400  
FXUS06 KWBC 152001  
PMDMRD  
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD  
300 PM EST FRI DECEMBER 15 2017  
 
6-10 DAY OUTLOOK FOR DEC 21 - 25 2017  
 
TODAY'S MODEL SOLUTIONS GENERALLY DEPICT HIGHLY AMPLIFIED 500-HPA FLOW OVER  
MUCH OF THE FORECAST DOMAIN. IN THE MEAN, BROAD CYCLONIC FLOW IS INDICATED OVER  
MUCH OF THE CONUS AS TROUGHING EXTENDS FROM EAST-CENTRAL CANADA TO THE  
SOUTHWESTERN CONUS. FARTHER TO THE SOUTH AND EAST, A RIDGE IS FORECAST NEAR  
CUBA AND ABOVE NORMAL HEIGHTS ASSOCIATED WITH THIS RIDGE EXTEND NORTHWARD TO  
THE SOUTHEASTERN CONUS AND MUCH OF THE EASTERN SEABOARD. A STRONG RIDGE IS  
FORECAST OVER THE EASTERN PACIFIC OFF THE WEST COAST OF THE CONUS EXTENDING  
NORTHWARD TO EASTERN MAINLAND ALASKA. ENSEMBLE SPREAD HAS ONCE AGAIN INCREASED  
OVER THE WESTERN CONUS DUE TO MODEL DIFFERENCES ON THE DETAILS OF DOWNSTREAM  
TROUGH DEVELOPMENT OVER THE SOUTHWESTERN CONUS. THE DETERMINISTIC 12Z GFS AND  
0Z ECMWF NOW DEPICT A CUTOFF 500-HPA LOW OVER OR NEAR THE SOUTHWESTERN CONUS  
INCREASING FORECAST UNCERTAINTY FOR THIS REGION. 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 PARTS OF  
THE SOUTHERN PANHANDLE). AS A POSITIVELY TILTED TROUGH DEEPENS OVER CENTRAL  
NORTH AMERICA, BELOW NORMAL TEMPERATURES ARE FAVORED FOR MUCH OF THE CENTRAL,  
WESTERN, AND NORTHERN CONUS. TELECONNECTIONS FROM A POSITIVE 500-HPA HEIGHT  
ANOMALY CENTER WEST OF BRITISH COLUMBIA, AND A NEGATIVE 500-HPA HEIGHT ANOMALY  
CENTER NEAR HUDSON BAY SUPPORT COLDER THAN NORMAL TEMPERATURES ACROSS MUCH OF  
THESE REGIONS. ABOVE NORMAL TEMPERATURES ARE FAVORED FOR MUCH OF THE  
SOUTHEASTERN CONUS CORRESPONDING TO RIDGING AND ABOVE NORMAL HEIGHTS. ENHANCED  
PROBABILITIES FOR NEAR NORMAL TEMPERATURES ARE INDICATED FOR PARTS OF THE  
SOUTHWESTERN CONUS TO REFLECT RELATIVELY HIGH MODEL UNCERTAINTY AND CONFLICTING  
GUIDANCE FROM THE DYNAMICAL AND STATISTICAL TEMPERATURE TOOLS.  
 
ABOVE NORMAL PRECIPITATION IS LIKELY ACROSS MOST OF ALASKA (WITH THE EXCEPTION  
OF THE PANHANDLE) 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 MUCH  
OF THE ALASKA PANHANDLE IN ASSOCIATION WITH THE STRONG RIDGE OFFSHORE OF  
WESTERN NORTH AMERICA. TROUGH DEVELOPMENT LEADS TO ENHANCED PROBABILITIES FOR  
ABOVE NORMAL PRECIPITATION FOR THE WEST-CENTRAL CONUS. ABOVE NORMAL  
PRECIPITATION IS MOST LIKELY FOR PARTS OF THE NORTHERN AND CENTRAL HIGH PLAINS  
DUE TO THE POTENTIAL FOR UPSLOPE FLOW. DRIER THAN NORMAL CONDITIONS ARE LIKELY  
FOR PARTS OF 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 FROM THE  
SOUTHERN PLAINS NORTHEASTWARD TO MOST OF THE EASTERN CONUS.  
 
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 10% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 8, 20% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 8, 5% OF TODAY'S OPERATIONAL 0Z GFS CENTERED ON DAY 8, 25% 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, 20% 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: ABOVE AVERAGE, 4 OUT OF 5, DUE TO  
GOOD MODEL AGREEMENT ON A HIGHLY AMPLIFIED FLOW PATTERN.  
 
8-14 DAY OUTLOOK FOR DEC 23 - 29 2017  
 
DURING THE WEEK TWO PERIOD, MODELS DEPICT AN AMPLIFIED PATTERN AS STRONG  
RIDGING CONTINUES OVER ALASKA AND OFF THE WEST COAST OF THE CONUS. DOWNSTREAM  
OF THIS RIDGE, TROUGHING AND BELOW NORMAL HEIGHTS ARE EXPECTED FROM  
EAST-CENTRAL CANADA TO THE SOUTHWESTERN CONUS, WHILE A RIDGE IS ANTICIPATED  
OVER THE SOUTHEASTERN CONUS. MODELS HAVE TRENDED WEAKER WITH THE RIDGE OVER THE  
SOUTHEAST RELATIVE TO YESTERDAY BUT STILL MAINTAIN ABOVE NORMAL HEIGHTS ACROSS  
MUCH OF THE REGION. THE WEEK TWO MANUAL 500-HPA HEIGHT BLEND REPRESENTS A  
COMPROMISE OF THE ECMWF, GEFS, AND CANADIAN ENSEMBLE MEAN SOLUTIONS.  
 
ABOVE NORMAL TEMPERATURES ARE LIKELY FOR ALASKA DUE TO THE AMPLIFIED RIDGE OVER  
THE STATE. BELOW NORMAL TEMPERATURES ARE FAVORED DOWNSTREAM ACROSS THE CENTRAL  
CONUS AND MUCH OF THE WESTERN CONUS AS TROUGHING CONTINUES OVER THESE REGIONS.  
HOWEVER, ENHANCED PROBABILITIES FOR NEAR NORMAL TEMPERATURES ARE INDICATED FOR  
PARTS OF THE SOUTHWESTERN CONUS TO REFLECT CONFLICTING DYNAMICAL AND  
STATISTICAL TEMPERATURE GUIDANCE. RIDGING LEADS TO ENHANCED ABOVE NORMAL  
TEMPERATURE PROBABILITIES FOR PARTS OF THE SOUTHEASTERN CONUS. BELOW NORMAL  
TEMPERATURES ARE FAVORED FOR THE GREAT LAKES AND NORTHEAST IN ASSOCIATION WITH  
THE TROUGH OVER EAST-CENTRAL CANADA.  
 
MOIST FLOW AHEAD OF A TROUGH NEAR THE WESTERN ALEUTIANS FAVORS ABOVE NORMAL  
PRECIPITATION FOR MOST OF MAINLAND ALASKA AS WELL AS MUCH OF THE ALEUTIANS.  
DRIER THAN NORMAL CONDITIONS ARE LIKELY FOR THE NORTHWESTERN CONUS AS WELL AS  
MUCH OF 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 LOWER MISSISSIPPI AND TENNESSEE VALLEYS NEAR THE  
WESTERN PERIPHERY OF THE RIDGE OVER THE SOUTHEASTERN CONUS AND FOR THE CENTRAL  
AND NORTHERN HIGH PLAINS DUE TO THE POTENTIAL FOR UPSLOPE FLOW.  
 
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 20% 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, 20% 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  
A PREDICTED AMPLIFIED PATTERN.  
 
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 - 20021129 - 19881215 - 19561129 - 19991225  
 
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:  
19851218 - 19881214 - 19851223 - 20021129 - 19991225  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 21 - 25 2017  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B B OREGON B B NRN CALIF N B  
SRN CALIF N N IDAHO B B NEVADA B B  
W MONTANA B A E MONTANA B A WYOMING B A  
UTAH B N ARIZONA N N 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 N A KENTUCKY N 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 N A RHODE IS N A  
PENN N A NEW JERSEY N A W VIRGINIA N A  
MARYLAND A A DELAWARE A A VIRGINIA A 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 A B  
 
 
 
8-14 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 23 - 29 2017  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B B OREGON B B NRN CALIF N B  
SRN CALIF N N IDAHO B B NEVADA N B  
W MONTANA B A E MONTANA B A WYOMING B A  
UTAH B N ARIZONA B N 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 N IOWA B A MISSOURI B A  
ARKANSAS B A LOUISIANA B A WISCONSIN B N  
ILLINOIS B A MISSISSIPPI B A MICHIGAN B A  
INDIANA B A OHIO B A KENTUCKY B A  
TENNESSEE N A ALABAMA N 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 N A S CAROLINA A A GEORGIA A A  
FL PNHDL A N FL PENIN A N 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 A 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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