PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830 AM EDT THU MAY 17 2018


30-DAY OUTLOOK DISCUSSION FOR JUNE 2018

THE JUNE 2018 TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON DYNAMICAL 
MODEL GUIDANCE, STATISTICAL TOOLS, CURRENT SOIL MOISTURE CONDITIONS, AND 
POTENTIAL INFLUENCES FROM MODES OF TROPICAL VARIABILITY. ENSO IS NOT A FACTOR 
IN THESE OUTLOOKS SINCE IT IS IN A NEUTRAL STATE AND IS PREDICTED TO REMAIN 
NEUTRAL. THE MADDEN-JULIAN OSCILLATION (MJO) WAS QUITE ACTIVE DURING THE PAST 
SIX MONTHS. AFTER A BRIEF WEAKENING DURING LATE APRIL, THE MJO STRENGTHENED BY 
EARLY MAY WITH ITS ENHANCED PHASE OVER THE WESTERN HEMISPHERE. DURING MID-MAY, 
THE ENHANCED PHASE OF THE MJO PROPAGATED EAST OVER AFRICA, WHILE A VERY ROBUST 
EQUATORIAL ROSSBY WAVE (ERW) SHIFTED WEST ACROSS THE INDIAN OCEAN. DYNAMICAL 
MODELS VARY ON THE AMPLITUDE OF THE MJO DURING THE NEXT TWO WEEKS. GIVEN THE 
CURRENT 200-HPA VELOCITY POTENTIAL ANOMALY FIELD, AN MJO SIGNAL IS EXPECTED TO 
CONTINUE ITS EASTWARD PROPAGATION BUT ITS INTERACTION WITH THE ERW INCREASES 
UNCERTAINTY ON ITS EVOLUTION THROUGH THE BEGINNING OF JUNE. DUE TO THIS 
UNCERTAINTY AND TIME OF YEAR, THE MJO IS EXPECTED TO PLAY LITTLE IF ANY ROLE IN 
THE LONGWAVE PATTERN ACROSS THE MID-LATITUDES OF NORTH AMERICA.  

THE DYNAMICAL MODEL CONSENSUS, INCLUDING THE NORTH AMERICAN MULTI-MODEL 
ENSEMBLE (NMME), SUPPORTS A BROAD AREA OF INCREASED CHANCES OF ABOVE-NORMAL 
TEMPERATURES THROUGHOUT THE CONTINENTAL U.S.  A STRONG INVERSE RELATIONSHIP 
EXISTS BETWEEN SOIL MOISTURE AND SURFACE TEMPERATURE DURING JUNE. SOIL MOISTURE 
CURRENTLY RANKS IN THE LOWEST 20TH PERCENTILE ACROSS THE SOUTHWESTERN U.S. AND 
MUCH OF THE CENTRAL AND SOUTHERN GREAT PLAINS WHERE RELATIVELY HIGH 
PROBABILITIES OF ABOVE-NORMAL TEMPERATURES ARE FORECAST. DECADAL TRENDS ALSO 
STRONGLY SUPPORT ABOVE-NORMAL TEMPERATURES ACROSS THESE AREAS. IN CONTRAST TO 
THE DROUGHT-STRICKEN SOUTHERN GREAT PLAINS, SOIL MOISTURE RANKS IN THE HIGHEST 
70TH OR EVEN 90TH PERCENTILE ACROSS MUCH OF THE GREAT LAKES REGION. GIVEN THIS 
HIGH SOIL MOISTURE CONTENT ALONG WITH SUPPORT FROM THE ECMWF MODEL, EQUAL 
CHANCES (EC) FOR BELOW-, NEAR-, OR ABOVE-NORMAL TEMPERATURES ARE FORECAST 
ACROSS PARTS OF THE GREAT LAKES REGION.  EC IS ALSO FORECAST FOR MUCH OF 
FLORIDA AND SOUTH GEORGIA, BASED ON DYNAMICAL MODELS AND THE EXPECTATION FOR 
ABOVE-NORMAL RAINFALL. 

ABOVE (BELOW)-NORMAL PRECIPITATION ACROSS THE SOUTHEAST, MID-ATLANTIC, AND 
PARTS OF THE GULF COAST (PACIFIC NORTHWEST, NORTHERN GREAT BASIN, AND NORTHERN 
ROCKIES) IS BASED ON DYNAMICAL MODELS AND DECADAL TRENDS. IF THE ENHANCED PHASE 
OF THE MJO CONTINUES ITS EASTWARD PROPAGATION TO THE WESTERN HEMISPHERE DURING 
JUNE AND/OR AN ATMOSPHERIC KELVIN WAVE EMERGES, THEN THE LARGE SCALE 
ENVIRONMENT COULD BE FAVORABLE FOR AN EARLY SEASON TROPICAL CYCLONE (TC) ACROSS 
THE GULF OF MEXICO. THE MJO EVOLUTION AND ITS POTENTIAL INFLUENCE ON TC 
FORMATION WILL BE CLOSELY MONITORED DURING THE REMAINDER OF MAY. THE LARGE 
COVERAGE OF EQUAL CHANCES FOR BELOW-, NEAR-, OR ABOVE-NORMAL PRECIPITATION IS 
DUE TO THE LOWER CONFIDENCE IN THE PRECIPITATION OUTLOOK AT A HALF MONTH LEAD 
AND THE LACK OF PREDICTABILITY OF CONVECTIVE RAINFALL ON A MONTHLY TIME SCALE. 
MODIFICATIONS TO THE COVERAGE AND PROBABILITIES IN THE PRECIPITATION OUTLOOK 
ARE ANTICIPATED WITH THE UPDATED OUTLOOK RELEASED ON MAY 31. 

THE DYNAMICAL MODEL GUIDANCE IS IN GOOD AGREEMENT WITH INCREASED CHANCES OF 
ABOVE-NORMAL TEMPERATURES ACROSS MOST OF ALASKA. THE HIGHEST PROBABILITIES FOR 
ABOVE-NORMAL TEMPERATURES ARE FORECAST ACROSS WESTERN ALASKA AND THE ALEUTIANS, 
BASED IN PART ON SEA SURFACE TEMPERATURES AVERAGING 1 TO 2 DEGREES C ABOVE 
NORMAL. THE NMME INDICATES ENHANCED ODDS FOR ABOVE-NORMAL PRECIPITATION 
THROUGHOUT MAINLAND ALASKA WITH THE HIGHEST ODDS ACROSS WESTERN ALASKA. 

FORECASTER: BRAD PUGH

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 JUN WILL BE ISSUED ON THU MAY 31 2018

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