21
Top line
Have to be careful using raw reports [(E)F1+ ~consistent)
No evidence for intensity changes
Tornado variability has increased over recent decades Fewer days with tors, more “big” days
Appears related to changes in environmental wind profile
Role of global warming? Variability changes consistent with models
Need to understand pattern changes
Brooks et al (2014)
145.5
67.5
24.5
12
Median for 1st of Month
Tornado Timing in Plains (Lu et al 2015)
No significant increase in annual number of outbreaks (>=6 (E)F1+)
Number of tornadoes per outbreak is increasing
Variance increasing
1960 1970 1980 1990 2000 20100
20
40
60(a) Number of tornado outbreaks per year
slope = -0.06 ' 0.10
1960 1970 1980 1990 2000 2010
10
15
20
25
(b) Mean number of tornadoes per outbreak
slope = 0.66% ' 0.26%
1960 1970 1980 1990 2000 2010
25
100
300
(c) Variance of the number of tornadoes per outbreak
slope = 2.89% ' 1.22%
mean10 15 20 25
va
ria
nce
101
102
103
54
55
56
57
58
59
60
61
62
6364
65
66
67
68
69
70
71
72
73
74
7576
7778
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
9596
9798
99
00
0102 03
04
0506
07
08
09
10
11
121314
(d) Number of tornadoes per outbreak
LS b = 4.33 ' 0.44, log a = -6.74 ' 1.12LC theory b = 3.98, log a = -5.8495% CI LS
[variance ~ mean4]Taylor power-law scaling
Tippett & Cohen (2016)
Similar behavior in an
environmental proxy
1980 1985 1990 1995 2000 2005 20100.5
1
1.5
2(a) Annual mean of occurrence proxy
slope = 0.88 ' 0.59
1980 1985 1990 1995 2000 2005 2010
12
14
16
18
(b) Mean of proxy for number/occurrence
slope = 0.66% ' 0.32%
1980 1985 1990 1995 2000 2005 2010
100
200
300
(c) Variance of proxy for number/occurrence
slope = 2.47% ' 1.14%
mean11 12 13 14 15 16 17 18 19
va
ria
nce
102
79
80
81
82
83
84
8586
87
88
89
90
91
92
93
94
95 96
97
98
99
0001
02
03
04
05
0607
08
0910
11
1213
(d) Environmental proxy for number/occurrence
LS b = 3.45 ' 0.42, log a = -4.41 ' 1.12LC theory b = 3.31, log a = -4.1995% CI LS
Variance ~ Mean4
Proxy = daily (CAPE x SRH2 | CAPE x SRH > 160,000)
Tippett & Cohen, 2016
The distribution of the number of tornadoes/outbreak is changing
Increasing mean Increasing variance
Suggests distribution is moving to the right (increasing mean) and high percentiles are moving faster (increasing variance)
More tornadoes in the most extreme outbreaks
threshold
Log(Number of tornadoes per outbreak)
0
10
20
30
40
50
60
70
80
90
100
Pe
rcen
tile
Cumulative frequency
Recent period
Early period
Change in number of tornadoes
More tornadoes in the most extreme outbreaks
Percentiles are increasing (quantile regression)
Higher percentiles are increasing (exponentially) faster
probability [%]0 20 40 60 80 100
lin
ear
tren
d [
torn
ado
es/y
ear]
10-4
10-3
10-2
10-1
100
(b) Linear growth rate
1965-2015 trends0.0055 exp(4.29 p)
year1960 1970 1980 1990 2000 2010
[to
rnadoe
s]
5
10
15
20
25
30
35
40(a) Percentiles of tornadoes per outbreak (6+)
20th %-tile40th %-tile60th %-tile80th %-tile
Dashed lines = quantile regression
Tippett et al., 2016
Similar growth in proxy
SRH is responsible for changes in the proxy. Not CAPE.
Not the expected signature of a warming climate.
Year1980 1985 1990 1995 2000 2005 2010 2015
(J k
g-1
)
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800(a) Percentiles of CAPE
Year1980 1985 1990 1995 2000 2005 2010 2015
(m2 s
-2)
# 104
2
3
4
5
6
7
8
9
10(b) Percentiles of SRH
Year1980 1985 1990 1995 2000 2005 2010 2015
En
viro
nm
enta
l pro
xy (
torn
adoes)
10
15
20
25
30
35
40(c) Percentiles of proxy > 12
20th %-tile40th %-tile60th %-tile80th %-tile
Percentile probability (%)0 20 40 60 80 100
Lin
ea
r tr
end (
torn
ad
oe
s y
r-1)
10-3
10-2
10-1
100
(d) Linear growth rate of proxy percentiles
Linear regression0.0086 exp(3.6 p)
CAPE SRH
Proxy Growth rate
‘79-’17 AVG. STP HOURS > 1
Gensini andBrooks (2018
‘50-’17 AVG. F1+ TORNADOES
Gensini andBrooks (2018
THEIL-SEN’S SLOPE (STP) ‘79-’17
Gensini andBrooks (2018
THEIL-SEN’S SLOPE (REPORTS) ’79-’17
Gensini andBrooks (2018
Gensini and Mote 2015
Used GCM to drive 4-km grid spacing model Looks like experimental weather prediction models
Sees many features of storms
Run for March-May for 11 years in late 20th, late 21st century
Lets us look at environments and storms
Gensini and Mote 2015
Energy
FavorableEnvironments
1980-1990 2080-2090
Projected increase (red), decrease (blue) in severe storms(downscaled)
Gensini and Mote 2015
Gensini and Mote 2015
Gensini and Mote 2015
Annual accumulated model severe storm occurrences (downscaled)
