398  
FXUS07 KWBC 201230  
PMD30D  
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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