NWS-PSU Case Study Site 2010 Severe Weather Case New Years Eve Severe Weather Event of 31 December 2010 by Richard H. Grumm National Weather Service State College PA 16083 Abstract: A surge of warm humid air into the central United States produced severe weather and tornadoes on 31 December 2010. There were 17 reports of severe weather on the 30 th and 126 reports of severe weather on the 31 st to include 44 tornadoes. The tornadoes in Missouri resulted in several fatalities. All the severe weather occurred on 31 December but due to 24 hour reporting times, 17 reports appear on 30 December 2010. The severe storms occurred in the warm surge ahead of a cold front. The warm surge brought an end to a prolonged period of cold weather and brought unseasonable warm moist air into the Midwest and eastern United States. The precipitable water anomalies were 2 to 3σ above normal and the 850 hpa temperatures were 1-2σ above normal in the warm sector. The early spring-like temperatures and moisture spawned the severe weather outbreak. 1. INTRODUCTION A winter severe event affected the central United States on 31 December 2010. Due to 1200 UTC reporting times, all severe reports prior to 1200 UTC 31 December appear as severe weather on 30 December 2010. Thus, though this appears to be a two day event reporting wise, all the severe weather was locally observed on New Year s Eve. There were 17 and 126 reports of severe weather on the 30 th and 31 st respectively (Fig. 1). There were 47 confirmed tornadoes, 44 of which occurred on the 31 st. The severe weather occurred in the warm sector in a plume high precipitable water (PW) air (Fig. 2) ahead of an advancing cold front (Fig. 3). The PW anomalies peak near +3σ above normal and the 850 hpa temperatures were near 2σ above normal. In addition to the high PW air, which provided moisture and instability, there was a strong low-level jet (LLJ). The 850 hpa winds in the LLJ were 2 to 3 σ above normal (Fig. 4) in the plume of warm moist air ahead of the front. Large scale lift was likely provided by the upper-level wave and accompanying cold front. The association of strong low-level wind anomalies and surges of anomalous PW air with severe weather has been demonstrated by Graham and Grumm (2010). Stuart and Grumm (2006) showed the value of standardized anomalies in identifying high impact winter storms in the eastern United States. Junker et al. (2008) showed the value of using standardized anomalies to identify heavy rainfall events in the western United States. Hamill et al. 2005 showed how anomalous flow can produce prolonged historic severe weather outbreaks. This event provides an opportunity to demonstrate the value of standardized anomalies to diagnose and forecast severe weather events. This paper will document the severe weather event of 31 December 2010. The focus is on the meteorological and climatological significance of this event an anomaly perspective. Using the concepts from Hart and Grumm (2001) and Stuart and Grumm (2006) standardized anomalies will be used to show that this event, like other wide spread high impact weather events (HIWE) had a clear signal in the standardized anomalies that may aid in anticipating similar events in the future. 2. Methods and Data
The overall pattern was reconstructed using the 00-hour forecasts from the operational GFS. The Japanese Re-analysis data (JRA25:Onagi 2007) was also used to show the pattern. The anomalies were derived using the GFS and comparing it to the 30-year mean and standard deviations computed from the NCEP/NCAR re-analysis data (Kalnay et. al 1996). All anomalies herein are shown as standardized anomalies (Hart and Grumm 2001). The GFS is run on a 27 km grid. However the data shown here is on a 1x1 degree grid. This should mitigate some of the resolution issues between the coarser climatology and the model forecast grids. These effects are normally of minimal impact for parameters above the planetary boundary layer. Some variables such as PW are sensitive and will show higher values in higher resolution models than in the re-analysis dataset. Forecasts from the NCEP Ensemble Forecast systems (EFSs) will be presented. Standardized anomalies will be presented as described above, computing anomalies from the ensemble mean and the NCEP/NCAR re-analysis data. Probabilities are derived using the ensemble output. These will be raw and uncalibrated probabilities unless specified otherwise. Severe weather reports and times were taken from the Storm Prediction Center (SPC) website. The graphical displays are shown in Figure 1. The tabular data (not shown) indicated that all the severe weather occurred on 31 December. However, 17 reports prior to 1200 UTC 31 December are listed under 30 December 2010. The times of the reports were used to make the 6-hourly images and to make select radar images. Radar images were gathered from the National Mosaic and multi-sensor precipitation website. For brevity, times will be denoted in the format 31/1200 UTC to signify 1200 UTC 31 December 2010. 3. The Storm system and impacts i. The pattern and key anomalies The evolution of the large scale pattern over North America is shown in Figure 5. These data imply strong flow in north Pacific over the large ridge (Fig. 5a) and a short wave moving into western North America. As the trough moved into the southwestern United States 500 hpa height anomalies fell to -2 to -3σ below normal (Figs. 5c-e). This feature was the large scale forcing mechanism for the event. The strong ridging to the east of this system allowed the surge of warm moist air into the Mississippi Valley and into the Great Lakes (Figs. 2 & 3). The 250 hpa winds showed a modest surge of strong winds ahead of the trough (Fig. 6) associated with the plume of high PW air (Fig. 2) and the strong 850 hpa LLJ (Fig. 3). The 850 hpa winds and v-wind anomalies (Fig. 7) showed a surge of 3σ above normal v-wind anomalies over Missouri at 30/1200 UTC and a broader area of 2-3σ above normal v-winds over the Midwest in general on 30 December (Figs. 7ac). The strong v-wind anomalies moved eastward and peaked near 3σ above normal over Illinois at 31/1200 UTC. These two surges of strong v-winds in the warm sector were in close proximity to the surge of high PW air (Fig. 2). The combination of strong shear implied by the strong and anomalous LLJ and the high PW air played a critical role in the forcing and fuel for the severe weather over the region (Fig. 1).
ii. Precipitation and Severe weather The precipitation associated with the event is shown in Figure 8. These data show southwest to northeast oriented streaks for rainfall. These streaks were likely associated with convective elements along the line of storms which moved from southwest to northeast across the region. Little rainfall was observed south of Arkansas. The heaviest rainfall was over northeastern Missouri and western Illinois where over 32 mm of estimated liquid equivalent precipitation was observed. The northern area of heavy rainfall aligned well with the axis of the severe weather shown in Figure 1. Figure 9 shows the 31/0800 UTC radar coverage focused over Missouri. These data show the cluster for storms (B) which produced some of the earlier severe weather in Figure 1. The western evolving line (A) produced most of the severe weather as it moved eastward and strengthened. The evolution of the line (A) in Figure 9 at 1200, 1300, 1700 and 1800 UTC is shown in Figure 10. These data show two supercells in eastern Oklahoma and a bow echo in eastern Missouri. Clearly, line A developed and produced the lion s share of the severe weather (Figure 1) in the area from Oklahoma to Illinois. Figure 11 shows the convection over the Gulf States. Little precipitation was observed in that region prior to 31/1800 UTC as the convection developed later in the evening of the 31 st and peaked in intensity over Alabama between 01/0300 and 01/0500 UTC. 4. Conclusions A high impact severe weather event affected the Mississippi Valley from Louisiana to Illinois on 31 December 2010. Due to reporting time issues, the event appeared to straddle two days. However most of the severe weather was observed on New Year s Eve, 31 December 2010. The New Years Eve event produced 126 severe reports to include 44 confirmed tornadoes. The 17 events on the 30 th were observed early on the 31 st. It should be noted (Fig. 11) that the severe weather event in the southern portion of the line occurred late in the evening hours of the 31 st in Mississippi and Alabama. The two deadly tornadoes in Missouri were in Pulaski and Phelps Counties. The data shown here suggests that a surge of unseasonably warm moist air, more characteristic of early spring conditions, along with a strong low-level jet contributed to this event. This plume of warm moist air surged poleward in advance of a strong upperlevel wave of Pacific origin. The combination of the high PW surge, strong low-level wind and the strong north-south oriented cold front produced nearly ideal conditions for a winter severe weather outbreak. 5. Acknowledgements The Storm Prediction Center for access to data and images. The National Mosaic Precipitation site for the hourly radar imagery. And finally, to Jason Krekeler for collecting images and verifying times. 6. References
Bradbury, J.A, Keim, B.D and C. P Wake, 2003: The Influence of Regional Storm Tracking and Teleconnections on Winter Precipitation in the Northeastern United States. Annals of the Association of American Geographers, 93(3), 2003, pp. 544 556. DeGaetano, A. T., M. E. Hirsch, and S. J. Colucci. 2002.Statistical prediction of seasonal East Coast winter storm frequency. Journal of Climate 15:1101 17. Graham, Randall A., Richard H. Grumm, 2010: Utilizing Normalized Anomalies to Assess Synoptic-Scale Weather Events in the Western United States. Wea. Forecasting, 25, 428-445. Grumm, R.H. and R. Hart. 2001: Standardized Anomalies Applied to Significant Cold Season Weather Events: Preliminary Findings. Wea. and Fore., 16,736 754. Hamill, Thomas M., Russell S. Schneider, Harold E. Brooks, Gregory S. Forbes, Howard B. Bluestein, Michael Steinberg, Daniel Meléndez, Randall M. Dole, 2005: Supplement to: The May 2003 Extended Tornado Outbreak. Bull. Amer. Meteor. Soc., 86, ES3 ES16. Hart, R. E., and R. H. Grumm, 2001: Using normalized climatological anomalies to rank synoptic scale events objectively. Mon. Wea. Rev., 129, 2426 2442. Stuart N. A., and R. H. Grumm, 2006: Using wind anomalies to forecast east coast winter storms. Wea. and Forecasting, 21, 952-968. Onogi, K., J. Tsutsui, H. Koide, M. Sakamoto, S. Kobayashi, H. Hatsushika, T. Matsumoto, N. Yamazaki, H. Kamahori, K. Takahashi, S. Kadokura, K. Wada, K. Kato, R. Oyama, T. Ose, N. Mannoji and R. Taira (2007) : The JRA-25 Reanalysis. J. Meteor. Soc. Japan, 85, 369-432.
Figure 1. Storm Prediction Center (SPC) severe weather reports for 30 and 31 December 2010. Data from the SPC Storm reports website. Return to text.
Figure 2. GFS 00-hour forecasts of precipitable water (mm) and precipitable water anomalies for the 6-hour periods from a) 1200 UTC 30 December through i) 1200 UTC 01 January 2010. Return to text.
Figure 3. As in Figure 2 except for 850 hpa temperatures ( C) and temperature anomalies. Return to text.
Figure 4. As in Figure 2 except for 850 hpa winds (ms-1) and 850 hpa total wind anomalies. Return to text.
Figure 5. GFS 00-hour forecasts of 500 hpa heights (m) and height anomalies (standardized anomalies) for the 12-hour periods from a) 1200 UTC 29 December through i) 1200 UTC 2 January 2011. Return to text.
Figure 6. As in Figure 5 except for 250 hpa winds and wind anomalies. Return to text.
Figure 7. As in Figure 4 except 850 hpa winds and v-wind anomalies for the 6-hour periods of a) 1200 UTC 30 December through i) 1200 UTC 01 January 2011. Return to text.
Figure 8. Stage-IV liquid precipitation for the period of 1200 UTC 30 to 1800 UTC 31 December 2010. Return to text.
B A Figure 9. Mosaic radar valid at 0800 UTC 31 December 2010. Point A shows the line which would produce the second wave of severe weather after 1200 UTC and Point B shows the convection that produced the earlier convection.
a. 1200 UTC c. 1300 UTC d. 1700 UTC b. 1800 UTC Figure 10. As in Figure 9 except for data valid at a) 1200 UTC, b) 1300 UTC, c) 1700 UTC and d) 1800 UTC 31 December 2010. Return to text.
Figure 11. As in Figure 9 except for radar valid at (upper) 2300 UTC 31 December 2010 and (lower) 0500 UTC 01 January 2011 focused over the central Gulf States. Return to text.