“Effects of Pacific Sea Surface Temperature (SST) Anomalies on the Climate of Southern South Carolina

and Northern Coastal Georgia ”

Whitney AlbrightJoseph CalderoneFrank Alsheimer

NWS Forecast Office Charleston

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Outline

• Introduction/Objectives• Background• Methodology• Results• Summary• Acknowledgements

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Introduction/Objectives

• Purpose: Quantify the effects of above or below normal Pacific SSTs on winter climatology in the southern South Carolina and northern coastal Georgia region

• Big Picture: Notify water managers and other weather sensitive industries to the potential of moderate to high impact weather as far in advance as possible

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Background

• The fluctuation of equatorial SSTs between the eastern and western Pacific, and the associated pressure fluctuation, is known as the El Niño Southern Oscillation (ENSO). SSTs above normal are considered El Niño events, while SSTs below normal are considered La Niña events.

• This atmospheric phenomenon is a result of the combination of several atmospheric and oceanic factors including changes in surface easterly winds, jet stream location, and subsurface oceanic temperatures.

http://www.bom.gov.au/lam/climate/levelthree/analclim/elnino.htm

• Neutral conditions

• El Niño conditions

• La Niña conditions

http://www.cpc.noaa.gov/products/analysis_monitoring/ensocycle/meansst.shtml

http://www.cpc.noaa.gov/products/analysis_monitoring/ensocycle/ensocycle.shtml

http://www.cpc.noaa.gov/products/analysis_monitoring/ensocycle/ensocycle.shtml

Background: Current Accepted Impacts_______________________________________

SOUTH CAROLINA &

GEORGIA

SOUTH CAROLINA &

GEORGIA

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Methodology: Procedure

• Step 1: Acquired raw SST anomaly values from the Climate Prediction Center (CPC) for 1950 to 2006 (values from the Nino 3.4 region)

http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/nino_regions.shtml

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Methodology: Procedure

• Step 2: Defined El Niño(EN)/La Niña(LN) Categories– Took average of monthly SST anomaly values for

December to April from 1950 to 2006– Then classified each year as a certain event

based on its average anomaly value

The categories were defined as follows:Strong EN ≥+0.65

Weak EN +0.30 to +0.64

Neutral -0.29 to +0.29

Weak LN -0.64 to -0.30

Strong LN ≤-0.65

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Methodology: Procedure

Step 3:– Acquired monthly maximum,

minimum, and average temperatures, and precipitation amounts from 1950 to 2006 for Charleston SC, Savannah GA, Walterboro SC and Fort Stewart GA from the National Climate Data Center (NCDC)

– Sorted data based on EN/LN category.

     

Average Max

Temp Values    

           

      CHS    

  DEC JAN FEB MAR APR

Strong EN 60.3 55.2 57.1 63.8 71.5

Weak EN 58.8 55.7 57.7 64.7 73.2

Neutral 59.8 57.8 60.3 66 72.8

Weak LN 58.2 57.5 60.1 65.4 73.3

Strong LN 60.5 60.5 62 66.7 73.6

Average 59.5 57.3 59.4 65.3 72.9

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Methodology: Procedure

– Found all days since 1950 when the minimum temperature was below 17 degrees and when the maximum temperature was below 32 degrees.

– Classify these days as having occurred during one of the defined categories.

      CHS    

  DEC JAN FEB MAR APR

Strong EN 2 3 4 0 0

Weak EN 0 7 2 1 0

Neutral 8 8 0 0 0

Weak LN 6 4 1 0 0

Strong LN 1 5 1 0 0

Total 17 27 8 1 0

Average 3.4 5.4 1.6 0.2 0.0

# OF DAYS WITH MIN TEMP

17 DEGREES OR BELOW

Step 4: Retrieved “extreme” temperature data for the 4 locations from NCDC

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Methodology: Procedure

• Step 5: Acquired severe hail, tornado, and severe wind data for the Charleston Weather Forecast Office County Warning Area from the NCDC Storm Events Database

– Found total number of days in each month for each year that the above conditions took place and sorted them by category.

___________________________________________________________ NUMBER OF DAYS PER MONTH ON WHICH HAIL OCCURRED FOR

GEORGIA AND SOUTH CAROLINA COUNTIES

  DEC JAN FEB MAR APR

Strong EN 0 7 4 17 23

Weak EN 0 0 4 11 28

Neutral 0 1 1 7 11

Weak LN 4 9 0 5 20

Strong LN 0 0 2 12 16

Average 0.8 3.4 2.2 10.4 19.6

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Results: Defined ENSO Categories

CHS Average Max Temp

50

55

60

65

70

75

DEC JAN FEB MAR APR

Deg

rees

F

Strong EN Weak EN Neutral Weak LN Strong LN Average

Maximum Daily Temperatures:• considerably below average during EN years due to lower pressures aloft suppressing jet stream and storm track across the southern U.S.• above average during Strong LN events due to higher pressure in the mid and upper atmosphere forcing jet stream and storm track north.

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Results: Defined ENSO Categories

Minimum Daily Temperatures:

• minimum daily temperatures show a similar trend to the maximums, although not as pronounced.

CHS Average Min Temp

40

45

50

55

60

DEC JAN FEB MAR APR

Deg

rees

F

Strong EN Weak EN Neutral Weak LN Strong LN Average

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Results: Defined ENSO Categories

Average Precipitation:

•Precipitation amounts are well above average during all EN events due to the increased frequency of storm systems.

•Precipitation amounts are well below average during LN events due to higher pressure and fewer storms.

CHS Average Precipitation

0

1

2

3

4

5

6

DEC JAN FEB MAR APR

Inch

es

Strong EN Weak EN Neutral Weak LN Strong LN Average

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Results: Defined ENSO Categories

CHS Strong EN Temp Departures

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

DEC JAN FEB MAR APR

Max depart. Min depart. Ave. depart

Strong El Niño Temperature Departures:

•max and min departures are negative for January through April

•max departures are more negative than min departures, indicating increased cloud cover

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Results: Defined ENSO Categories

CHS Strong LN Departures

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

DEC JAN FEB MAR APR

Max depart. Min depart. Ave. depart

Strong La Niña Temperature Departures:

•max and min departures are positive

•max departures are greater than min departures due to decreased cloud cover.

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Results: CHS Extremes

CHS Min Temp Days

0

1

2

3

4

5

6

7

8

9

DEC JAN FEB MAR

Strong EN Weak EN Neutral Weak LN Strong LN Average

CHS Minimum Temperature Extremes:

•Dec and January show the most neutral influence

•The later winter months are dominated by EN events as strong late season storms bring cold air southward behind them.

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Results: Severe Hail Data

Total Hail Days

0123456789

101112131415161718192021222324252627282930

FEB MAR APR

Strong EN Weak EN Neutral Weak LN Strong LN Average

Total CWA hail days:

Most late winter and early spring hail events take place during EN years, likely due to:

• lower pressure aloft introducing colder air, destabilizing the atmosphere.

• stronger jet stream winds increasing upper level divergence and

shear.

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Summary

For the Charleston, SC County Warning Area:• Maximum, minimum, and average

temperatures are generally below normal during El Niño events and above normal during La Niña events.

• Precipitation is well above normal during El Niño events and well below normal during La Niña events.

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Summary (Cont.)

• During El Niño, the maximum temperature anomalies are significantly colder than the minimum temperature anomalies.

• During La Niña, the maximum temperature anomalies are significantly warmer than the minimum temperature anomalies.

• Extreme cold is more likely in late winter during El Niño events.

• Severe Hail is more likely during El Niño events.

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Acknowledgements

Data for this project was taken from NOAA archives.

– SST values were gathered from the Climate Prediction Center at: http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml

– Temperature, Precipitation, Tornado, wind, hail, and extreme weather data was taken from the Northeast Regional Climate Center at: http://xmacis.nrcc.cornell.edu/CHS/xmacis_options

Thank you!