588  
FXUS07 KWBC 191231  
PMD30D  
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
830 AM EDT THU SEP 19 2024  
 
30-DAY OUTLOOK DISCUSSION FOR OCTOBER 2024  
 
THE OCTOBER TEMPERATURE AND PRECIPITATION OUTLOOKS ARE CHARACTERIZED BY LOW  
FORECAST PROBABILITIES AND OUTLOOK COVERAGE - NOT ATYPICAL FOR AN OCTOBER  
MONTHLY OUTLOOK. ONGOING CLIMATE CONDITIONS IN MID-SEPTEMBER INDICATE A  
CONTINUED SLOW TREND TOWARD POTENTIAL LA NINA CONDITIONS LATER THIS AUTUMN, A  
BETTER ORGANIZING MJO AS WELL AS ANOMALOUS COASTAL SEA SURFACE TEMPERATURES  
(SSTS) - PRIMARILY FOR WATERS IN PROXIMITY TO ALASKA. ALTHOUGH NOT IMPACTFUL IN  
A PREDICTABILITY CONTEXT THIS LATE IN THE YEAR, SOIL MOISTURE CONTINUES TO  
DECREASE IN MANY AREAS ACROSS THE CONUS, WITH THE ONGOING IMPACTFUL DROUGHT IN  
PARTS OF THE OHIO VALLEY AND WESTERN MID-ATLANTIC CONTINUING TO WORSEN.  
 
PREPARATION OF THE OCTOBER TEMPERATURE AND PRECIPITATION OUTLOOKS PRIMARILY  
UTILIZED SUBSEASONAL DYNAMICAL AND STATISTICAL MODEL GUIDANCE, POTENTIAL  
TELECONNECTION ASSOCIATED WITH AN ACTIVE MJO, LONG TERM TRENDS AS WELL AS IN  
SOME PLACES COASTAL SSTS. ANY POTENTIAL IMPACTS FROM SLOWLY DEVELOPING LA NINA  
CONDITIONS ARE NOT CONSIDERED IN THE OCTOBER OUTLOOK TO ANY LARGE DEGREE.  
 
THE TEMPERATURE OUTLOOK FAVORS ABOVE-NORMAL TEMPERATURES FOR THE SOUTHWESTERN  
CONUS, THE CENTRAL AND SOUTHERN ROCKIES, AND SOUTHERN TEXAS, CONSISTENT WITH  
THE MAJORITY OF SUBSEASONAL DYNAMICAL MODEL GUIDANCE AND MOST OF THE NMME AND  
C3S PARTICIPANT MODELS. STRONG WARMER-THAN-NORMAL TEMPERATURE TRENDS AND  
FORECAST MODEL GUIDANCE ELEVATES CHANCES FOR ABOVE-NORMAL MONTHLY MEAN  
TEMPERATURES FOR THE NORTHEAST, MID-ATLANTIC AND PARTS OF THE EASTERN GREAT  
LAKES.  
 
THERE IS A LARGE AREA OF "EQUAL CHANCES" OR EC FORECAST FROM THE PACIFIC  
NORTHWEST EASTWARD TO INCLUDE THE NORTHERN AND CENTRAL PLAINS, MISSISSIPPI  
VALLEY AND SOUTHEAST. THE ABOVE AVERAGE COVERAGE OF EC IN THE OUTLOOK IN THESE  
AREAS IS ASSOCIATED WITH HIGHLY VARYING DYNAMICAL MODEL GUIDANCE ON THE  
SUBSEASONAL TIME SCALE. THIS INCLUDES THE LATEST ECMWF EXTENDED RANGE FORECAST  
WHICH DEPICTS WEAK SIGNALS IN THIS REGION OVER THE COURSE OF THE MONTH OF  
OCTOBER.  
 
ALTHOUGH ASSOCIATED IMPACTS FROM ANOMALOUS TROPICAL CONVECTION ARE LESS LIKELY  
IN AUTUMN THEN DURING WINTER AND EARLY SPRING, THAT POTENTIAL STILL EXISTS AND  
IS AT ODDS WITH MUCH OF THE DYNAMICAL MODEL GUIDANCE. UNCERTAINTY IN ANY  
MID-LATITUDE TELECONNECTION FROM THE MJO FURTHER COMPLICATES THE FORECAST IN  
THIS AREA AS MJO LAGGED COMPOSITES OF 200-HPA HEIGHT AND 850-HPA TEMPERATURE  
FOR MJO RMM PHASES 6 AND 7 SUPPORT TROUGHING AND FAVORED BELOW-NORMAL  
TEMPERATURES FOR PARTS OF THE WESTERN AND CENTRAL CONUS DURING THE FIRST HALF  
OF OCTOBER. A MULTIPLE LINEAR REGRESSION (MLR) FORECAST TOOL UTILIZING THE MJO,  
ENSO AND LONG-TERM TRENDS TARGETING THE FIRST TWO WEEKS OF OCTOBER INDICATES  
ELEVATED ODDS FOR BELOW-NORMAL TEMPERATURES IN PARTS OF THE NORTH-CENTRAL  
CONUS.  
 
FOR ALASKA, ANOMALOUS SSTS AND SOME FORECAST GUIDANCE SUPPORTS FAVORED  
ABOVE-NORMAL (BELOW-NORMAL) TEMPERATURES FOR THE NORTHERN ALASKA (SOUTHWEST  
ALASKA) PORTIONS OF THE STATE.  
 
THE OCTOBER PRECIPITATION OUTLOOK FAVORS BELOW-NORMAL PRECIPITATION FOR AN AREA  
FROM THE SOUTHWEST U.S. AND CENTRAL ROCKIES EASTWARD TO INCLUDE MUCH OF THE  
CENTRAL PLAINS AND PARTS OF THE CENTRAL MISSISSIPPI VALLEY. THIS FORECAST IS  
PRIMARILY BASED ON A HIGH DEGREE OF AGREEMENT IN BIAS-CORRECTED AND CALIBRATED  
DYNAMICAL MODEL GUIDANCE FROM THE NMME AND C3S MODEL SUITES AS WELL AS THE  
ECMWF EXTENDED RANGE FORECAST.  
 
ELEVATED ODDS FOR ABOVE-NORMAL PRECIPITATION IS FORECAST FOR THE CENTRAL AND  
EASTERN GULF COAST, PARTS OF THE SOUTHEAST, MID-ATLANTIC COAST AND MUCH OF THE  
NORTHEAST. LONG TERM WETTER-THAN-NORMAL PRECIPITATION TRENDS (I.E., OCN) AND  
SOME SUBSEASONAL DYNAMICAL MODEL GUIDANCE SUPPORT THE FORECAST IN THE NORTHEAST  
AND MID-ATLANTIC AREAS. FOR THE SOUTHEAST AND GULF COAST AREAS, THE OUTLOOK IS  
DRIVEN BY POTENTIAL TROPICAL MOISTURE ENTERING THIS REGION OF THE CONUS  
ASSOCIATED WITH THE MJO ENTERING RMM PHASES 8 AND 1 DURING EARLY OCTOBER.  
DYNAMICAL MODEL GUIDANCE FROM SOME SOURCES ALSO SUPPORTS THIS FORECAST, MAINLY  
FOR FLORIDA AND EXTREME SOUTHEAST COASTAL AREAS. IN ADDITION, A SMALL AREA OF  
ENHANCED ODDS FOR WETTER-THAN-NORMAL CONDITIONS IS FORECAST FOR NORTHERN  
WASHINGTON STATE INDICATED IN SOME FORECAST TOOLS.  
 
FOR ALASKA, MODEL GUIDANCE IS GENERALLY CONSISTENT WITH WET CONDITIONS FOR  
AREAS IN WESTERN AND NORTHERN ALASKA, SO ABOVE-NORMAL PRECIPITATION SLIGHTLY  
FAVORED IN THOSE PORTIONS OF THE STATE. LARGE UNCERTAINTY ASSOCIATED WITH  
HIGHLY CONFLICTING FORECAST TOOLS ANY POTENTIAL MJO IMPACTS MADE EC THE PRUDENT  
FORECAST FOR MOST OF THE OHIO VALLEY AND MUCH OF THE MIDWEST AT THIS TIME.  
 
FORECASTER: JON GOTTSCHALCK  
 
THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1991 AND 2020, 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 OCT WILL BE ISSUED ON MON SEPTEMBER 30 2024  
 
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1991-2020 BASE PERIOD.  
 
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