573  
FXUS06 KWBC 072001  
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 07 2017  
 
6-10 DAY OUTLOOK FOR DEC 13 - 17 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, ASSOCIATED WITH WHAT APPEARS TO BE A  
SOUTHWESTWARD EXTENSION OF THIS TROUGH TO BAJA CALIFORNIA. 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. THE AMPLIFIED WAVE-NUMBER 5  
PATTERN THAT WAS CLEARLY INDICATED BY MOST MODELS YESTERDAY ACROSS THE NORTHERN  
HEMISPHERE HAS BECOME LESS WELL DEFINED, WHICH MAY BE AN EARLY SIGN OF AN  
UPCOMING PATTERN CHANGE.  
 
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. MID-LEVEL RIDGING AND ASSOCIATED ABOVE NORMAL  
HEIGHTS FORECAST OVER THE WESTERN CONUS LEAD TO INCREASED CHANCES OF ABOVE  
NORMAL TEMPERATURES THERE. THE REDUCTION IN ENHANCED ABOVE NORMAL TEMPERATURE  
PROBABILITIES ACROSS THE NORTHERN INTERMOUNTAIN REGION IS BASED ON SNOW COVER  
AND LOW-LEVEL INVERSIONS. 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 DAKOTAS EASTWARD TO THE  
CENTRAL GREAT LAKES REGION, DUE TO FRONTAL ACTIVITY. BELOW NORMAL PRECIPITATION  
IS LIKELY FOR MOST OF THE REMAINDER OF THE CONUS, WITH HIGHER PROBABILITIES (AT  
LEAST 50 PERCENT) OF BELOW NORMAL PRECIPITATION FROM NORTHERN CALIFORNIA AND  
MUCH OF THE PACIFIC NORTHWEST TO IDAHO AND CONTINUING SOUTHEASTWARD FROM THERE  
INTO UTAH. HIGHER 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 6-10 DAY OUTLOOK IS BASED PRIMARILY ON THE AUTOMATED TEMPERATURE AND  
PRECIPITATION FORECASTS (USED AS A FIRST-GUESS), THE CONSOLIDATION FORECASTS,  
DYNAMICAL MODEL FORECASTS, AND GEFS AND ECMWF CALIBRATED REFORECASTS.  
 
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 TO  
HIGH SPREAD AMONG THE COMPONENT ENSEMBLE MEMBERS OVER THE EASTERN PACIFIC AND  
WESTERN CONUS. LOW SPREAD IS INDICATED OVER THE CENTRAL AND EASTERN CONUS.  
 
8-14 DAY OUTLOOK FOR DEC 15 - 21 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 WITH CONSIDERABLE DEAMPLIFICATION. THIS  
SIGNALS AT LEAST A TEMPORARY BREAK IN THE HIGHLY AMPLIFIED FLOW PATTERN ACROSS  
NORTH AMERICA, BUT ONLY TIME WILL TELL IF THE HIGHLY AMPLIFIED FLOW PATTERN  
WILL BE RE-ESTABLISHED SHORTLY THEREAFTER. 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 RAPID POLEWARD RETREAT OF THE FAVORED  
BELOW NORMAL TEMPERATURES OVER THE SOUTHEAST, AND AN OVERALL REDUCTION IN THE  
PROBABILITIES FOR RELATIVELY COLD TEMPERATURES IN THE EAST. THE SECOND  
ADJUSTMENT INVOLVES THE EXPECTED EXPANSION OF FAVORED ABOVE NORMAL TEMPERATURES  
INTO THE MIDDLE AND LOWER MISSISSIPPI VALLEY REGION. THE THIRD ADJUSTMENT  
RESULTS IN THE DECREASE IN THE PROBABILITIES FOR ANOMALOUS WARMTH ACROSS ALASKA.  
 
FOR THE WEEK-2 PRECIPITATION OUTLOOK, MODIFICATIONS INCLUDE: A REDUCTION IN THE  
PROBABILITIES FAVORING ABOVE NORMAL PRECIPITATION IN ALASKA, AN EXPANSION OF  
FAVORED ABOVE NORMAL PRECIPITATION ACROSS THE NORTHERN HIGH PLAINS, AND A BREAK  
IN THE DRIER PATTERN ANTICIPATED OVER THE GULF COAST REGION. THIS LAST FEATURE  
IS MANIFESTED AS A BROAD CORRIDOR OF NEAR NORMAL PRECIPITATION THAT IS FAVORED  
TO DEVELOP OVER MUCH OF THE GULF COAST REGION AND UPPER TENNESSEE VALLEY. THE  
0Z AND 12Z DETERMINISTIC GFS RUNS PREDICT A SURFACE HIGH WILL MOVE OFF THE  
SOUTHEAST COAST, ALLOWING THE RETURN OF GULF MOISTURE ACROSS THE GULF COAST  
STATES. THE INTERMEDIATE 6Z GFS RUN, HOWEVER, MINIMIZES MOISTURE RETURN ACROSS  
THE GULF COAST STATES AND SOUTHEAST.  
 
THE 8-14 DAY OUTLOOK IS BASED PRIMARILY ON THE AUTOMATED TEMPERATURE AND  
PRECIPITATION FORECASTS (USED AS A FIRST-GUESS), THE CONSOLIDATION FORECASTS,  
DYNAMICAL MODEL FORECASTS, AND GEFS AND ECMWF CALIBRATED REFORECASTS. THE LAST  
THREE DETERMINISTIC GFS RUNS (0Z, 6Z, AND 12Z) WERE ALSO USED IN FORMULATING  
THE OFFICIAL PRECIPITATION OUTLOOK.  
 
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 25% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 11, 25% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 11, 30% 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: 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:  
20071121 - 19851211 - 19641118 - 20021124 - 19521123  
 
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:  
20021123 - 19641118 - 20071120 - 19851211 - 20051214  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 13 - 17 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 N WYOMING A B  
UTAH A B ARIZONA A B COLORADO A B  
NEW MEXICO A B N DAKOTA A A S DAKOTA A N  
NEBRASKA A B KANSAS A B OKLAHOMA A 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 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 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 15 - 21 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 N E MONTANA A A WYOMING A N  
UTAH A B ARIZONA A B COLORADO A B  
NEW MEXICO A B N DAKOTA A A S DAKOTA A A  
NEBRASKA A N KANSAS A B OKLAHOMA A B  
N TEXAS A B S TEXAS A B W TEXAS A B  
MINNESOTA N A IOWA N N MISSOURI A B  
ARKANSAS A B LOUISIANA A N WISCONSIN B N  
ILLINOIS N B MISSISSIPPI A N MICHIGAN B A  
INDIANA B N OHIO B N KENTUCKY B N  
TENNESSEE N N ALABAMA N N NEW YORK B N  
VERMONT B N NEW HAMP B N MAINE B N  
MASS B N CONN B N RHODE IS B N  
PENN B N NEW JERSEY B N W VIRGINIA B N  
MARYLAND B B DELAWARE B B VIRGINIA B B  
N CAROLINA B B S CAROLINA N B GEORGIA N N  
FL PNHDL N N FL PENIN N 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 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.  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page