National Weather Service-Pennsylvania State University Weather Events

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1 National Weather Service-Pennsylvania State University Weather Events Historic Ohio Valley January Severe weather and Tornado Event by Richard H. Grumm National Weather Service State College PA and Kyle Imhoff The Pennsylvania State University Abstract: A strong cold front ripped across the Midwest and into the northeastern United States on 17 January Unseasonably warm moist air ahead of the front provided moisture and added instability. This resulted in widespread severe weather mainly before 1800 UTC in the Ohio Valley and another widespread convective severe wind event in the eastern Great Lakes. Overall, there were 165 reports of severe weather, including 14 confirmed tornadoes, on 17 January 2012, a relatively high number of severe reports for mid-winter. Southern Indiana and Kentucky were particularly hard hit with 10 verified tornadoes which based on the climatology is an historic event. The region averages about 0.37 tornadoes per year during the month of January. Other big tornado events in this region included 3 tornadoes in 1964 and 1997, 5 tornadoes in 2008 and 6 tornadoes in January This paper will document the historic tornado and severe weather event of 17 January 2012.

2 1. INTRODUCTION A cold front moving through the Ohio Valley on 17 January 2012 triggered showers and thunderstorms during the morning and early afternoon hours. Many thunderstorms reached severe limits (Fig. 1) and 14 tornadoes were reported. There 9 tornadoes in Indiana and Kentucky, all in the Louisville County warning area (Fig. 1;Table 1), the 9 tornadoes included at least 2 EF2 tornadoes. This represents a relatively exceptional event as the region averages about 0.37 tornadoes per year during the month of January. Significant January tornado events in this region included 3 tornadoes in 1964 and 1997, 5 tornadoes in 2008 and 6 tornadoes in January Thus, the 10 tornadoes on 17 January 2012 is quite a remarkable event. A surge of unseasonably warm moist air (Fig. 2) moved into the Ohio Valley on January The precipitable water values reached 30 mm ahead of the front and were generally 2 to 3σ above normal. The air rapidly dried out after 1200 UTC 17 January as the frontal system moved to the east. The surge of high PW focused over northern Ohio and western Pennsylvania between 1800 and 0000 UTC (Fig. 2c-d) and was in close proximity to the cluster of damaging convective winds (Fig. 1) which was observed in that region. The generally high standardized anomalies, derived using global re-analysis data (R-Climate: Hart and Grumm 2001) likely provided some signals as to the potential for a significant high impact weather event (Sills 2008). This paper will document the pattern and the R-climate anomalies associated with the historic Ohio Valley tornado event of 17 January The focus is on the R-Climate based standardized anomalies as a tool to both analyze and predict this and similar events. The forecast section of this paper will show the value of using climate data and internal ensemble prediction system climate data to better anticipate and predict extreme weather events. 2. Methods and Data The National Centers for Environmental Predictions (NCEP) North American Meso-model (NAM) and the Rapid Update Cycle ( RUC) are used to re-produce the conditions associated with the storm to include the large scale pattern. The standardized anomalies are displayed in standard deviations from normal as in Hart and Grumm (2001) and are computed using the climatology from the NCEP/NCAR global reanalysis data (Kalnay et al. 1996). The focus is on the pattern and anomalies associated with the storm. The value of EFS and anomalies with EFS data are presented. Ensemble data shown here are from the NCEP Global Ensemble forecast system which is run at 75km in horizontal resolution. The emphasis here is on products which may aid in predicting high wind events. This includes the probability of strong winds at various levels to include 10m, 850 hpa, 700 hpa and 500 hpa. These data were also used to examine the pattern using the 27.5km NCEP GFS 00-hour forecasts. The pattern and standardized anomalies followed the methods outlined in Hart and Grumm (2001) and the GFS 00-hour forecasts were used to establish the pattern and standardized anomalies. The term R-Climate is used in reference to analysis and forecasts which use re-analysis climate data to diagnose or forecast the departures from normal.

3 Figure 1. Storm reports for the Storm prediction center (SPC) for 17 January Data are color coded by event type. Lower image is the track and intensity of tornadoes in the Louisville Country Warning area. Images courtesy of the Storm Prediction Center and the WFO in Louisville, Kentucky. Return to text. The severe weather reports were obtained from the real-time Storm Prediction Center (SPC). Comparative data from were also from the SPC website and were put into MySQL for obtaining statistics and comparative data.

4 For brevity, times are presented as day and hour in the format 17/1200 UTC and 18/0000 UTC which would be 1200 UTC 17 January 2012 and 0000 UTC 18 January 2012 respectively. Fully qualified dates are limited to comparative data from times outside of January The Storm system and impacts i. The large scale pattern The 500 hpa pattern over the United States from 16/0000 through 18/1200 UTC (Fig. 3) shows a deep trough in the western United States and a weak ridge with above normal heights in the Mississippi Valley from 16/0000 through 17/0000 UTC. These data are in 12 hour increments and miss some key intermediate times which can be addressed on a regional scale. The 250 hpa winds (Fig. 4) were not overly impressive over the central United States though a modest jet entrance and exit circulation was implied in the anomalies at 17/1200 UTC (Fig. 4d) with an enhanced westerly jet over the Great lakes and second jet over the southern plains. The feature of note at 250 hpa was clearly the developing anomalous Pacific jet which would peak at over 4s above normal by 18/0000 UTC. There was clearly an impressive high impact system affecting the West Coast of North America. At least a part of the energy coming out of the southern plains was related to this developing strong trough and evolving Pacific jet. \ ii. Regional pattern and key anomalies The surge of high PW air (Fig. 2) was associated with a strong 850 hpa jet (Fig. 5). The wind anomalies in the 850 hpa jet were on the order of 3 to 4s above normal as shown in these 6-hourly data. The largest 850 hpa wind anomalies were observed at 17/1200 UTC in the Ohio Valley primarily over northern Kentucky and southern Ohio. This strong low-level jet (Fig. 5) and moisture surge (Fig. 2) were on the warm side of a weak surface cyclone (Fig. 6) which raced across Missouri (Fig. 6a) and into Ontario (Fig. 6d). The 850 hpa temperature field showed that in the warm air temperatures were 1 to 2s above normal. Behind the front, the temperatures were close to the climatic values. Though over the Ohio Valley and Louisville, the 850 hpa temperatures fell from over 8C to around -8C in about 12 hours suggesting quite a strong cold frontal passage affecting the region (Figs. 7c&e). A similarly strong cold frontal push and temperature change affected northeastern Ohio and western Pennsylvania between 17/1800 and 18/0600 UTC, implying that the cold front played a significant role in this event. Hourly RUC-13 data was used to show the evolution of the system. The RUC-13 PW and PW anomalies from 17/ /1700 UTC (Fig 8) and 850 hpa temperatures (Fig. 9) from 17/ /1900 UTC show the evolution of the frontal system over the Ohio Valley. The PW data show the evolution of the frontal system and show PW anomalies in southern Illinois and Indiana of 3-4σ above normal at 17/1200 UTC in which most of this area was enclosed by the 30 mm PW contour (Fig. 8a). These data allow for the approximate frontal location in hourly increments. The hourly RUC data are quite flexible and facilitate examining features in 1-, 2-, 3- or any other increment.

5 Though ultimately these data showed the same general pattern-evolution as the NAM and GFS (not shown). iii. Forecasts For brevity the 12km NAM PW fields from the 17/0000 UTC forecast cycle is shown in 3-hourly increments during the frontal passage in the Ohio Valley (Fig. 10). Other fields were very similar to the observed data and are not shown. These data show the passage of the frontal system with similar timing and intensity as the observed fields. The 4km NAM synthetic radar from the 17/0600 and 17/1200 UTC forecast cycles are shown (Figs. 11 & 12). These data show the evolution of a line of showers and thunderstorms in the morning hours. The 17/0600 UTC forecasts showed an organized line moving through Louisville at about UTC (Fig. 10e-f). The 17/0600 and 17/1200 UTC cycles showed similar timing. The 17/0600 UTC implied some intense cells along the line of showers and implied thunderstorms. There were clearly some large implied cells along the line in the 17/0600 UTC run. The shorter-term run initialized at 17/1200 UTC showed strong storms and a more linear feature, if not oddly curved convective feature, near Louisville (Fig. 11c-d). iv. Observations The composite radar in hourly increments from 17/1200 through 17/1800 UTC is shown in Figure 13. These data show the strong echoes along a southwest to northeast oriented line over Illinois at 17/1200 UTC which rapidly moved to the south and east. The overall pattern is similar to the NAM 4km forecasts (Figs. 11 &12) though the NAM was not as strong and suffered timing and intensity issues. The storms were over the Ohio Valley and entered western Kentucky by 17/1507 UTC. There were some subtle breaks in the line in southern Indiana and Kentucky. Some of these breaks, often referred to as a broken S pattern are often associated with quasi-linear convective systems (QLCS: Trapp et al. 2005). Several unpublished works use this broken S signature as a potential location for tornadoes along a multi-cellular line of storms. Table 1 shows the tornadoes in the Louisville County warning area from the SPC storm data site. These data are included in Figure 1 along with storm survey plots from the WFO in Louisville. These storms and reports in the Ohio Valley were clearly associated with the QLCS line shown in Figure 13. Table 2 shows the SPC dataset tornado data for this region since Clearly, the 2012 event was a record event. They also showed that QLCS tornadoes are quite common in the cold season. 4. Conclusions A surge of unseasonably warm moist air ahead of an approaching cold front produced severe thunderstorms on 17 January With 10 reported tornadoes in southern Indiana and northern Kentucky, this was likely the largest January tornado outbreaks in this region (Table 2) producing 10 tornadoes setting a new record number of tornadoes for the month and eclipsing the month of January 2006 when 6 tornadoes were observed.

6 This strong severe weather event and mini-tornado event was associated with a surge of high PW air and strong low-level winds ahead of a strong cold front. The PW and wind anomalies in the warm air were on the order of 2-3σ above normal. Based on hourly RUC-13 data there were times when both PW and 850 hpa wind anomalies were on the order of 3-4σ above normal. The R-climate based anomalies provide signals to when conditions deviate significantly from normal. High PW events with strong lowlevel winds are often associated with heavy rain events or severe weather events. In this case it was a severe event. It is believed that significant anomalies in R-climate may aid in better anticipating significant high impact weather events. The forecasts shown here suggest that the 12km NAM correctly timed the front. Furthermore, the 4km NAM (Figs. 11 &12) correctly simulated the presence of a line of storms moving into the Ohio Valley (Fig. 13), within a few hours of observations (Fig. 13). The radar and the forecasts implied a QLCS type event with the potential for some strong cells along the line. Interestingly, Trapp et. al (2006: Fig 2) showed that about 39% of tornadoes in Kentucky and 50% of all tornadoes in Indiana are associated with lines of thunderstorms. Trapp et al (2005: Fig 3) also showed that QLCS tornadoes are generally weaker than those associated with persistent rotating supercells. From a climatological perspective, this event was a significant tornado event in the Ohio Valley. Large events with more than 1-3 tornadoes are relatively rare (Table 2) and 10 events for the month is a monthly record, thus 10 tornadoes in one morning in one day is an impressive tornado event. 5. Acknowledgements Thanks to the Storm Prediction Center for real-time data access and images and for the data for climatological referencing. Additional thanks to the National Weather Service Office in Louisville including Tom Reaugh and John Gordon for links and crosschecking data. Thanks to the Pennsylvania State University and the National Weather Service in State College for support of student volunteers to conduct research and case studies. 6. References Graham, Randall A., and Richard H. Grumm, 2010: Utilizing Normalized Anomalies to Assess Synoptic-Scale Weather Events in the Western United States. Wea. Forecasting, 25, Grumm, R.H 2011: The Central European and Russian Heat Event of July-August 2010.BAMS, 92, Grumm, R.H. and R. Hart. 2001: Standardized Anomalies Applied to Significant Cold Season Weather Events: Preliminary Findings. Wea. and Fore., 16, Hart, R. E., and R. H. Grumm, 2001: Using normalized climatological anomalies to rank synoptic scale events objectively. Mon. Wea. Rev., 129, Trapp,R.J, S.A. Tassendorf, E.S. Godfrey, H. Brooks, 2005: Tornadoes from squall lines and bow echoes.part I: Climatological Distributions. WAF,23-34.

7 Figure 2. NCEP NAM 00-hour forecasts of precipitable water (mm) and precipitable water anomalies in 6-hour increments from a) UTC 17 January through f) 1800 UTC January Return to text.

8 Figure 3. As in Figure 2 except for 500 hpa heights (m) and height anomalies in 12 hour increments from a) 0000 UTC 16 January 2012 through f) 1200 UTC 18 January Return to text.

9 Figure 4. As in Figure 3 except for 250 hpa winds (kts) and 250 hpa wind anomalies. Return to text

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11 Figure 5. As in Figure 4 except 850 hpa winds and anomalies in 6-hour increments from a) 0000 UTC 17 January through f) 0600 UTC 8 January Return to text.

12 Figure 6. As in Figure 5 except for mean sea level pressure (hpa) and pressure anomalies. Return to text.

13 Figure 7. As in Figure 5 except for 850 hpa temperatures ( C) and temperature anomalies. Return to text.

14 Figure 8. As in Figure 5 except for hourly RUC-13 data showing precipitable water and precipitable water anomalies in 1-hourly increments from a) 1200 UTC through f) 1700 UTC 17 January Return to text.

15 Figure 9. As in Figure 8 except for RUC 850 hpa temperatures in hourly intervals from a) 1400 UTC 17 January through f) 1700 UTC 17 January Return to text.

16 Figure 10. NAM forecasts of precipitable water (mm) from the NAM initialized at 0000 UTC 17 January 2012 showing the PW and PW anomalies in 3-hour forecast increments from a) 1200 UTC through f) 2100 UTC 17 January Return to text.

17 Figure 11. NCEP 4km NAM initialized at 0600 UTC 17 January 2012 showing forecasts of composite reflectivity (dbz) in hourly increments from a) 1200 UTC through f) 1700 UTC 17 January Return to text.

18 Figure 12. As in Figure 11 except forecasts initialized at 1200 UTC 17 January 2012 valid in hourly increments from a) 1400 UTC through f) 1900 UTC 17 January Return to text.

19 Figure 13.Composite radar data in hourly increments from 1200 UTC (upper left) to 1800 UTC (lower right) on 17 January Data from the National Mosaic and multi-sensor QPF site. Return to text.

20 Time F-Scale Location County State Lat Lon 1444 EF0 3 SW HUNTINGBURG DUBOIS IN EF1 5 NE HUNTINGBURG DUBOIS IN EF0 MADISON JEFFERSON IN EF1 FLOYDS KNOBS FLOYD IN EF0 1 NNE CLARKSVILLE CLARK IN EF1 2 N ST. MATTHEWS JEFFERSON KY EF1 1 NNW FERN CREEK JEFFERSON KY EF1 4 NNE MIDWAY SCOTT KY EF2 2 N RAPIDS SIMPSON KY EF2 7 SW SCOTTSVILLE ALLEN KY Table 1. List of times and EF scale for storms affecting Indiana and Kentucky on 17 January Other data include the Location, County, State, and Latitude and longitude of the tornado. Data from the Storm Prediction Center website. Note the Simpson and Allen tornado was one tornado affecting two counties. Return to text. Year Tornadoes Table 2. January tornadoes by year from SPC data Return to text.