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PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830 AM EDT THU JUN 21 2018
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS
THE JULY-AUGUST-SEPTEMBER (JAS) 2018 TEMPERATURE OUTLOOK FAVORS ABOVE-NORMAL
TEMPERATURES ACROSS A MAJORITY OF THE FORECAST DOMAIN, ALTHOUGH
EQUAL CHANCES
OF BELOW-, NEAR-, OR ABOVE-NORMAL TEMPERATURES ARE FORECAST ACROSS THE NORTHERN
GREAT PLAINS AND UPPER MISSISSIPPI VALLEY. THE HIGHEST PROBABILITIES FOR
ABOVE-NORMAL TEMPERATURES ARE FORECAST ACROSS PARTS OF THE GREAT BASIN AND
PACIFIC NORTHWEST. THE JAS 2018 PRECIPITATION OUTLOOK FEATURES ENHANCED ODDS
FOR ABOVE NORMAL PRECIPITATION ACROSS THE MID-ATLANTIC AND EXTENDING FROM
SOUTHERN CALIFORNIA AND THE DESERT SOUTHWEST NORTHEAST TO THE GREAT BASIN AND
CENTRAL ROCKIES. INCREASED CHANCES FOR ABOVE NORMAL PRECIPITATION ARE ALSO
FORECAST ACROSS MAINLAND ALASKA AND THE ALEUTIANS. BELOW-NORMAL PRECIPITATION
IS FAVORED ACROSS THE WESTERN GULF COAST, LOWER MISSISSIPPI VALLEY, AND PACIFIC
NORTHWEST.
DURING THE FALL AND WINTER 2018-19, THE TEMPERATURE AND PRECIPITATION OUTLOOKS
ARE CONSISTENT WITH INCREASING ODDS OF
EL NINO DEVELOPMENT AND ITS TYPICAL
INFLUENCES. CHANCES FOR ABOVE NORMAL PRECIPITATION HAVE INCREASED ACROSS THE
SOUTHERN TIER OF THE CONUS, COMPARED TO PREVIOUS OUTLOOKS. ODDS FOR ABOVE
NORMAL TEMPERATURES CONTINUE TO INCREASE DURING THE WINTER 2018-19, FROM THE
PACIFIC NORTHWEST EAST TO THE NORTHERN GREAT PLAINS AND UPPER MISSISSIPPI
VALLEY.
EQUAL CHANCES (EC) ARE FORECAST IN AREAS WHERE THE LIKELIHOOD OF SEASONAL MEAN
TEMPERATURES OR SEASONAL ACCUMULATED PRECIPITATION AMOUNTS ARE EXPECTED TO BE
SIMILAR TO CLIMATOLOGICAL PROBABILITIES.
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
OCEANIC AND ATMOSPHERIC OBSERVATIONS ACROSS THE EQUATORIAL PACIFIC INDICATE
ENSO-NEUTRAL CONDITIONS PERSISTED THROUGH MAY. THE OBSERVED WEEKLY SSTS,
CENTERED ON JUNE 13, FEATURE POSITIVE
ANOMALIES OF MORE THAN 0.5 DEGREE C FROM
140-100 DEGREES W AND ALSO WEST OF THE DATE LINE. POSITIVE SUBSURFACE
TEMPERATURE
ANOMALIES (AVERAGED ACROSS 180-100 DEGREES W) CONTINUED TO
INCREASE, DUE TO ANOTHER DOWNWELLING OCEANIC KELVIN WAVE.
OUTGOING LONGWAVE RADIATION
(OLR) ANOMALIES INDICATED SUPPRESSED
CONVECTION
FROM PAPUA NEW GUINEA EAST TO THE CENTRAL EQUATORIAL PACIFIC OCEAN FROM MAY 18
TO JUNE 12. THE WIND
ANOMALIES AT THE LOWER AND UPPER-LEVELS WERE NEAR AVERAGE
ACROSS THE EQUATORIAL PACIFIC. THESE ATMOSPHERIC INDICATORS ARE CONSISTENT WITH
ENSO NEUTRAL CONDITIONS.
PROGNOSTIC DISCUSSION OF
SST FORECASTS
THE
CPC SST CONSOLIDATION (CON) FOR THE NINO 3.4 REGION INDICATES AN INCREASE
IN
ANOMALIES TO +0.5 DEGREES C BY SON WITH POSITIVE
ANOMALIES PEAKING CLOSER TO
1.0 DEGREES C DURING NDJ AND DJF 2018-19. THE
SST CONSTRUCTED
ANALOG AND MARKOV
MODEL INDICATE PEAK
ANOMALY VALUES GREATER THAN 1.0 C THIS UPCOMING WINTER. THE
CPC/IRI CONSENSUS FORECAST FAVORS THE ONSET OF
EL NINO DURING THE NORTHERN
HEMISPHERE FALL WITH PROBABILITIES OF
EL NINO ABOVE 60 PERCENT FROM NDJ 2018-19
JFM 2019.
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
THE INCREASING LIKELIHOOD OF
EL NINO DEVELOPMENT CONTINUES TO PLAY A MAJOR
FACTOR IN THE FALL AND WINTER 2018-19 OUTLOOKS. TOOLS USED FOR THE SEASONAL
OUTLOOKS INCLUDED
DYNAMICAL MODEL FORECAST GUIDANCE SUCH AS THE NORTH AMERICAN
MULTI-MODEL ENSEMBLE (NMME), THE
ENSO-
OCN STATISTICAL MODEL, THE
SST
CONSTRUCTED
ANALOG MODEL, AND
EL NINO COMPOSITES. A RELATIVELY NEW TOOL IN OUR
SUITE IS THE CBAM TOOL, OR CALIBRATION, BRIDGING, AND MERGING FORECAST TOOL.
THIS USES A BAYESIAN APPROACH TO THE NMME MODEL CONSOLIDATION AS WELL AS A
HYBRIDIZATION WHEREIN EACH CONSTITUENT MODEL'S NINO 3.4 FORECAST IS 'BRIDGED'
TO THE PREDICTAND VIA LINEAR REGRESSION. THE OUTLOOKS DURING THE 2019 WARM
SEASON WERE BASED PRIMARILY ON DECADAL
TRENDS.
PROGNOSTIC DISCUSSION OF OUTLOOKS - JAS 2018 TO JAS 2019
TEMPERATURE
ABOVE-NORMAL TEMPERATURES ARE FAVORED FOR MUCH OF THE
CONUS AND ALASKA DURING
JAS WITH THE HIGHEST PROBABILITIES FORECAST ACROSS THE GREAT BASIN AND PACIFIC
NORTHWEST, BASED ON EXCELLENT AGREEMENT AMONG TOOLS INCLUDING A STRONG DECADAL
SIGNAL. PROBABILITIES FOR ABOVE NORMAL TEMPERATURES WERE REDUCED ACROSS THE
SOUTHWEST FROM THE PREVIOUS OUTLOOK DUE TO INCREASING FORECAST CONFIDENCE IN A
WETTER PATTERN. ABOVE NORMAL TEMPERATURES ARE FAVORED TO INCLUDE MORE OF THE
SOUTH-CENTRAL U.S. DURING JAS, COMPARED TO LAST MONTH, WITH THE CONSIDERATION
OF LOW SOIL MOISTURE TO START THE OUTLOOK PERIOD ACROSS THE OZARKS REGION, A
DRIER
TREND IN THE SEASONAL TOOLS, AND CONSISTENCY WITH THE JULY TEMPERATURE
OUTLOOK. ALSO, THE IMME INDICATES POSITIVE TEMPERATURES
ANOMALIES FOR THE
MIDDLE MISSISSIPPI VALLEY DURING THIS TIME PERIOD.
EQUAL CHANCES FOR BELOW-,
NEAR-, OR ABOVE-NORMAL TEMPERATURES ARE FORECAST FOR THE NORTHERN GREAT PLAINS
AND UPPER MISSISSIPPI VALLEY WHERE FORECAST CONFIDENCE IS LOWEST.
THE INCREASING CHANCES FOR
EL NINO DEVELOPMENT WERE A FACTOR IN THE TEMPERATURE
OUTLOOK, BEGINNING IN THE FALL AND BECOMING MORE PROMINENT DURING THE WINTER
2018-19. BASED ON
EL NINO COMPOSITES, PROBABILITIES FOR ABOVE NORMAL
TEMPERATURES WERE INCREASED ACROSS MUCH OF MAINLAND ALASKA AND ALONG THE
NORTHERN TIER OF THE
CONUS WITH A DECREASE IN THE COVERAGE OF ABOVE NORMAL
TEMPERATURES THROUGHOUT THE SOUTHERN TIER OF THE
CONUS. AN EXPECTED LACK OF SEA
ICE ELEVATES CHANCES FOR ABOVE NORMAL TEMPERATURES ACROSS NORTHERN ALASKA
DURING THE FALL SEASON. THE TEMPERATURE OUTLOOK AT THE LONGER LEAD TIMES IS
BASED LARGELY ON
TRENDS.
PRECIPITATION
THE PRECIPITATION OUTLOOKS ARE BASED ON THE LATEST
DYNAMICAL MODEL GUIDANCE,
THROUGH NDJ, ALONG WITH THE TYPICAL INFLUENCES FROM
EL NINO DURING THE FALL AND
WINTER 2018-19. COMPARED TO THE PREVIOUS OUTLOOK FOR JAS, ODDS FOR ABOVE NORMAL
PRECIPITATION WERE EXPANDED TO INCLUDE MORE OF THE DESERT SOUTHWEST AND
SOUTHERN CALIFORNIA. THIS IS CONSISTENT WITH THE NMME AND POTENTIAL RAINFALL
ASSOCIATED WITH EAST PACIFIC TROPICAL CYCLONES, WHICH ARE MORE LIKELY TO AFFECT
THESE AREAS DURING A DEVELOPING
EL NINO. THE LATEST PRECIPITATION TOOLS,
INDICATE LITTLE TO NO SUPPORT FOR THE INCREASED CHANCES OF BELOW NORMAL
PRECIPITATION FOR FLORIDA, SO THAT WAS REMOVED FROM THE PREVIOUS OUTLOOK. THE
NMME INDICATES RELATIVELY HIGH ODDS FOR BELOW NORMAL PRECIPITATION EXTENDING
FROM THE CARIBBEAN REGION WEST TO THE GULF OF MEXICO AND MUCH OF TEXAS AND THE
LOWER MISSISSIPPI VALLEY. THEREFORE, INCREASED CHANCES FOR BELOW NORMAL
PRECIPITATION WERE INTRODUCED TO PARTS OF TEXAS AND THE LOWER MISSISSIPPI
VALLEY FOR JAS. PRECIPITATION TOOLS REMAINED CONSISTENT FEATURING ENHANCED ODDS
FOR ABOVE (BELOW) NORMAL PRECIPITATION ACROSS PARTS OF THE EASTERN U.S.
(PACIFIC NORTHWEST) AND A RELATIVELY WET PATTERN FOR MUCH OF ALASKA.
EL NINO PRECIPITATION COMPOSITES WERE RELIED UPON IN THE OUTLOOKS DURING THE
FALL AND WINTER SEASONS WHEN ABOVE-NORMAL PRECIPITATION BECOMES MORE LIKELY
ACROSS THE SOUTHWEST, SOUTHERN GREAT PLAINS, GULF COAST STATES, AND SOUTHEAST.
THE STRONGEST WET
SIGNAL EXISTS ACROSS FLORIDA DURING NDJ AND DJF, WHILE A DRY
SIGNAL EXISTS FROM THE GREAT LAKES SOUTH TO THE OHIO VALLEY DURING JFM AND FMA.
THE PRECIPITATION OUTLOOK ACROSS ALASKA DURING THE FALL AND WINTER IS
CONSISTENT WITH THE
SST CONSTRUCTED
ANALOG.
AT THE LONGER LEADS, MJJ THROUGH JAS 2019, THE TILT IN THE ODDS TOWARDS ABOVE
NORMAL PRECIPITATION ACROSS PARTS OF THE CENTRAL AND EASTERN U.S. IS CONSISTENT
WITH
TRENDS. ALSO, THE FAVORED AREA FOR BELOW-MEDIAN PRECIPITATION ACROSS THE
NORTHWESTERN
CONUS DURING THESE OUTLOOK PERIODS IS RELATED TO
TRENDS.
FORECASTER: BRAD PUGH
THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1981 AND 2010, FOLLOWING
THE WORLD METEROLOGICAL ORGANIZATION CONVENTION OF USING THE MOST RECENT 3
COMPLETE DECADES AS THE CLIMATIC REFERENCE PERIOD. THE PROBABILITY
ANOMALIES
FOR TEMPERATURE AND PRECIPITATION BASED ON THESE NEW NORMALS BETTER REPRESENT
SHORTER TERM CLIMATIC
ANOMALIES THAN THE FORECASTS BASED ON OLDER NORMALS.
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/LONG_RANGE/TOOLS.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/PRODUCTS/SOILMST_MONITORING/US/OUTLOOK/OUTLOOK.SHTM
L
(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 JUL 19 2018
1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE W
