line, indicative of self-sustaining RIJ. The system appeared to weaken over West Virginia, likely due to terrain. However, the KLWX 0.5 degree velocity data implied strong winds in excess of 60kts were present along and behind the multi-cellular line. As the leading edge of the derecho approached the KLWX RDA, the wind data clearly defined the massive derecho and winds in the 60 to at times 100kt range.

The reflectivity data implied a much weaker system. Warning decisions with bow echoes and strong derechos are often best produced monitoring the base winds. This event showed the evolution of a stratiform rain region over the RIJ (Fig.1 House et al. 1989). This region of enhanced returns behind the line typically lies above the descending inflow air into the system. This region was termed the region of heavy stratiform rain. The evolution of this feature in Ohio was likely a good indication of the strength of the rear to front flow. The relatively weak echoes at times along the line is often the result of the fast moving outflow developing new elements rapidly along the line. Thus, winds are often a good diagnostic tool in events of this nature. 7. References Associated Press 2012a: East Coast outage could last most of the month. And similar stories 30 July and 1 July 2012. Associated Press 2012b: US Storms death toll rises to 24. And similar stories 1-2 July 2012. Associated Press 2012c: This summer is what Global warming looks like. And similar stories 3 July 2012. Bentley, M.L. and J.M. Sparks: 2003: A 15 year climatology of derecho-producing mesoscale convective systems over the central and eastern United States. Climate. Res. 24, 129-139. Bentley, M. L., and T. L. Mote, 1998: A climatology of derecho-producing mesoscale convective systems in the central and eastern United States 1986-95. Part I: Temporal and spatial distribution. Bull. Amer. Meteor. Soc., 79, 2527-2540. Bentley, M. L., and T. L. Mote, 2000a: Reply to "Comments on a climatology of derechoproducing mesoscale convective systems in the central and eastern United States, 1986-1995. Part I: Temporal and spatial distribution." Bull. Amer. Meteor. Soc., 81, 1055-1060 Bentley, M. L., 1997: Synoptic conditions favorable for the formation of the 15 July 1995 southeastern Canada/northeastern U.S. derecho event. Nat. Wea. Digest, 21, No. 2, 31-39. Bosart, L. F., W. E. Bracken, A. Seimon, J. W. Cannon, K. D. LaPenta, and J. S. Quinlan, 1998: Large-scale conditions associated with the northwesterly flow intense derecho events of 14-15 July 1995 in the northeastern United States. Preprints, 19th Conf. on Severe Local Storms, Minneapolis, MN, Amer. Meteor. Soc., 503-506. Cannon, J. W., K. D. LaPenta, J. S. Quinlan, L. F. Bosart, W. E. Bracken, and A. Seimon, 1998: Radar characteristics of the 15 July 1995 northeastern U. S. derecho. Preprints, 19th Conf. on Severe Local Storms, Minneapolis, MN, Amer. Meteor. Soc., 400-443. Coniglio, M.C, S.F Corfidi, J.S. Kain 2011: Environment and Early Evolution of the 8 May 2009 Derecho-Producing convective system,mwr, 139,1083-1102. Doty, B.E. and J.L. Kinter III, 1995: Geophysical Data Analysis and Visualization using GrADS. Visualization Techniques in Space and Atmospheric Sciences, eds. E.P. Szuszczewicz and J.H. Bredekamp, NASA, Washington, D.C., 209-219. Davies, J. M., 2006a: Tornadoes in Environments with Small Helicity and/or High LCL Heights. Wea. Forecasting, 21, 579 594. doi: http://dx.doi.org/10.1175/waf928.1 Davies, J.M.. (2006b) Tornadoes with Cold Core 500-mb Lows. Weather and Forecasting 21:6, 1051-1062Online publication date: 1-Dec-2006. Abstract. Full Text. PDF (1512 KB)

Grams,J.S, R. L. Thompson, D. V. Snively, J. A. Prentice, G. M. Hodges, L. J. Reames. (2012) A Climatology and Comparison of Parameters for Significant Tornado Events in the United States. Weather and Forecasting 27:1, 106-123 Online publication date: 1-Feb-2012. http://journals.ametsoc.org/doi/pdf/10.1175/waf-d-11-00008.1 Galarneau, T. J., Jr., L. F. Bosart, and A. R. Aiyyer, 2008: Closed anticyclones of the subtropics and middle latitudes: A 54-yr climatology (1950-2003) and three case studies. Synoptic-Dynamic Meteorology and Weather Analysis and Forecasting: A Tribute to Fred Sanders, Meteor. Monogr., No. 55, Amer. Meteor. Soc., 349-392. [Available at the AMS Online Store.] Galarneau, T. J., and L. F. Bosart, 2006: Ridge Rollers: Mesoscale Disturbances on the Periphery of Cutoff Anticyclones. Preprints, Severe Local Storms Special Symposium, Atlanta, GA, Amer. Meteor. Soc. 7pp. Grams, J. S.,W.A.Gallus Jr., S. E.Koch, L. S.Wharton,A. Loughe, and E. E. Ebert, 2006: The use of a modified Ebert McBride technique to evaluate mesoscale model QPF as a function of convective system morphology during IHOP 2002. Wea Forecasting, 21, 288 306. Houze, R.A, S.A. Rutledge, MI. Biggerstaff, and BF Smull, 1989: Interpretation of Doppler weather radar displays of mid latitude convective systems. BAMS,70,608-619. Johns, R.H, and W.D Hirt 1987: Derechoes: Widespread convectively induced windstorms. Wea. Forecasting,2,32-49. Markowski, P. M., J. M. Straka, and E. N. Rasmussen, 2002: Direct surface thermodynamic observations within rear-flank downdrafts of nontornadic and tornadic supercells. Mon.Wea. Rev., 130, 1692 1721. Rutledge, G.K., J. Alpert, and W. Ebuisaki, 2006: NOMADS: A Climate and Weather Model Archive at the National Oceanic and Atmospheric Administration. Bull. Amer. Meteor. Soc., 87, 327-341. Markowski, P, Y. Richardson, E. Rasmussen, J. R. Davies-Jones, R. J. Trapp, 2008: Vortex Lines within Low-Level Mesocyclones Obtained from Pseudo-Dual-Doppler Radar Observations. Mon. Wea. Rev., 136, 3513 3535. doi: http://dx.doi.org/10.1175/2008mwr2315.1 Rotunno, R., JB Klemp, and ML Weisman, 1988: A theory for strong long lived squall lines.jas,45,463-485. Schoen, J.M W. S. Ashley. 2011: A Climatology of Fatal Convective Wind Events by Storm Type. Weather and Forecasting 26:1, 109-121. Online publication date: 1-Feb-2011. Abstract. Full Text. PDF (1569 KB) Trapp, R. J., S. A. Tessendorf, E. S. Godfrey, H. E. Brooks, 2005: Tornadoes from Squall Lines and Bow Echoes. Part I: Climatological Distribution. Wea. Forecasting, 20, 23 34. doi: http://dx.doi.org/10.1175/waf-835.1 Weisman, ML, JB Klemp, and R. Rotuno,1988: The structure and evolution of numerically simulated squall lines. JAS,45,1990-2013.

Figure 3. GFS 00-hour forecasts of 500 heights (m) and anomalies in 12 hour periods from a) 0000 UTC 28 June 2012 through f) 1200 UTC 30 June 2012. Return to text.

Figure 4. JRA25 data showing the pattern over the United States at 0000 UTC 15 July 1995 data included a) 250 hpa winds and wind anomalies, b) 500 hp hpa heights and anomalies, c) 700 hpa winds and anomalies, and d) precipitable water and precipitable water anomalies. Return to text.

Figure 5. As in Figure 3 except for precipitable water in 6-hour increments from a) 0600 UTC 29 June through f) 1200 UTC 30 June 2012. Return to text.

Figure 6. As in Figure 3 except for 700 hpa winds and wind anomalies in 6-hour increments. Return to text.

Figure 7. As in Figure 3 except for 500 hpa winds and wind anomalies in 6-hour increments. Return to text.

Figure 8. As in Figure 3 except for 850 hpa moisture flux and wind anomalies in 6-hour increments. Return to text.

Figure 9. As in Figure 3 except for GFS 00-hour forecasts of Convective available potential energy. Return to text.

Figure 10. GOES IR imagery and 1-hour lightning data on 29 June 2012 valid at a) 1402 UTC, b) 1702 UTC, c) 1902 UTC, and d) 1902 UTC. Return to text.

Figure 11. As in Figure 10 except 30 June 2012 valid at a) 0015 UTC, b) 0215 UTC, c) 0315 UTC and d) 0715 UTC. Return to text.

Figure 12. NMQ Q2 composite reflectivity showing the evolution of the intial bow over Illinios around 1600 UTC and the bow turning right over Indiana at 1900 UTC then racing across Ohio at 2100 UTC. Return to text.

Figure 13. As in Figure 12 except for 2200 UTC 29 June, 0000 UTC 30 June and 0100 UTC 30 June 2012. Return to text.

Figure 14. KLWC radar showing 0.5 degree reflectivity and 0.5 degree base velocity. Upper panels is 0114 UTC and lower panel is 0144 UTC. Return to text.

Figure 15. As in Figure 14 except valid at 0231 and 0252 UTC. Return to text.

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