320
FXUS05 KWBC 191249
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EDT THU JUN 19 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 MAY AND EARLY JUNE 2008, AS REFLECTED BY
CHANGES IN SEA SURFACE TEMPERATURES (SSTS) ACROSS THE EQUATORIAL PACIFIC OCEAN.
SSTS IN THE EAST-CENTRAL PACIFIC OCEAN REMAIN BELOW NORMAL AND ARE
SUFFICIENTLY COOL TO MAINTAIN THE PERSISTENT ATMOSPHERIC ANOMALIES ASSOCIATED
WITH LA NINA. HOWEVER SSTS ALONG THE EQUATOR ARE NOW ABOVE NORMAL FROM ABOUT
130W TO NEAR THE SOUTH AMERICAN COAST, AND THE BELOW NORMAL WATER TEMPERATURES
IN THE CENTRAL PACIFIC ARE CONFINED TO A SHALLOW LAYER NEAR THE SURFACE.
TOGETHER, THESE OBSERVATION SUGGEST THAT THE ENSO STATE IS CURRENTLY IN
TRANSITION FROM LA NINA TO NEUTRAL CONDITIONS.
THERE CONTINUES TO BE CONSIDERABLE DISAGREEMENT IN THE FORECAST FOR NINO 3.4
SST ANOMALIES IN THE NEXT FEW MONTHS. THE NCEP CFS MODEL PREDICTS THAT NINO
3.4 SST ANOMALIES WILL BECOME SLIGHTLY POSITIVE BY LATE SUMMER, FOLLOWED BY A
GRADUAL RETURN TO NEAR ZERO ANOMALIES BY THE END OF THE YEAR WHILE THE
STATISTICAL MODELS FOR SST RUN AT NCEP HOLD NINO 3.4 SST ANOMALIES STEADY AT
AROUND -0.5 C. FOR THE NEXT FEW MONTHS. A CONSENSUS OF THESE FORECASTS
SUGGESTS NEUTRAL ENSO CONDITIONS, WITH NINO 3.4 SST ANOMALIES OF AROUND -0.3 C
IN THE NEXT FEW SEASONS.
THE TEMPERATURE OUTLOOK FOR JAS 2008 CALLS FOR ABOVE NORMAL TEMPERATURES IN THE
SOUTHWESTERN U.S., EXTENDING NORTHWARD TO INCLUDE MUCH OF THE GREAT BASIN AND
INTERIOR CALIFORNIA. THIS AREA REFLECTS RECENT TEMPERATURE TRENDS, WITH
ADDITIONAL SUPPORT FROM FORECASTS FROM STATISTICAL TOOLS. DRY SOIL MOISTURE
CONDITIONS IN PARTS OF CALIFORNIA CONTRIBUTED TO ANTICIPATED ABOVE NORMAL
TEMPERATURES IN INTERIOR CALIFORNIA. ABOVE NORMAL TEMPERATURES ARE ALSO
EXPECTED IN THE NORTHEASTERN U.S. BASED ON THE CON TOOL. BELOW NORMAL SSTS
ALONG THE PACIFIC COAST OF NORTH AMERICA WILL ELEVATE CHANCES OF BELOW NORMAL
TEMPERATURES IN ADJACENT COASTAL AREAS FROM JAS THROUGH SON.
ABOVE MEDIAN PRECIPITATION IS CALLED FOR IN SOUTHERN ALASKA FROM JAS THROUGH
SON 2008. BELOW MEDIAN RAINFALL AMOUNTS ARE EXPECTED IN PARTS OF THE PACIFIC
NORTHWEST FROM JJA THROUGH ASO. ABOVE MEDIAN RAINFALL IS PREDICTED FOR
SECTIONS OF THE NORTHEAST AND THE SOUTHEAST FROM JAS TO SON.
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 MAY 2008, AS REFLECTED BY CHANGES IN SEA
SURFACE TEMPERATURES (SSTS) ACROSS THE EQUATORIAL PACIFIC OCEAN. SSTS IN THE
EAST-CENTRAL PACIFIC OCEAN REMAIN BELOW NORMAL AND ARE SUFFICIENTLY COOL TO
MAINTAIN THE PERSISTENT ATMOSPHERIC ANOMALIES ASSOCIATED WITH LA NINA.
CONVECTION CONTINUES TO BE SUPRESSED IN THE CENTRAL EQUATORIAL PACIFIC OCEAN,
WITH ENHANCED LOW LEVEL EASTERLY WINDS AND ENHANCED UPPER LEVEL WESTERLIES OVER
THE TROPICAL PACIFIC REGION. SSTS ALONG THE EQUATOR ARE NOW ABOVE NORMAL FROM
ABOUT 130W TO NEAR THE SOUTH AMERICAN COAST. SST ANOMALIES IN EARLY JUNE ARE
-.6 , -.4, +.2 AND +.5 DEGREES C IN THE NINO 4, NINO 3.4, NINO 3, AND NINO 1+2
REGIONS, RESPECTIVELY. WATER TEMPERATURES IN THE UPPER 300 M OF THE CENTRAL
PACIFIC OCEAN NEAR THE EQUATOR HAVE INCREASED DRAMATICALLY SINCE FEBRUARY AND
ARE NOW SLIGHTLY ABOVE NORMAL, SO BELOW NORMAL OCEAN TEMPERATURES ARE NOW
CONFINED TO A SHALLOW LAYER NEAR THE SURFACE. TOGETHER, THESE OBSERVATION
SUGGEST THAT THE ENSO STATE IS CURRENTLY IN TRANSITION FROM LA NINA TO ENSO
NEUTRAL CONDITIONS.
PROGNOSTIC DISCUSSION OF SST FORECASTS
MOST RECENT DYNAMICAL AND STATISTICAL SST FORECASTS FOR THE NINO 3.4 REGION
INDICATE THAT THE LATE SUMMER AND EARLY FALL SSTS WILL RANGE BETWEEN -0.5 AND
+0.5 C, INDICATING ENSO-NEUTRAL CONDITIONS. THE NCEP CFS CONTINUES TO BE ONE
OF THE WARMEST MODELS, PREDICTING NINO 3.4 ANOMALIES OF +0.5 C BY THE AUGUST,
HOWEVER SST ANOMALIES PREDICTED BY THE CFS GRADUALLY DECREASE PAST AUGUST AND
REACH NEAR ZERO ANOMALIES BY DECEMBER. STATISTICAL SST FORECASTS RUN AT NCEP
KEEP NINO 3.4 SSTS STEADY AT AROUND -0.5 C THROUGH THE END OF THE YEAR. A
CONSOLIDATION OF THESE FORECASTS SUGGESTS THAT NINO 3.4 SST ANOMALIES MAY PEAK
IN LATE SUMMER AT AROUND -0.3 C, THEN DECREASE TO AROUND -0.6 BY NDJ BEFORE
RETURNING TO NEAR ZERO BY AMJ 2009. TAKING THE SPREAD IN MODEL PREDICTIONS
INTO ACCOUNT, AND CONSIDERING CURRENT OBSERVATIONS AND SST FORECASTS FROM
MODELS RUN AT OTHER CENTERS THAT ARE NOT INCLUDED IN THE CONSOLIDATION
FORECAST, ENSO NEUTRAL CONDITIONS ARE EXPECTED WITH NINO 3.4 SSTS EXPECTED TO
BE WITHIN 0.5 DEGREES OF NORMAL THROUGH EARLY SPRING 2009.
ATMOSPHERIC CONDITIONS RELATED TO LA NINA OFTEN PERSIST FOR A FEW MONTHS AFTER
SSTS RETURN TO ENSO-NEUTRAL CONDITIONS. THUS RESIDUAL LA NINA IMPACTS MAY HAVE
A SLIGHT POSITIVE IMPACT ON HURRICANE ACTIVITY IN THE ATLANTIC AND SLIGHTLY
SUPPRESS HURRICANE ACTIVITY IN THE EASTERN PACIFIC IN THE UPCOMMING SEASON,
HOWEVER GIVEN THAT ENSO IS EXPECTED TO TRANSITION TO NEUTRAL CONDITIONS BY LATE
SUMMER, ITS INFLUENCE IS NOT EXPECTED TO BE STRONG. THE CURRENT SST FORECAST
REMAINS CONSISTENT WITH THOSE AVAILABLE AT THE TIME THE NOAA HURRICANE OUTLOOK
WAS RELEASED IN EARLY JUNE (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 TOOL IS NOT AVAILABLE
FOR ALASKA, SO THE FORECAST THERE IS BASED MOSTLY ON OCN, CCA, SMLR AND THE
CFS. ENSO IS NOT EXPECTED TO HAVE AN IMPACT ON THIS SET OF FORECASTS, ASIDE
FROM THE RESIDUAL EFFECTS OF THIS PAST WINTERS LA NINA, WHICH INCLUDE THE
INITIAL SOIL MOISTURE PATTERN OVER THE U.S., AND BELOW NORMAL SSTS IN PACIFIC
ADJACENT NORTH AMERICA.
THE TEMPERATURE AND PRECIPITATION FORECAST FOR ALL LEADS IS BASED ON THE 5-TOOL
CON FORECAST. 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 SOIL
MOISTURE IN THE CENTRAL U.S., AND DRY SOIL MOISTURE CONDITIONS IN CALIFORNIA.
THE CFS DROPS OUT OF THE CON AFTER LEAD 6 (DJF), AND ONLY STATISTICAL TOOLS
(OCN, CCA, SMLR, ECCA) CONTRIBUTE TO CON AFTER THAT.
PROGNOSTIC DISCUSSION OF OUTLOOKS - JAS 2008 TO JAS 2009
TEMPERATURE:
THE OUTLOOK FOR JAS 2008 CALLS FOR ABOVE NORMAL TEMPERATURES IN THE
SOUTHWESTERN U.S., EXTENDING NORTHWARD TO INCLUDE MUCH OF THE GREAT BASIN AND
INTERIOR CALIFORNIA. THIS AREA REFLECTS OCN, CCA, AND THE IRI MULTI-MODEL
ENSEMBLE FORECASTS. DRY SOIL MOISTURE CONDITIONS IN PARTS OF CALIFORNIA
CONTRIBUTED TO ANTICIPATED ABOVE NORMAL TEMPERATURES IN INTERIOR CALIFORNIA.
ABOVE NORMAL TEMPERATURES ARE ALSO EXPECTED IN THE NORTHEASTERN U.S. BASED ON
THE CONSOLIDATION FORECAST. BELOW NORMAL SSTS IN THE ALONG THE PACIFIC COAST
OF NORTH AMERICA WILL ELEVATE CHANCES OF BELOW NORMAL TEMPERATURES IN ADJACENT
COASTAL AREAS FROM JAS THROUGH SON.
THE TEMPERATURE FORECASTS FOR OND 2008 AND BEYOND PRIMARILY REFLECT TEMPERATURE
TRENDS AND INDICATES THE AREA OF ENHANCED CHANCES OF ABOVE NORMAL TEMPERATURES
WILL GRADUALLY EXPAND TO INCLUDE MOST OF THE COUNTRY BY DJF 2008-2009 EXCEPT
FOR THE AREAS IN THE FAR WEST. SIGNALS FOR ENHANCED CHANCES OF ABOVE NORMAL
TEMPERATURES WEAKEN IN THE TRANSITION SEASONS, SO THE AREA OF ABOVE NORMAL
DIMINISHES WITH LEAD TIME IN THE SPRING, REACHING A MINIMUM IN MAM WHEN ONLY
THE SOUTHWESTERN U.S. AND THE GREAT BASIN SHOW ELEVATED CHANCES OF ABOVE NORMAL
TEMPERATURES. THE AREA OF EXPECTED ABOVE NORMAL TEMPERATURES THEN GRADUALLY
EXPANDS AS THE SUMMER SEASON APPROACHES. OCN INDICATES ELEVATED CHANCES OF
ABOVE NORMAL TEMPERATURES WILL COVER MUCH OF ALASKA FROM AMJ TO JAS 2009.
PRECIPITATION:
ABOVE MEDIAN PRECIPITATION IS CALLED FOR IN SOUTHERN ALASKA FROM JAS THROUGH
SON 2008 DUE MANLY TO SMLR. BELOW MEDIAN RAINFALL AMOUNTS ARE EXPECTED IN
SECTIONS OF THE NORTHWESTERN CONUS FROM JJA THROUGH ASO FROM THE CCA OCN.
ABOVE MEDIAN RAINFALL IS PREDICTED FOR SECTIONS OF THE NORTHEAST AND THE
SOUTHEAST FORM JAS TO SON DUE MOSTLY TO SMLR COMBINED WITH WEAK TRENDS. THERE
IS A TENDENCY FOR ABOVE MEDIAN PRECIPITATION FROM THE OHIO VALLEY TO NEW YORK,
FROM NDJ 2008/2009 TO JFM 2009, DUE MAINLY TO WEAK SIGNALS FROM OCN AND THE
CFS. BELOW MEDIAN PRECIPITATION AMOUNTS ARE EXPECTED FOR PARTS OF THE
SOUTHEASTERN CONUS FROM NDJ 2008-2009 TO MAM 2009 WITH ALL TOOLS CONTRIBUTING.
THERE ARE CONSISTENT SIGNALS AMONG THE TOOLS FOR BELOW-MEDIAN PRECIPITATION IN
THE NORTHERN ROCKIES FROM JFM-FMA 2009. AN AREA OF EXPECTED BELOW MEDIAN
PRECIPITATION AMOUNTS FORECAST FOR PARTS OF THE CENTRAL ROCKIES IN AMJ 2009 IS
BASED ON THE CON TOOL. THIS AREA GRADUALLY SHIFTS TOWARD THE PACIFIC NORTHWEST
BY JAS 2009 WHERE IT IS SUPPORTED BY STRONG INDICATIONS FROM BOTH CCA AND OCN.
THERE ARE SOME WEAK INDICATIONS FOR ABOVE MEDIAN PRECIPITATION IN PARTS OF
TEXAS FROM MJJ TO JJA 2009, AND IN NEW ENGLAND FROM AMJ TO JAS 2009.
NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES).
FORECASTER: DAVID UNGER
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 JUL 17 2008
1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001
FORECAST RELEASE.
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