938  
FXUS06 KWBC 192053  
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 19 2017  
 
6-10 DAY OUTLOOK FOR DEC 25 - 29 2017  
 
TODAY'S MODEL FORECASTS ARE IN GOOD AGREEMENT ON A PREDICTED AMPLIFIED 500-HPA  
CIRCULATION PATTERN FOR THE 6-10 DAY PERIOD. ENSEMBLE PREDICTION SYSTEMS FROM  
THE NCEP GEFS, ECMWF, AND ENVIRONMENT CANADA PREDICT A STRONG RIDGE OVER THE  
NORTH PACIFIC AND ALASKA, A DOWNSTREAM TROUGH EXTENDING FROM NORTHERN QUEBEC  
INTO THE NORTH-CENTRAL CONUS, AND ABOVE NORMAL 500-HPA HEIGHTS OVER THE WESTERN  
CONUS, AS WELL AS THE SOUTH-CENTRAL CONUS AND SOUTHEAST. THE ECMWF ENSEMBLE  
AVERAGE PREDICTS A SLIGHTLY MORE AMPLIFIED TROUGH OVER THE NORTH-CENTRAL CONUS,  
WITH NEGATIVE 500-HPA HEIGHT ANOMALIES EXTENDING FURTHER WEST AND SOUTH,  
RELATIVE TO THE AVERAGE OF ENSEMBLE MEMBERS FROM THE ENVIRONMENT CANADA AND  
NCEP GEFS PREDICTION SYSTEMS. THE GREATER AMPLITUDE 500-HPA FLOW PATTERN OF THE  
ECMWF ENSEMBLE PREDICTION SYSTEM IS WEIGHTED MORE HEAVILY IN THE OFFICIAL  
500-HPA HEIGHT BLEND.  
 
ABOVE NORMAL TEMPERATURES ARE LIKELY FOR MOST OF ALASKA, EXCEPT FOR  
SOUTHEASTERN REGIONS OF THE STATE, UNDER LARGE POSITIVE 500-HPA HEIGHT  
ANOMALIES AND ANOMALOUS SOUTHERLY FLOW. BELOW NORMAL TEMPERATURES ARE MORE  
LIKELY FOR THE SOUTHERN ALASKA PANHANDLE, UNDER NORTHERLY FLOW AHEAD OF THE  
PREDICTED RIDGE. BELOW NORMAL TEMPERATURES ARE LIKELY FOR A LARGE AREA OF THE  
CONUS, UNDER A PREDICTED AMPLIFIED TROUGH AND AN INFLUX OF ARCTIC AIR.  
PROBABILITIES EXCEED 80 PERCENT OVER A LARGE AREA OF THE NORTHERN CONUS. UNDER  
PREDICTED ANOMALOUS SOUTHERLY FLOW AND ABOVE NORMAL 500-HPA HEIGHTS, ABOVE  
NORMAL TEMPERATURES ARE LIKELY FOR THE FLORIDA PENINSULA. ABOVE NORMAL  
TEMPERATURES ARE MOST LIKELY FOR PARTS OF CALIFORNIA INTO ARIZONA AND SOUTHERN  
NEVADA, UNDER ABOVE NORMAL 500-HPA HEIGHTS.  
 
BELOW NORMAL PRECIPITATION IS LIKELY FOR SOUTHERN ALASKA UNDER A PREDICTED  
RIDGE. THE PREDICTED TROUGH OVER THE CENTRAL CONUS ENHANCES THE PROBABILITY OF  
ABOVE NORMAL PRECIPITATION FROM EASTERN MONTANA AND WYOMING INTO PARTS OF THE  
CENTRAL AND SOUTHERN PLAINS STATES, ACROSS THE SOUTHEAST AND NORTHEASTWARD INTO  
THE MID-ATLANTIC AND NEW ENGLAND, FOLLOWING THE PREDICTED MEAN FRONTAL  
BOUNDARY. BELOW NORMAL PRECIPITATION IS LIKELY FOR THE WEST UNDER PREDICTED  
ANOMALOUS NORTHERLY 500-HPA FLOW. THE GEFS ENSEMBLE INDICATES A GREATER  
PROBABILITY OF ABOVE NORMAL PRECIPITATION FOR PARTS OF THE SOUTHWEST, HOWEVER  
THE DRIER FORECAST OF THE ECMWF ENSEMBLE WAS FAVORED. BELOW NORMAL  
PRECIPITATION IS LIKELY FOR EASTERN REGIONS OF THE NORTHERN PLAINS WITH AN  
INFLUX OF DRY ARCTIC AIR.  
 
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 15% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 8, 20% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 8, 45% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 8, AND 20%  
OF TODAY'S 0Z CANADIAN ENSEMBLE MEAN CENTERED ON DAY 8  
 
 
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, WITH SOME AREAS OF  
DISAGREEMENT IN THE PRECIPITATION FORECAST.  
 
8-14 DAY OUTLOOK FOR DEC 27, 2017 - JAN 02, 2018  
 
MODEL FORECASTS PREDICT A SLIGHTLY LESS AMPLIFIED 500-HPA TROUGH, AS A RESULT  
OF INCREASING ENSEMBLE SPREAD AND FORECAST UNCERTAINTY, ALONG WITH SOME  
EASTWARD PROGRESSION OVER THE CONUS IN THE WEEK 2 PERIOD. THE ECMWF ENSEMBLE  
AVERAGE MAINTAINS A MORE AMPLIFIED TROUGH INTO THE WEEK 2 PERIOD, RELATIVE TO  
THE NCEP GEFS AND ENVIRONMENT CANADA ENSEMBLE PREDICTION SYSTEMS.  
 
ABOVE NORMAL TEMPERATURES REMAIN VERY LIKELY FOR MOST OF ALASKA, EXCEPT FOR  
SOUTHEASTERN REGIONS OF THE STATE, UNDER THE PREDICTED RIDGE. BELOW NORMAL  
TEMPERATURES ARE MOST LIKELY FOR THE ALASKA PANHANDLE, UNDER ANOMALOUS  
NORTHERLY FLOW. BELOW NORMAL TEMPERATURES CONTINUE TO BE LIKELY FOR A LARGE  
AREA OF THE CONUS, UNDER THE PREDICTED TROUGH. ABOVE NORMAL TEMPERATURES ARE  
LIKELY OVER PARTS OF SOUTHERN CALIFORNIA AND THE SOUTHWEST WITH AN INFLUX OF  
PACIFIC AIR PREDICTED FOR THE REGION. AREAS WITH THE GREATEST PROBABILITIES OF  
BELOW NORMAL TEMPERATURES HAVE SHIFTED SLIGHTLY EASTWARD IN WEEK 2, RELATIVE TO  
THE 6-10 DAY PERIOD FORECAST, WITH THE EASTWARD PROGRESSION OF THE TROUGH OVER  
THE CENTRAL CONUS.  
 
WITH THE PREDICTED RIDGE OVER ALASKA, BELOW NORMAL PRECIPITATION IS LIKELY OVER  
MOST AREAS OF THE STATE OUTSIDE THE CLIMATOLOGICALLY DRY NORTH SLOPE. THE  
PRECIPITATION FORECAST OVER THE CONUS FOR WEEK 2 IS VERY SIMILAR TO THE 6-10  
DAY PERIOD FORECAST. ABOVE NORMAL PRECIPITATION IS LIKELY FROM EASTERN MONTANA  
AND WYOMING ACROSS THE CENTRAL AND SOUTHERN GREAT PLAINS INTO THE SOUTHEAST,  
OHIO VALLEY, AND MID-ATLANTIC.  
 
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, 45% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 11, AND 20%  
OF TODAY'S 0Z CANADIAN ENSEMBLE MEAN CENTERED ON DAY 11  
 
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: ABOUT AVERAGE, 3 OUT OF 5, DUE TO  
A LESS AMPLIFIED PREDICTED CIRCULATION PATTERN IN WEEK 2, RELATIVE TO THE 6-10  
DAY PERIOD.  
 
FORECASTER: D COLLINS  
 
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:  
19791203 - 19531229 - 19601229 - 19921223 - 20071213  
 
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:  
19791203 - 19921222 - 20071212 - 19531228 - 19711216  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 25 - 29 2017  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B B OREGON B B NRN CALIF N B  
SRN CALIF A B IDAHO B B NEVADA B B  
W MONTANA B A E MONTANA B A WYOMING B A  
UTAH B B ARIZONA A N COLORADO B A  
NEW MEXICO B N N DAKOTA B B S DAKOTA B N  
NEBRASKA B N KANSAS B A OKLAHOMA B A  
N TEXAS B A S TEXAS B A W TEXAS B A  
MINNESOTA B B IOWA B N MISSOURI B N  
ARKANSAS B A LOUISIANA B A WISCONSIN B B  
ILLINOIS B N MISSISSIPPI B A MICHIGAN B N  
INDIANA B N OHIO B N KENTUCKY B A  
TENNESSEE B A ALABAMA B 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 B A W VIRGINIA B A  
MARYLAND B A DELAWARE B A VIRGINIA B A  
N CAROLINA B A S CAROLINA B A GEORGIA B A  
FL PNHDL N N FL PENIN A N AK N SLOPE A N  
AK ALEUTIAN A B AK WESTERN A B AK INT BSN A B  
AK S INT A B AK SO COAST A B AK PNHDL B B  
 
 
 
8-14 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 27, 2017 - JAN 02, 2018  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B B OREGON B B NRN CALIF N B  
SRN CALIF A N IDAHO B N NEVADA N B  
W MONTANA B N E MONTANA B A WYOMING B A  
UTAH N N ARIZONA A N COLORADO B A  
NEW MEXICO N A N DAKOTA B N 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 B IOWA B N MISSOURI B A  
ARKANSAS B A LOUISIANA B A WISCONSIN B B  
ILLINOIS B A MISSISSIPPI B A MICHIGAN B N  
INDIANA B N OHIO B A KENTUCKY B A  
TENNESSEE B A ALABAMA B A NEW YORK B N  
VERMONT B B NEW HAMP B N MAINE B B  
MASS B N CONN B N RHODE IS B N  
PENN B A NEW JERSEY B N W VIRGINIA B A  
MARYLAND B A DELAWARE B A VIRGINIA B A  
N CAROLINA B A S CAROLINA B A GEORGIA B A  
FL PNHDL N A FL PENIN A A AK N SLOPE A N  
AK ALEUTIAN A B AK WESTERN A B AK INT BSN A B  
AK S INT N B AK SO COAST N B AK PNHDL B 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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