530  
FXUS06 KWBC 212047  
PMDMRD  
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD  
300 PM EST THU DECEMBER 21 2017  
 
6-10 DAY OUTLOOK FOR DEC 27 - 31 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 500-HPA FLOW PATTERN OF THE ECMWF  
ENSEMBLE PREDICTION SYSTEM IS WEIGHTED MORE HEAVILY IN THE OFFICIAL 500-HPA  
HEIGHT BLEND BASED ON CONSIDERATIONS OF RECENT FORECAST SKILL.  
 
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 SOUTHEASTERLY FLOW, ABOVE NORMAL TEMPERATURES ARE FAVORED FOR  
THE FLORIDA PENINSULA. ABOVE NORMAL TEMPERATURES ARE MOST LIKELY FOR LARGE  
PARTS OF CALIFORNIA INTO THE GREAT BASIN AND SOUTHWEST, UNDER PREDICTED ABOVE  
NORMAL HEIGHTS.  
 
ABOVE NORMAL PRECIPITATION IS FAVORED FOR SOUTHWESTERN ALASKA AND THE ALEUTIANS  
AHEAD OF A PREDICTED TROUGH. BELOW NORMAL PRECIPITATION IS LIKELY FOR MOST OF  
ALASKA UNDER A PREDICTED RIDGE. THE PREDICTED TROUGH OVER THE CENTRAL EASTERN  
CONUS ENHANCES THE PROBABILITY OF ABOVE NORMAL PRECIPITATION FOR THE PARTS OF  
THE NORTHERN ROCKIES INTO THE GREAT PLAINS STATES AND ACROSS THE CENTRAL AND  
EASTERN CONUS, FOLLOWING THE PREDICTED MEAN FRONTAL BOUNDARY. BELOW NORMAL  
PRECIPITATION IS FAVORED FOR CALIFORNIA AND PARTS OF NEVADA AND THE SOUTHWEST  
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, 15% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 8, 15% OF TODAY'S GFS SUPERENSEMBLE MEAN CENTERED ON DAY 8, 30% OF  
TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 8, 10% OF TODAY'S OPERATIONAL  
0Z ECMWF 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 29, 2017 - JAN 04, 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 AND ENVIRONMENT CANADA ENSEMBLE AVERAGES MAINTAIN A MORE  
AMPLIFIED TROUGH INTO THE WEEK 2 PERIOD, RELATIVE TO THE NCEP GEFS ENSEMBLE  
PREDICTION SYSTEM.  
 
ABOVE NORMAL TEMPERATURES REMAIN LIKELY FOR NORTHWESTERN MAINLAND ALASKA, UNDER  
THE PREDICTED RIDGE. BELOW NORMAL TEMPERATURES ARE MOST LIKELY FOR THE ALASKA  
PANHANDLE, UNDER ANOMALOUS NORTHERLY FLOW. BELOW NORMAL TEMPERATURES CONTINUE  
TO BE FAVORED 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. 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 PARTS OF THE NORTHERN INTERMOUNTAIN REGION EASTWARD ACROSS THE  
CENTRAL AND EASTERN CONUS.  
 
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 10% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 11, 15% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 11, 15% OF TODAY'S GFS SUPERENSEMBLE MEAN CENTERED ON DAY 11, 40% 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: Y. FAN  
 
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  
JANUARY 18.  
 
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:  
19921223 - 19711216 - 19791208 - 19791203 - 20071207  
 
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:  
19791207 - 20071207 - 19921222 - 19781202 - 19701221  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 27 - 31 2017  
 
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 B ARIZONA A B COLORADO B A  
NEW MEXICO A B 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 A  
ILLINOIS B A MISSISSIPPI B A MICHIGAN B A  
INDIANA B A OHIO B A KENTUCKY B A  
TENNESSEE B A ALABAMA B A NEW YORK B A  
VERMONT B N NEW HAMP B A 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 A GEORGIA B A  
FL PNHDL A A FL PENIN A A AK N SLOPE A B  
AK ALEUTIAN A A 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 29, 2017 - JAN 04, 2018  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B N OREGON B A NRN CALIF A N  
SRN CALIF A B IDAHO B A NEVADA A N  
W MONTANA B A E MONTANA B A WYOMING B A  
UTAH A N ARIZONA A N COLORADO B A  
NEW MEXICO A N 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 B A WISCONSIN B A  
ILLINOIS B A MISSISSIPPI B A MICHIGAN B A  
INDIANA B A OHIO B A 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 B A FL PENIN A A AK N SLOPE N B  
AK ALEUTIAN A A AK WESTERN A B AK INT BSN N B  
AK S INT N B AK SO COAST N N AK PNHDL B N  
 
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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