Devastating Tornadoes of 22 May 2011-Draft by

Richard H. Grumm National Weather Service State College, PA

Abstract: A series of tornadoes struck the central United States on Sunday 22 May 2011. Tornadoes

were observed from Wisconsin southwestward into Oklahoma. An intense tornado struck the city of Joplin, Missouri resulting in over 116 fatalities. The Joplin tornado will likely rank as one of the deadliest tornadoes since the 9 June 1953 Worcester (94) and 8 June 1953 Flint tornadoes (116). The event of 22 May 2011 is the second deadly tornado outbreak of 2011 producing over 50 fatalities, coming just three weeks after the super outbreak of 25-28 April 2011 which resulted in 327 fatalities.

The event of 22 May 2011 was associated with a moist unstable air with energy helicity index values over 5 in the southern Plains. Supercell thunderstorms developed and produced the tornadoes. Many of the standard parameters were well above levels often considered favorable for severe weather and tornadoes.

This event will likely end up as one of the top 4 deadliest single tornadoes since the 1920s.

1. INTRODUCTION

A devastating severe weather event affected the central United States on 22 May 2011. Severe weather to

include over 55 tornadoes was observed from Texas to Michigan (Fig. 1). Tornadoes were observed from

Oklahoma into Missouri and from Iowa across Minnesota and Wisconsin. At least one tornado related

fatality was reported in Minnesota and a single tornado in Joplin Missouri produced 90 fatalities (AP

2011). The Joplin tornado will likely rank as one the single most deadly tornado in the United States since

1953 (AP 2011). It surpassed the 9 June 1053 Worcester, MA tornado which caused 94 fatalities and tied

the 8 June 1953 Flint tornado produced 116 fatalities1

This tragic event shard many of the common characteristics often associated with tornado outbreaks.

These conditions and the climate anomalies of several fields will be shown here. Hart and Grumm (2001)

and Graham and Grumm (2010) have demonstrated the value of standardized anomalies in identifying

meteorologically and climatologically significant events The range of events spans identified by this

method spans heat waves, snow storms (Stuart and Grumm 2006), historic floods (Bodner et al.

2011;Junker et al.. 2008), and severe weather events.

. These number will likely change. The deadliest

single tornado was observed on 18 March 1925 when the tri-State tornado killed 695 people as it cut a

291-mile long path from Missouri, across Illinois into Indiana.

The ingredients associated with severe events often include high convective available potential energy

(CAPE), shear, and lift (Doswell et al. 1996;Doswell 1982; Davies and Johns 1982) . High values of low-

level moisture, often gauged by precipitable water (PW) are often found in close proximity to high values

of CAPE. The importance of mid-level dry air over this region, often associated with elevated mixed

layers (EMLs: Banacos et al. 2010;Carlson and Ludlam 1968; Carlson et al. 1983) are often good

1 Data and names of the tornadoes from the WIKI site http://en.wikipedia.org/wiki/Flint%E2%80%93Worcester_tornado_outbreak_sequence#June_8.2C_1953_event.

indicators for the potential for severe thunderstorms. Some of the more notable supercell storms and

severe outbreaks have been associated with the presence of EML’s to include the widespread tornado

event of 31 May 1985 (Banacos and Ekster 2010).

This paper will document the historic tornado event of 28 April 2011. The focus is on the synoptic scale

pattern and the anomalies associated with this meteorologically and climatologically significant event.

The NCEP GFS 00-hour forecasts are used to show the pattern. Forecasts from the NCEP ensemble

forecast systems (EFS) and GFS forecasts are presented to show the value of anomalies in anticipating

potential high impact severe weather events.

2. METHODS AND DATA

Figure 1. Severe weather reports by type from the Storm Prediction Center. Data is color coded by type. Courtesy of the Storm Prediction Center.

The 500 hPa heights, 850 hPa temperatures and winds, other standard level fields were derived from the

NCEP Global Forecast System (GFS), North American Mesoscale Model (NAM), Global Ensemble

Forecast System (GEFS), Short Range Ensemble Forecast (SREF) and the NCEP/NCAR (Kalnay et al.

1996) reanalysis data. The means and standard deviations used to compute the standardized anomalies

were from the NCEP/NCAR data as described by Hart and Grumm (2001). Anomalies were displayed in

standard deviations from normal, as standardized anomalies and are used to show the anomalies,

probability of heavy rainfall and Quantitative Precipitation Forecasts (QPF) associated with this event.

All data were displayed using GrADS (Doty and Kinter 1995).

The standardized anomalies computed as:

SD = (F – M)/σ (1)

Where F is the value from the reanalysis data at each grid point, M is the mean for the specified date and

time at each grid point and σ is the value of 1 standard deviation at each grid point.

Model and ensemble data shown here were primarily limited to the GFS and GEFS. The NAM and SREF

data were also available for use in this study. Displays will focus on the observed pattern and some

forecast issues associated with the pattern.

Both the unified precipitation dataset (UPD: Seo 1998) and the stage-IV precipitation data (Lin and

Mitchell 2005; Nelson et. al. 2010) were used to evaluate the rainfall associated with this event. The

stage-IV data are presented in this document.

In addition to computing standardized anomalies for distinct times associated with individual

meteorological rainfall events, anomalies were computed by averaging the fields and each instantaneous

standardized anomaly value over 1 to 2 day periods. This was facilitated identifying the signal and the

persistence in the long-term signal of the pattern. This concept was then used to obtain multi-day pattern

forecasts from the NCEP GFS and GEFS.

Images of Energy helicity indices were produced using the RUC surface based CAPE and Helicity using

the following equation:

EHI = (CAPE * HELICITY)/160000 (2)

For brevity, times will be displayed in day and hour format such a 23/0000 UTC signifies 23 May 2011 at

0000 UTC.

3. METEOROLOGICAL OVERVIEW

i. Synoptic scale pattern

The 250 hPa pattern (Fig. 2) showed a ridge over the eastern United States with a trough over the

western United States (Fig. 3). A strong 250 hPa jet was present south of the 500 hPa low. The 1 to 3s

above normal 250 hPa jet over New Mexico and Texas implied a strong jet exit region over the southern

Plains. There was clearly diffluence of over the region affected by the southern extent of the tornadoes in

Figure 1. By 23/0600 UTC there was an implied coupled jet region over the Mid-Mississippi valley with

a hint of a southerly wind over 1s above normal from Missouri to Michigan (Fig. 2f).

The RUC precipitable water (PW:Fig. 4) and anomalies showed the surge of high PW air over the

Plains into the upper-Midwest. Joplin, Missouri (red square) was in a region of abnormally high PW with

PW values in excess of 3s above normal. The corresponding 850 hPa winds (Fig. 5) showed strong

southwesterly flow at 850 hPa with 2 to 3s above normal winds. Close to the 850 hPa low in Minnesota

(Fig. 5a-e) there were 2-3s above normal winds near the tornadoes in Minnesota and Wisconsin.

The convective available potential energy (CAPE:Fig 6) and EHI (Fig 7) showed the extensive

area of high instability over the southern Plains into Minnesota and Michigan. The highest CAPE was

over the southern Plains as analyzed by the RUC. The EHI was greater than 2 over a broad region of the

central Plains. The highest EHI values were focused over the southern Plains from Oklahoma to Missouri

and eastward across Arkansas (Fig. 7a-f).

The overall pattern and potential instability was generally well predicted and is not shown here.

ii. radar

.

The composite reflectivity for select times (1800, 1900, 2000 and 23000 UTC) over the upper-

Midwest is shown in Figure 8. These data show the flow about the 850 hPa low (Fig. 5). The strong low-

level 850 hP jet likely played a role in the evolution of the convection and contributed to the shear. There

were two distinct broken lines of convective cells which developed, one over Minnesota and the other

over Wisconsin. Both lines were associated with strong shear and high CAPE, the CAPE was over

2400JKg-1 in the RUC analysis (Fig. 6) and in a local EHI maximum (Fig. 7) which peaked between 4-5

around 22/1900 UTC. The high CAPE and shear clearly contributed to the high EHI in this region and

thus the increased threat of tornadoes.

Composite radar images over the southern Plains (Fig. 9) at 22/2200, 22/2300 and 23/0030 show

the evolution of the storms over Kansas and Missouri. The large supercell over Kansas at 22/2200 UTC

would move over Joplin, Missouri. Strong storms and a more continuous line of storms is evident over

central Missouri at 23/0030 UTC. This line produced the area of tornadoes over central Missouri (Fig. 1).

A debris ball was clearly evident in the high resolution reflectivity data (Fig. 10) after the storm

struck Joplin. In addition to the debris ball in the hook associated the massive supercell, a tornado vortex

signature (TVS) was clearly evident in the storm relative velocity, embedded within the larger

mesocyclone encompassing the front and rear flanks down drafts of the storm. The reflectivity data shows

a nearly textbook supercell with a massive front flank down draft (FFD) region north of the hook. The

rear flank downdraft (RFD) is well developed. The debris ball was in the TVS. The KSGF radar is located

to the east (right) in the image. Though not shown, the mesocyclone and the TVS feature persisted and

travelled eastward across a large swath of southwestern Missouri.

4. CONCLUSIONS

A severe massive severe weather event produced over 760 reports of severe weather to include 51

tornadoes on 22 May 2011. At least two tornadoes produced fatalities including a tornado in Minnesota

and a massive tornado which struck the city of Joplin, Missouri. To date 116 fatalities have been reported

in Joplin and the death toll may rise. The Joplin tornado currently is tied with the Flint, Michigan tornado

of 8 June 1953 which produced 116 fatalities. Both are well behind the historic Tri-State tornado of 18

March 1925 which produced an estimated 695 fatalities and the 9 April 1947 Woodward tornado which

caused 181 (160)2

A massive tornado outbreak affected the southern United States on 25-28 April 2011 which

resulted in 327 tornado related fatalities. These deaths were attributed to multiple tornadoes. On 8 and 9

June 1953 violent tornadoes affected Michigan and Massachusetts respectively. There were 8 tornadoes in

Michigan on 8 June which produced 125 fatalities of which 116 were attributed to the 18.9 mile long F5

tornado which ripped through Flushing and Columbiaville, MI. The 116 fatalities were in Genesee

County Michigan. The 9 June Worcester F4 tornado cut a 46 mile long path as it moved over Petersham

and Fayville in Worcester County, Massachusetts.

fatalities.

The event of 22 May 2011 was associated with a surge of warm moist air and a surge of strong

low-level winds. The tornadoes in Minnesota and Wisconsin had high CAPE and shear which produced

EHI’s over 4. The strong winds and close proximity to the 850 hPa low likely contributed to the shear and

favorable environment for tornadoes. In the southern plains, the strong diffluent jet, high PW air, strong

shear and high CAPE likely contributed to the tornado threat. The EHI in this region peaked over 10. This

was clearly a dangerous situation and was well predicted and out-looked for the threat of severe weather

and tornadoes.

5. Acknowledgements 2 Grazillus lists this as one event it may have been a family of tornadoes.

Thanks to the Storm Prediction Center for storm reports and NCDC for access to level-II radar data so

rapidly after the event.

6. REFERENCES

Associated Press, 2011a: 90 Dead in Joplin Missouri after deadliest American tornado in 60

years (Daily wire reports with similar titles were published from 23 to 24 May 2011.)

Associated Press, 2011b: Survivors spin tales of dread and loss after twister (Daily wire reports

with similar titles were published from 23 to 24 Mayl 2011.)

Banacos, Peter C., Michael L. Ekster, 2010: The Association of the Elevated Mixed Layer

with Significant Severe Weather Events in the Northeastern United States. Wea.

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predictability associated with warm season precipitation episodes. J. Atmos. Sci.,

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Carlson, T. N., and F. H. Ludlam, 1968: Conditions for the occurrence of severe local

storms. Tellus, 20, 203–226.

Carlson, T. N., S. G. Benjamin, G. S. Forbes, and Y. F. Li, 1983: Elevated mixed layers in

the regional severe storm environment: Conceptual model and case studies. Mon.

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strong and violent tornadoes. 1. Wind shear and helicity. The Tornado: Its

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Geophys. Union, 573-582.

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Symposium on Precipitation Extremes, Albuquerque, NM, Amer. Meteor. Soc., 66-70.

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Figure 2. GFS 250 hPa winds (ms-1) and total wind anomalies in 6-hour increments from a) 0000 UTC 21 to f) 0600 UTC 23 May 2011. Return to text.

Figure 3. As in Figure 2 except for 500 hPa heights and height anomalies. Return to text.

Figure 4. As in Figure 2 except for RUC precipitable water and precipitable water anomalies in 1 hour increments from a) 1800 UTC 22 May through f) 2300 UTC 22 May 2011. Return to text.

Figure 5. As in Figure 3 except for 850 hPa winds and wind anomalies. Return to text.

Figure 6. As in Figure 4 except for RUC surface based CAPE (JKG-1) contours event 1200JKG-1 and shading as indicated by color bar. Return to text.

Figure 7. As in Figure 4 except for RUC surface based EHI contours event 2 and shading as indicated by color bar. Return to text.

Figure 8. Composite radar focused over the Upper Great Lakes showing radar clockwise from upper left at 1800, 1900, 2000 and 2300 UTC 22 May 2011. Courtesy National Mosaic and Mult-sensor QPE website. Return to text.

Figure 9. As in Figure 8 except over the southern Plains valid from top at 2200 UTC and 2300 UTC 22 May and 0030 UTC 23 May 2011. Return to text.

Figure 10. KSGF radar at 0.50 degrees showing reflectivity and storm relative velocity as 2243 UTC 22 May 2011. Display is from the Gibson Ridge, GR2Analysist software from NCDC recovered data. Return to text.