PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 300 PM EDT SUN APR 30 2017 30-DAY OUTLOOK DISCUSSION FOR MAY 2017 ENSO NEUTRAL CONDITIONS CONTINUED ACROSS THE PACIFIC OCEAN. THE SEA-SURFACE TEMPERATURES IN THE NINO 1+2, NINO4, AND NINO 3.4 REGIONS INCREASED. THE MJO REMAINED WEAK, THOUGH SOME MODELS DO INDICATE A STRENGTHENING SIGNAL ACROSS THE WESTERN HEMISPHERE, SO THERE COULD BE SOME RELATED IMPACTS DURING THE LATTER HALF OF MAY. UNCERTAINTY ABOUT THE DEVELOPMENT OF AN MJO, THEN THE ATTENDANT, LAGGED IMPACTS, RESULTS IN THE MJO BEING OF MINIMAL CONSEQUENCE IN THE UPDATED OUTLOOK. THE OUTLOOKS ARE CONSISTENT WITH SOME OF THE MJO LAGGED COMPOSITES CENTERED ON MAY. THE UPDATED TEMPERATURE OUTLOOK REFLECTS GUIDANCE FOR EARLY IN THE MONTH WHERE TEMPERATURES ARE FORECAST TO BE BELOW AVERAGE ACROSS THE GREAT PLAINS, MIDWEST, AND MISSISSIPPI VALLEY. THAT PREDICTED COOLER AIR IS THEN LIKELY TO SLIDE SOUTH AND EAST, SO THE UPDATED OUTLOOK NOW REFLECTS THAT LIKELY COOLER FIRST HALF OF THE MONTH FROM THE SOUTHERN GREAT PLAINS TO THE OHIO VALLEY AND ACROSS TO THE MID-ATLANTIC. ACROSS THE SOUTHWEST AND GREAT BASIN, THE OUTLOOK IS RELATIVELY UNCHANGED, WITH THE HIGHEST ODDS OF ABOVE NORMAL TEMPERATURES SHIFTED NORTHWARD SLIGHTLY, GIVEN A PREDICTED COOLER PERIOD, MID-MONTH, OVER ARIZONA. UNCERTAINTY ACROSS THE NORTHERN GREAT PLAINS, NORTHERN ROCKIES, AND PACIFIC NORTHWEST, IS HIGH, SO NO TILT IN THE ODDS IS INDICATED FOR THOSE REGIONS. TEMPERATURES OVER MUCH OF ALASKA ARE PREDICTED TO BE ABOVE NORMAL, WITH A WARMER START TO THE MONTH. UNCERTAINTY IS HIGHEST OVER SOUTHEAST ALASKA AND THE ALASKA PANHANDLE. THE PRECIPITATION OUTLOOK HAS BEEN REVISED CONSIDERABLY, GIVEN THE STRONG SIGNALS IN SHORT-TERM MODEL GUIDANCE AND OFFICIAL PRODUCTS. AN ACTIVE PERIOD IS FORECAST EARLY IN THE MONTH FROM THE GULF COAST TO THE NORTHEAST. A RELATIVELY SHORT WAVELENGTH AND A PREDICTED TROUGH OVER THE ROCKIES FOR THE MIDDLE OF THE MONTH SUPPORTS A BROAD SWATH OF FAVORED ABOVE MEDIAN PRECIPITATION FROM THE NORTHERN ROCKIES TO FOUR CORNERS REGION, WHERE MEDIAN PRECIPITATION AMOUNTS ARE LOW, SO EVEN A SHORT PERIOD OF WETNESS WOULD FAVOR ABOVE MEDIAN PRECIPITATION FOR THE ENTIRE MONTH. MODEL GUIDANCE AND OFFICIAL OUTLOOKS COVERING MOST OF MAY, FAVORS DRIER THAN MEDIAN CONDITIONS FOR THE PACIFIC NORTHWEST COAST, AND PORTIONS OF THE MIDDLE AND UPPER MISSISSIPPI VALLEY. ----------- THE FORECAST MESSAGE FOR THE MAY TEMPERATURE AND PRECIPITATION OUTLOOKS ISSUED ON APRIL 20 IS BELOW. ------------------- 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. THE NEXT MONTHLY OUTLOOK...FOR JUN ... WILL BE ISSUED ON THU MAY 18 2017 THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD. $$