867
FXUS05 KWBC 151330
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EDT THU MAY 15 2008
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS
THE MAIN FACTORS WHICH USUALLY INFLUENCE THE SEASONAL CLIMATE OUTLOOK INCLUDE:
1) EL NINO AND LA NINA - WHICH COMPRISE EL NINO/SOUTHERN OSCILLATION OR ENSO.
2) TRENDS - APPROXIMATED BY THE OCN TOOL AS THE DIFFERENCE BETWEEN THE MOST
RECENT 10-YEAR MEAN OF TEMPERATURE OR 15-YEAR MEAN OF PRECIPITATION FOR A GIVEN
LOCATION AND TIME OF YEAR AND THE 30-YEAR CLIMATOLOGY PERIOD (CURRENTLY
1971-2000).
3) THE TROPICAL 30-60 DAY OSCILLATION - SOMETIMES CALLED MADDEN JULIAN
OSCILLATION (MJO) - AFFECTS CLIMATE VARIABILITY WITHIN SEASONS.
4) THE NORTH ATLANTIC OSCILLATION (NAO) AND THE PACIFIC NORTH AMERICAN (PNA)
PATTERNS - WHICH AFFECT THE TEMPERATURE ANOMALY PATTERN ESPECIALLY DURING THE
COLD SEASONS. THESE PHENOMENA ARE CURRENTLY KNOWN TO BE PREDICTABLE ONLY OVER A
WEEK OR SO.
5) THE PACIFIC DECADAL OSCILLATION (PDO) - AN ENSO-LIKE PATTERN OF CLIMATE
VARIABILITY AFFECTING BOTH THE TROPICS AND THE NORTH PACIFIC AND NORTH AMERICAN
REGIONS, BUT WHICH VARIES ON A MUCH LONGER TIME-SCALE THAN ENSO.
6) PERSISTENTLY DRY OR WET SOILS IN THE SUMMER AND SNOW AND ICE COVER ANOMALIES
IN THE WINTER. THESE FACTORS TEND TO PERSIST FOR LONG PERIODS AND ACT AS A KIND
OF MEMORY IN THE CLIMATE SYSTEM.
7) STATISTICAL FORECAST TOOLS - CANONICAL CORRELATION ANALYSIS (CCA), SCREENING
MULTIPLE LINEAR REGRESSION (SMLR), AND ENSEMBLE CCA (ECCA).
8) DYNAMICAL FORECAST MODELS - INCLUDING THE NCEP CLIMATE FORECAST SYSTEM (CFS).
9) AN OBJECTIVE CONSOLIDATION (ABBREVIATED CON IN THE TEXT) OF THE OCN, CCA,
SMLR, ECCA, AND CFS FORECASTS IS USED AS A FIRST GUESS IN PREPARING THE
FORECAST MAPS. THIS TECHNIQUE MAKES OPTIMUM USE OF THE KNOWN SKILL OF OUR
FORECAST TOOLS.
LA NINA CONTINUED TO WEAKEN DURING APRIL 2008, AS REFLECTED BY CHANGES IN SEA
SURFACE TEMPERATURES (SSTS) ACROSS THE EQUATORIAL PACIFIC OCEAN. NEGATIVE SST
ANOMALIES IN THE CENTRAL AND EAST-CENTRAL EQUATORIAL PACIFIC HAVE WEAKENED,
WHILE POSITIVE SST ANOMALIES ARE CONFINED TO PARTS OF THE EASTERN EQUATORIAL
PACIFIC. THE LATEST WEEKLY SSTS IN THE WESTERNMOST NINO-4 AND NINO-3.4 REGIONS
ARE BETWEEN 0.6C AND 0.8C BELOW AVERAGE, WHILE DEPARTURES IN THE EASTERNMOST
NINO-3 AND NINO-1+2 REGIONS ARE 0C AND -0.3C RESPECTIVELY.
SSTS REMAIN SUFFICIENTLY COOL TO MAINTAIN THE PERSISTENT ATMOSPHERIC ANOMALIES
ASSOCIATED WITH LA NINA. ENHANCED LOW-LEVEL EASTERLY WINDS AND UPPER-LEVEL
WESTERLY WINDS CONTINUED ACROSS THE CENTRAL EQUATORIAL PACIFIC, CONVECTION
REMAINED SUPPRESSED THROUGHOUT THE CENTRAL EQUATORIAL PACIFIC, AND ENHANCED
CONVECTION COVERED THE FAR WESTERN PACIFIC. COLLECTIVELY, THESE ATMOSPHERIC AND
OCEANIC CONDITIONS INDICATE AN ONGOING LA NINA.
A MAJORITY OF THE RECENT DYNAMICAL AND STATISTICAL SST FORECASTS FOR THE NINO
3.4 REGION INDICATE LA NINA WILL PERSIST THROUGH MAY-JUNE-JULY 2008).
THEREAFTER, THERE IS CONSIDERABLE SPREAD IN THE FORECASTS, WITH THE MAJORITY
REFLECTING ENSO-NEUTRAL CONDITIONS (AVERAGE SST OF -0.5 TO 0.5 IN THE NINO-3.4
REGION) DURING THE SECOND HALF OF THE YEAR. HOWEVER, THE SPREAD OF THE MODELS
SPANS THE POSSIBILITY OF A RETURN TO LA NINA OR EVEN AN EL NINO BY THE END OF
2008. BASED ON CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS AND RECENT TRENDS, A
TRANSITION FROM LA NINA TO ENSO-NEUTRAL CONDITIONS IS POSSIBLE DURING JUNE-JULY
2008.
ATMOSPHERIC CONDITIONS RELATED TO LA NINA OFTEN PERSIST FOR A COUPLE MONTHS
AFTER SSTS RETURN TO ENSO-NEUTRAL CONDITIONS. EXPECTED LA NINA IMPACTS DURING
MAY-JULY 2008 INCLUDE A CONTINUATION OF ABOVE-AVERAGE PRECIPITATION OVER
INDONESIA AND BELOW-AVERAGE PRECIPITATION OVER THE CENTRAL EQUATORIAL PACIFIC.
THE TEMPERATURE OUTLOOK FOR JJA 2008 CALLS FOR ABOVE NORMAL TEMPERATURES IN
SOUTHWESTERN SECTIONS OF ALASKA, BASED ON MAINLY STATISTICAL FORECAST TOOLS.
SUB-NORMAL TEMPERATURES ARE EXPECTED IN SECTIONS OF THE FAR NORTHWEST, DUE TO
COOL SST ANOMALIE NEARBY. SUB-NORMAL TEMPERATURES ARE ALSO CALLED FOR FROM
IOWA SOUTHEASTWARD THROUGH THE TENNESSEE VALLEY TO GEORGIA AND NORTHERN
FLORIDA, BASED ON ALL FORECAST TOOLS. ABOVE NORMAL TEMPERATURES ARE EXPECTED
FOR THE SOUTHWEST, AND IN THE NORTHEAST BASED ON NEARLY ALL TOOLS. SUB-NORMAL
TEMPERATURES ARE EXPECTED ALONG SECTIONS OF THE IMMEDIATE WEST COAST THROUGH
SON, DUE TO COOL SST ANOMALIES. ELSEWHERE, THE FORECAST CALLS FOR EQUAL
CHANCES (EC) OF ABOVE, NEAR AND BELOW AVERAGE TEMPERATURES.
ABOVE-MEDIAN PRECIPITATION IS CALLED FOR IN ALASKA FROM JJA THROUGH ASO 2008.
SUB-MEDIAN RAINFALL IS EXPECTED IN SECTIONS OF THE NORTHWEST FROM JJA THROUGH
ASO, WHILE ABOVE-MEDIAN RAINFALL IS PREDICTED FOR SECTIONS OF THE NORTHEAST AND
THE SOUTHEAST. THERE IS A TENDENCY FOR ABOVE-MEDIAN PRECIPITATION FROM THE
OHIO VALLEY TO NEW YORK, AND SUB-MEDIAN PRECIPITATION FOR SECTIONS OF THE
SOUTHEAST FROM NDJ-JFM. RELATIVE DRYNESS IS PREDICTED IN SECTIONS OF THE
NORTHWEST AND THE SOUTHEAST FROM DJF-MAM. SMALL, BUT CONSISTENT SIGNALS FOR
BELOW-MEDIAN PRECIPITATION IN THE INTER-MOUNTAIN WEST AND SECTIONS OF THE
NORTHEAST AND TEXAS ARE PREDICTED FOR AMJ-JJA 2009.
BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS
NOTE: FOR GRAPHICAL DISPLAYS OF THE FORECAST TOOLS DISCUSSED BELOW SEE:
HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/PREDICTIONS/90DAY/TOOLS/BRIEFING
CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS
LA NINA CONTINUED TO WEAKEN DURING APRIL 2008, AS REFLECTED BY CHANGES IN SEA
SURFACE TEMPERATURES (SSTS) ACROSS THE EQUATORIAL PACIFIC OCEAN. NEGATIVE SST
ANOMALIES IN THE CENTRAL AND EAST-CENTRAL EQUATORIAL PACIFIC HAVE WEAKENED,
WHILE POSITIVE SST ANOMALIES ARE CONFINED TO PARTS OF THE EASTERN EQUATORIAL
PACIFIC. THE LATEST WEEKLY SSTS IN THE WESTERNMOST NINO-4 AND NINO-3.4 REGIONS
ARE BETWEEN 0.6C AND 0.8C BELOW AVERAGE, WHILE DEPARTURES IN THE EASTERNMOST
NINO-3 AND NINO-1+2 REGIONS ARE 0C AND -0.3C RESPECTIVELY.
POSITIVE SUBSURFACE OCEAN TEMPERATURES AT THERMOCLINE DEPTH HAVE CONTINUED TO
INCREASE IN CENTRAL AND EAST-CENTRAL EQUATORIAL PACIFIC. WHILE THIS INCREASE
HAS RESULTED IN POSITIVE HEAT CONTENT ANOMALIES (AVERAGE TEMPERATURES IN THE
UPPER 300M OF THE OCEAN), A SHALLOW LAYER OF NEGATIVE ANOMALIES IN THE CENTRAL
PACIFIC CONTINUES TO PERSIST BETWEEN THE SURFACE AND 100M. DESPITE THESE
CHANGES, SSTS REMAIN SUFFICIENTLY COOL TO MAINTAIN THE PERSISTENT ATMOSPHERIC
ANOMALIES ASSOCIATED WITH LA NINA. ENHANCED LOW-LEVEL EASTERLY WINDS AND
UPPER-LEVEL WESTERLY WINDS CONTINUED ACROSS THE CENTRAL EQUATORIAL PACIFIC,
CONVECTION REMAINED SUPPRESSED THROUGHOUT THE CENTRAL EQUATORIAL PACIFIC, AND
ENHANCED CONVECTION COVERED THE FAR WESTERN PACIFIC. COLLECTIVELY, THESE
ATMOSPHERIC AND OCEANIC CONDITIONS INDICATE AN ONGOING LA NINA.
PROGNOSTIC DISCUSSION OF SST FORECASTS
A MAJORITY OF THE RECENT DYNAMICAL AND STATISTICAL SST FORECASTS FOR THE NINO
3.4 REGION INDICATE LA NINA WILL PERSIST THROUGH MAY-JUNE-JULY 2008).
THEREAFTER, THERE IS CONSIDERABLE SPREAD IN THE FORECASTS, WITH THE MAJORITY
REFLECTING ENSO-NEUTRAL CONDITIONS (-0.5 TO 0.5 IN THE NINO-3.4 REGION) DURING
THE SECOND HALF OF THE YEAR. HOWEVER, THE SPREAD OF THE MODELS SPANS THE
POSSIBILITY OF A RETURN TO LA NINA OR EVEN AN EL NINO BY THE END OF 2008. BASED
ON CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS AND RECENT TRENDS, A TRANSITION
FROM LA NINA TO ENSO-NEUTRAL CONDITIONS IS POSSIBLE DURING JUNE-JULY 2008.
ATMOSPHERIC CONDITIONS RELATED TO LA NINA OFTEN PERSIST FOR A COUPLE MONTHS
AFTER SSTS RETURN TO ENSO-NEUTRAL CONDITIONS. EXPECTED LA NINA IMPACTS DURING
MAY-JULY 2008 INCLUDE A CONTINUATION OF ABOVE-AVERAGE PRECIPITATION OVER
INDONESIA AND BELOW-AVERAGE PRECIPITATION OVER THE CENTRAL EQUATORIAL PACIFIC.
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
THE TEMPERATURE AND PRECIPITATION OUTLOOKS FOR ALL LEAD TIMES ARE BASED ON THE
CONSOLIDATION (CON), A SKILL-WEIGHTED AND CALIBRATED OBJECTIVE BLEND OF THE
CFS, CCA, SMLR, OCN, AND ECCA FORECAST TOOLS. THE CON TOOL IS NOT AVAILABLE
FOR ALASKA, SO THE FORECAST THERE IS BASED MOSTLY ON OCN, CCA, SMLR AND THE CFS.
THE TEMPERATURE FORECAST FOR EARLY LEADS IS BASED ON THE 5-TOOL CON, WHICH
INCLUDES ECCA FOR THE FIRST TIME. LOCAL FACTORS ALSO AFFECT THE FIRST SEVERAL
LEADS OF THE TEMPERATURE FORECAST. THESE INCLUDE COLD SST ANOMALIES IN THE
EASTERN NORTH PACIFIC ALONG THE WEST COAST OF NORTH AMERICA AND SOUTH OF
ALASKA, AMPLE SNOW PACK IN SECTIONS OF THE NORTHWEST, AMPLE SOIL MOISTURE IN
THE CENTRAL U.S, AND COOL SST ANOMALIES ADJACENT TO THE FLORIDA PENINSULA AND
ALONG THE GULF COAST. THE CFS DROPS OUT OF THE CON AFTER LEAD 6 (NDJ), AND
ONLY STATISTICAL TOOLS (OCN, CCA, SMLR, ECCA) CONTRIBUTE TO CON AFTER THAT.
THIS FORECAST OVER THE CONUS RELIES MORE HEAVILY ON THE 5-TOOL CON FOR
PRECIPITATION THAN FOR TEMPERATURE, BECAUSE THE PRECIPITATION SIGNAL IS
GENERALLY LESS WELL DEFINED IN TIME AND SPACE COMPARED WITH THAT OF
TEMPERATURE, MAKING THE RELATIVE CONTRIBUTIONS OF THE TOOLS IMPOSSIBLE TO
BALANCE SUBJECTIVELY. THE CON IS THE PRIMAR INPUT FOR ALL LEADS.
PROGNOSTIC DISCUSSION OF OUTLOOKS - JJA 2008 TO JJA 2009
TEMPERATURE:
THE TEMPERATURE OUTLOOK FOR JJA 2008 CALLS FOR ABOVE NORMAL TEMPERATURES IN
SOUTHWESTERN SECTIONS OF ALASKA, BASED ON OCN, CCA, SMLR. SUB-NORMAL
TEMPERATURES ARE EXPECTED IN SECTIONS OF THE FAR NORTHWEST, DUE TO COOL SST
ANOMALIE NEARBY. SUB-NORMAL TEMPERATURES ARE ALSO CALLED FOR FROM IOWA
SOUTHEASTWARD THROUGH THE TENNESSEE VALLEY TO GEORGIA AND NORTHERN FLORIDA,
BASED ON THE ECCA, SMLR, CCA, CFS (AS COMBINED IN THE CON), THE CAS AND THE
SCRIPPS DYNAMICAL MODEL. ABOVE NORMAL TEMPERATURES ARE EXPECTED FOR THE
SOUTHWEST, BASED ON NEARLY ALL TOOLS, AND IN THE NORTHEAST, BASED ON THE CON
AND THE IRI. SUB-NORMAL TEMPERATURES ARE EXPECTED ALONG SECTIONS OF THE
IMMEDIATE WEST COAST THROUGH SON, DUE TO COOL SST ANOMALIES, THE CON AND THE
IRI MODEL. ELSEWHERE, THE FORECAST CALLS FOR EQUAL CHANCES (EC) OF ABOVE, NEAR
AND BELOW AVERAGE TEMPERATURES.
PRECIPITATION:
ABOVE-MEDIAN PRECIPITATION IS CALLED FOR IN ALASKA FROM JJA THROUGH ASO 2008
DUE MAINLY TO THE SMLR. SUB-MEDIAN RAINFALL IS EXPECTED IN SECTIONS OF THE
NORTHWEST FROM JJA THROUGH ASO, WHILE ABOVE-MEDIAN RAINFALL IS PREDICTED FOR
SECTIONS OF THE NORTHEAST AND THE SOUTHEAST. THERE IS VIRTUALLY NO COHERENT
PRECIPITATION SIGNAL FOR SON AND OND. THE CON INDICATES A TENDENCY FOR
ABOVE-MEDIAN PRECIPITATION FROM THE OHIO VALLEY TO NEW YORK, AND SUB-MEDIAN
PRECIPITATION FOR SECTIONS OF THE SOUTHEAST FROM NDJ-JFM. RELATIVE DRYNESS IS
PREDICTED IN SECTIONS OF THE NORTHWEST AND THE SOUTHEAST FROM DJF-MAM. SMALL,
BUT CONSISTENT SIGNALS FOR BELOW-MEDIAN PRECIPITATION IN THE INTER-MOUNTAIN
WEST AND SECTIONS OF THE NORTHEAST AND TEXAS ARE PREDICTED FOR AMJ-JJA 2009.
ONCE AGAIN, THE PRIMARY TOOL FOR THE PRECIPITATION FORECAST IS THE CON.
NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES).
FORECASTER: ED O'LENIC
FOR A DESCRIPTION OF OF THE STANDARD FORECAST TOOLS - THEIR SKILL- AND THE
FORECAST FORMAT PLEASE SEE OUR WEB PAGE AT
HTTP:/WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/PREDICTIONS/90DAY/DISC.HTML
(USE LOWER CASE LETTERS)
INFORMATION ON THE FORMATION OF SKILL OF THE CAS FORECASTS MAY BE FOUND AT:
HTTP://WWW.CPC.NCEP.NOAA.GOV/SOILMST/FORECASTS.HTML (USE LOWERCASE LETTERS)
NOTES - THESE CLIMATE OUTLOOKS ARE INTENDED FOR USE PRIOR TO THE START OF THEIR
VALID PERIOD. WITHIN ANY GIVEN VALID PERIOD OBSERVATIONS AND SHORT AND MEDIUM
RANGE FORECASTS SHOULD BE CONSULTED.
THIS SET OF OUTLOOKS WILL BE SUPERSEDED BY THE ISSUANCE OF THE NEW SET NEXT
MONTH ON THU JUN 19 2008
1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001
FORECAST RELEASE.
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