899  
FXUS06 KWBC 132020  
PMDMRD  
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD  
300 PM EST WED DECEMBER 13 2017  
 
6-10 DAY OUTLOOK FOR DEC 19 - 23 2017  
 
TODAY'S MODEL SOLUTIONS GENERALLY DEPICT MODERATELY AMPLIFIED 500-HPA FLOW OVER  
MUCH OF THE FORECAST DOMAIN AND A POTENTIAL PATTERN CHANGE DURING THE PERIOD.  
IN THE MEAN, BROAD CYCLONIC FLOW IS INDICATED OVER MUCH OF THE EASTERN  
TWO-THIRDS OF THE CONUS ASSOCIATED WITH A TROUGH CENTERED OVER EAST-CENTRAL  
CANADA. A STRONG RIDGE IS FORECAST OVER THE EASTERN PACIFIC OFF THE WEST COAST  
OF THE CONUS EXTENDING NORTHWARD TO CENTRAL MAINLAND ALASKA. FARTHER TO THE  
SOUTH, RIDGING IS FORECAST NEAR CUBA AND ABOVE NORMAL HEIGHTS ASSOCIATED WITH  
THIS RIDGE EXTEND NORTHWARD TO PARTS OF THE SOUTHEASTERN CONUS. ENSEMBLE SPREAD  
IS HIGH OVER THE WESTERN CONUS IN ASSOCIATION WITH POTENTIAL TROUGH DEVELOPMENT  
DURING THE MIDDLE AND END OF THE 6 TO 10 DAY PERIOD. THE OFFICIAL MANUAL  
500-HPA HEIGHT BLEND IS BASED PRIMARILY ON THE ENSEMBLE MEANS FROM THE  
CANADIAN, ECMWF, AND GEFS ENSEMBLE SYSTEMS.  
 
THE RIDGE EXPECTED OVER MAINLAND ALASKA INCREASES PROBABILITIES FOR ABOVE  
NORMAL TEMPERATURES ACROSS MOST OF THE STATE (WITH THE EXCEPTION OF THE  
PANHANDLE). CYCLONIC FLOW AND BELOW NORMAL HEIGHTS LEAD TO ENHANCED  
PROBABILITIES FOR BELOW NORMAL TEMPERATURES FOR MUCH OF THE NORTHEAST AND GREAT  
LAKES REGION. BELOW NORMAL TEMPERATURES ARE ALSO FAVORED FOR PARTS OF THE  
NORTHWESTERN CONUS UNDERNEATH ANOMALOUS NORTHERLY 500-HPA FLOW. CATEGORICAL  
TEMPERATURE PROBABILITIES ACROSS THE NORTHERN AND CENTRAL CONUS WERE GENERALLY  
SHIFTED COLDER RELATIVE TO AUTOMATED GUIDANCE AS TELECONNECTIONS FROM A  
POSITIVE HEIGHT ANOMALY CENTER OVER THE GULF OF ALASKA, AND A NEGATIVE HEIGHT  
ANOMALY CENTER OVER HUDSON BAY SUPPORT COLDER THAN NORMAL TEMPERATURES ACROSS  
MUCH OF THESE REGIONS. ABOVE NORMAL TEMPERATURES ARE FAVORED FOR MUCH OF THE  
SOUTHERN HALF OF THE CONUS CORRESPONDING TO AN EXPECTED MEAN LOW AMPLITUDE FLOW  
PATTERN AND ABOVE NORMAL HEIGHTS. ENHANCED ABOVE NORMAL TEMPERATURE  
PROBABILITIES ARE RELATIVELY WEAK FOR THE CENTRAL AND SOUTHERN PLAINS TO  
REFLECT A POTENTIAL TRANSITION FROM ABOVE NORMAL TEMPERATURES EARLY IN THE  
PERIOD TO BELOW NORMAL TEMPERATURES NEAR THE END OF THE PERIOD.  
 
ABOVE NORMAL PRECIPITATION IS LIKELY ACROSS WESTERN AND CENTRAL ALASKA EAST OF  
A TROUGH EXPECTED OVER THE BERING SEA. DRIER THAN NORMAL CONDITIONS ARE FAVORED  
OVER MUCH OF THE WEST COAST OF THE CONUS AND THE ALASKA PANHANDLE IN  
ASSOCIATION WITH THE STRONG RIDGE OFFSHORE OF WESTERN NORTH AMERICA. TROUGH  
DEVELOPMENT OVER THE WESTERN CONUS LEADS TO ENHANCED PROBABILITIES FOR ABOVE  
NORMAL PRECIPITATION FROM PARTS OF THE SOUTHWEST TO THE NORTHERN PLAINS. ABOVE  
NORMAL PRECIPITATION IS MOST LIKELY FOR PARTS OF THE NORTHERN AND CENTRAL HIGH  
PLAINS DUE TO THE POTENTIAL FOR UPSLOPE FLOW. CYCLONIC FLOW AND BELOW NORMAL  
HEIGHTS LEAD TO ENHANCED PROBABILITIES FOR ABOVE NORMAL PRECIPITATION ACROSS  
MUCH OF THE GREAT LAKES REGION. DRIER THAN NORMAL CONDITIONS ARE LIKELY FOR THE  
FLORIDA PENINSULA IN ASSOCIATION WITH RIDGING OVER THE CARIBBEAN. THE POTENTIAL  
FOR MOIST FLOW AROUND THE WESTERN PERIPHERY OF THIS RIDGE LEADS TO ENHANCED  
PROBABILITIES FOR ABOVE NORMAL PRECIPITATION FOR MUCH OF THE REMAINDER OF THE  
SOUTHEASTERN CONUS. BELOW NORMAL PRECIPITATION IS FAVORED FOR PARTS OF THE  
MIDDLE MISSISSIPPI AND OHIO VALLEYS AND MID-ATLANTIC STATES UNDERNEATH FAST  
NORTHWESTERLY OR WESTERLY MID-LEVEL FLOW.  
 
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 15% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 8, 15% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 8, 10% OF TODAY'S OPERATIONAL 0Z GFS CENTERED ON DAY 8, 5% OF TODAY'S  
OPERATIONAL 6Z GFS CENTERED ON DAY 8, 20% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN  
CENTERED ON DAY 8, 5% OF YESTERDAY'S 12Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY  
7, 5% OF TODAY'S OPERATIONAL 0Z ECMWF CENTERED ON DAY 8, AND 25% OF TODAY'S 0Z  
CANADIAN ENSEMBLE MEAN CENTERED ON DAY 8  
 
 
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: AVERAGE, 3 OUT OF 5, DUE TO FAIRLY  
GOOD MODEL AGREEMENT OFFSET BY A POTENTIAL PATTERN CHANGE DURING THE OUTLOOK  
PERIOD.  
 
8-14 DAY OUTLOOK FOR DEC 21 - 27 2017  
 
DURING THE WEEK TWO PERIOD, MODELS DEPICT AN AMPLIFIED PATTERN AS A RIDGE  
STRENGTHENS OVER ALASKA AND OFF THE WEST COAST OF THE CONUS. DOWNSTREAM OF THIS  
RIDGE, A POSITIVELY TILTED TROUGH IS EXPECTED TO AMPLIFY OVER EAST-CENTRAL  
CANADA EXTENDING SOUTHWEST TO THE WEST-CENTRAL CONUS, WHILE A RIDGE IS  
ANTICIPATED TO BUILD OVER THE SOUTHEASTERN CONUS. THE AMPLIFICATION OF THE  
PATTERN IS EXPECTED TO RESULT IN RISING HEIGHTS OVER ALASKA AND FALLING HEIGHTS  
OVER MUCH OF THE NORTHERN PLAINS AND WEST-CENTRAL CONUS. THE WEEK TWO MANUAL  
500-HPA HEIGHT BLEND REPRESENTS A COMPROMISE OF THE CANADIAN, ECMWF, AND GEFS  
ENSEMBLE MEAN SOLUTIONS.  
 
ABOVE NORMAL TEMPERATURES ARE LIKELY FOR ALASKA AS A RIDGE AMPLIFIES OVER THE  
STATE. BELOW NORMAL TEMPERATURES ARE FAVORED DOWNSTREAM ACROSS THE NORTHERN  
THIRD OF THE CONUS AS WELL AS MUCH OF THE CENTRAL CONUS AS A TROUGH DEEPENS  
OVER CENTRAL NORTH AMERICA. RIDGING LEADS TO ENHANCED ABOVE NORMAL TEMPERATURE  
PROBABILITIES FOR THE SOUTHEASTERN CONUS. ABOVE NORMAL TEMPERATURES ARE WEAKLY  
FAVORED FOR THE SOUTHWESTERN CONUS CONSISTENT WITH CALIBRATED TEMPERATURES FROM  
THE GEFS AND ECMWF ENSEMBLE MEMBERS.  
 
MOIST FLOW AHEAD OF A TROUGH OVER THE WESTERN ALEUTIANS FAVORS ABOVE NORMAL  
PRECIPITATION FOR WESTERN AND CENTRAL MAINLAND ALASKA AS WELL AS THE EASTERN  
ALEUTIANS. DRIER THAN NORMAL CONDITIONS ARE LIKELY FOR MUCH OF THE NORTHWESTERN  
CONUS AS WELL AS THE ALASKA PANHANDLE DUE TO THE RIDGE EXPECTED OFF THE COAST.  
ABOVE NORMAL PRECIPITATION IS FAVORED FOR MUCH OF THE REMAINDER OF THE CONUS  
UNDERNEATH CYCLONIC FLOW. ABOVE NORMAL PRECIPITATION PROBABILITIES ARE THE  
HIGHEST FOR PARTS OF THE TENNESSEE AND LOWER MISSISSIPPI VALLEYS AHEAD OF THE  
POSITIVELY TILTED TROUGH OVER THE WEST-CENTRAL CONUS, AND FOR THE NORTHERN AND  
CENTRAL HIGH PLAINS DUE TO THE POTENTIAL FOR UPSLOPE FLOW. RIDGING AND ABOVE  
NORMAL HEIGHTS LEAD TO ENHANCED PROBABILITIES FOR BELOW NORMAL PRECIPITATION  
OVER PARTS OF THE FLORIDA PENINSULA.  
 
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 25% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 11, 15% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 11, 25% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 11, 5% OF  
YESTERDAY'S 12Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 10, 25% OF TODAY'S 0Z  
CANADIAN ENSEMBLE MEAN CENTERED ON DAY 11, AND 5% OF YESTERDAY'S 12Z CANADIAN  
ENSEMBLE MEAN CENTERED ON DAY 10  
 
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: ABOVE AVERAGE, 4 OUT OF 5, DUE TO  
PREDICTED PATTERN AMPLIFICATION.  
 
FORECASTER: SCOTT H  
 
NOTES:  
 
AUTOMATED FORECASTS ARE ISSUED ON SATURDAY AND SUNDAY. OCCASIONALLY MANUAL  
INTERVENTION IS NECESSARY TO ADDRESS QUALITY CONTROL AND CONSISTENCY ISSUES. IN  
THESE CASES, FORECASTS ARE MANUALLY DRAWN BUT A FULL DISCUSSION IS NOT ISSUED.  
 
THE NOTATION FOR THE CATEGORICAL FORECAST INDICATED ON THE MAPS IS THE SAME AS  
THAT IN THE TABLES: A-ABOVE N-NEAR NORMAL B-BELOW  
 
THE TEMPERATURE MAP SHOWS REGIONS WITH > 33% CHANCE OF BEING WARMER (ORANGE,  
"A"), COLDER (BLUE, "B"), OR CLOSE TO (UNSHADED, "N"). HISTORICAL AVERAGE  
VALUES FOR THE CALENDAR PERIOD OF THE FORECAST (DASHES, "F"). LABELS ON THE  
SHADED LINES GIVE THE PROBABILITY (> 33%) OF THE MORE LIKELY CATEGORY (B OR A).  
PROBABILITY OF N IS ALWAYS < 40%.  
 
THE PRECIPITATION MAP SHOWS REGIONS WITH > 33% CHANCE OF BEING WETTER (GREEN,  
"A"), DRIER (TAN, "B"), OR CLOSE TO (UNSHADED, "N"). HISTORICAL MEDIAN VALUES  
FOR THE CALENDAR PERIOD OF THE FORECAST (DASHES, "INCHES"). LABELS ON THE  
SHADED LINES GIVE THE PROBABILITY (> 33%) OF THE MORE LIKELY CATEGORY (B OR A).  
PROBABILITY OF N IS ALWAYS < 40%.  
 
IN THE SOUTHWEST AND OTHER CLIMATOLOGICALLY DRY REGIONS - THERE WILL BE A  
GREATER THAN 33.3% CHANCE OF NO PRECIPITATION AND OCCASIONALLY EVEN A NORMAL  
(I.E. MEDIAN) VALUE OF ZERO - ESPECIALLY DURING THE DRY SEASONS. IN SUCH CASES  
A FORECAST OF NEAR NORMAL IS EFFECTIVELY A FORECAST OF LITTLE OR NO  
PRECIPITATION.  
 
THE CLIMATE PREDICTION CENTER USES 1981-2010 BASE PERIOD MEANS FOR  
TEMPERATURE...PRECIPITATION...AND 500-HPA HEIGHTS AS REFERENCE IN THE CLIMATE  
OUTLOOKS.  
 
THE NEXT SET OF LONG-LEAD MONTHLY AND SEASONAL OUTLOOKS WILL BE RELEASED ON  
DECEMBER 21.  
 
ANALOGS TO THE 5 DAY MEAN OBSERVED PATTERN CENTERED 3 DAYS AGO (D-3)  
FOR THE REGION FROM 20N TO 70N LATITUDE AND 175E TO 60W LONGITUDE  
INCLUDE THE 5 DAY PERIODS CENTERED ON THE FOLLOWING DATES:  
19561128 - 19621211 - 19851219 - 19601222 - 19631201  
 
ANALOGS TO THE 7 DAY MEAN OBSERVED PATTERN CENTERED 4 DAYS AGO (D-4)  
FOR THE REGION FROM 20N TO 70N LATITUDE AND 175E TO 60W LONGITUDE  
INCLUDE THE 7 DAY PERIODS CENTERED ON THE FOLLOWING DATES:  
19561127 - 20021125 - 19851221 - 19601224 - 19631202  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 19 - 23 2017  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B B OREGON N B NRN CALIF A B  
SRN CALIF A N IDAHO N N NEVADA A B  
W MONTANA B A E MONTANA B A WYOMING N A  
UTAH A N ARIZONA A A COLORADO A A  
NEW MEXICO A N N DAKOTA N A S DAKOTA N A  
NEBRASKA A A KANSAS A B OKLAHOMA A N  
N TEXAS A N S TEXAS A N W TEXAS A N  
MINNESOTA B A IOWA N B MISSOURI A B  
ARKANSAS A A LOUISIANA A A WISCONSIN B N  
ILLINOIS N B MISSISSIPPI A A MICHIGAN B A  
INDIANA N B OHIO N N KENTUCKY N N  
TENNESSEE A A ALABAMA A A NEW YORK B N  
VERMONT B N NEW HAMP B N MAINE B N  
MASS B N CONN B N RHODE IS B N  
PENN N N NEW JERSEY N B W VIRGINIA N N  
MARYLAND N B DELAWARE N B VIRGINIA N N  
N CAROLINA A A S CAROLINA A A GEORGIA A A  
FL PNHDL A N FL PENIN A B AK N SLOPE A A  
AK ALEUTIAN A A AK WESTERN A A AK INT BSN A A  
AK S INT A A AK SO COAST A A AK PNHDL B B  
 
 
 
8-14 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 21 - 27 2017  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B B OREGON B B NRN CALIF A B  
SRN CALIF A N IDAHO B B NEVADA N B  
W MONTANA B A E MONTANA B A WYOMING B A  
UTAH N A ARIZONA A A COLORADO B A  
NEW MEXICO B A N DAKOTA B A S DAKOTA B A  
NEBRASKA B A KANSAS B A OKLAHOMA B A  
N TEXAS B A S TEXAS B A W TEXAS B A  
MINNESOTA B A IOWA B A MISSOURI B A  
ARKANSAS B A LOUISIANA N A WISCONSIN B A  
ILLINOIS B A MISSISSIPPI N A MICHIGAN B A  
INDIANA B A OHIO B A KENTUCKY B A  
TENNESSEE N A ALABAMA A A NEW YORK B A  
VERMONT B A NEW HAMP B A MAINE B A  
MASS B A CONN B A RHODE IS B A  
PENN B A NEW JERSEY N A W VIRGINIA N A  
MARYLAND N A DELAWARE N A VIRGINIA N A  
N CAROLINA A A S CAROLINA A A GEORGIA A A  
FL PNHDL A A FL PENIN A B AK N SLOPE A A  
AK ALEUTIAN A A AK WESTERN A A AK INT BSN A A  
AK S INT A A AK SO COAST A A AK PNHDL N B  
 
LEGEND  
TEMPS WITH RESPECT TO NORMAL PCPN WITH RESPECT TO MEDIAN  
A - ABOVE N - NEAR NORMAL A - ABOVE N - NEAR MEDIAN  
B - BELOW B - BELOW  
 
THE FORECAST CLASSES REPRESENT AVERAGES FOR EACH STATE. NORMAL  
VALUES - WHICH MAY VARY WIDELY ACROSS SOME STATES - ARE  
AVAILABLE FROM YOUR LOCAL WEATHER SERVICE FORECAST OFFICE.  
 
FOR ADDITIONAL INFORMATION SEE MESSAGE FXUS06 KWBC - ON AWIPS AS  
PMDMRD.  
 

 
 
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