Popular version
Edited by Ken Scheeringa
2 Apr 2009
An Introduction to ENSO
and its impact on Indiana
Weather and Climate
Joseph W. Mays, Data Specialist
Dr. Dev Niyogi, State Climatologist
Ken Scheeringa, Associate State Climatologist
Indiana State Climate Office
201, Life Science Plant and Soils Laboratory
915 W. State Street
Purdue University
West Lafayette, IN 47907-2054
Phone: (765) 494-6574
Email: [email protected]
Web: www.iclimate.org
INTRODUCTION
There are multiple natural occurrences that contribute to variations in global and
local weather. Many of these occurrences are overlooked except by scientists.
However El Niño is one of the most publicized because it impacts not only weather but
world economies as well. What impact does this event, and together with La Niña
forming a part of the El Niño-Southern Oscillation (ENSO), have on weather around the
globe, in the United States, and in Indiana?
This publication was written to help you better understand the climate events that
are known as ENSO. It will provide you with information about El Niño and La Niña,
their behavior, and the impacts these events have on a global and local scale.
BACKGROUND – E
N
S
O
El
Nino
Southern
Oscillation
WHAT ARE EL NIÑO, LA NIÑA, AND THE SOUTHERN OSCILLATION?
The ocean and atmosphere are a coupled system. For example, a change in the
atmosphere may affect ocean temperatures or currents. These ocean changes may
then feed back and cause another change in the atmosphere to complete the cycle. El
Niño and La Niña are alternating patterns of ocean surface temperature, wind flow, and
air pressure. This occurs by exchanging energy between the ocean and the
atmosphere in the Pacific near the equator. The name ENSO wraps all these energy
changes together into one term.
Neutral conditions
Normal – or neutral – conditions exist when neither El Nino nor La Nina is active. Trade
winds near the equator blow towards the west. These winds push warm ocean surface
water westward, building up a mound of warm water off the east coast of Indonesia.
The sea surface may build to as much as 1½ feet higher there than along the west
coast of South America! The Indonesian surface waters may reach temperatures that
are 14°F warmer than those across the ocean in the eastern Pacific.
This temperature difference plays an important part in setting up world circulation
patterns, both in the atmosphere and in the ocean. Many natural events are set in
motion. The jet stream, high altitude wind currents, adjust their travel path around the
globe to align with changing temperature patterns. This in turn causes weather patterns
to adjust.
Strong upwelling of cold, nutrient rich waters from the ocean bottom are brought to
the ocean surface along the western coast of South America. This new surface water is
known as a “cold tongue” which travels north along the western coast of South America
and then westward along the equator. Once this colder water reaches Indonesia at the
other end of the Pacific, it sinks. Along the way to Indonesia, air rises in areas of
warmer water producing strong storms. These storms bring rain to Indonesia, Australia,
and other countries in the western Pacific.
El Niño
During an El Niño the atmosphere and ocean change from their normal state. An El
Niño occurs when the tropical Pacific sea surface temperatures rise higher than normal
over large areas of the Pacific ocean. If these temperatures are 1°F or more above
normal for three consecutive months, El Niño conditions – also called a warm period or
event – are present.
If these warm
conditions persist for five consecutive
months, then an El Niño episode is said to
exist.
Another evidence of an El Niño is the
change in trade wind patterns over the
Pacific. The previously strong trade winds
blowing from east to west weaken, may
disappear, or even reverse direction and
blow from west to east. The warm ocean
water that was piled up near Indonesia is
now free to backflow to the central and
eastern Pacific, spreading out as it travels
eastward.
Water temperatures in the central Pacific
usually range from 60-75°F. Under El Niño
conditions these temperatures may rise
higher than 80°F once the “cold tongue”
disappears. The region of warmest water
temperatures, greater than 80°F, are known
as the warm pool. The warm pool normally
exists in the western Pacific, heating up the
humid air above this region and building
into the area of strongest thunderstorms.
However, in an El Nino the warm pool now
covers much of the equatorial Pacific, and
the storms leave the west Pacific and settle
over the central Pacific.
These changes in sea surface
temperatures cause ocean flow patterns to
change as well. Upwelling of cold water
from the ocean bottom slows down and
becomes less efficient off the western coast
of South America.
Impacts of these
changes – both local and global – will be
discussed in a later section.
El Niños do not come and go on a fixed
routine schedule, but can return anytime
from two to seven years later. On average
a warm event takes place every three to
four years.
Figure 1 – Pacific conditions during
normal, El Niño, and La Niña events.
Created from NOAA / PMEL / TAO diagrams at
http://www.pmel.noaa.gov/tao/proj_over/diagrams/index
.html
La Niña
La Niña – sometimes referred to as the anti-El Niño, El Viejo, or El Diablo – is the
opposite of El Niño. The definition of a La Niña event follows similar criteria as for an El
Niño but now sea surface temperatures in the Pacific must be 1°F or more below
normal. These conditions – called a cold period or event – must be met for at least a
three consecutive month period for a La Niña to exist. A La Niña episode exists if these
cold periods persist for five consecutive months or more.
La Niñas are direct opposites to El Niños. Recall that during an El Niño, the normal
trade winds become weak or even disappear. In a La Niña, however, the trade winds
which blow to the west in neutral conditions become even stronger. The strong winds
bunch the warmest water in the western Pacific into a pile, allowing cold water to upwell
from the ocean bottom in the eastern Pacific. This upwelling replaces the lost warm
surface water along Peru and Ecuador and spreads as a “cold tongue” well into the
central Pacific. With the warm water now concentrated around Indonesia, the air above
this region becomes humid and rises, building into strong storms which bring heavy
rains to the western Pacific islands.
Event Cycles
El Niños and La Niñas do not have a fixed life cycle nor necessarily follow one
another in turn. It is possible for an El Niño to end, to move into neutral conditions, then
see a new El Nino return. The same is true for La Niñas.
For example, El Niño conditions were present from August 1977 through February
1978. Neutral conditions took over from March 1978 through May 1982, then a warm
event returned beginning in April 1982. In fact, the 1982-1983 El Niño was one of the
strongest and most destructive on record.
El Niños are slightly more common than La Niñas. Since 1950 there have been 19
El Niño’s and 14 La Niña’s (Table 1).
Though quite opposite in nature, there is an important parallel between El Niño and
La Niña: they both tend to be strongest during the northern hemisphere winter.
Weather abnormalities occur during summer as well but typically the ENSO events are
less widespread and weaker. Spring and autumn are weather transition periods so
impacts tend to be smaller.
Warm Events
(El Niño)
June 1951 – February 1952
March 1953 – January 1954
April 1957 – June 1958
May 1963 – February 1964
May 1965 – June 1966
August 1968 – March 1970
August 1969 – February 1970
May 1972 – March 1973
August 1976 – February 1978
August 1979 – May 1980
March 1982 – July 1983
July 1986 – February 1988
February 1991 – July 1992
February 1993 – September 1993
June 1994 – April 1995
April 1997 – April 1998
June 2002 – March 2003
July 2004 – January 2005
August 2006 – January 2007
Cold Events
(La Niña)
December 1950 – March 1951
June 1954 – December 1956
May 1964 – January 1965
December 1967 – March 1968
July 1970 – January 1972
June 1973 – March 1976
October 1983 – February 1984
November 1985 – March 1986
April 1988 – July 1989
September 1995 – April 1996
July 1998 – June 2000
October 2000 – February 2001
December 2005 – March 2006
August 2007 – June 2008
Table 1 – List of warm and cold events.
Southern Oscillation
Another part of ENSO is the Southern Oscillation. While El Niño and La Niña are
tied to ocean sea surface temperature cycles, the Southern Oscillation is defined by
atmospheric pressure. The Southern Oscillation is the difference in air pressure
between Tahiti in French Polynesia and Darwin, Australia. It has been discovered that
when eastern Pacific surface waters are abnormally warm, as during an El Niño event,
sea level atmospheric pressure falls in the eastern Pacific but rises in the western
Pacific. The opposite is true during La Niña. This overall ocean-atmosphere coupling is
known as the El Niño/Southern Oscillation, or ENSO.
The Southern Oscillation is measured using the Southern Oscillation Index (SOI). If
the atmospheric pressure difference between Tahiti and Darwin is negative then the
Pacific is abnormally warm. Prolonged periods of negative values indicate an El Niño.is
in progress. The opposite is true for La Niña.
IMPACTS – INDIANA
Abnormal weather during ENSO events is common around the Great Lakes. Both El
Niño and La Niña effects tend to peak during winter in Indiana. However, El Niño
effects seem to strengthen sooner (November) and weaken later (April) than during La
Niña. For the most part, all of Indiana experiences the same degree of unusual weather.
For example, in warm events the entire state tends to be abnormally warm rather than
just one area.
During El Niño
For a visual representation of this section visit the expanded version of this paper
online.
A major reason that weather conditions vary during an ENSO event is due to
changes in wave patterns in the upper atmosphere. The most significant and well
known of these waves would be the jet streams.
Two major jet streams affect weather in the United States – the Polar jet stream and
the Subtropical Pacific jet stream. During an El Niño the favorite paths traveled by
these two jet streams changes. The Subtropical Pacific jet stream moves slightly to the
south and enters the U.S. over southern California. Storm systems generally ride on
top of jet streams. As the Subtropical Pacific jet stream recedes southward, many
storm systems are driven further south than usual across the southeast U.S states.
Meanwhile the Polar jet stream recedes to the north, slowing the frequency of storm
systems and bringing less cold weather into the northern U.S. Abnormally warmer
weather is observed from Washington through Michigan. With these storm tracks split
to the north and south, the northern and central portions of the country, specifically the
region directly south of the Great Lakes, becomes quite dry.
These effects are often seen in Indiana. Though there is a significant warming just
north of Indiana, the temperature impact of El Niño in Indiana is mixed. The overall
trend in the state during El Niño is an annual cooling with an average temperature of
51.5°F. While the overall trend is cooling, conditions vary by month. During a warm
event temperatures are below normal in January, February, April, June, August,
October, and November. The remaining five months experience warmer than normal
conditions but the magnitudes of change are not as large as the cooler months.
December is typically the warmest month during El Niño at nearly a degree above
normal. March, May, July, and September are warmer than usual as well.
The biggest impact of El Niño on Indiana weather is the amount of precipitation the
state receives. Once again the annual average is not too different from normal. During
El Niño Indiana receives approximately 40.6 inches, which is a tad below the normal of
41.3 inches. The state experiences seven months where precipitation totals are below
normal: January, February, March, May, August, October, and November. Once more
the largest differences are during the spring and early summer. April, June, July, and
December receive more precipitation than normal.
So what would be the month by month weather outlook during an El Niño year? The
year would more than likely begin cool and dry, especially in February. March would
remain dry but would experience a slight warming. Cooler weather would return in April
and excess precipitation may fall for the first time. In May conditions would revert back
to those of March, warm and dry. June and July may bring moist weather with warmer
conditions later in this period. The summer may end dry and very cool but that would
not last as conditions become warm and moist in September. For the first time during
the year two months would have similar weather as October and November tend to be
cool and dry during an El Niño. December is typically warm and wet.
During La Niña
Wind patterns in the upper atmosphere are quite different in a La Niña . During a
cold episode, the Subtropical Pacific jet stream will arch northward and enter the United
States over Washington and Oregon. With the Subtropical Pacific jet stream so far
north, warm air from southern states is transported to the Central Plain states, Midwest,
Ohio Valley, and Mid-Atlantic. Near the Dakotas the Subtropical Pacific jet stream
merges with the Polar jet stream, which has plunged further south. This merger,
coupled with the increase in temperatures and abundance of moisture from the Gulf of
Mexico, results in abnormally wet conditions south of the Great Lakes. This clash of
very different air masses also produces more severe weather.
Since Indiana is located in the region with the most weather activity, conditions can
be considerably different than they normally are. Both temperature and precipitation
can swing widely above and below normal yet annually average near normal. In a La
Niña year, the average statewide temperature runs approximately 0.3°F above the
normal of 51.8°F. January, February, June, July, August, September, October, and
December all historically have warmer temperatures during a cold event in the Pacific.
The month with the biggest change – October – isn’t part of the winter period when La
Niña is typically strongest. Yet all three winter months still experience large changes.
The remaining four months, March, April, May, and November, experience cooling
during a La Niña event. In summary unusually cool temperatures are not as abundant,
nor as intense, as warmer temperatures.
Normally Indiana receives a statewide average of 41.3 inches of precipitation per
year. During La Niña the average increases slightly to 41.6 inches. However it is more
useful to examine the impacts by month. January, February, March, June, and
December all experience more precipitation than normal during cold events. Notice
again that all of the winter months are included. There are only five months that see an
increase in precipitation but because of the size of the increases – specifically February
– the annual average is shifted above normal. There are six abnormally dry months:
April, May, July, August, September, and November. October has statistically seen
exactly normal precipitation during La Niña (2.9 inches).
If a La Niña were to occur for an entire calendar year, what conditions should be
expected? The temperature and precipitation historical observations suggest we can
anticipate a warm and wet beginning of the year (January and February). Moist
conditions would persist in March but a long cool spell would begin. May would be the
first month with drier conditions but the cooling intensifies. A sudden switch back to
warm, moist conditions in June would be followed by warm but dry conditions in July,
August, and September. October would bring extremely warm weather with near
average precipitation. November and December would be opposites to one another.
After a cool and dry November the year would end with a warm and wet December..
These evaluations are based solely on historical climate data and do not take into
account forecasts and other natural occurrences, such as volcano eruptions.. Odds are
high that these monthly predictors will not all hold true during individual La Niña events.
Month
January
February
El Niño
All warm & wet
All dry; all but southeast warm
La Niña
All warm & wet
All warm; all but north central wet
March
All dry; all but southeast warm
April
All cool and wet
All but north central warm; east central, south
central, and south west wet
May
June
All cool and wet
July
August
October
All but west central warm; north and central wet
All cool; all but northwest and north central dry
Northwest, north central, west central cool; south
wet
All cool; north and west central wet
November
All cool; all but south dry
December
All warm; south wet
September
All cool; all but south central and
southeast dry
All warm and dry
All but southeast warm; northeast,
west central, central wet
All but southwest warm; all but
northeast wet
All warm and dry
All warm; all but northeast dry
All warm; all dry except southeast
All warm and wet
All but north central and northeast
cool; all dry
All warm; all but southeast dry
IMPACTS – GLOBAL
Since the ocean and atmosphere are coupled, the slightest changes during ENSO
signal temporary global weather changes. Such changes occur at the same time but
can be quite opposites depending on world location. Precipitation and temperatures
may swing to greater extremes in some areas than predicted. These changes are not
concentrated solely in the Pacific; they are felt worldwide.
El Niño impacts
¾ December – February
Impacts during the northern hemisphere winter (December through February) vary
widely from warm and dry to wet and cool. Countries in southern Asia, such as India,
Thailand, and Vietnam, experience abnormally warm conditions.
These warm
conditions are also felt in Japan, eastern China, the Philippines, Indonesia and Papua
New Guinea. The latter three countries also experience below normal precipitation,
resulting in widespread drought.
Table 2 – General regional conditions by month during the extreme phases of ENSO.
Figure 2 – Typical jet stream patterns during winter and the resulting
anomalous temperature and precipitation patterns during La
Niña (top) and El Niño (bottom).
The Americas also feel the effects of El Niño. In South America, Brazil experiences
all kinds of unusual weather. For example, in the northeast conditions are dry but in the
south, near Uruguay, it is wet. The southwest is warm. The northwestern coast near
Ecuador and Peru becomes warm and wet.
In North America, eastern and western Canada, including Alaska, is much warmer
than usual. In the southern U.S and in northern Mexico more rain and the threat of
flooding is common. Cooler weather is typical from Texas east along the Gulf of Mexico.
This is a result of a change in the jet stream path over the U.S. as already discussed.
Another impact of the shifted jet stream is an increased likelihood of severe weather for
Texas, Louisiana, Mississippi, Alabama, Georgia, and Florida.
¾ June – August
As spring comes to a close, the impacts of El Niño change during the northern
hemisphere summer (June through August). Southern Asia and the Pacific islands
warm again to normal temperatures, although India becomes drier. The islands also
remain dry. A vast section of the western South American coast becomes warmer than
normal, and there is a spike in precipitation in central Chile. The conditions Brazil saw
during the winter disappear. All that remains is abnormally warm temperatures, which
blanket most of the country. Countries bordering the Caribbean Sea become warm and
dry. Effects in North America are small during the summer.
La Niña impacts
¾ December – February
La Niña impacts also leave their mark just like those of El Niño. These impacts are
widespread and variable with especially untamed behavior during the northern
hemisphere winter. Comparing La Niña averages with climate normals leads to a
pronounced trend. La Niña’s greatly agitate the usual weather patterns of each region.
For example, a city that is usually warm and dry will become even warmer and drier
during a cold event. An example of this can be seen in the Pacific islands. This region,
usually quite moist, experiences an increase in rainfall during La Niña due to the shift in
storm clouds westward.
As you may have guessed, the regions that are affected during El Niño are also
affected by La Niña. The impacts, much like the behaviors themselves, are opposite
one other. During winter, Japan is abnormally cool, Alaska and western Canada are
cool and wet, the Midwestern U.S. is wet, and the southern U.S. and northern Mexico
become dry and warmer than usual. The variations in Brazil weather return during a La
Niña winter; however, only two regions experience abnormal conditions. Northern
Brazil is unusually wet while the west becomes quite cool. With storm systems shoved
further west, Ecuador and Peru become warm and dry.
¾ June – August
During the summer humid conditions expand from the Philippines and Indonesia
north into India, Vietnam, Thailand, and China. This wet region also experiences below
normal temperatures. Meanwhile northeastern Australia becomes quite warm while the
western coast of South America cools. Southern Brazil and Uruguay witness below
average precipitation while countries bordering the Caribbean Sea experience cool and
moist conditions. Again, North America sees few unusual weather patterns during La
Niña summers.
Summary
Unusual weather spells are not as drastic in Indiana as they can be in the Pacific
Northwest or Southeast. The state undergoes moderate temperature and precipitation
fluctuations during both El Niño and La Niña events. The most obvious changes usually
occur from November through March. The general climate conditions discussed here
do not always hold true for every part of the state. For a more regional look at ENSO
impacts visit this text online.
ALL TABLES AND IMAGES BELOW ARE FOR THE EXTENDED PAPER
ON THE WEB, NOT THE PUBLICATION.
Indiana (Statewide)
Normal
Month
January
February
March
April
May
June
July
August
September
October
November
December
Temp.
(°F)
26.9
30.7
39.9
51.6
61.5
70.6
74.3
72.4
65.5
54.0
42.2
31.2
Precip.
(inches)
2.68
2.35
3.33
3.97
4.40
4.15
4.32
3.62
3.17
2.90
3.41
2.97
Departure from
Normal During
El Niño
Temp.
(°F)
-0.66
-0.75
0.52
-0.68
0.70
-0.64
0.04
-1.30
0.21
-0.74
-0.65
0.99
Precip.
(inches)
-0.24
-0.78
-0.48
0.42
-0.07
0.05
0.17
-0.14
0.07
-0.01
-0.05
0.21
Departure from
Normal During
La Niña
Temp.
(°F)
0.64
0.61
-0.07
-0.08
-0.26
0.19
0.14
0.68
0.16
1.58
-0.26
0.62
Precip.
(inches)
0.39
0.72
0.06
-0.09
-0.44
0.19
-0.56
-0.05
-0.24
0.01
-0.33
0.06
Table 3 – Data for Indiana. Normals and departures computed from data for
1950 through 2006.
Indiana Climate Division 1 (Northwest)
Normal
Month
January
February
March
April
May
June
July
August
September
October
November
December
Temp.
(°F)
23.4
27.5
37.1
49.0
59.6
69.2
73.0
71.0
64.2
52.8
40.2
28.3
Precip.
(inches)
2.01
1.73
2.67
3.83
3.78
4.28
4.25
3.67
3.30
3.10
2.99
2.47
Departure from
Normal During
El Niño
Temp.
(°F)
1.27
1.59
1.10
-0.62
0.07
-0.85
0.05
-0.96
-0.32
-0.55
-1.17
1.96
Precip.
(inches)
0.14
-0.47
-0.35
0.25
-0.18
0.35
0.61
0.41
-0.34
0.36
-0.08
-0.12
Departure from
Normal During
La Niña
Temp.
(°F)
1.05
2.16
-0.83
0.53
0.26
0.61
0.59
1.77
0.34
1.44
-0.04
0.32
Precip.
(inches)
0.29
0.49
-0.38
-0.15
-0.36
0.25
-0.09
-0.17
-0.66
0.32
-0.57
-0.29
Table 4 – Data for northwest Indiana. Normals and departures computed
from data for 1950 through 2006.
Indiana Climate Division 2
(North Central)
Normal
Month
January
February
March
April
May
June
July
August
September
October
November
December
Temp.
(°F)
24.0
27.6
37.1
49.2
59.6
69.1
72.8
70.7
63.8
52.4
40.3
28.8
Precip.
(inches)
2.20
1.87
2.62
3.72
3.78
4.10
4.28
3.70
3.20
2.95
3.01
2.55
Departure from
Normal During
El Niño
Departure from
Normal During
La Niña
Temp.
(°F)
1.21
1.28
0.99
-0.57
-0.11
-0.87
0.19
-0.88
-0.24
-0.47
-1.05
1.70
Temp.
(°F)
1.08
2.56
-0.83
0.68
0.20
0.52
0.50
1.64
0.18
1.59
0.03
0.19
Precip.
(inches)
0.22
-0.59
-0.27
0.34
-0.15
0.26
0.67
0.18
-0.24
0.16
-0.02
-0.26
Precip.
(inches)
0.25
0.47
-0.30
-0.19
-0.11
0.11
-0.16
-0.06
-0.57
0.44
-0.36
-0.38
Table 5 – Data for north central Indiana. Normals and departures computed
from data for 1950 through 2006.
Indiana Climate Division 3
(Northeast)
Normal
Month
January
February
March
April
May
June
July
August
September
October
November
December
Temp.
(°F)
23.9
27.2
36.6
48.8
59.3
68.9
72.6
70.6
63.6
52.1
40.1
28.7
Precip.
(inches)
2.19
1.88
2.65
3.61
3.83
4.01
3.98
3.57
3.12
2.76
3.00
2.56
Departure from
Normal During
El Niño
Departure from
Normal During
La Niña
Temp.
(°F)
1.26
1.10
1.40
-0.16
0.19
-0.49
0.39
-0.63
0.04
-0.28
-0.97
1.83
Temp.
(°F)
1.06
2.53
-0.60
0.82
0.43
0.85
0.79
1.79
0.30
1.73
0.16
0.27
Precip.
(inches)
0.29
-0.64
-0.53
0.31
-0.18
0.15
0.72
-0.22
-0.06
0.29
-0.01
-0.19
Precip.
(inches)
0.26
0.32
-0.21
-0.28
0.10
-0.01
-0.24
0.30
-0.55
0.52
-0.30
-0.31
Table 6 – Data for northeast Indiana. Normals and departures computed
from data for 1950 through 2006.
Indiana Climate Division 4
(West Central)
Normal
Month
January
February
March
April
May
June
July
August
September
October
November
December
Temp.
(°F)
26.3
30.5
39.9
51.9
61.8
70.9
74.5
72.4
65.6
54.1
42.2
30.6
Precip.
(inches)
2.50
2.12
3.18
3.91
4.40
4.29
4.31
3.70
3.18
2.95
3.11
5.16
Departure from
Normal During
El Niño
Temp.
(°F)
1.12
1.01
0.68
-0.78
0.25
-0.60
-0.04
-0.82
-0.18
-0.41
-1.15
1.44
Precip.
(inches)
0.25
-0.66
-0.61
0.61
-0.14
0.83
0.22
-0.07
-0.14
0.24
-0.13
-0.17
Departure from
Normal During
La Niña
Temp.
(°F)
1.29
2.66
-0.93
0.44
0.12
0.41
0.31
1.73
0.30
1.62
-0.20
0.41
Precip.
(inches)
0.41
0.72
-0.63
-0.51
0.23
0.65
-0.72
-0.79
-0.51
0.37
-0.37
-0.18
Table 7 – Data for west central Indiana. Normals and departures computed
from data for 1950 through 2006.
Indiana Climate Division 5
(Central)
Normal
Month
January
February
March
April
May
June
July
August
September
October
November
December
Temp.
(°F)
26.7
30.5
39.7
51.5
61.3
70.5
74.0
72.0
65.2
53.7
42.0
30.9
Precip.
(inches)
2.67
2.30
3.23
3.95
4.46
3.98
4.23
3.42
3.17
2.88
3.29
5.27
Departure from
Normal During
El Niño
Departure from
Normal During
La Niña
Temp.
(°F)
1.07
0.80
0.77
-0.42
0.30
-0.46
0.37
-0.51
0.18
-0.22
-0.94
1.61
Temp.
(°F)
1.56
2.82
-0.59
0.67
0.24
0.52
0.51
1.74
0.39
1.71
-0.03
0.61
Precip.
(inches)
0.36
-0.73
-0.90
0.42
-0.02
0.80
0.04
-0.33
-0.04
-0.08
-0.12
-0.13
Table 8 – Data for central Indiana. Normals and departures computed
from data for 1950 through 2006.
Precip.
(inches)
0.37
0.48
-0.46
-0.17
0.08
0.62
-0.55
-0.64
-0.30
0.27
-0.32
-0.11
Indiana Climate Division 6
(East Central)
Normal
Month
January
February
March
April
May
June
July
August
September
October
November
December
Temp.
(°F)
25.9
29.4
38.6
50.3
60.3
69.4
73.0
71.0
64.2
52.8
41.3
30.2
Precip.
(inches)
2.56
2.16
3.03
3.90
4.31
4.15
4.19
3.43
2.90
2.79
3.17
3.54
Departure from
Normal During
El Niño
Departure from
Normal During
La Niña
Temp.
(°F)
0.90
0.53
0.64
-0.46
0.06
-0.75
0.06
-0.70
0.00
-0.31
-1.06
1.38
Temp.
(°F)
1.40
2.73
-0.68
0.77
0.18
0.36
0.24
1.26
0.12
1.48
-0.18
0.37
Precip.
(inches)
0.37
-0.65
-1.01
0.31
0.01
0.91
0.19
-0.47
-0.07
-0.05
-0.08
-0.22
Precip.
(inches)
0.55
0.44
-0.33
-0.22
-0.10
0.27
-0.45
-0.56
-0.31
0.35
-0.38
-0.08
Table 9 – Data for east central Indiana. Normals and departures computed
from data for 1950 through 2006.
Indiana Climate Division 7
(Southwest)
Normal
Departure from
Normal During
El Niño
Month
Temp.
(°F)
Precip.
(inches)
Temp.
(°F)
Precip.
(inches)
January
February
March
April
May
June
July
August
September
October
November
December
30.7
34.8
43.8
55.3
64.5
73.2
76.9
75.2
68.2
56.8
45.0
34.5
3.19
3.01
4.10
4.21
4.62
3.91
4.10
3.32
3.23
3.15
3.97
9.08
0.80
0.20
0.14
-0.78
0.24
-0.35
0.45
-0.19
0.13
-0.35
-0.99
1.24
0.05
-0.69
-1.37
1.19
-0.02
0.13
-0.15
-0.44
0.52
-0.02
0.07
0.22
Departure from
Normal During
La Niña
Tem
p.
(°F)
1.47
2.51
-1.18
0.21
0.14
-0.06
0.28
1.45
0.31
1.44
-0.37
0.64
Table 10 – Data for southwest Indiana. Normals and departures computed
from data for 1950 through 2006.
Precip.
(inches)
0.42
0.90
-0.32
-0.13
-0.65
0.55
-0.77
-0.38
-0.42
0.10
-0.34
-0.09
Indiana Climate Division 8
(South Central)
Normal
Month
January
February
March
April
May
June
July
August
September
October
November
December
Temp.
(°F)
30.4
34.3
42.9
54.1
63.2
71.6
75.5
73.9
66.8
55.4
44.3
34.0
Precip.
(inches)
3.46
3.08
4.23
4.34
4.97
4.26
4.38
3.73
3.27
2.96
3.86
3.61
Departure from
Normal During
El Niño
Departure from
Normal During
La Niña
Temp.
(°F)
0.96
0.20
0.16
-0.65
0.31
-0.19
0.65
-0.21
0.13
-0.39
-0.85
1.06
Temp.
(°F)
1.55
2.52
-1.07
0.27
0.07
0.28
0.43
1.67
0.37
1.44
-0.39
0.62
Precip.
(inches)
0.14
-0.70
-1.51
1.13
0.31
0.34
-0.36
-0.25
0.41
-0.35
0.04
0.30
Precip.
(inches)
0.65
1.03
0.07
-0.26
-0.37
0.65
-0.80
-0.33
-0.26
0.17
-0.22
-0.02
Table 11 – Data for south central Indiana. Normals and departures computed
from data for 1950 through 2006.
Indiana Climate Division 9
(Southeast)
Normal
Month
January
February
March
April
May
June
July
August
September
October
November
December
Temp.
(°F)
30.3
34.0
42.6
53.7
63.1
71.6
75.6
74.0
67.0
55.5
44.2
34.1
Precip.
(inches)
3.39
2.99
3.95
4.10
4.73
4.09
4.33
3.68
3.17
2.91
3.64
5.60
Departure from Departure from
Normal During Normal During
El Niño
La Niña
Temp.
(°F)
0.62
-0.04
-0.15
-0.55
0.12
-0.43
0.33
-0.51
0.07
-0.52
-0.87
1.10
Precip.
(inches)
0.30
-0.76
-1.32
1.05
0.13
0.49
-0.17
-0.22
0.02
-0.27
0.00
0.23
Temp.
(°F)
1.38
2.29
-1.19
0.18
-0.13
0.24
0.30
1.51
0.23
1.21
-0.59
0.53
Precip.
(inches)
0.55
1.01
0.12
-0.34
-0.39
0.60
-0.50
-0.47
0.02
0.36
-0.34
0.04
Table 12 – Data for southeast Indiana. Normals and departures computed from
data for 1950 through 2006.
Figure 3 – Anomalous precipitation by month (January through June) during an El Niño.
Figure 4 – Anomalous precipitation by month (July through December) during an El
Niño.
Figure 5 – Anomalous temperature by month (January through June) during an El
Niño.
Figure 6 – Anomalous temperature by month (July through December) during an El
Niño.
Figure 7 – Anomalous precipitation by month (January through June) during a La
Niña.
Figure 8 – Anomalous precipitation by month (July through December) during a La
Niña.
Figure 9 – Anomalous temperature by month (January through June) during a La Niña.
Figure 10 – Anomalous temperature by month (July through December) during a La
Niña.