PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SAT APR 30 2016

30-DAY OUTLOOK DISCUSSION FOR MAY 2016

THE UPDATED MONTHLY OUTLOOK FOR MAY IS QUITE SIMILAR TO THAT ISSUED ON APRIL 
21. THE FORECAST IS MODIFIED BY TAKING ADVANTAGE OF SHORT-TERM WEATHER AND 
CLIMATE FORECASTS ISSUED WITHIN THE PAST ONE TO TWO DAYS. SINCE THE 
IMPLEMENTATION OF THE EXPERIMENTAL WEEKS 3+4 FORECAST, THE ZERO-LEAD MONTHLY 
FORECASTS LARGELY SERVE THE ROLE OF AGGREGATING FORECASTS FOR WEEK-1 ISSUED BY 
WPC AND THE WEEKS 2-4 FORECASTS ISSUED BY CPC. AT THIS TIME, SUCH AN EFFORT IS 
LARGELY SUBJECTIVE, BUT BENEFITS FROM THE CFS FORECASTS, FOR WHICH WE HAVE AN 
EXPLICIT MAY FORECAST BASED ON THE MOST RECENT MODEL RUNS. 

EARLY IN THE MONTH, ANOMALOUS TROUGHING IS FORECAST FOR MUCH OF THE CONUS FROM 
THE SOUTHWEST TO THE EASTERN U.S. THIS IS EXPECTED TO CONTRIBUTE TO 
BELOW-NORMAL TEMPERATURES AND ABOVE-MEDIAN PRECIPITATION FOR PARTS OF THE GREAT 
BASIN, ROCKIES, SOUTHWEST, AND SOUTHERN PLAINS. UNSETTLED WEATHER AND 
COOLER-THAN-NORMAL TEMPERATURES ARE FORECAST TO EXTEND TOWARD THE EAST COAST 
AND GREAT LAKES EARLY IN THE MONTH. HOWEVER, A WARMING TREND IS EXPECTED DURING 
WEEK-2 FOR MUCH OF THE EASTERN U.S., AND DYNAMICAL AND STATISTICAL GUIDANCE FOR 
WEEKS 3+4 FAVORS A WARMER-THAN-NORMAL PATTERN CENTERED ON THE EAST-CENTRAL 
CONUS. COMBINING THESE EFFECTS FAVORS A MODEST TILT TOWARD ABOVE-NORMAL 
TEMPERATURES FOR THE EASTERN CONUS FOR THE MONTH. FARTHER WEST, PROBABILITIES 
OF BELOW-NORMAL TEMPERATURES ARE ENHANCED RELATIVE TO THE MID-MONTH OUTLOOK, 
WHERE MODEL GUIDANCE STRONGLY FAVORS BELOW-NORMAL 500-HPA HEIGHTS FOR THE MONTH.

THE PRECIPITATION OUTLOOK TAKES ADVANTAGE OF HEAVY PRECIPITATION FORECAST OVER 
THE NEXT FEW DAYS, WHILE ALSO ATTEMPTING TO UTILIZE LOW-FREQUENCY CLIMATE 
VARIABILITY. THEREFORE, PROBABILITIES ARE HIGHEST WHERE THERE IS A CONFLUENCE 
OF SHORT-TERM PRECIPITATION ANOMALIES AND LOWER FREQUENCY CLIMATE SIGNALS. AS 
WITH TEMPERATURE, THE SPATIAL DISTRIBUTION OF PROBABILITIES IS QUITE SIMILAR TO 
THE 0.5-MONTH LEAD OUTLOOK.

THE PREVIOUS DISCUSSION ISSUED WITH THE 0.5-MONTH LEAD FORECAST FOLLOWS.
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THE MAY 2016 OUTLOOK IS CONSTRUCTED BASED ON THE LOW-FREQUENCY CLIMATE SIGNALS 
MANIFEST IN THE DYNAMICAL AND STATISTICAL GUIDANCE. MOST GUIDANCE IS IN GOOD 
AGREEMENT ON THE GENERAL STRUCTURE OF FORECAST PROBABILITIES, AND SHORTER TERM 
OUTLOOKS ARE CONSULTED TO REFINE THE FORECAST. THERE IS LITTLE IN THE WAY OF 
COHERENT MJO ACTIVITY TO INFLUENCE THE OUTLOOK; THE MJO'S INFLUENCE IS 
DIMINISHED IN THE WARM SEASON, AND PLAYS NO ROLE HERE IN INFORMING THE MONTHLY 
FORECAST. SOIL MOISTURE, HOWEVER, IS TAKEN INTO ACCOUNT, AS INCREASING INCIDENT 
SOLAR RADIATION ALLOWS IT TO EXERT MORE INFLUENCE ON LOCAL TEMPERATURES. 

THE CALIBRATED NMME TEMPERATURE PROBABILITIES INDICATE A FAIRLY WEAK TILT 
TOWARD WARMER-THAN-NORMAL TEMPERATURES ACROSS THE NORTHERN TIER OF THE CONUS, 
ALASKA, AND PARTS OF THE EASTERN CONUS. A NOTABLE WEAKNESS IS FORECAST OVER THE 
SOUTH-CENTRAL AND SOUTHWESTERN U.S. THIS IS GENERALLY CONSISTENT WITH LAGGED 
ENSO REGRESSIONS (USING LATE WINTER NINO 3.4 VALUES), OBJECTIVE COMPOSITE 
ANALOGS BASED ON THE RECENTLY OBSERVED SSTS IN THE TROPICAL AND NORTHERN 
PACIFIC AND ATLANTIC BASINS, AS WELL AS STATISTICALLY DERIVED LOCAL SOIL 
MOISTURE IMPACTS. THE SECULAR TREND EXPLAINS LESS VARIANCE ON MONTHLY 
TIMESCALES THAN ON SEASONAL TIMESCALES, BUT GENERALLY SUPPORTS THE SPATIAL 
STRUCTURE OF FORECAST TEMPERATURE PROBABILITIES. 

ENHANCED PROBABILITIES OF ABOVE-NORMAL TEMPERATURES ARE INDICATED FOR MUCH OF 
THE WESTERN, NORTHERN, AND EASTERN CONUS, BASED ON THE ABOVE FACTORS. THE 
LOWEST PROBABILITIES ARE FORECAST OVER NORTHERN NEW ENGLAND AND THE NORTHERN 
PLAINS. THE FORMER IS DUE TO HIGHER-FREQUENCY PATTERNS THAT FAVOR ANOMALOUS 
NORTHERLY FLOW INTO EARLY MAY FOR THAT REGION, WHILE THE LATTER IS DUE TO 
TRENDS AND SOIL MOISTURE TOOLS. THE LATEST CFS FORECASTS, WEEK 3/4 GUIDANCE 
FROM BOTH THE CFS AND ECMWF, SOIL MOISTURE CONSIDERATIONS, AND LAGGED ENSO 
REGRESSIONS FAVOR ENHANCED PROBABILITIES OF BELOW-NORMAL TEMPERATURES ACROSS A 
PORTION OF THE SOUTHWESTERN AND SOUTH-CENTRAL CONUS.

ALL OF THE AFOREMENTIONED OBJECTIVE GUIDANCE IS IN FAIRLY GOOD AGREEMENT ON THE 
FORECAST PRECIPITATION OUTLOOK AS WELL. MODEST PROBABILITIES FAVORING 
ABOVE-MEDIAN PRECIPITATION ARE DEPICTED FOR MUCH OF THE CENTRAL AND SOUTHERN 
CONUS, EXTENDING WESTWARD TO PARTS OF CALIFORNIA AND THE GREAT BASIN.


FORECASTER: STEPHEN BAXTER


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 19 2016


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

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