30 Day Narrative

286 
FXUS07 KWBC 301900
PMD30D
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SUN SEP 30 2018
30-DAY OUTLOOK DISCUSSION FOR OCTOBER 2018
THE UPDATE TO THE MID-MONTH OCTOBER TEMPERATURE AND PRECIPITATION OUTLOOK 
PRIMARILY UTILIZES INFORMATION FROM SHORT-RANGE, MEDIUM-RANGE, EXTENDED-RANGE 
MODEL GUIDANCE AND CHANGES IN INTEGRATED MONTHLY DYNAMICAL MODEL GUIDANCE 
INFORMATION FROM MID-MONTH. THE UPDATED OUTLOOKS DEPICTS SOME SUBSTANTIAL 
CHANGES IN SOME AREAS AS MODEL GUIDANCE HAS BEEN QUITE VARIABLE AT TIMES OVER 
THE PAST SEVERAL DAYS. 
THE TEMPERATURE OUTLOOK UPDATE MAINTAINS HIGH PROBABILITIES FOR ABOVE-NORMAL 
TEMPERATURES FOR MOST OF ALASKA AND FACTORS LISTED AT MID-MONTH HAVE NOT 
CHANGED AND MODEL GUIDANCE HAS REMAINED CONSISTENT. ANTICIPATION OF ROBUST 
TROUGHING IMPACTING NORTH AMERICA DESCRIBED EARLIER THIS MONTH CONTINUES TO BE 
A MAJOR FACTOR IN THE OUTLOOK AS THE ENTRY OF COLDER AIR INTO THE INTERIOR 
PORTION OF THE CONUS REMAINS FAVORED. THE LATEST GUIDANCE, HOWEVER, NOW 
INDICATES MORE AMPLIFIED, FULL LATITUDE TROUGHING SHIFTED TO THE WEST-CENTRAL 
CONUS FOR MUCH OF THE FIRST HALF OF THE MONTH. AREAS NOW MOST FAVORED FOR 
BELOW-NORMAL TEMPERATURES HAVE INCREASED IN COVERAGE AND SHIFTED WESTWARD TO 
FOCUS ON THE NORTHERN ROCKIES AND NORTHERN GREAT PLAINS AND TO LESSER 
CONFIDENCE FOR AN AREA CENTERED ACROSS CALIFORNIA. THIS IS TWO CATEGORY CHANGE 
IN SOME AREAS OF THE WESTERN CONUS FROM THE PREVIOUS OUTLOOK WHERE RIDGING WAS 
INITIALLY FAVORED.
MIXED SIGNALS OVER THE COURSE OF THE MONTH FROM DYNAMICAL MODEL GUIDANCE MAKES 
A FORECAST OF EQUAL CHANCES (EC) THE MOST PRUDENT OUTLOOK AT THIS TIME IN THE 
REMAINING AREAS OF THE WESTERN CONUS. ABOVE-NORMAL TEMPERATURES REMAIN FAVORED 
FROM THE PREVIOUS OUTLOOK IN THE SOUTHEAST, BUT HAVE BEEN EXPANDED IN COVERAGE 
AND PROBABILITIES INCREASED SUBSTANTIALLY AS THE ANTICIPATED 500-HPA FLOW 
PATTERN DURING THE FIRST HALF OF OCTOBER FAVORS STRONGLY AMPLIFIED RIDGING FOR 
THE EASTERN CONUS. A PARTICULAR CHALLENGE IN THE TEMPERATURE OUTLOOK IS ACROSS 
THE EASTERN GREAT LAKES REGION AND NORTHEAST WHERE THERE REMAINS UNCERTAINTY 
FOR HOW MUCH COLDER AIR IS ABLE TO ENTER THIS REGION AFTER MID-MONTH AS 
INDICATED BY SOME WEEK 3-4 FORECAST MODEL GUIDANCE AND TO THE EXTENT THAT THE 
EXTENDED-RANGE STRONGLY FAVORED ABOVE-NORMAL TEMPERATURE FORECAST IS EVENTUALLY 
REALIZED. 
THE UPDATED OCTOBER PRECIPITATION OUTLOOK CONTINUES TO DEPICT AN ENHANCED 
LIKELIHOOD FOR ABOVE-NORMAL PRECIPITATION FOR SOUTHWEST ALASKA AND MUCH OF THE 
SOUTHERN TIER OF THE CONUS, AS WELL AS ENHANCED ODDS FOR BELOW-NORMAL 
PRECIPITATION FOR THE PACIFIC NORTHWEST, CONSISTENT IN MOST PLACES WITH 
INFORMATION LISTED AT MID-MONTH. ONE ADDITION IS AN ENHANCED LIKELIHOOD FOR 
BELOW-NORMAL PRECIPITATION FOR NORTHEAST ALASKA AS A RESULT OF SOME RIDGING IN 
THIS AREA. HIGH ODDS FOR TROPICAL CYCLONE ROSA AND/OR ITS REMAINING MOISTURE TO 
IMPACT MUCH OF THE SOUTHWEST CONUS HAVE DRAMATICALLY INCREASED PROBABILITIES 
FOR ABOVE-NORMAL PRECIPITATION FOR OCTOBER IN THIS AREA AS WELL AS WARRANTING 
AN EXPANSION OF COVERAGE FOR PARTS OF CALIFORNIA, NEVADA AND THE CENTRAL 
ROCKIES AS IT INTERACTS WITH A SHORTWAVE TROUGH ENTERING THE PACIFIC COAST 
EARLY IN THE MONTH. 
THE ANTICIPATED HIGHLY AMPLIFIED 500-HPA FLOW PATTERN OF A TROUGH - RIDGE 
PATTERN FROM THE WESTERN CONUS TO THE EASTERN CONUS FAVORS A VERY ACTIVE 
PATTERN DURING THE FIRST HALF OF OCTOBER WITH A CONSIDERABLY ENHANCED 
LIKELIHOOD OF STRONG CYCLONES, PRECIPITATION AND ASSOCIATED IMPACTS FOR A 
RATHER LARGE REGION STRETCHING FROM THE CENTRAL CONUS TO THE GREAT LAKES AND 
POTENTIALLY NEW ENGLAND AND THE OHIO VALLEY. THIS IS A CONCERN AS THE HIGHEST 
PROBABILITIES FOR ABOVE-NORMAL PRECIPITATION ARE ANTICIPATED TO BE OVER SOME 
REGIONS IN THE MIDWEST THAT HAVE SEEN RECENT FLASH FLOODING AND CONSIDERABLY 
ABOVE-NORMAL STREAMFLOWS. A GENERALLY DRY START TO THE MONTH IN PARTS OF THE 
MID-ATLANTIC AND SOUTHEAST CONUS ARE OFFSET BY A SHIFT TO POTENTIALLY ELEVATED 
ODDS OF ENHANCED WETNESS AFTER MID-MONTH SO EC IS FORECAST.  
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**********         PREVIOUS MID-MONTH DISCUSSION IS BELOW           **********
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ON MOST OCCASIONS, PREDICTABILITY REACHES A GENERAL MINIMUM OVERALL DURING THE 
MONTH OF OCTOBER FOR THE U.S. FORECAST DOMAIN AS IT IS IN THE MIDDLE OF THE 
SHOULDER SEASON (SEP-OCT-NOV) THAT RESIDES BETWEEN THE TRANSITION FROM THE 
SUMMER MONTHS TO THE COLD SEASON. THE HALF-MONTH LEAD MONTHLY FORECAST SUCH AS 
THE OCTOBER TEMPERATURE AND PRECIPITATION OUTLOOK PRESENTED HERE INCLUDES 
INFORMATION ACROSS MULTIPLE TIME SCALES (THE EXTENDED RANGE, SUBSEASONAL, AND 
THE SEASONAL BACKGROUND STATE). THESE FACTORS INFLUENCE THE EVENTUAL OBSERVED 
MONTHLY MEAN TEMPERATURE AND TOTAL PRECIPITATION AMOUNTS. THE TYPICAL GREATER 
UNCERTAINTY RESULTS IN A RATHER SIZABLE FORECAST AREA DEPICTING EQUAL CHANCES 
(EC) FOR THE INITIAL OCTOBER OUTLOOK.
A REVIEW OF THE MJO CURRENTLY INDICATES THAT IT REMAINS GENERALLY POORLY 
DEFINED AND THE ANOMALOUS TROPICAL CONVECTION IN RECENT WEEKS HAS BEEN 
DOMINATED BY HIGHER FREQUENCY TROPICAL SUBSEASONAL VARIABILITY SUCH AS 
ATMOSPHERIC KELVIN WAVES AND BURSTS IN TROPICAL CYCLONE ACTIVITY. SOME MODELS 
DO INDICATE POTENTIAL IMPROVED MJO ORGANIZATION ACROSS THE WESTERN HEMISPHERE 
AS WE ENTER EARLY OCTOBER, BUT UNTIL THAT PROVES TO BE THE CASE, POTENTIAL MJO 
INFLUENCE WAS NOT LARGELY UTILIZED IN THE CURRENT OUTLOOK. 
THE OCTOBER TEMPERATURE OUTLOOK FAVORS ABOVE NORMAL TEMPERATURES FOR ALL OF 
ALASKA AND MOST OF THE WESTERN CONUS WITH HIGH PROBABILITIES FOR MUCH OF THE 
ALASKA REGION INCLUDING GREATER THAN 80% PROBABILITY FOR PORTIONS OF NORTHWEST 
MAINLAND ALASKA. THE TRENDS ASSOCIATED WITH LATE ARRIVAL OF SEA ICE, MUCH ABOVE 
NORMAL SEA SURFACE TEMPERATURES (SSTS) ALONG MUCH OF THE COASTAL AREAS OF THE 
STATE, AND STRONG RIDGING AND SOUTHERLY FLOW ANTICIPATED EARLY IN THE MONTH ARE 
THE BASIS FOR THIS FORECAST. FOR THE WESTERN CONUS, NEARLY UNANIMOUS DYNAMICAL 
MODEL FORECAST GUIDANCE, LARGE AREAS OF BELOW NORMAL SOIL MOISTURE CONDITIONS 
AND STRONG LONG TERM TEMPERATURE TRENDS SUPPORT THE FORECAST IN THIS REGION.
ABOVE NORMAL TEMPERATURES ARE ALSO MOST LIKELY FOR AREAS OF THE SOUTHEAST, 
TENNESSEE VALLEY, AND MID-ATLANTIC AS SUBTROPICAL RIDGING, ABOVE NORMAL 500-HPA 
HEIGHT DEPARTURES, AND SURFACE MEAN SOUTHERLY FLOW ARE STILL ANTICIPATED TO 
PLAY A ROLE DURING THE MONTH. THE PROBABILITIES ARE MORE MODEST, HOWEVER, AS 
DYNAMICAL MODEL FORECAST GUIDANCE IS LESS DEFINITIVE IN THIS REGION AND SOME 
AREAS HAVE SUBSTANTIAL POSITIVE SOIL MOISTURE DEPARTURES AND PERHAPS REMAINING 
STANDING WATER FROM AN OBSERVED VERY WET SUMMER AND, MOST RECENTLY, IMPACTS 
FROM HURRICANE FLORENCE.
THE MOST CHALLENGING ASPECT OF THE TEMPERATURE OUTLOOK RESIDES ACROSS THE 
NORTHERN AND CENTRAL PLAINS, GREAT LAKES AND OHIO VALLEY REGIONS. INDICATIONS 
IN LATE SEPTEMBER ARE THAT A ROBUST RIDGE WILL DEVELOP ACROSS ALASKA WHICH MAY 
FAVOR DOWNSTREAM TROUGHING ON AVERAGE DURING EARLY PORTIONS OF OCTOBER. THE 
LATEST WEEK 3-4 FORECAST GUIDANCE FROM THE CFS AND ECMWF FAVOR THIS TO PERSIST 
SIGNIFICANTLY INTO OCTOBER WITH ELEVATED ODDS FOR BELOW NORMAL TEMPERATURES. IN 
ADDITION TO THE GENERAL UNCERTAINTY FOR THE FINAL TWO WEEKS IN OCTOBER, THIS IS 
ALSO AT ODDS WITH NMME DYNAMICAL MODEL GUIDANCE AND LONG TERM TRENDS SO EC IS 
CURRENTLY FORECAST FOR MUCH OF THIS AREA, HOWEVER, A REGION IS HIGHLIGHTED 
FAVORING BELOW NORMAL TEMPERATURES IN THE CENTRAL PLAINS AT THIS TIME. 
AREAS SHOWN IN WHITE LABELED EC DEPICT A FORECAST WHERE THE PROBABILITIES FOR 
EITHER OF THREE CATEGORIES, BELOW-, NEAR- OR ABOVE-NORMAL MONTHLY MEAN 
TEMPERATURE ARE NOT SIGNIFICANTLY DIFFERENT FROM CLIMATOLOGICAL PROBABILITIES.
THE OCTOBER PRECIPITATION OUTLOOK WAS PARTICULARLY DIFFICULT THIS MONTH AS 
SIGNALS IN FORECAST GUIDANCE PRODUCTS ARE WEAK AND OFTEN CONFLICTING IN NATURE. 
THE OUTLOOK DEPICTS AN ENHANCED LIKELIHOOD FOR ABOVE NORMAL PRECIPITATION FOR 
MOST OF WESTERN AND CENTRAL ALASKA. MORE OPEN WATERS AND ABOVE NORMAL SSTS AS 
WELL AS GENERALLY CONSISTENT DYNAMICAL MODEL GUIDANCE ARE THE RATIONALE FOR THE 
OUTLOOK IN THIS REGION. POTENTIAL TROUGHING AS NOTED ABOVE ACROSS THE INTERIOR 
OF NORTH AMERICA WITH SOME EXTENSION INTO THE CONUS FAVORS ABOVE NORMAL 
PRECIPITATION FOR SIGNIFICANT PORTIONS OF THE SOUTHERN TIER OF THE CONUS AND 
THE EASTERN SEABOARD.  THIS IS CONSISTENT TO FIRST ORDER WITH THE LATEST WEEK 
3-4 DYNAMICAL MODEL GUIDANCE FROM THE ECMWF AND CFS. LONG TERM POSITIVE 
PRECIPITATION TRENDS ALSO CONTRIBUTE TO THE OUTLOOK ALONG PARTS OF THE EASTERN 
SEABOARD. ANTICIPATED RIDGING ON AVERAGE DURING THE FIRST HALF OF THE MONTH 
FAVORS BELOW NORMAL PRECIPITATION IN AREAS OF THE PACIFIC NORTHWEST DOING THE 
MONTH OF OCTOBER. 
AREAS SHOWN IN WHITE LABELED EC DEPICT A FORECAST WHERE THE PROBABILITIES FOR 
EITHER OF THREE CATEGORIES, BELOW-, NEAR- OR ABOVE-NORMAL MONTHLY TOTAL 
PRECIPITATION ARE NOT SIGNIFICANTLY DIFFERENT FROM CLIMATOLOGICAL PROBABILITIES.
FORECASTER: JON GOTTSCHALCK
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 NOV ... WILL BE ISSUED ON THU OCT 18 2018
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.
$$