PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300PM EDT WEDNESDAY APR 30 2014

30-DAY OUTLOOK DISCUSSION FOR MAY 2014

THE UPDATE TO THE MONTHLY OUTLOOK FOR MAY 2014 IS BASED ON SHORT- AND 
EXTENDED-RANGE FORECASTS FROM NUMERICAL WEATHER PREDICTION MODELS COMBINED WITH 
FACTORS THAT INFLUENCE CLIMATIC CONDITIONS SUCH AS THE ENSO STATE, SOIL 
MOISTURE AND SEA SURFACE TEMPERATURE (SST) ANOMALIES, AND CLIMATE MODEL 
PREDICTIONS FOR LATER IN THE MONTH.  

THE POSITIVE SST ANOMALIES IN THE EQUATORIAL PACIFIC OCEAN CONTINUE TO 
STRENGTHEN AND ARE ON TRACK WITH PREDICTIONS EARLIER IN APRIL. THE DEVELOPING 
EL NINO CONDITIONS WILL LIKELY SUPPRESS ANY MID-LATITUDE INFLUENCE OF A 
PREDICTED ACTIVE MJO EXPECTED IN EARLY MAY. TEMPERATURES PREDICTED FOR THE 
FIRST TWO WEEKS OF MAY ARE IN GENERAL AGREEMENT WITH THE PATTERN INDICATED ON 
THE PREVIOUS TEMPERATURE OUTLOOK FOR MAY MEAN TEMPERATURE ISSUED IN MID-APRIL.  
A MEAN FRONTAL BOUNDARY IS EXPECTED TO EXTEND FROM THE NORTHERN ROCKY MOUNTAINS 
TO THE OHIO VALLEY DURING THE FIRST HALF OF MAY.  THIS SUPPORTS THE ENHANCED 
CHANCES FOR BELOW-NORMAL TEMPERATURES FROM THE NORTHERN ROCKIES TO THE UPPER 
GREAT LAKES THAT WERE ALREADY INDICATED IN THE MAY OUTLOOK ISSUED EARLIER THIS 
MONTH. ABOVE-NORMAL TEMPERATURES EXPECTED TO THE SOUTH OF THE ANTICIPATED 
FRONTAL BOUNDARY STRENGTHEN THE SIGNAL FOR ABOVE-NORMAL TEMPERATURES FROM THE 
SOUTHERN GREAT PLAINS EASTWARD, RESULTING IN A SLIGHT EXPANSION OF THE AREA TO 
PARTS OF THE TENNESSEE RIVER VALLEY COMPARED TO THE EARLIER OUTLOOK.  
BELOW-NORMAL MEAN TEMPERATURES ARE EXPECTED IN THE FIRST HALF OF MAY FOR PARTS 
OF THE SOUTHWESTERN CONUS, HOWEVER, DRY SOIL MOISTURE CONDITIONS CONTINUE TO 
FAVOR ABOVE-NORMAL MEAN MONTHLY TEMPERATURES THERE, WITH LOWER CONFIDENCE THAN 
INDICATED IN THE MID-MONTH OUTLOOK.  

THERE ARE SUBSTANTIAL REVISIONS TO THE PRECIPITATION OUTLOOK FOR MAY ISSUED 
EARLIER THIS MONTH. AN EXPECTED ACTIVE MEAN FRONTAL BOUNDARY IN EARLY MAY 
ENHANCES CHANCES FOR ABOVE-MEDIAN PRECIPITATION AMOUNTS FROM THE NORTHERN 
ROCKIES TO THE OHIO RIVER VALLEY.  RAINY CONDITIONS IN EARLY MAY ARE EXPECTED 
FOR THE PACIFIC NORTHWEST, RESULTING IN A REVISION OF THE OUTLOOK THERE TO 
FAVOR ABOVE-MEDIAN MONTHLY PRECIPITATION AMOUNTS. A FRONTAL BOUNDARY IS 
EXPECTED TO PRODUCE SIGNIFICANT RAINFALL FOR FLORIDA IN THE FIRST FEW DAYS OF 
MAY, FURTHER ENHANCING THE CHANCES FOR ABOVE-MEDIAN MAY PRECIPITATION TOTALS 
OVER FLORIDA.  WEATHER CONDITIONS IN EARLY MAY IN ALASKA ARE IN ROUGH AGREEMENT 
WITH THE OUTLOOK FOR BOTH TEMPERATURE AND PRECIPITATION ISSUED IN MID-APRIL.

THE FOLLOWING DISCUSSION IS REPRODUCED FROM THE PROGNOSTIC DISCUSSION FOR THE 
MONTHLY OUTLOOK ISSUED IN MID-APRIL.

RECENT ATMOSPHERIC AND OCEANIC CONDITIONS IN THE TROPICAL PACIFIC BASIN 
CONTINUE TO INDICATE ENSO-NEUTRAL CONDITIONS IN EARLY APRIL. PACIFIC SEA 
SURFACE TEMPERATURE (SST) ANOMALIES HAVE BEEN STEADILY RISING ALONG EQUATOR 
THROUGHOUT MUCH OF THE CENTRAL AND EASTERN PACIFIC OCEAN AND ARE NOW ABOVE 
AVERAGE EXCEPT ALONG THE SOUTH AMERICAN COAST.  THERE ARE MANY INDICATORS THAT 
SUGGEST THAT THE ENSO STATE IS EVOLVING TOWARD EL NINO. THESE INCLUDE RECENTLY 
OBSERVED WESTERLY WIND ANOMALIES OVER MUCH OF THE CENTRAL AND WESTERN 
EQUATORIAL PACIFIC, A MARKED INCREASE IN SUB-SURFACE OCEANIC HEAT CONTENT IN 
THE PAST FEW WEEKS, AND A SLOW PROGRESSION OF ENHANCED CONVECTION ALONG THE 
EQUATOR TOWARD THE CENTRAL PACIFIC. IN ADDITION, THERE IS AN INCREASING 
CONSENSUS AMONG DYNAMICAL AND STATISTICAL FORECASTS THAT POSITIVE SST ANOMALIES 
IN THE ENSO CRITICAL REGIONS OF THE PACIFIC WILL REACH MINIMAL THRESHOLDS FOR 
EL NINO CONDITIONS BY SUMMER 2014. COMPOSITES OF PAST YEARS IN WHICH EL NINO 
CONDITIONS DEVELOPED IN SUMMER WERE CONSIDERED FOR THE MAY OUTLOOK.  

THE MAY OUTLOOK FOR MONTHLY MEAN TEMPERATURES INDICATES ELEVATED CHANCES FOR 
BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHERN ROCKIES, THE NORTHERN 
GREAT PLAINS, AND THE UPPER GREAT LAKES. THIS IS DUE TO INDICATIONS FROM THE 
BOTH SMLR AND CFS, AND IS CONSISTENT WITH TEMPERATURES FROM COMPOSITES OF PAST 
YEARS WITH DEVELOPING EL NINO CONDITIONS. ABOVE-NORMAL SOIL MOISTURE CONTENT IN 
THE NORTHERN ROCKIES MAY ALSO ENHANCE THE CHANCES FOR BELOW-NORMAL 
TEMPERATURES. THE CHANCES FOR BELOW-NORMAL TEMPERATURES NEAR THE SHORES OF THE 
GREAT LAKES ARE FURTHER ENHANCED BY THE SIGNIFICANTLY BELOW-NORMAL WATER 
TEMPERATURES THAT ARE EXPECTED TO PERSIST INTO MAY. MOST TOOLS INDICATE 
ENHANCED ODDS FOR ABOVE-NORMAL TEMPERATURES FOR MUCH OF THE SOUTHWESTERN 
QUARTER OF THE CONUS AND PARTS OF THE SOUTHERN GREAT PLAINS. DRY SOIL MOISTURE 
CONDITIONS ARE EXPECTED TO HELP INCREASE THE ODDS OF ABOVE NORMAL TEMPERATURES 
IN THESE REGIONS. ABOVE-NORMAL SSTS NEAR SOUTHERN FLORIDA HELP ELEVATE CHANCES 
FOR ABOVE-NORMAL AIR TEMPERATURES THERE. MANY MODELS AND STATISTICAL TOOLS 
POINT TO AN INCREASED CHANCE FOR ABOVE-NORMAL TEMPERATURES ALONG THE WEST COAST 
OF NORTH AMERICA AND MOST OF ALASKA. IN AREAS WHERE CLIMATE SIGNALS ARE WEAK 
AND/OR NOT RELIABLE, EQUAL CHANCES (EC) OF BELOW-, NEAR- AND ABOVE-NORMAL MEAN 
MONTHLY TEMPERATURES ARE INDICATED.

THE NMME, IMME AND CFS, FAVOR BELOW-MEDIAN PRECIPITATION IN THE PACIFIC 
NORTHWEST AND ALSO THE ALASKA PANHANDLE. THE NMME FAVORS ABOVE-MEDIAN 
PRECIPITATION AMOUNTS NEAR FLORIDA. COMPOSITES BASED ON YEARS WITH DEVELOPING 
EL NINO CONDITIONS ALSO SUPPORT DRY TENDENCIES IN THE PACIFIC NORTHWEST, AND 
TENDENCIES FOR WET CONDITIONS IN FLORIDA. ELSEWHERE, THE LACK OF CONSISTENT 
SIGNALS AMONG TOOLS SUGGEST EQUAL CHANCES (EC) FOR BELOW- NEAR- OR ABOVE-MEDIAN 
PRECIPITATION AMOUNTS. IT IS NOTEWORTHY THAT THE VARIOUS MODELS IN THE NMME 
SHOW NO CONSISTENT SIGNAL FOR THE SOUTHERN HIGH PLAINS AND WEST TEXAS IN SPITE 
OF VERY DRY INITIAL SOIL MOISTURE CONDITIONS IN SOME OF THESE REGIONS.

THE MAIN FACTORS THAT USUALLY INFLUENCE THE MONTHLY CLIMATE OUTLOOK INCLUDE:
1) EL NINO AND LA NINA - WHICH COMPRISE ENSO. IMPACTS OF THESE EVENTS ARE 
SUMMARIZED BY SEPARATING 3-MONTH OBSERVATIONS FROM THREE OR MORE DECADES INTO 
EL NINO, NEUTRAL AND LA NINA SETS, AVERAGING EACH SEPARATELY, AND THEN 
COMPUTING ANOMALIES. THESE ARE CALLED "COMPOSITES" AND USED AT TIMES TO 
SUBJECTIVELY MODIFY THE FORECAST.
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 
1981-2010).
3) THE TROPICAL 30-60 DAY OSCILLATION - CALLED THE MADDEN JULIAN OSCILLATION 
(MJO) - AFFECTS CLIMATE VARIABILITY WITHIN SEASONS.
4) THE ARCTIC OSCILLATION (AO), THE SIMILAR NORTH ATLANTIC OSCILLATION (NAO), 
AND THE PACIFIC NORTH AMERICAN (PNA) PATTERNS - WHICH AFFECT THE TEMPERATURE 
ANOMALY PATTERN ESPECIALLY DURING BOREAL WINTER AND ARE GENERALLY CONSIDERED TO 
HAVE LOW PREDICTABILITY.
5) THE PACIFIC DECADAL OSCILLATION (PDO) - AN ENSO-LIKE PATTERN OF CLIMATE 
VARIABILITY AFFECTING 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 SPRING AND 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 MODELS - CANONICAL CORRELATION ANALYSIS (CCA), 
SCREENING MULTIPLE LINEAR REGRESSION (SMLR), CONSTRUCTED ANALOG (CA), AND 
ENSEMBLE CCA (ECCA).
8) DYNAMICAL FORECAST MODELS - INCLUDING THE NCEP CLIMATE FORECAST SYSTEM 
VERSION 2 (CFS) AND FOR THE ZERO-LEAD UPDATE FORECASTS THE NCEP GLOBAL ENSEMBLE 
FORECAST SYSTEM (GEFS).  AN EXPERIMENTAL FORECAST SYSTEM, THE NATIONAL 
MULTI-MODEL ENSEMBLE (NMME), COMPRISED OF SEVERAL DYNAMICAL MODELS IS ALSO USED.


FORECASTER: DAVID UNGER


THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1981 AND 2010, FOLLOWING
THE WORLD METEOROLOGICAL ORGANIZATION CONVENTION OF USING THE MOST RECENT 3 
COMPLETE DECADES AS THE CLIMATE 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.



THE NEXT MONTHLY OUTLOOK...FOR JUN ... WILL BE ISSUED ON THU MAY 15 2014


THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.

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