PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830 AM EDT THU APR 20 2017

30-DAY OUTLOOK DISCUSSION FOR MAY 2017

ENSO NEUTRAL CONDITIONS ARE PRESENT ACROSS THE PACIFIC OCEAN.  SOME ATMOSPHERIC 
VARIABLES, SUCH AS LOW-LEVEL WINDS AND OUTGOING LONGWAVE RADIATION (OLR) STILL 
HAVE SOME RESEMBLANCE TO CANONICAL LA NINA PATTERNS, THOUGH OTHERS (UPPER-LEVEL 
WINDS) ARE LESS COHERENT. OLR STILL INDICATES SUPPRESSED (ENHANCED) CONVECTION 
NEAR THE DATE LINE (MARITIME CONTINENT). A KEY DIFFERENCE THIS MONTH, IS THAT 
THE SUPPRESSED CONVECTION EXTENDS NORTHEASTWARD, RATHER THAN BEING SYMMETRIC 
ALONG THE EQUATOR. THIS ASYMMETRY HAS ALLOWED SOME CONVECTION TO DEVELOP FROM 
160W TO 120W, JUST SOUTH OF THE EQUATOR. 

THE MJO PLAYED A SMALL ROLE IN THE TROPICAL PACIFIC DURING MARCH. SOME SHORTER 
PERIOD VARIABILITY WAS EVIDENT ACROSS THE EASTERN PACIFIC, BUT THE PATTERN OVER 
THE CENTRAL PACIFIC WAS HIGHLY LINKED TO THE LONG-TERM PATTERN. FORECASTS OF 
THE MJO INDICATE AN AMPLIFICATION OVER THE WESTERN PACIFIC, THOUGH THE 
INCOHERENCE OF THE OBSERVED SIGNAL INCREASES UNCERTAINTY. THE MJO IS NOT LIKELY 
TO PLAY A LARGE ROLE IN THE MONTHLY VARIABILITY OVER NORTH AMERICA DURING MAY.

OTHER FACTORS, SUCH AS ANTECEDENT SOIL MOISTURE AND SNOW PACK, WERE CONSIDERED. 
SOIL MOISTURE IS ANOMALOUSLY HIGH OVER PORTIONS OF THE MIDWEST, WHICH HAS A 
LAGGED RELATIONSHIP WITH BELOW NORMAL TEMPERATURES. ABOVE NORMAL SNOW PACK OVER 
THE CENTRAL AND NORTHERN ROCKIES WAS ALSO CONSIDERED IN THE TEMPERATURE OUTLOOK.

DYNAMIC MODELS FROM THE NMME SUITE GENERALLY INDICATED ABOVE NORMAL 
TEMPERATURES FOR MOST OF THE CONUS AND ALASKA. PROBABILITIES WERE WEAKEST FROM 
CALIFORNIA TO THE PACIFIC NORTHWEST AND NORTHERN ROCKIES. MORE RECENT TRENDS IN 
MODEL GUIDANCE  (CFS FOR THE MONTH OF MAY, GUIDANCE FOR THE WEEK 3-4 PERIOD, 
AND THE LAST FEW DAYS OF THE 8-14 DAY PERIOD) INDICATE A COOL START TO THE 
MONTH OVER THE NORTHERN ROCKIES AND GREAT PLAINS. THE OUTLOOK REFLECTS THE 
COMBINATION OF NMME MODELS AND MORE RECENT MODEL INPUTS, AS WELL AS THE 
ANTECEDENT CONDITIONS MENTIONED ABOVE. THE OUTLOOK INDICATES ABOVE NORMAL 
TEMPERATURES ARE FAVORED FOR THE SOUTHWEST, TEXAS, AND FROM THE SOUTHEAST TO 
THE GREAT LAKES AND NORTHEAST.

SIGNALS FOR PRECIPITATION ANOMALIES IN THE INDIVIDUAL NMME MODELS ARE QUITE 
STRONG, BUT SIGNALS IN THE MEAN ARE QUITE A BIT WEAKER AS THE MODELS EXHIBIT 
POOR AGREEMENT IN THE OVERALL PATTERN. AFTER CALIBRATION, WEAK SIGNALS REMAIN 
OVER WESTERN ALASKA, THE NORTHERN HIGH PLAINS, THE GREAT LAKES, AND NORTHEAST. 
SOME OF THE MODELS IN THE NMME SUITE INDICATED EXTREME ANOMALIES (IN BOTH 
TEMPERATURE AND PRECIPITATION), SO THOSE MODELS WERE CONSIDERED OUTLIERS. TO 
BROADEN THE MODEL INPUTS AND LESSEN THE IMPACT OF THE EXTREME ANOMALIES, THE 
IMME WAS ALSO USED AS AN INPUT FOR THE PRECIPITATION OUTLOOK. THE OFFICIAL 
OUTLOOK INDICATES BELOW MEDIAN PRECIPITATION IS FAVORED FOR WESTERN ALASKA, THE 
ALASKA PANHANDLE, AND THE GREAT LAKES, ALL CONSISTENT WITH MODEL OUTPUT. ABOVE 
MEDIAN PRECIPITATION IS FAVORED OVER THE NORTHERN HIGH PLAINS AND ALONG THE 
GULF COAST, CONSISTENT WITH MODEL OUTPUT AND IN SOME CASES, TRENDS.


FORECASTER: MATTHEW ROSENCRANS


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.



AN UPDATED MONTHLY OUTLOOK... FOR MAY WILL BE ISSUED ON SUN APRIL 30 2017


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

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