Significant Tornado Risk for AIRGAS Locations East of the Continental Divide. Scott A. Yuknis. Climate Impact Company, Inc.

Transcription

1 Significant Tornado Risk for AIRGAS Locations East of the Continental Divide Scott A. Yuknis Climate Impact Company, Inc. January

2 Significant Tornado Risk for AIRGAS, an Air Liquide Company Locations East of the Continental Divide Scott A. Yuknis, Climate Impact Company, Inc. An assessment of tornado intensity risk for AIRGAS business locations east of the Continental Divide is provided as general guidance for proper construction of tornado storm shelters. The goal is to estimate the highest tornado intensity risk for each location based on climatology provided primarily by the NOAA Storm Prediction Center (SPC). The discussion and conclusions provided are an extension of research produced for a similar project issued in December 2014 for Air Liquide. Introduction: Significant tornadoes only are considered in this report. A significant tornado is identified as a strong (F2 or F3) tornado or violent (F4 or F5) tornado on the Fujita tornado intensity scale (Table 1). The SPC climatology used in this report is based on the Fujita tornado intensity scale originally developed in The Enhanced Fujita (EF) tornado intensity scale was revised during a research project and introduced by NOAA in 2006 (Table 2). Intensity Wind Characteristics speed F Weak; shallow-rooted trees pushed over F Weak; mobile homes overturned, attached garages may be destroyed F Strong; large trees uprooted, mobile homes destroyed F Strong; most trees in forest uprooted; heavy cars thrown off ground F Violent; well-constructed homes destroyed; large missiles generated F Violent; strong framed houses lifted, carried a distance, destroyed Table 1: The original Fujita tornado intensity scale definitions as developed in 1972 are indicated. 2

3 Intensity Wind Changes from original classification speed EF Weak; a stronger tornado with a more narrow wind speed range EF Weak; similar intensity EF Strong; not as intense as previous and with more narrow range EF Strong; not as intense as previous and with more narrow range EF Violent; not as intense as previous and with more narrow range EF5 >200 Violent; much lower qualification Table 2: The Enhanced Fujita tornado intensity scale introduced operationally by NOAA in 2006 is indicated. F2 and higher intensity (F2+) tornadoes represent approximately 10% of the tornadoes occurring annually in the U.S. with 2% reaching violent intensity causing 67% of U.S. deaths attributed to tornadoes. 1 The National Climate Data Center (NCDC) estimates slightly higher values. Most deaths in the U.S. caused by tornadoes occur when tornado strength is at least F2 intensity. Various climatology sets exist for U.S. tornadoes. In this report the climatology of F2 (or higher) tornado risk calculated by SPC for each week of the year is used to estimate tornado intensity risk for all AIRGAS locations east of the Continental Divide to be consistent with the previous assessment issued in late 2014 for Air Liquide. Additionally, the NCDC tornado data is also used. The F2+ risk calculated by SPC will identify what AIRGAS locations are at risk for F2+ intensity tornadoes, what time of year the risk is present and what time of year the risk is greatest. The NCDC data is used for the higher intensity tornado risk. Disclaimer: In this report an estimate of maximum tornado intensity risk using climatology data primarily from SPC and NCDC for AIRGAS locations east of the Continental Divide is provided. This report is intended for AIRGAS only. There is no guarantee that the estimated 1 P. Concannon, H. Brooks and C. Doswell III, 2000: Climatological Risk of Strong and Violent Tornadoes in the United States. 3

4 highest risk indicated in this report for a given AIRGAS location cannot be exceeded by an unusually intense storm. AIRGAS locations near the Gulf of Mexico Coast or East U.S. Coast have added risk of high wind associated with tropical cyclones. This report accounts for tornado risk however comments regarding high wind associated with tropical cyclone risk is added for coastal regions. Climate Impact Company (CIC) is providing an estimated maximum intensity weather risk event for a given AIRGAS location across the U.S. to the east of the Continental Divide. This report is not an engineering study. Please consult guidance available for construction of storm shelters based severe weather events most of which is provided by the Federal Emergency Management Agency (FEMA). Methodology: A state-by-state assessment for the Central and East U.S. where AIRGAS points of interest are located is provided. Locations with similar climatology are grouped together. Depending on location, land mass type and proximity to the ocean or the Great Lakes tornado climatology can vary even within a given state. Therefore several assessment results within any given state are possible. SPC presents F2 or greater (F2+) tornado intensity risk in 8 categories (Table 3). Each intensity category represents risk within 25 miles of a given point where a F2+ tornado can occur for a given week of the year based on climatology. As an example, category 1 for a given location implies frequency of F2+ tornadoes during the 30-year climatology for that week is 1.2 tornadoes or 0.01% frequency per 30 years. The maximum risk (category 8) is >0.35% frequency for the 30- year climatology implying that for a given location during the week of interest an F2+ tornado occurs 38.3 times during a 30-year period (or 1.3 times per year). 4

5 Risk 0.01% 0.05% 0.10% 0.15% 0.20% 0.25% 0.30% 0.35%+ Category #days/ years #days/ year 1 day in years Table 3: Based on NOAA/SPC risk probabilities of F2+ tornado intensity Climate Impact Company assigns a risk category where 1 is minimal risk and 8 is maximum risk. Using the SPC risk assessment the number of days in the climatology when F2+ tornadoes occur is also indicated. According to Concannon, Brooks and Doswell coupled with NCDC data (Fig. 1-2) the occurrence correlation ratio of F2+ tornado risk to F3+ tornado risk is approximately 5:1. Using the 5:1 occurrence correlation ratio an estimate of number of days when F3+ tornadoes occur for each risk category is provided (Table 4). Fig. 1: Annual state-by-state number of tornadoes based on climatology provided by NCDC is indicated. 5

6 Fig. 2: Annual state-by-state number of EF3-EF5 tornadoes based on climatology provided by NCDC is indicated. Risk 0.01% 0.05% 0.10% 0.15% 0.20% 0.25% 0.30% 0.35%+ Category F2+ #days/ years F2+ #days/ year F2+ 1 day in years F #days/year 1 day in years Table 4: F2+ and F3+ risk occurrence of tornado frequency based on NCDC data is indicated. Category 1 F2+ intensity risk implies an F2+ intensity tornado occurs for a given location once every 25 years while an F3+ intensity tornado occurs once every 125 years. CIC considers a statistically significant high impact event such as an F2+ tornado to occur at least once within the 30 year climatology 2. In human terms a severe weather event such a F2+ tornado occurring within one human generation is considered 2 National Drought Mitigation Center (web site): What is climatology? 6

7 statistically significant and to be accounted (and prepared) for. If strong or violent tornado risk is identified within the standard 30-year climatology CIC will recognize that maximum risk and make recommendations to AIRGAS to design a tornado shelter based on that maximum risk. As an example any AIRGAS location in category 1 for F2+ tornado risk (Table 3) which identifies F2+ tornado once every 25 years should build a tornado shelter that can withstand F2 tornado intensity wind. The F3+ intensity risk (Table 4) indicates F3+ tornado risk within a 30-year climatology beginning at category 2. Therefore any AIRGAS location determined at risk of category 2 F3+ tornadoes should build a tornado shelter that can withstand F3 tornado wind speeds. Violent tornado (F4 and F5) risk is confined to the Central, East- Central, Southeast and Mid-Atlantic states (Fig. 3). On average 7 violent tornadoes occur nationally in 1 year. The bulk of that risk is contained within the Central U.S. states from Kansas and Oklahoma to Texas to the eastern Great Plains and into the Southeast region. Using NCDC data to determine which states approximate risk of F4+ tornadoes within a 30 year standard climatology identifies 8 states and 5 borderline states (Fig. 4). Most AIRGAS locations within the 8 states identified likely require tornado shelters able to withstand F4+ tornado intensity wind. The risk correlation for F4+ tornadoes is based on the climatology of F4+ tornadoes (Fig. 4) versus F3+ tornadoes (Fig. 2). The correlation is applied to frequency of F2+ and F3+ tornadoes to determine when an event occurs within the 30-year climatology. 7

8 Fig. 3: Provided by ustornadoes.com using NCDC data the number of violent tornadoes observed in each state occurring between 1950 and 2011 is indicated. Fig. 4: Converting number of F4+ tornadoes occurring to risk per year during the 30-year standard climatology is indicated. Values are rounded up therefore any value of 0.5 or greater (red) is considered 1 therefore statistically significant identifying states where tornado shelters able to sustain F4+ intensity should be assembled. Borderline states for F4+ tornado risk are also identified (purple). 8

9 Summary: The intent of this report is a climatology study of tornado intensity risk for the U.S. to the east of the Continental Divide for AIRGAS business locations. Described is already calculated F2+ tornado risk by SPC divided into 8 risk categories by CIC. Using various climatology provided by NOAA a correlation to the identified F2+ risk as defined by SPC is made by CIC for F3+ and F4+ tornadoes. CIC identifies any F2+ tornado occurring at least once within a 30-year standard climatology as statistically significant to AIRGAS in that tornadoes of that intensity are recognized when determining strength of a storm shelter to provide protection against tornadoes. In the stateby-state summaries specific risk is addressed as state-by-state climatology can vary depending on proximity to different terrain and oceans or lakes. AIRGAS State-by-State Assessment Texas Texas contains 7 AIRGAS locations of interest. The state is divided into 5 regions: Northeast Texas, Upper Texas Coast, South-central Texas Coast, South-central Texas and Western Texas (Fig. 5). A tornado risk for each region is indicated with some variation for areas near the coast. A tropical cyclone risk is provided for locations near the coast. In Texas the F4+ tornado value of 0.85 (Fig. 4) converts to a category 5 on the tornado occurrence correlation scale indicated in Table 3 and Table 4. The value of 0.85 represents approximately 30% of the risk of occurrence of F3 tornado intensity in Texas placing F4+ risk in category 5. The evaluation for F4+ risk category will vary from state to state. 9

10 Fig. 5: AIRGAS points of interest across Texas separated into 5 regions is indicated. The first region of Texas considered is the Upper Texas Coast. This zone is where Channelview, La Porte and Alvin are located. Reviewed is weekly risk of F2+ tornado risk based on SPC climatology and adjusted for F3+ and F4+ tornado intensity based on risk correlations described in this report. The weekly assessment indicates two peaks of risk during the year. As expected April and May is the peak tornado risk with a second less intense peak occurring in November (Fig. 6). The weekly assessment indicates that all AIRGAS locations reach category 2 on the tornado occurrence correlation identified in Table 4. Implied is a 1-in-25 year risk of a F3 tornado for each location. Of course the upper Texas coast is also a target area for hurricanes. Based on wind speeds of inland-traveling category 4 hurricanes (Lili, 2002; Rita, 2005; and Ike, 2008) the Alvin/Channelview/La Porte area is at risk of category 3 hurricane force wind (Fig. 7). Using the new Enhanced Fujita (EF) tornado intensity scale a category 3 hurricane equates to an EF2 tornado intensity. A correlation of EF tornado intensity to hurricane category is indicated in Table 5. 10

11 Fig. 6: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for the upper Texas coast is indicated. 11

12 Fig. 7: Based on inland wind speeds of weakening category 4 hurricanes Lili, Rita and Ike an estimate of expected wind speeds for inland travelling category 4 hurricanes is indicated. Wind speed (mph) EF1 TORN EF2 TORN EF3 TORN CAT-1 CAT-2 HURR HURR CAT-3 HURR CAT-4 HURR Table 5: Correlation EF tornado intensity to category of hurricane intensity is indocated. In summary, AIRGAS locations south of Houston in the upper coast of Texas qualify for risk of F3 intensity tornadoes. Climatology indicates severe wind risk due to category 3 hurricane intensity which equates to an EF2 tornado (Table 6). CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for the AIRGAS upper Texas Coast region. Tornado category Hurricane category Hurricane category = tornado category Overall Channelview F3 3 EF2 F3 La Porte F3 3 EF2 F3 Alvin F3 3 EF2 F3 Table 6: Tornado risk category assigned to AIRGAS locations in the upper Texas coast region and categorical hurricane risk converted to tornado intensity is indicated. Overall F3 intensity storm shelters are recommended for this area. The second region of Texas considered is the south-central Texas coast. Corpus Christi is the point of interest. Similar to the upper Texas coast there are two periods of peak severe weather occurring in early May and toward November 1 st. During the spring severe weather peak climatology reveals risk of an F3 tornado occurring at least once within the standard 30-year climatology (Fig. 8). 12

13 The hurricane risk is based on landfall of 3 nearby major hurricanes including Bret (category 4; 1999), Allen (category 5; 1980) and Beulah (category 5; 1967). Averaged is how long high wind lasted with each storm into southern Texas adding the estimates for the upper Texas coast indicated earlier in this report. The Corpus Christi location is at risk of a category 3 hurricane matching an EF2 intensity hurricane (Fig. 9). In summary, the AIRGAS location of Corpus Christi in the south-central coast of Texas qualify for risk of F3 intensity tornadoes and severe wind risk due to hurricanes at EF2 tornado intensity (Table 7). CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for the AIRGAS southcentral Texas Coast region. Fig. 8: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for the southcentral Texas coast is indicated. 13

14 Fig. 9: Based on inland wind speeds of weakening major hurricanes Allen, Beulah and Bret an estimate of expected wind speeds for inland travelling intense hurricanes is indicated. Corpus Christi Tornado category Hurricane category Hurricane category = tornado category Overall F3 3 EF2 F3 Table 7: Tornado risk category assigned to AIRGAS location in the south-central Texas coast region and categorical hurricane risk converted to tornado intensity is indicated. Overall F3 intensity storm shelters are recommended for this area. The third region of Texas considered is south-central Texas. San Antonio is the point of interest. South-central Texas observes one strong peak of occurrence of severe weather during spring with a second much weaker peak in late October (Fig. 10). The tornado intensity risk is stronger than the Texas coastal region but not quite strong enough to warrant F4 tornado intensity construction requirements for proposed storm shelters. The south-central Texas region is just beyond category 1 hurricane intensity risk. 14

15 Fig. 10: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for south-central Texas is indicated. In summary, the AIRGAS location in the south-central Texas region qualify for risk of F3 intensity tornadoes. The F3 risk is somewhat stronger than the borderline risk indicated for coastal Texas however not quite strong enough to recommend F4 tornado intensity structural guidelines for a storm shelter. CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for the AIRGAS south-central Texas region. The fourth region of Texas considered is northeast Texas. Waxahachie is the point of interest. During late April peak high intensity tornado risk for the U.S. is present across northeast Texas just north of Dallas and across most of eastern Oklahoma (Fig. 11). The weekly assessment of northeast Texas tornado risk clearly identifies a robust F4 tornado intensity risk for March, April and May (Fig. 12). 15

16 Fig. 11: Annual peak risk of the most intense tornadoes in the U.S. north of Dallas in late April. Fig. 12: Based on the SPC climatology of F2+ tornado 16

17 report the weekly maximum tornado intensity risk for northeast Texas is indicated. In summary, the AIRGAS location in the south-central Texas region qualify for risk of F4 intensity tornadoes. The F4 tornado intensity risk is robust. The maximum tornado intensity risk across the U.S. occurs during late April in eastern Oklahoma and southward to just north of Dallas. CIC recommends that construction of storm shelters to protect against tornado risk have F4 tornado intensity resistance for the AIRGAS northeast Texas region. The fifth region of Texas considered is western Texas. Odessa is the point of interest. In western Texas severe weather occurrence spikes during mid-to-late May at which time a clear risk of F4 tornado intensity is indicated (Fig. 13). Only a slight increase in activity is indicated briefly during October. Fig. 13: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for northwest Texas is indicated. 17

18 In summary, the AIRGAS location in the western Texas region qualify for risk of F4 intensity tornadoes. The F4 tornado intensity risk is robust. A second spike in activity during mid-to-late autumn common in eastern Texas is not nearly as robust in northwest Texas. CIC recommends that construction of storm shelters to protect against tornado risk have F4 tornado intensity resistance for the AIRGAS western Texas region. Louisiana There are three regions of interest to AIRGAS in Louisiana (Fig. 14. The most concentrated area of interest is in the southeast portion of the state given 3 locations: Baton Rouge, Covington and Harvey. There is one location in southwest Louisiana (Lake Charles) and northwest Louisiana (Shreveport). Fig. 14: AIRGAS points of interest across Louisiana are indicated. The first region of Louisiana considered is the southeast section. This zone includes Baton Rouge, Covington and Harvey. In southeast Louisiana tornado risk occurrence spikes in April and again in late November (Fig. 15). The spring spike occurs along the southern periphery of the maximum activity centered in the Great Plains/Mid- South U.S. while the stronger late November risk is part of the southern U.S. storm track capable of producing severe weather as the 18

19 continent cools north of a still very warm Gulf of Mexico surface. Each spike of activity qualifies for F3 tornado risk. Southeast Louisiana is a target for hurricanes. Harvey is very close to the category 4 hurricane wind speed climatology risk (Fig. 16) also qualifying for F3 tornado risk as indicated above. Covington and Baton Rouge are in the category 2 hurricane wind speed climatology risk zone. CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for the AIRGAS southeast Louisiana region. Fig. 15: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for southeast Louisiana is indicated. 19

20 Fig. 16: Based on inland wind speeds of weakening major hurricanes Gustav, Rita and Katrina an estimate of expected wind speeds for inland travelling intense hurricanes is indicated. The second region of Louisiana considered is the southwest section. This zone includes Lake Charles. Similar to southeast Louisiana 2 peak tornado risk periods appear in the climatology (Fig. 17). The first is in late April and not quite as strong as the second peak occurring in November. Once again, the explanation is that southwest Louisiana is south of the primary tornado risk area in the U.S. during spring while in the core of the storm track during late autumn. Each spike qualifies as F3 tornado risk. Lake Charles is susceptible to inland-moving hurricane strikes. Lake Charles is in the category 2 hurricane category risk zone (Fig. 16). CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for the AIRGAS southwest Louisiana region. 20

21 Fig. 17: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for southwest Louisiana is indicated. The third region of Louisiana considered is the northwest section. This zone includes Shreveport. Two spikes of peak occurrence are evident in Shreveport (Fig. 18). The first peak is exceptionally strong occurring in April and qualifying as F4 tornado risk. The second spike occurring in late autumn isn t quite as strong. The spring spike is more closely situated near the core of U.S. springtime tornadoes (Fig. 19). Shreveport is too far inland for substantial hurricane force wind risk. CIC recommends that construction of storm shelters to protect against tornado risk have F4 tornado intensity resistance for the AIRGAS northwest Louisiana region. 21

22 Fig. 18: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for northwest Louisiana is indicated. Fig. 19: Highest significant tornado risk of the year in Louisiana occurs during late April centered on northwest Louisiana according to SPC. 22

23 Mississippi, Alabama and Georgia Three states in the Southeast U.S. are of interest to AIRGAS operations (Fig. 20). The locations are Star, MS; Tuscaloosa, AL; and Jefferson, Augusta and Pelham, GA. Fig. 20: AIRGAS points of interest across Mississippi, Alabama and Georgia are indicated. The first Southeast U.S. state considered is Mississippi. This zone includes the town of Star. Two spikes of peak occurrence are evident at Star (Fig. 21). The first spike is close enough to the core of springtime tornado risk to qualify for F4 tornado risk. The second peak occurring in late autumn is not quite as extreme. CIC recommends that construction of storm shelters to protect against tornado risk have F4 tornado intensity resistance for the AIRGAS south-central Mississippi region. 23

24 Fig. 21: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for south-central Mississippi is indicated. The second Southeast U.S. state considered is Alabama. This zone includes the town of Tuscaloosa. Two spikes of peak occurrence are evident at Tuscaloosa (Fig. 22). The first and second peak are similarly intense each representing risk of F3 tornadoes. CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for the AIRGAS central Alabama region. 24

25 Fig. 22: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for central Alabama is indicated. The third Southeast U.S. state considered is Georgia. This zone includes Jefferson, Pelham and Augusta. Two spikes of peak occurrence are evident for each location (Fig. 23). The first peak is stronger than the second however each qualifies as F3 tornado risk intensity. Each location is far enough inland that severe weather high wind risk far outweighs risk of high velocity wind due to inland-moving hurricanes. CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for the AIRGAS locations in Georgia. 25

26 Fig. 23: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for Georgia is indicated. Florida There is one location of AIRGAS interest in Florida: Miami (Fig. 24). This location is south of the tornado risk belt in the U.S. but at significant risk to high wind due to hurricanes. The hurricane risk assessment is done for the Southeast U.S. and Florida (Fig. 25) and based on landfall of 5 major hurricanes including Wilma (category 5; 2005), Dennis (category 4; 2005), Ivan (category 5; 2004). Opal (category 4; 1995) and Andrew (category 5; 1992). Miami is at risk of a category 4 hurricane matching an EF3 intensity tornado (wind) risk. CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance (due to hurricane risk) for the AIRGAS location in southern Florida. 26

27 Fig. 24: AIRGAS points of interest in Florida are indicated. Fig. 25: Based on inland wind speeds of weakening major hurricanes Wilma, Dennis, Ivan, Opal and Andrew an estimate of expected wind speeds for inland travelling intense hurricanes for the Southeast U.S. Coast including Florida is indicated. 27

28 Mid-Atlantic Region AIRGAS has operational locations in the Mid-Atlantic region located in South Carolina and Virginia (Fig. 26). Rock Hill and Gaston are located in central South Carolina. Richmond and Chester are located in eastcentral Virginia while Hopewell is on the coast. Fig. 26: AIRGAS points of interest in the Mid-Atlantic region are indicated. The first region is central South Carolina. This zone considers 2 locations quite close: Gaston and Rock Hill. Tornado risk peaks during April and easily qualifies as F3 intensity (Fig. 27). A second peak occurs in September and barely qualifies as a F3 tornado intensity risk. CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for the AIRGAS central South Carolina region. 28

29 Fig. 27: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for central South Carolina is indicated. The second region is east-central Virginia. This zone considers 2 locations quite close: Richmond and Chester. Interestingly, tornado risk peaks for an extended period of time from mid-spring to autumn as F3 intensity (Fig. 28). CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for the AIRGAS east-central Virginia region. 29

30 Fig. 28: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for central eastcentral Virginia is indicated. The third region is central coastal Virginia. Hopewell, Virginia is located on the central coast of the state. Hopewell tornado risk peak is during springtime and does not quite qualify for F3 tornado intensity (Fig. 29). Given the coastal location hurricane intensity risk is assessed. The Hopewell area is at risk of hurricane strikes although maximum wind risk is judged lower than the tornado risk for this location (Fig. 30). CIC recommends that construction of storm shelters to protect against tornado risk have F2 tornado intensity resistance for the AIRGAS central coastal Virginia region. 30

31 Fig. 29: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for coastal Virginia is indicated. Fig. 30: Based on inland wind speeds of weakening major hurricanes Sandy, Isabel, Floyd and Hugo an estimate of expected wind speeds for inland travelling intense hurricanes for the Mid-Atlantic is indicated. 31

32 New England Region AIRGAS has operational locations in the New England region located in Connecticut and Massachusetts (Fig. 31). Fig. 31: AIRGAS points of interest in New England are indicated. A look near the Connecticut coast. Bozrah, Connecticut is located near the coast which helps to hold down the tornado risk for this location. Maximum tornado intensity risk is in the F2 category with the peak occurring during the summer season (Fig. 32). CIC recommends that construction of storm shelters to protect against tornado risk have F2 tornado intensity resistance for the AIRGAS location near coastal Connecticut location. 32

33 Fig. 32: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for near the Connecticut coast is indicated. East-central Massachusetts assessment. Littleton, Massachusetts is located in east-central to northeast Massachusetts. Peak tornado intensity occurs during mid-summer when risk of F3 tornadoes are indicated (Fig. 33). The distance away from moderating influence of the ocean enables a significant severe weather risk for this location. CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for the AIRGAS location in east-central Massachusetts. 33

34 Fig. 33: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for east-central Massachusetts is indicated. Ohio & Tennessee Valley Region There are considerable points of AIRGAS interest in the Midwest U.S. (Fig. 34) including the Ohio and Tennessee Valley(s). The most dominant presence is in Ohio. Of the 5 AIRGAS locations in Ohio 3 are located south of Cleveland. AIRGAS locations are scattered in western Tennessee and Kentucky to southwest of Chicago. 34

35 Fig. 34: AIRGAS points of interest in the Midwest are indicated. An assessment in Ohio: 3 AIRGAS points of interest are south of Cleveland including Independence, Canton and Oakwood Village. Also included for northern Ohio is Perrysburg which is southwest of Toledo. In these regions there is one peak tornado risk annually extending across a lengthy period of time from mid-spring through the first half of summer (Fig. 35). The peak risk is for F3 intensity tornadoes. AIRGAS has one location in southwest Ohio: Dayton. In this location the peak tornado risk is similar to northern Ohio although slightly higher intensity risk but still within F3 tornado (risk) limit (Fig. 36). A second peak almost qualifying for F3 tornado intensity occurs during autumn. CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for AIRGAS locations in Ohio. 35

36 Fig. 35: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for northern Ohio is indicated. Fig. 36: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for southwest Ohio is indicated. 36

37 A look at western portions of Kentucky and Tennessee: AIRGAS has 2 points of interest in western Kentucky: Calvert City and Hopkinsville. Each location observes 2 peak tornado risk(s) annually. The first is potent and occurs during April when a borderline F4 tornado risk is evident (Fig. 37). Similarly, there are 2 tornado risk peaks annually although each is slightly stronger than Kentucky (Fig. 38). The spring peak is clearly into F4 tornado risk while the second peak is weaker. Both southwest Kentucky and western Tennessee of located in the eastern portion of the U.S. tornado belt warranting F4 tornado risk during spring peak. CIC recommends that construction of storm shelters to protect against tornado risk have F4 tornado intensity resistance for the AIRGAS locations in southwest Kentucky and western Tennessee. Fig. 37: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for southwest Kentucky is indicated. 37

38 Fig. 38: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for western Tennessee is indicated. Indiana and Illinois review: AIRGAS has one location of interest each in northwest Indiana and in Illinois to the southwest of Chicago. These locations are New Carlisle, IN and Minooka, IL. In northwest Indiana there is an elongated peak risk from mid-spring to early summer (Fig. 39). The peak risk intensity is in the F3 category. A second less intense peak occurs in late autumn. In northern Illinois similar results are indicated however the F3 tornado intensity risk duration is longer while the second peak occurring during late autumn slightly less intense (Fig. 40). CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for the AIRGAS locations in northwest Indiana and northern Illinois. 38

39 Fig. 39: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for northwest Indiana is indicated. Fig. 40: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for northern Illinois is indicated. 39

40 Upper Midwest The final region evaluated for AIRGAS points of interest east of the Continental Divide for tornado shelter construction is the Upper Midwest (Fig. 41). In this region AIRGAS has 3 points of interest in Wisconsin and one in southwest Michigan. Fig. 41: AIRGAS points of interest in the Upper Midwest are indicated. A look at central and southern Wisconsin: AIRGAS has 3 points of interest across central and southern Wisconsin including Stanley, Waupin and Madison. Each are in approximately the same tornado risk zone. Peak tornado risk occurs over an extended period at F3 intensity for each location (Fig. 41). The risk begins in early spring and lasts through the summer season. CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for the AIRGAS locations in central and south Wisconsin. 40

41 Fig. 41: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for central and south Wisconsin is indicated. A look at southeast Michigan: AIRGAS has one location of interest in southeast Michigan: Blissfield. There is one peak tornado risk in this location extending from spring to summer at F3 intensity (Fig. 42). CIC recommends that construction of storm shelters to protect against tornado risk have F3 tornado intensity resistance for the AIRGAS locations in southeast Michigan. 41

42 Fig. 42: Based on the SPC climatology of F2+ tornado report the weekly maximum tornado intensity risk for southeast Michigan is indicated. AIRGAS Tornado Risk Summary The Climate Impact Company assessment of tornado risk east of the Continental Divide for purposes of storm shelter construction for 40 AIRGAS locations is summarized. Of the 40 locations considered all but 9 qualify for F3 tornado intensity based on NOAA/SPC and NOAA/NCDC climatology. 7 locations qualify for the more robust F4 tornado intensity risk located in Texas to the Mid-South U.S. Only 2 locations (near the Connecticut coast and central Virginia coast) qualify as F2 tornado intensity. 42

43 Fig. 43: Summary of tornado risk intensity east of the Continental Divide for AIRGAS locations. Zone/State Location Tornado Risk Category Upper Texas Coast Channelview 3 Upper Texas Coast La Porte 3 Upper Texas Coast Alvin 3 South Texas Coast Corpus Christi 3 South-Central Texas San Antonio 3 Northeast Texas Waxahachie 4 West Texas Odessa 4 Southeast Louisiana Baton Rouge 3 Southeast Louisiana Covington 3 Southeast Louisiana Harvey 3 Southwest Louisiana Lake Charles 3 Northwest Louisiana Shreveport 4 West Mississippi Star 4 43

44 Central Alabama Tuscaloosa 3 North Georgia Jefferson 3 South Georgia Pelham 3 Northeast Georgia Augusta 3 South Florida Miami 3 South Carolina Rock Hill 3 South Carolina Gaston 3 East-Central Virginia Chester 3 East-Central Virginia Richmond 3 Coastal Virginia Hopewell 2 South Connecticut Bozrah 2 North Massachusetts Littleton 3 Northeast Ohio Canton 3 Northeast Ohio Oakwood Village 3 Northeast Ohio Independence 3 Northwest Ohio Perrysburg 3 Southwest Ohio Dayton 3 Western Kentucky Calvert City 4 Western Kentucky Hopkinsville 4 Northwest Tennessee Union City 4 Northwest Tennessee Clarksville 4 Northwest Indiana New Carlisle 3 Northeast Illinois Minooka 3 Southeast Michigan Blissfield 3 South Wisconsin Madison 3 Central Wisconsin Waupin 3 West Wisconsin Stanley 3 Table 8: Summary of AIRGAS locations east of the Continental Divide and their tornado intensity risk. 44