306  
FXUS06 KWBC 122024  
PMDMRD  
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD  
300 PM EST TUE DECEMBER 12 2017  
 
6-10 DAY OUTLOOK FOR DEC 18 - 22 2017  
 
TODAY'S MODEL SOLUTIONS GENERALLY DEPICT LOW TO 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 THE EASTERN  
TWO-THIRDS OF THE CONUS ASSOCIATED WITH A TROUGH CENTERED OVER EAST-CENTRAL  
CANADA. A STRENGTHENING 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 NEAR THE 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, GEFS,  
AND ECMWF ENSEMBLE SYSTEMS.  
 
ABOVE NORMAL TEMPERATURES ARE FAVORED FOR MUCH OF THE SOUTHERN CONUS  
CORRESPONDING TO AN EXPECTED MEAN LOW AMPLITUDE FLOW PATTERN AND ABOVE NORMAL  
HEIGHTS. CYCLONIC FLOW AND BELOW NORMAL HEIGHTS LEAD TO ENHANCED PROBABILITIES  
FOR BELOW NORMAL TEMPERATURES FOR PARTS OF THE NORTHEAST. NEAR NORMAL  
TEMPERATURES ARE FAVORED ACROSS MUCH OF THE REMAINDER OF THE NORTHERN TIER OF  
THE CONUS TO REFLECT A POTENTIAL TRANSITION FROM ABOVE NORMAL TEMPERATURES  
EARLY IN THE PERIOD TO BELOW NORMAL TEMPERATURES NEAR THE END OF THE PERIOD.  
CATEGORICAL TEMPERATURE PROBABILITIES ACROSS THE NORTHERN CONUS WERE GENERALLY  
SHIFTED COLDER RELATIVE TO AUTOMATED GUIDANCE AS TELECONNECTIONS FROM A  
POSITIVE HEIGHT ANOMALY CENTER SOUTH OF THE ALASKA PENINSULA AND A NEGATIVE  
HEIGHT ANOMALY CENTER OVER HUDSON BAY BOTH SUPPORT COLDER THAN NORMAL  
TEMPERATURES ACROSS MUCH OF THE NORTHERN CONUS. THE RIDGE EXPECTED OVER  
MAINLAND ALASKA INCREASES PROBABILITIES FOR ABOVE NORMAL TEMPERATURES ACROSS  
MOST OF THE STATE (WITH THE EXCEPTION OF THE PANHANDLE).  
 
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 SOUTHERN TWO-THIRDS OF THE CONUS FROM THE PLAINS WESTWARD  
UNDERNEATH ABOVE NORMAL HEIGHTS. CYCLONIC FLOW LEADS TO ENHANCED PROBABILITIES  
FOR ABOVE NORMAL PRECIPITATION ACROSS MUCH OF THE NORTHERN TIER OF THE CONUS.  
DRIER THAN NORMAL CONDITIONS ARE LIKELY FOR THE FLORIDA PENINSULA IN  
ASSOCIATION WITH MEAN SURFACE HIGH PRESSURE. THE POTENTIAL FOR MOIST RETURN  
FLOW AROUND THIS SURFACE HIGH LEADS TO ENHANCED PROBABILITIES FOR ABOVE NORMAL  
PRECIPITATION FOR PARTS OF THE TENNESSEE AND LOWER MISSISSIPPI VALLEYS. BELOW  
NORMAL PRECIPITATION IS FAVORED FOR PARTS OF THE MID-ATLANTIC STATES UNDERNEATH  
FAST 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, 5% OF TODAY'S OPERATIONAL 0Z 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, 10% OF TODAY'S OPERATIONAL 0Z ECMWF CENTERED  
ON DAY 8, 25% OF TODAY'S 0Z CANADIAN ENSEMBLE MEAN CENTERED ON DAY 8, AND 5% OF  
YESTERDAY'S 12Z CANADIAN ENSEMBLE MEAN CENTERED ON DAY 7  
 
 
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: AVERAGE, 3 OUT OF 5, DUE TO FAIR  
MODEL AGREEMENT.  
 
8-14 DAY OUTLOOK FOR DEC 20 - 26 2017  
 
DURING THE WEEK TWO PERIOD, MODELS DEPICT A TRANSITION TO A MORE 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 A TROUGH DEEPENS OVER CENTRAL NORTH AMERICA. ABOVE NORMAL  
TEMPERATURE PROBABILITIES ARE ENHANCED ACROSS MUCH OF THE SOUTHERN CONUS  
UNDERNEATH NEAR TO ABOVE NORMAL HEIGHTS.  
 
MOIST FLOW AHEAD OF A TROUGH OVER THE WESTERN ALEUTIANS FAVORS ABOVE NORMAL  
PRECIPITATION FOR WESTERN AND CENTRAL MAINLAND ALASKA AS WELL AS THE CENTRAL  
AND EASTERN ALEUTIANS. DRIER THAN NORMAL CONDITIONS ARE LIKELY FOR MUCH OF THE  
WESTERN QUARTER OF THE CONUS AS WELL AS THE ALASKA PANHANDLE DUE TO THE RIDGE  
EXPECTED OFF THE COAST. ABOVE NORMAL PRECIPITATION IS FAVORED FROM THE SOUTHERN  
PLAINS TO THE EAST COAST AHEAD OF THE POSITIVELY TILTED TROUGH OVER THE  
WEST-CENTRAL CONUS. THERE ARE ELEVATED CHANCES FOR NEAR TO ABOVE NORMAL  
PRECIPITATION ACROSS THE NORTHERN TIER OF THE CONUS EAST OF THE ROCKIES  
UNDERNEATH CYCLONIC FLOW AND BELOW NORMAL HEIGHTS. ABOVE NORMAL PRECIPITATION  
IS FAVORED FOR MUCH OF THE HIGH PLAINS AND PARTS OF THE ROCKIES DUE TO A  
PREDICTED TROUGH AND THE POTENTIAL FOR UPSLOPE FLOW.  
 
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 15% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 11, 20% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 11, 30% 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: AVERAGE, 3 OUT OF 5, DUE TO  
PREDICTED PATTERN AMPLIFICATION OFFSET BY LARGE DISAGREEMENTS BETWEEN  
STATISTICAL AND DYNAMICAL MODEL GUIDANCE ON THE TEMPERATURE OUTLOOK ACROSS MUCH  
OF THE CONUS.  
 
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:  
19851219 - 19561126 - 19631201 - 20021126 - 19601222  
 
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:  
19561126 - 20021125 - 19851221 - 19631201 - 19601223  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 18 - 22 2017  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON N B OREGON N B NRN CALIF A B  
SRN CALIF A B IDAHO A N NEVADA A B  
W MONTANA N A E MONTANA N A WYOMING A A  
UTAH A B ARIZONA A N COLORADO A N  
NEW MEXICO A B N DAKOTA A A S DAKOTA A N  
NEBRASKA A B KANSAS A B OKLAHOMA A B  
N TEXAS A N S TEXAS A N W TEXAS A B  
MINNESOTA A A IOWA A B MISSOURI A B  
ARKANSAS A A LOUISIANA A N WISCONSIN N A  
ILLINOIS A B MISSISSIPPI A A MICHIGAN N A  
INDIANA A N OHIO N N KENTUCKY A A  
TENNESSEE A A ALABAMA A A NEW YORK B A  
VERMONT B A NEW HAMP B A MAINE B A  
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 B  
N CAROLINA A N S CAROLINA A N GEORGIA A N  
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 N B  
 
 
 
8-14 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 20 - 26 2017  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B B OREGON B B NRN CALIF A B  
SRN CALIF A B IDAHO B B NEVADA N B  
W MONTANA B A E MONTANA B A WYOMING B A  
UTAH N N ARIZONA A N COLORADO N A  
NEW MEXICO A A N DAKOTA B A S DAKOTA B A  
NEBRASKA B A KANSAS N N OKLAHOMA N A  
N TEXAS A A S TEXAS A A W TEXAS A A  
MINNESOTA B A IOWA B N MISSOURI N N  
ARKANSAS A A LOUISIANA A A WISCONSIN B A  
ILLINOIS N N MISSISSIPPI A A MICHIGAN B A  
INDIANA N A OHIO N A KENTUCKY A A  
TENNESSEE A 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 N 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 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 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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