126  
FXUS06 KWBC 062041  
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 06 2017  
 
6-10 DAY OUTLOOK FOR DEC 12 - 16 2017  
 
TODAYS ENSEMBLE MEAN SOLUTIONS ARE IN GOOD AGREEMENT ON THE EXPECTED BROAD  
SCALE 500-HPA CIRCULATION PATTERN DURING THE 6-10 DAY PERIOD. A HIGH AMPLITUDE  
RIDGE IS FORECAST ALONG OR NEAR THE WEST COAST OF NORTH AMERICA, FLANKED BY  
DEEP TROUGHS ON EITHER SIDE OF THIS FEATURE. THE TROUGH TO THE WEST EXTENDS  
FROM THE BERING SEA AND THE ALEUTIANS SOUTHEASTWARD ACROSS THE EAST-CENTRAL  
PACIFIC TO THE HAWAIIAN ARCHIPELAGO. THE TROUGH TO THE EAST OF THE RIDGE IS  
PREDICTED OVER EASTERN NORTH AMERICA, WITH A SOUTHWESTWARD EXTENSION TO BAJA  
CALIFORNIA. AN AMPLIFIED WAVE-NUMBER 5 PATTERN IS GENERALLY PREDICTED ACROSS  
THE NORTHERN HEMISPHERE. ALL MODELS DEPICT A WELL-DEFINED DIPOLE PATTERN IN THE  
ANTICIPATED 500-HPA HEIGHT ANOMALY FIELD, WITH ABOVE NORMAL HEIGHTS FORECAST  
OVER WESTERN NORTH AMERICA, AND BELOW NORMAL HEIGHTS PROJECTED OVER EASTERN  
NORTH AMERICA.  
 
BELOW NORMAL TEMPERATURES ARE FAVORED FROM NEAR THE MISSISSIPPI RIVER EASTWARD  
TO THE ATLANTIC COAST, UNDERNEATH THE PREDICTED DEEP TROUGH AND ACCOMPANYING  
WELL BELOW NORMAL HEIGHTS. ABOVE NORMAL HEIGHTS FORECAST OVER THE WESTERN CONUS  
AND SOUTHEASTERLY SURFACE FLOW OVER THE SOUTHWEST CONUS LEAD TO INCREASED  
CHANCES OF ABOVE NORMAL TEMPERATURES THERE. THE PREDICTED ANOMALOUS TROUGH OVER  
THE ALEUTIANS AND THE EAST-CENTRAL PACIFIC LEADS TO SOUTH-SOUTHWESTERLY FLOW  
NEAR THE SURFACE OVER MUCH OF ALASKA, ENHANCING THE CHANCES OF ABOVE NORMAL  
TEMPERATURES.  
 
EAST OF THE MID-LEVEL TROUGH PREDICTED OVER THE ALEUTIANS, SOUTHWESTERLY FLOW  
AT THE SURFACE INCREASES CHANCES OF ABOVE NORMAL PRECIPITATION OVER MOST OF  
ALASKA. ABOVE NORMAL PRECIPITATION IS FAVORED FROM THE UPPER MISSISSIPPI VALLEY  
EASTWARD ACROSS THE GREAT LAKES AND NORTHERN NEW ENGLAND, DUE TO FRONTAL  
ACTIVITY. BELOW NORMAL PRECIPITATION IS LIKELY FOR MOST OF THE CONUS, WITH HIGH  
PROBABILITIES OF BELOW NORMAL PRECIPITATION FROM NORTHERN CALIFORNIA AND MUCH  
OF THE PACIFIC NORTHWEST TO IDAHO; CONTINUING SOUTHEASTWARD FROM THERE INTO  
UTAH. HIGH PROBABILITIES OF BELOW NORMAL PRECIPITATION ARE ALSO INDICATED  
ACROSS THE EASTERN SECTIONS OF THE SOUTHERN PLAINS AND THE LOWER MISSISSIPPI  
VALLEY. THESE TWO REGIONS OF HIGHER PROBABILITIES FOR BELOW NORMAL  
PRECIPITATION ARE ATTRIBUTED TO THE EXPECTED PRESENCE OF A HIGHLY AMPLIFIED  
RIDGE OVER THE WEST AND BROAD NORTHWESTERLY FLOW DOWNSTREAM OVER MOST OF THE  
REMAINDER OF THE CONUS.  
 
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 20% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 8, 20% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 8, 10% OF TODAY'S OPERATIONAL 6Z GFS CENTERED ON DAY 8, 20% 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  
GENERALLY GOOD AGREEMENT AMONG THE PREDICTION TOOLS, BUT OFFSET BY MODERATE  
SPREAD AMONG THE COMPONENT ENSEMBLE MEMBERS. THE TWO AREAS WITH GREATEST SPREAD  
ARE NORTHERN ALASKA DUE TO DIFFERENCES IN PREDICTED AMPLITUDE OF THE RIDGE, AND  
OVER THE SOUTHWEST, ASSOCIATED WITH POTENTIAL UNDERCUTTING OF THE WESTERN RIDGE.  
 
8-14 DAY OUTLOOK FOR DEC 14 - 20 2017  
 
THE 500-HPA FLOW PATTERN DURING THE 8-14 DAY PERIOD IS PREDICTED TO BE SIMILAR  
TO THAT OF THE 6-10 DAY PERIOD, THOUGH PERHAPS SHIFTED SLIGHTLY TO THE WEST  
WITH MODEST DEAMPLIFICATION. INSPECTION OF THE WEEK-2 SPAGHETTI CHARTS  
CONTINUES TO REVEAL MODERATE TO LARGE SPREAD OVER THE EASTERN PACIFIC AND  
WESTERN CONUS, AND LOW SPREAD OVER THE CENTRAL AND EASTERN CONUS.  
 
THE PREDICTED SURFACE TEMPERATURE AND PRECIPITATION PATTERNS ARE SIMILAR TO  
THOSE EXPECTED FOR THE 6-10 DAY PERIOD, THOUGH WITH A FEW DIFFERENCES. THE  
FIRST OF SEVERAL ADJUSTMENTS INVOLVES A SLIGHT WESTWARD SHIFT OF THE BELOW  
NORMAL TEMPERATURES INTO THE NORTHERN PLAINS REGION. MJO-RELATED TROPICAL  
CONVECTION THAT IS FORECAST TO MOVE OUT OVER THE WESTERN PACIFIC OFTEN LEADS TO  
EXTRA- TROPICAL WAVE BREAKING, WHICH IN TURN IS OFTEN ASSOCIATED WITH COLDER  
AIR MOVING INTO THE NORTH-CENTRAL CONUS ABOUT 10-15 DAYS LATER; HENCE, DURING  
THE UPCOMING WEEK-2 PERIOD. THE SECOND ADJUSTMENT INVOLVES THE POLEWARD RETREAT  
OF THE BELOW NORMAL TEMPERATURES PREDICTED OVER FLORIDA, TO NEAR THE GEORGIA  
BORDER, WHICH HAS THE SUPPORT OF SOME OF THE DYNAMICAL GUIDANCE, SUCH AS THE  
GEFS AND EUROPEAN ENSEMBLE CALIBRATED REFORECAST TEMPERATURE TOOLS, AND THE  
TEMPERATURE CONSOLIDATION FORECAST. A THIRD AND FINAL ADJUSTMENT INVOLVES THE  
ANTICIPATED TRANSITION FROM RELATIVELY COLD, DRY CONDITIONS ACROSS THE CENTRAL  
AND EASTERN GULF COAST REGION TO A MILDER, WETTER PATTERN AS THE COLDER AIR  
RETREATS.  
 
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, 10% OF TODAY'S OPERATIONAL 0Z GFS CENTERED ON DAY 11, 10% OF TODAY'S  
OPERATIONAL 6Z GFS CENTERED ON DAY 11, 20% 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 IS: NEAR AVERAGE, 3 OUT OF 5, DUE  
TO GOOD AGREEMENT AMONG THE ENSEMBLE MEANS, BUT MODERATE TO HIGH SPREAD AMONG  
THE ENSEMBLE MEMBERS OVER THE EASTERN PACIFIC AND WESTERN CONUS. SPREAD IS LOW  
OVER THE CENTRAL AND EASTERN CONUS.  
 
FORECASTER: ANTHONY A  
 
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:  
19521122 - 19601205 - 19961215 - 19821122 - 19821208  
 
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:  
19521121 - 20021122 - 19821207 - 19601205 - 19851211  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 12 - 16 2017  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON A B OREGON A B NRN CALIF A B  
SRN CALIF A B IDAHO A B NEVADA A B  
W MONTANA A B E MONTANA A B WYOMING A B  
UTAH A B ARIZONA A B COLORADO A B  
NEW MEXICO A B N DAKOTA A N S DAKOTA A N  
NEBRASKA A B KANSAS A B OKLAHOMA N B  
N TEXAS N B S TEXAS N B W TEXAS A B  
MINNESOTA B A IOWA N N MISSOURI N B  
ARKANSAS N B LOUISIANA B B WISCONSIN B A  
ILLINOIS B B MISSISSIPPI B B MICHIGAN B A  
INDIANA B N OHIO B N KENTUCKY B B  
TENNESSEE B B ALABAMA B B NEW YORK B A  
VERMONT B A NEW HAMP B N MAINE B A  
MASS B N CONN B N RHODE IS B N  
PENN B N NEW JERSEY B B W VIRGINIA B N  
MARYLAND B B DELAWARE B B VIRGINIA B B  
N CAROLINA B B S CAROLINA B B GEORGIA B B  
FL PNHDL B B FL PENIN B 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 N  
 
 
 
8-14 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 14 - 20 2017  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON A B OREGON A B NRN CALIF A B  
SRN CALIF A B IDAHO A B NEVADA A B  
W MONTANA A B E MONTANA A A WYOMING A N  
UTAH A B ARIZONA A B COLORADO A B  
NEW MEXICO A B N DAKOTA B A S DAKOTA N A  
NEBRASKA N N KANSAS N B OKLAHOMA N B  
N TEXAS A B S TEXAS A B W TEXAS A B  
MINNESOTA B A IOWA B N MISSOURI B B  
ARKANSAS N B LOUISIANA N N WISCONSIN B N  
ILLINOIS B B MISSISSIPPI N N MICHIGAN B A  
INDIANA B N OHIO B N KENTUCKY B B  
TENNESSEE B B ALABAMA B N NEW YORK B N  
VERMONT B N NEW HAMP B B MAINE B N  
MASS B B CONN B B RHODE IS B B  
PENN B N NEW JERSEY B B W VIRGINIA B N  
MARYLAND B B DELAWARE B B VIRGINIA B B  
N CAROLINA B N S CAROLINA B N GEORGIA B A  
FL PNHDL B A FL PENIN N 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 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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