Nina Pahola AlarcónManager Houston, TX Nina Pahola AlarcónManager Houston, TX.
La Nina Springs and Severe Weather in Southwest Michigan
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Transcript of La Nina Springs and Severe Weather in Southwest Michigan
La Nina Springs and Severe Weather in Southwest
MichiganDoes having a La Nina
Impact Severe Weather Frequencies?
What We Will Look At
• Tornadoes frequency since 1950• Trends of Tornadoes since 1950• Mean Number of Tornadoes by Phases of ENSO• Tornado Frequency as a function of ENSO phase• Severe storms by season for La Nina and El Nino• Severe Storms by Season for ENSO phase• Possible reason for difference in numbers by ENSO type– Mean Jet Stream for La Nina– El Nino in winter and spring
Tornado Trends By Year for the GRR CWA
19861987
19881989
19901991
19921993
19941995
19961997
19981999
20002001
20022003
20042005
20062007
20082009
2010
02468
101214161820
Tornaodes By Year and Strength
F0 F1 F2 F3 ALL
Year
Num
ber b
y Ye
ar
Tornado Numbers and Winter NAO
1950195219541956195819601962196419661968197019721974197619781980198219841986198819901992199419961998200020022004200620082010
-5.00
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
0
5
10
15
20
25
30
35
40
45
50
NAO compared to Tornado Numbers
NAO for the Winter Polynomial (NAO for the Winter)Tornado Numbers Per Year Polynomial (Tornado Numbers Per Year)
Axis Title
Axis Title
Tornado Trends Since 1950
19501952
19541956
19581960
19621964
19661968
19701972
19741976
19781980
19821984
19861988
19901992
19941996
19982000
20022004
20062008
20100
5
10
15
20
25
Tornado Trends Since 1950
All Tornadoes Moving average (All Tornadoes) F2 Tornadoes F3 Torandoes
Year
Num
ber P
er Y
ear
All peak years for Tornadoes, since 1950, had a moderate or strong La Nina the preceding winter.
Tornado – ENSO Index – NAO IndexTornado Peaks - NAO - ENSO
NAO ENSO Year Severe TORNADO0.67 -1.2 1956 41 23-0.08 -1.6 1976 90 230.47 -0.8 1965 51 20-0.20 -0.7 2001 159 190.21 -0.4 1967 38 16-0.76 0.6 1977 35 15-0.39 -1.8 1974 58 140.42 0.4 1991 106 14-0.49 -0.1 1979 52 13-0.30 -0.7 1968 54 13-0.91 -1.8 1989 45 130.31 -0.6 1975 97 11-0.11 -0.5 1986 37 11
Tornado Trends
• No statistically significant change in tornado numbers, by year since 1950– There is an average of 12 years between peaks and
minimums in yearly Tornado Number• Seems to be some relation to the NAO – NAO negative , tornadoes are more frequent– NAO positive , tornado numbers are suppressed
• La Nina actually is a bigger player for increased tornadoes
Compare Mean ENSO for High and Low Numbers of Tornadoes
Low T Avg High T Avg
-0.80
-0.70
-0.60
-0.50
-0.40
-0.30
-0.20
-0.10
0.00
0.10
0.20ENSO Mean Compared to Tornado Frequency
Yearly Tornadoes
El Nino
La Nina
Tornadoes and ENSO
• Now we will see if ENSO Phase makes any difference to tornado frequency– We will look at this by season for each phase of
ENSO
Tornado Frequency By ENSO Event
La Nina Neutral El Nino0
1
2
3
4
5
6
7
8
Avg # TOR
Avg # TOR
Type of ENSO Event
# of
Tor
ando
es
Results
• For La Nina, there is a statistically significant increase in tornado frequency at the 95 % confidence level
• All of the peaks in tornado frequency since 1950 have been years with a moderate or stronger La Nina during the winter preceding the event
• For La Nina we average about 8 tornados per season since 1950
• For El Nino we average around 5 per year since 1950
Now Let’s Consider Sever Storms in General
• Does ENSO phase have an impact of severe storm frequency?
• Does ENSO phase impact which season of the year severe storms are most prominent?
Severe Storm Frequency for the GRR CWA since 1986
19861987
19881989
19901991
19921993
19941995
19961997
19981999
20002001
20022003
20042005
20062007
20082009
20100
50
100
150
200
250
# of Severe Storms by Year
# of Severe Storms by Year Moving average (# of Severe Storms by Year)
Axis Title
Num
ber o
f Eve
nts
Severe Weather Trends
• There is a statistically significant increase in severe storm frequency since the 1950’s to the past 10 years
• Most of this increase is related to how we gathered the data– Different MIC’s had different methods to gather the data
• Charles Snyder …1970’s and 1980’s• Dean Gulezian…..1990’s• Dan H. ……………..1996-2007• Dan C. ……………..since @2007
La Nina And Storm Frequency By Season
Winter Spring Sum Summer Fall Sum Sum0
20
40
60
80
100
120
140
La Nina Severe Storm Frequency
Ave Strong Avg Mdt Avg Weak Normal
Season
# of
Sto
rms
EL Nino Storm Frequency By Season
Winter Spring Sum Summer Fall Sum Sum0
20
40
60
80
100
120
140
El Nino Severe Storm Frequecy by Season
Ave Strong Avg Mdt Avg Weak Normal
Season
# of
Sto
rms
Does ENSO Impact Seasonal Storm Frequency ?
Winter Spring Summer Fall Sum
-20.0
-15.0
-10.0
-5.0
0.0
5.0
10.0
15.0
Severe Storm Frequency for the GRR CWA /ENSO Type by Season
La Nina Mdt El Nino Mdt
Season
Freq
uenc
y Co
mpa
red
Nor
mal
Trends in Severe Storms Due to ENSO Phase
• For both winter, spring, and summer La Nina has a significant increase in the numbers of events compared to El Nino– Average 6 more in the winter, compared to El Nino– Average 8 more in the spring, compared to El Nino– Average 10 more in the summer
• Fall sees a suppression for both compared to ENSO neutral
• For the entire season there is typically 24 more severe storm events during La Nina years
Let’s see why there would be a difference
We will look at the 300 mb mean jet core for
both La Nina and El Nino years
Moderate or Strong La Nina Winter Mean 300 mb Scalar Wind Speed
Moderate or Strong El Nino Winter Mean 300 mb Scalar Wind Speed
Moderate or Strong La Nina Spring Mean 300 mb Scalar Wind Speed
Moderate or Strong El Nino Spring Mean 300 mb Scalar Wind Speed
*Spring is March through May, but most of our severe storms are May
through August
*So, lets look at the jet core in May to see how far north it gets during a typical La Nina Spring*
300 mb Jet Core in MaySW MI in the entrance region of Jet
Note the 850 mb jet location for May during Moderate La Nina’s
*It would seem this may be what we are looking for
• The low level jet aimed at SW MI• The exit region of the polar jet is just
to our NE
Conclusions
• There is a statistically significant increase in severe storms and tornados during La Nina years
• Seems the jet core is farther north in both the winter and spring during La Nina years
• Since severe storms are typically related to high winds and jet level, it would make sense the Grand Rapids CWA would see more frequent severe storms during La Nina years than for El Nino year