127
FXUS05 KWBC 171231
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EDT THU JUL 17 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.
THE EQUATORIAL PACIFIC RETURNED TO ENSO NEUTRAL CONDITIONS DURING JUNE 2008, AS
SEA SURFACE TEMPERATURES (SSTS) ACROSS THE CENTRAL EQUATORIAL PACIFIC OCEAN
WARMED TO NEAR THE CLIMATOLOGICAL AVERAGE. AS WITH PREVIOUS TRANSITIONS FROM A
LA NINA TO AN ENSO NEUTRAL STATE, A WEAK LA NINA ATMOSPHERIC CIRCULATION
CONTINUES OVER THE TROPICAL PACIFIC OCEAN. SSTS IN THE EASTERN EQUATORIAL
PACIFIC HAVE BEEN WARMING AND IN THE LAST SEVERAL WEEKS, ABOVE NORMAL SSTS HAVE
EXTENDED WESTWARD FROM NEAR THE SOUTH AMERICAN COAST TO CURRENTLY AROUND 140 W
LONGITUDE. BELOW NORMAL SUBSURFACE WATER TEMPERATURES IN THE EQUATORIAL PACIFIC
HAVE DIMINISHED IN AREA, DEPTH AND MAGNITUDE. THESE OBSERVATIONS SUGGEST THAT
THE ENSO STATE HAS TRANSITIONED FROM LA NINA TO NEUTRAL CONDITIONS.
THERE IS CONSIDERABLE DISAGREEMENT IN THE FORECAST FOR NINO 3.4 SST ANOMALIES
IN THE NEXT FEW MONTHS. THE NCEP CFS MODEL FORECASTS NINO 3.4 SST ANOMALIES TO
BECOME POSITIVE DURING THE LATE SUMMER, THEN GRADUALLY RETURN TO NEAR ZERO BY
THE END OF THE YEAR. IN CONTRAST, THE NCEP STATISTICAL MODELS EITHER MAINTAIN
NINO 3.4 SST ANOMALIES NEAR THE CURRENT VALUE AROUND -0.5 C OR COOL SSTS TO
AROUND -1 C TOWARDS THE END OF THE YEAR, AS IS THE CASE FOR THE CONSTRUCTED
ANALOG FORECAST. A CONSENSUS OF THE FORECASTS MAINTAINS ENSO NEUTRAL
CONDITIONS, WITH NINO 3.4 SST ANOMALIES NEAR OR SLIGHTLY BELOW ZERO INTO THE
BEGINNING OF NEXT YEAR.
THE TEMPERATURE OUTLOOK FOR ASO 2008 CALLS FOR ABOVE NORMAL TEMPERATURES ACROSS
MOST OF THE SOUTHERN THIRD OF THE U.S., INCLUDING PARTS OF SOUTHERN CALIFORNIA
EXTENDING EASTWARD TO INCLUDE MUCH OF THE SOUTHWEST, TEXAS AND THE GULF COAST
STATES. IN ADDITION, ABOVE NORMAL TEMPERATURES ARE EXPECTED FOR ASO 2008 IN THE
GREAT LAKES REGION AND NORTHEAST U.S. THESE EXPECTED AREAS OF ABOVE ARE DUE
PRIMARILY TO RECENT TEMPERATURE TRENDS AND FOLLOW CLOSELY THE RECENT OBJECTIVE
CONSOLIDATION FORECAST, WITH ADDITIONAL SUPPORT FROM THE STATISTICAL FORECAST
TOOLS AND PARTIAL SUPPORT FROM THE CFS FORECAST. INCREASED CHANCES OF BELOW
NORMAL TEMPERATURES ARE PREDICTED FOR ASO 2008 FOR THE PACIFIC COASTS OF
WASHINGTON AND OREGON AND THE SOUTH COAST OF ALASKA MAINLY DUE TO BELOW NORMAL
SSTS ALONG THE PACIFIC COAST OF NORTH AMERICA, WITH SOME SUPPORT FROM RECENT
TEMPERATURE TRENDS FOR THIS SEASON ALONG THE PACIFIC NORTHWEST COAST.
THERE IS AN ENHANCED LIKELIHOOD OF ABOVE MEDIAN PRECIPITATION FOR ASO 2008 FOR
THE NORTHEAST AND PARTS OF THE HIGH AND CENTRAL PLAINS AS INDICATED BY THE
OBJECTIVE CONSOLIDATION DUE SOMEWHAT TO RECENT TRENDS. THE INCREASED LIKELIHOOD
OF ABOVE MEDIAN RAINFALL FOR THE EASTERN GULF AND SOUTHERN ATLANTIC COASTS IS
DUE TO RECENT TRENDS RESULTING FROM GREATER THAN NORMAL CLIMATOLOGICAL TROPICAL
ACTIVITY. BELOW MEDIAN PRECIPITATION AMOUNTS EXPECTED FOR PARTS OF THE PACIFIC
NORTHWEST ARE FORECAST BY THE OBJECTIVE CONSOLIDATION DUE TO RECENT TRENDS.
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 CONDITIONS WERE REPLACED BY ENSO NEUTRAL CONDITIONS DURING JUNE 2008,
AS INDICATED BY SEA SURFACE TEMPERATURES (SSTS) ACROSS THE EQUATORIAL PACIFIC
OCEAN. SSTS IN THE EAST-CENTRAL PACIFIC OCEAN ARE NOW LESS THAN ONE HALF OF
ONE DEGREE CELSIUS BELOW ZERO. CONVECTION CONTINUES TO BE SLIGHTLY SUPPRESSED
IN THE CENTRAL EQUATORIAL PACIFIC OCEAN, WHILE LOW LEVEL EASTERLY WINDS AND
UPPER LEVEL WESTERLIES REMAIN ENHANCED OVER THE TROPICAL PACIFIC REGION,
REFLECTING THE RESIDUAL INFLUENCE OF THIS YEARS LA NINA. SSTS ALONG THE EQUATOR
ARE ABOVE NORMAL FROM ABOUT 140 W TO NEAR THE SOUTH AMERICAN COAST. SST
ANOMALIES IN EARLY JULY WERE VERY NEAR ZERO IN THE NINO 3.4 REGION, FROM 170 W
TO 120 W LONGITUDE AND 5 S TO 5 N LATITUDE. WATER TEMPERATURES IN THE UPPER 300
M OF THE EQUATORIAL PACIFIC HAVE INCREASED SUBSTANTIALLY SINCE FEBRUARY AND ARE
NOW ABOVE NORMAL FOR MUCH OF THE BASIN. THE CURRENT STATE OF THE TROPICAL
PACIFIC OCEAN AND ATMOSPHERE IS REPRESENTATIVE OF ENSO NEUTRAL CONDITIONS
FOLLOWING A LA NINA EVENT.
PROGNOSTIC DISCUSSION OF SST FORECASTS
MOST DYNAMICAL AND STATISTICAL SST FORECASTS FOR THE NINO 3.4 REGION PREDICT
SSTS IN THE RANGE BETWEEN -0.5 AND +0.5 C, INDICATING ENSO-NEUTRAL CONDITIONS,
THROUGH AUTUMN AND INTO NEXT YEAR. THE NCEP CFS OBTAINS ONE OF THE WARMER MODEL
SOLUTIONS WITH POSITIVE NINO 3.4 SST ANOMALIES BY AUGUST, FOLLOWED BY A GRADUAL
COOLING TO NEAR THE CURRENT NEGATIVE ANOMALY BY THE END OF THIS YEAR. NCEP
STATISTICAL SST FORECASTS AND SEVERAL OTHER MODELS MAINTAIN NEGATIVE NINO 3.4
SST ANOMALIES THROUGH 2008 INTO 2009. A CONSOLIDATION OF NCEP FORECASTS
SUGGESTS THAT NINO 3.4 SST ANOMALIES ARE MOST LIKELY TO REMAIN SLIGHTLY BELOW
ZERO THROUGH THE SPRING OF 2009. CONSIDERING CURRENT OBSERVATIONS AND SST
FORECASTS FROM STATISTICAL AND DYNAMICAL MODELS FROM NCEP AND FROM OTHER
CENTERS NOT INCLUDED IN THE CONSOLIDATION FORECAST, ENSO NEUTRAL CONDITIONS ARE
MOST LIKELY INTO EARLY NEXT YEAR WITH NINO 3.4 SST ANOMALIES EXPECTED TO BE
WITHIN ONE HALF OF ONE DEGREE CELSIUS OF ZERO.
ATMOSPHERIC CONDITIONS RELATED TO LA NINA OFTEN PERSIST FOR A FEW MONTHS AFTER
SSTS RETURN TO ENSO NEUTRAL CONDITIONS. RESIDUAL LA NINA ATMOSPHERIC CONDITIONS
MAY SLIGHTLY ENHANCE TROPICAL ACTIVITY IN THE ATLANTIC AND SLIGHTLY SUPPRESS
TROPICAL ACTIVITY IN THE EASTERN PACIFIC IN THE LATE SUMMER. IF THE ATMOSPHERE
FURTHER TRANSITIONS TO AN ENSO NEUTRAL STATE IN AUTUMN, THERE WOULD BE A
REDUCTION IN ANY IMPACT LATER IN THE HURRICANE SEASON. (SEE THE NOAA 2008
HURRICANE SEASON OUTLOOK DISCUSSION FOR MORE INFORMATION).
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 FORECAST IS NOT AVAILABLE
FOR ALASKA, SO THE FORECAST THERE IS BASED MOSTLY ON OCN, CCA, SMLR AND THE CFS
FORECASTS. THE ENSO STATE IS NOT EXPECTED TO HAVE AN IMPACT ON THE COMING
SEASONAL TEMPERATURE AND PRECIPITATION OUTLOOKS, WITH THE EXCEPTION OF RESIDUAL
INDIRECT EFFECTS OF THIS PAST WINTERS LA NINA, SUCH AS BELOW NORMAL SSTS ALONG
MUCH OF THE PACIFIC COAST OF NORTH AMERICA AND CURRENT SOIL MOISTURE
CONDITIONS. THE TEMPERATURE AND PRECIPITATION OUTLOOKS FROM ASO 2008 TO ASO
2009 CLOSELY FOLLOW THE CON FORECAST. COLD SST ANOMALIES IN THE EASTERN NORTH
PACIFIC ALONG THE WEST COAST OF NORTH AMERICA AND SOUTH COAST OF ALASKA IMPACT
ONLY THE ASO 2008 FORECAST. POSITIVE SOIL MOISTURE ANOMALIES IN THE CENTRAL
U.S. MAY IMPACT THE FIRST TWO THREE-MONTH SEASONS. THE CFS FORECAST IS ONLY
AVAILABLE AND PART OF THE CONSOLIDATION THROUGH JFM 2009.
PROGNOSTIC DISCUSSION OF OUTLOOKS - ASO 2008 TO ASO 2009
TEMPERATURE:
THE OUTLOOK FOR ASO 2008 INDICATES ENHANCED PROBABILITIES OF ABOVE NORMAL
TEMPERATURES FROM THE DESERT SOUTHWEST EXTENDING EASTWARD ACROSS TEXAS INTO THE
GULF COAST STATES TO THE ATLANTIC COAST OF GEORGIA AND FLORIDA, AND ALSO FOR
MOST OF THE NORTHEAST U.S. WITH CURRENT ENSO NEUTRAL CONDITIONS, EXPECTED ABOVE
NORMAL TEMPERATURES IN THE ASO 2008 SEASON ARE LARGELY DUE TO RECENT
TEMPERATURE TRENDS WITH SOME IMPACT OF DRIER THAN NORMAL CONDITIONS IN THE
SOUTHERN STATES. ABOVE NORMAL TEMPERATURES IN THE NORTHEASTERN U.S. ARE BASED
ON THE CONSOLIDATION FORECAST. BELOW NORMAL SSTS ALONG THE COASTS OF THE
PACIFIC NORTHWEST AND ALASKA INCREASE THE CHANCES OF BELOW NORMAL TEMPERATURES
IN ADJACENT COASTAL AREAS FOR ASO 2008 AND ARE SUPPORTED BY RECENT TEMPERATURE
TRENDS FOR THE PACIFIC NORTHWEST COAST.
TEMPERATURE FORECASTS AFTER ASO 2008 CLOSELY FOLLOW THE CONSOLIDATION FORECAST
DERIVED FROM THE CFS, OCN, CCA, ECCA AND SMLR. CURRENT ENSO NEUTRAL CONDITIONS
AND UNCERTAINTY IN THE FUTURE ENSO STATE MEAN THAT ALL SEASONAL TEMPERATURE
FORECASTS ARE LARGELY IMPACTED BY TEMPERATURE TRENDS. THE AREA OF ENHANCED
CHANCES OF ABOVE NORMAL TEMPERATURES EXPANDS TO INCLUDE MOST OF THE U.S. EXCEPT
FOR THE AREA WEST OF THE ROCKY MOUNTAINS FOR THE NDJ 2008-2009 THROUGH JFM 2009
SEASONS. THE AREAS OF GREATER THAN CLIMATOLOGICAL PROBABILITIES OF ABOVE NORMAL
TEMPERATURES DECREASE SUBSTANTIALLY THROUGH THE NEXT FEW THREE-MONTH PERIODS
BEFORE EXPANDING TO COVER MOST OF THE WESTERN U.S. IN NEXT SUMMERS JAS 2009
OUTLOOK. THE OUTLOOK FOR ASO 2009 LOOKS VERY SIMILAR TO THE FIRST SEASONAL
OUTLOOK FOR ASO 2008, DUE TO THE IMPORTANT INFLUENCE OF THE TEMPERATURE TRENDS.
THE OUTLOOKS FOR ALASKA ARE DERIVED MAINLY FROM THE RECENT TEMPERATURE TRENDS
WITH SUPPORT FROM THE CCA.
PRECIPITATION:
ELEVATED PROBABILITIES FOR ABOVE MEDIAN PRECIPITATION IN THE ASO AND SON 2008
OUTLOOKS FOR FLORIDA AND PARTS OF THE GULF AND ATLANTIC COASTS, THE NORTHEAST,
AND PARTS OF THE CENTRAL PLAINS ARE DERIVED FROM THE CONSOLIDATION FORECAST, AS
IS AN ELEVATED PROBABILITY FOR BELOW MEDIAN PRECIPITATION FOR PARTS OF THE
PACIFIC NORTHWEST IN ASO 2008. ALL OF THE PRECIPITATION FORECASTS FOR ASO AND
SON 2008 ARE SUPPORTED BY RECENT PRECIPITATION TRENDS. THE ABOVE MEDIAN
PRECIPITATION FORECAST FOR COASTAL AREAS IN THE SOUTHEAST INTO SON 2008 ARE
RELATED TO INCREASED TROPICAL ACTIVITY DURING RECENT YEARS AND ARE INCLUDED IN
THE JAS AND ASO 2009 OUTLOOKS. AREAS OF BELOW MEDIAN PRECIPITATION ARE FORECAST
FOR PARTS OF THE DESERT SOUTHWEST FROM OND 2008 TO DJF 2008-2009 AND FOR MUCH
OF THE SOUTHEAST FROM NDJ 2008-2009 TO MAM 2009 RESULTING FROM RECENT
PREDICTABLE PRECIPITATION TRENDS AS INDICATED BY THE CONSOLIDATION. AREAS OF
INCREASED PROBABILITY FOR ABOVE MEDIAN PRECIPITATION CENTERED AROUND THE TEXAS
PANHANDLE FROM DJF 2008-2009 TO FMA 2009 AND CENTERED AROUND NORTH DAKOTA FROM
AMJ TO MJJ 2009 ALSO REPRESENT RECENT TRENDS AS INDICATED BY THE CONSOLIDATION.
NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES).
FORECASTER: DAN COLLINS
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 AUG 21 2008
1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001
FORECAST RELEASE.
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page