879  
FXUS06 KWBC 252025  
PMDMRD  
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD  
300 PM EST MON DECEMBER 25 2017  
 
6-10 DAY OUTLOOK FOR DEC 31, 2017 - JAN 04, 2018  
 
TODAY'S ENSEMBLE MEAN FORECASTS ARE IN GOOD AGREEMENT ON A PREDICTED AMPLIFIED  
500-HPA CIRCULATION PATTERN FOR THE 6-10 DAY PERIOD OVER THE FORECAST DOMAIN.  
TROUGHS ARE ANTICIPATED OVER THE CENTRAL AND EASTERN CONUS, AND THE BERING SEA,  
WHILE A RIDGE IS EXPECTED ALONG THE U.S. WEST COAST EXTENDING  
NORTH/NORTHWESTWARD TO ALASKA. THE ENSEMBLE SPAGHETTI CHARTS INDICATE LOW TO  
MODERATE SPREAD OVER THE CENTRAL AND EASTERN CONUS, AND MODERATE TO LARGE SPREAD  
OVER THE WESTERN CONUS AND EASTERN PACIFIC. THE PNA INDEX WHICH RECENTLY HAS  
BEEN WEAKLY POSITIVE IS FORECAST TO BE WEAKLY POSITIVE AT DAY 7, BE MODERATELY  
POSITIVE AT DAY 10, AND BE CLOSE TO ZERO BY DAY 14. THE AO INDEX WHICH HAS  
RECENTLY BEEN POSITIVE IS EXPECTED TO BE NEAR ZERO AT DAY 7, BE WEAKLY POSITIVE  
AT DAY 10, AND CLOSE TO ZERO AT DAY 14. THERE IS RELATIVELY LARGE SPREAD OF THE  
FORECAST AO INDEX AMONG ENSEMBLE MEMBERS. TODAY'S 500-HPA BLEND CHART DEPICTS  
BELOW NORMAL HEIGHTS FOR THE EASTERN TWO-THIRDS OF THE CONUS, THE ALEUTIANS,  
AND THE WESTERN THIRD OF MAINLAND ALASKA, WHILE ABOVE NORMAL HEIGHTS ARE  
ANTICIPATED FOR THE WESTERN THIRD OF THE CONUS, THE ALASKA PANHANDLE, AND THE  
EASTERN TWO-THIRDS OF THE ALASKA MAINLAND.  
 
BELOW NORMAL HEIGHTS TILT THE ODDS TO NEAR TO BELOW NORMAL TEMPERATURES FOR  
MUCH OF THE THE EASTERN TWO-THIRDS OF THE CONUS, WHILE ABOVE NORMAL HEIGHTS  
FAVOR NEAR TO ABOVE NORMAL TEMPERATURES FOR THE WESTERN THIRD OF THE NATION.  
DUE TO THE EXPECTATION OF AN AMPLIFIED CIRCULATION PATTERN, THERE ARE HIGH  
PROBABILITIES FOR BELOW NORMAL TEMPERATURES NEAR THE GREAT LAKES. ABOVE NORMAL  
HEIGHTS AND/OR ANOMALOUS SOUTHERLY FLOW ENHANCE PROBABILITIES FOR ABOVE NORMAL  
TEMPERATURES FOR THE ALEUTIANS AND WESTERN AND CENTRAL MAINLAND ALASKA.  
 
ABOVE NORMAL HEIGHTS AND/OR ANOMALOUS NORTHERLY FLOW FAVOR NEAR TO BELOW NORMAL  
PRECIPITATION FOR MUCH OF THE CONUS. THE EXCEPTION IS ACROSS THE SOUTHERN TIER  
OF THE CONUS FROM TEXAS TO FLORIDA WHERE MOISTURE RETURN NEAR A FRONTAL SYSTEM  
ENHANCES PROBABILITIES FOR ABOVE NORMAL PRECIPITATION. THE TROUGH FORECAST OVER  
THE BERING SEA TILT THE ODDS TO ABOVE NORMAL PRECIPITATION FOR THE ALEUTIANS AND  
SOUTHWESTERN MAINLAND ALASKA. ABOVE NORMAL HEIGHTS FAVOR BELOW NORMAL  
PRECIPITATION FOR PARTS OF EAST-CENTRAL ALASKA.  
 
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 10% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 8, 10% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 8, 20% OF TODAY'S GFS SUPERENSEMBLE MEAN CENTERED ON DAY 8, 5% OF  
TODAY'S OPERATIONAL 0Z GFS CENTERED ON DAY 8, 5% OF TODAY'S OPERATIONAL 6Z GFS  
CENTERED ON DAY 8, 15% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 8,  
20% OF YESTERDAY'S 12Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 7, 10% 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 AN AMPLIFIED CIRCULATION PATTERN.  
 
8-14 DAY OUTLOOK FOR JAN 02 - 08 2018  
 
DURING WEEK 2, MODEL FORECASTS PREDICT A SOMEWHAT LESS AMPLIFIED 500-HPA TROUGH  
OVER THE EASTERN AND CENTRAL U.S. RELATIVE TO THE 6-10 DAY PERIOD. THE ECMWF  
ENSEMBLE MEAN IS A BIT QUICKER TO RAISE HEIGHTS NEAR THE GREAT LAKES. ENSEMBLE  
SPREAD REMAINS LOW TO MODERATE OVER MOST OF THE CENTRAL AND EASTERN CONUS, AND  
IS RELATIVELY LARGE OVER THE WESTERN CONUS AND EASTERN PACIFIC. THE EXPECTED  
500-HPA HEIGHT ANOMALY PATTERN FOR WEEK-2 IS VERY SIMILAR TO THAT FORECAST FOR  
THE 6-10 DAY PERIOD, ALTHOUGH HEIGHTS ARE EXPECTED TO FALL SLIGHTLY OVER PARTS  
OF THE SOUTHERN PLAINS DURING WEEK-2.  
 
BELOW NORMAL TEMPERATURES REMAIN LIKELY FOR MUCH OF THE CENTRAL AND EASTERN  
CONUS DUE TO BELOW NORMAL HEIGHTS. NEAR TO ABOVE NORMAL HEIGHTS AND/OR  
ANOMALOUS SOUTHERLY FLOW ENHANCE PROBABILITIES FOR ABOVE NORMAL TEMPERATURES  
FOR MOST OF THE WESTERN THIRD OF THE CONUS AND MUCH OF ALASKA.  
 
THE TROUGH OVER THE EASTERN CONUS AND THE EXPECTATION OF A STALLED FRONTAL  
SYSTEM OVER THE SOUTHEAST CONUS ENHANCE PROBABILITIES FOR ABOVE NORMAL  
PRECIPITATION FOR THE GULF COAST REGION AND PARTS OF THE SOUTHEAST. ELSEWHERE  
OVER THE CONUS, ANOMALOUS NORTHERLY FLOW AND/OR ABOVE NORMAL HEIGHTS TILT THE  
ODDS TO NEAR TO BELOW NORMAL PRECIPITATION. THE TROUGH FORECAST OVER THE BERING  
SEA FAVORS ABOVE NORMAL PRECIPITATION FOR MUCH OF WESTERN AND CENTRAL MAINLAND  
ALASKA, THE ALASKA PANHANDLE, AND THE ALEUTIANS.  
 
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 15% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 11, 25% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 11, 15% OF TODAY'S GFS SUPERENSEMBLE MEAN CENTERED ON DAY 11, 10% OF  
TODAY'S OPERATIONAL 6Z GFS CENTERED ON DAY 11, 10% OF TODAY'S 0Z EUROPEAN  
ENSEMBLE MEAN CENTERED ON DAY 11, AND 25% OF YESTERDAY'S 12Z EUROPEAN ENSEMBLE  
MEAN CENTERED ON DAY 10  
 
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: ABOUT AVERAGE, 3 OUT OF 5, DUE TO  
GOOD MODEL AGREEMENT OFFSET BY THE EXPECTATION OF A DEAMPLIFYING CIRCULATION  
PATTERN.  
 
FORECASTER: RANDY S  
 
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:  
19831217 - 19880103 - 19851213 - 19790104 - 19910103  
 
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:  
19880106 - 19790103 - 19831219 - 19581205 - 19851213  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 31, 2017 - JAN 04, 2018  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON A N OREGON A B NRN CALIF A B  
SRN CALIF A B IDAHO A B NEVADA A B  
W MONTANA A N E MONTANA A N WYOMING A N  
UTAH A B ARIZONA A B COLORADO A N  
NEW MEXICO A B N DAKOTA N B S DAKOTA N N  
NEBRASKA B N KANSAS B N OKLAHOMA B N  
N TEXAS B A S TEXAS B A W TEXAS B N  
MINNESOTA B B IOWA B B MISSOURI B B  
ARKANSAS B N LOUISIANA B A WISCONSIN B B  
ILLINOIS B B MISSISSIPPI B A MICHIGAN B B  
INDIANA B B OHIO B B KENTUCKY B B  
TENNESSEE B B ALABAMA B N NEW YORK B B  
VERMONT B B NEW HAMP B B MAINE B B  
MASS B B CONN B B RHODE IS B B  
PENN B B NEW JERSEY B B W VIRGINIA B B  
MARYLAND B B DELAWARE B B VIRGINIA B B  
N CAROLINA B B S CAROLINA B N GEORGIA B A  
FL PNHDL B A FL PENIN B A AK N SLOPE N N  
AK ALEUTIAN A A AK WESTERN A A AK INT BSN A B  
AK S INT A A AK SO COAST A A AK PNHDL A A  
 
 
 
8-14 DAY OUTLOOK TABLE  
OUTLOOK FOR JAN 02 - 08 2018  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON A N OREGON A N NRN CALIF A B  
SRN CALIF A B IDAHO A N NEVADA A B  
W MONTANA A N E MONTANA A N WYOMING A N  
UTAH A B ARIZONA A B COLORADO A B  
NEW MEXICO A B N DAKOTA N N S DAKOTA N N  
NEBRASKA N B KANSAS N B OKLAHOMA B B  
N TEXAS B N S TEXAS B N W TEXAS N N  
MINNESOTA N N IOWA B B MISSOURI B B  
ARKANSAS B N LOUISIANA B A WISCONSIN B B  
ILLINOIS B B MISSISSIPPI B A MICHIGAN B B  
INDIANA B B OHIO B B KENTUCKY B B  
TENNESSEE B N ALABAMA B A NEW YORK B B  
VERMONT B B NEW HAMP B B MAINE B N  
MASS B N CONN B N RHODE IS B N  
PENN B B NEW JERSEY B N W VIRGINIA B B  
MARYLAND B B DELAWARE B N VIRGINIA B N  
N CAROLINA B N S CAROLINA B A GEORGIA B A  
FL PNHDL B A FL PENIN B A AK N SLOPE N N  
AK ALEUTIAN A A AK WESTERN A A AK INT BSN A N  
AK S INT A A AK SO COAST A A AK PNHDL A A  
 
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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