170  
FXUS06 KWBC 202013  
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 20 2017  
 
6-10 DAY OUTLOOK FOR DEC 26 - 30 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 AND ACROSS THE SOUTHERN CONUS. THE ECMWF ENSEMBLE AVERAGE PREDICTS THE  
TROUGH OVER THE NORTH-CENTRAL CONUS, WITH NEGATIVE 500-HPA HEIGHT ANOMALIES  
EXTENDING FURTHER WEST AND SOUTH, RELATIVE TO THE NCEP GEFS ENSEMBLE AVERAGE,  
WHICH CENTERS THE TROUGH FURTHER EAST. THE 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 POSITIVE 500-HPA HEIGHT ANOMALIES.  
BELOW NORMAL TEMPERATURES ARE MORE LIKELY FOR THE 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 FROM THE NORTHERN PLAINS ACROSS THE GREAT LAKES TO NEW ENGLAND.  
UNDER PREDICTED 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 THE GREAT BASIN AND SOUTHWEST,  
WITH THE EXPECTED INFLUX OF WARM PACIFIC AIR.  
 
BELOW NORMAL PRECIPITATION IS LIKELY FOR MOST OF ALASKA UNDER A PREDICTED  
RIDGE, OUTSIDE OF THE CLIMATOLOGICALLY DRY NORTH SLOPE REGION. THE PREDICTED  
TROUGH OVER THE CENTRAL CONUS ENHANCES THE PROBABILITY OF ABOVE NORMAL  
PRECIPITATION TO THE EAST OF THE NORTHERN ROCKIES INTO THE CENTRAL AND SOUTHERN  
PLAINS STATES, ACROSS THE CENTRAL MISSISSIPPI VALLEY AND NORTHEASTWARD INTO THE  
MID-ATLANTIC AND SOUTHERN NEW ENGLAND, FOLLOWING THE PREDICTED MEAN FRONTAL  
BOUNDARY. BELOW NORMAL PRECIPITATION IS LIKELY FOR CALIFORNIA AND PARTS OF  
NEVADA UNDER PREDICTED ANOMALOUS NORTHERLY 500-HPA FLOW.  
 
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, 50% 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 28, 2017 - JAN 03, 2018  
 
IN THE WEEK 2 PERIOD, MODEL FORECASTS PREDICT A SLIGHTLY LESS AMPLIFIED 500-HPA  
TROUGH, RELATIVE TO THE 6-10 DAY PERIOD, AS A RESULT OF INCREASING ENSEMBLE  
SPREAD AND FORECAST UNCERTAINTY, ALONG WITH SOME EASTWARD PROGRESSION OVER THE  
CONUS. 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 LIKELY FOR MOST OF ALASKA, UNDER THE PREDICTED  
RIDGE, EXCEPT FOR SOUTHEASTERN REGIONS OF THE STATE. 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 THE SOUTHWEST  
CONUS WITH AN INFLUX OF PACIFIC AIR PREDICTED FOR THE REGION.  
 
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 ACROSS THE CENTRAL AND  
LOWER MISSISSIPPI VALLEY AND FROM THE SOUTHEAST TO SOUTHERN NEW ENGLAND IN THE  
EAST. THE LIKELIHOOD OF ABOVE NORMAL PRECIPITATION INCREASES IN WEEK 2 FOR  
FLORIDA, AS MEAN 500-HPA HEIGHTS DECREASE IN MODEL FORECASTS.  
 
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 10% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 11, 20% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 11, 50% 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: ABOVE AVERAGE, 4 OUT OF 5, DUE TO  
AN AMPLIFIED PREDICTED CIRCULATION PATTERN, OFFSET BY INCREASING ENSEMBLE  
SPREAD.  
 
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 - 19921222 - 19711216 - 19781202 - 19531229  
 
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:  
19791206 - 19921222 - 19711215 - 20071207 - 19841223  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 26 - 30 2017  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B B OREGON B N NRN CALIF A B  
SRN CALIF A B IDAHO B N NEVADA A B  
W MONTANA B A E MONTANA B A WYOMING B A  
UTAH A N ARIZONA A N COLORADO B A  
NEW MEXICO A A N DAKOTA B A S DAKOTA B A  
NEBRASKA B A KANSAS B A OKLAHOMA B A  
N TEXAS B A S TEXAS N A W TEXAS B A  
MINNESOTA B B IOWA B A MISSOURI B A  
ARKANSAS B A LOUISIANA B A WISCONSIN B N  
ILLINOIS B A MISSISSIPPI B A MICHIGAN B N  
INDIANA B A OHIO B A KENTUCKY B A  
TENNESSEE B A ALABAMA B A NEW YORK B N  
VERMONT B N NEW HAMP B N MAINE B B  
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 N GEORGIA B N  
FL PNHDL N B FL PENIN A N AK N SLOPE A N  
AK ALEUTIAN A N AK WESTERN A B AK INT BSN A B  
AK S INT N B AK SO COAST N B AK PNHDL B B  
 
 
 
8-14 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 28, 2017 - JAN 03, 2018  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B N OREGON B N NRN CALIF A B  
SRN CALIF A B IDAHO B N NEVADA A B  
W MONTANA B A E MONTANA B A WYOMING B A  
UTAH A N ARIZONA A N COLORADO B A  
NEW MEXICO A 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 B IOWA B A MISSOURI B A  
ARKANSAS B A LOUISIANA B A WISCONSIN B N  
ILLINOIS B A MISSISSIPPI B A MICHIGAN B N  
INDIANA B A OHIO B A KENTUCKY B A  
TENNESSEE B A ALABAMA B A NEW YORK B N  
VERMONT B N NEW HAMP B N MAINE B N  
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 B A FL PENIN A A AK N SLOPE A N  
AK ALEUTIAN A N 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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