374  
FXUS06 KWBC 082010  
PMDMRD  
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD  
300 PM EST FRI DECEMBER 08 2017  
 
6-10 DAY OUTLOOK FOR DEC 14 - 18 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, ALTHOUGH MODELS HAVE VERY RECENTLY  
TRENDED TOWARD A MORE DE-AMPLIFIED FLOW PATTERN. 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 BUT ONE MODEL  
(THE 12Z DETERMINISTIC GFS) 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 EARLIER THIS WEEK ACROSS THE NORTHERN HEMISPHERE HAS BECOME LESS  
WELL DEFINED, AND SEEMS TO BE TRANSITIONING TOWARD A WAVE-NUMBER 3 OR 4  
PATTERN, FAVORING AN UPCOMING PATTERN CHANGE.  
 
BELOW NORMAL TEMPERATURES ARE FAVORED FOR MUCH OF THE GREAT LAKES REGION, OHIO  
VALLEY, AND EAST COAST STATES, 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 MONTANA TO MICHIGAN, DUE TO  
FRONTAL ACTIVITY. BELOW NORMAL PRECIPITATION IS LIKELY FOR MOST OF THE  
REMAINDER OF THE CONUS, WITH PROBABILITIES IN EXCESS OF 60 PERCENT FOR NORTHERN  
CALIFORNIA, OREGON, AND NORTHERN NEVADA. THE WIDESPREAD PATTERN OF ANOMALOUS  
DRYNESS ACROSS MUCH OF THE CONUS IS A COMMONLY OBSERVED FEATURE OF A WESTERN  
RIDGE-EASTERN TROUGH SET-UP, ASSOCIATED WITH LARGE-SCALE SUBSIDENCE AND DRY,  
NORTHWESTERLY FLOW. MINIMAL PROBABILITY TILTS TOWARDS BELOW-NORMAL  
PRECIPITATION ARE DEPICTED ACROSS THE TENNESSEE VALLEY AND CENTRAL GULF COAST  
REGION. THIS IS ATTRIBUTED TO A PREDICTED ANTICYCLONE OFF THE SOUTHEAST COAST,  
AND ACCOMPANYING SOUTHERLY RETURN FLOW OF GULF MOISTURE.  
 
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, HISTORICAL ANALOGS, 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, 5% OF TODAY'S OPERATIONAL 0Z GFS CENTERED ON DAY 8, 5% OF TODAY'S  
OPERATIONAL 6Z GFS CENTERED ON DAY 8, 25% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN  
CENTERED ON DAY 8, 5% 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 16 - 22 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.  
 
FOR THE FIRST TIME THIS WORKWEEK, THERE ARE SIGNIFICANT DIFFERENCES PREDICTED  
BETWEEN THE 6-10 DAY AND 8-14 DAY OFFICIAL TEMPERATURE AND PRECIPITATION  
PATTERNS, ESPECIALLY TEMPERATURE. MOST MODEL SOLUTIONS PREDICT A VERY RAPID  
POLEWARD RETREAT OF THE ANOMALOUS COLD ACROSS THE EASTERN CONUS, WITH A FEW  
SHOWING LITTLE RESIDUAL COLD REMAINING OVER THE EAST IN WEEK-2. ALTHOUGH RAPID  
TEMPERATURE TRANSITIONS CAN OCCUR, IT IS THOUGHT THAT THIS ONE MAY BE TOO  
QUICK. ACCORDINGLY, THE RATE OF THE ANTICIPATED TRANSITION WAS TEMPERED,  
MAINTAINING A SOMEWHAT LARGER AREA OF BELOW NORMAL TEMPERATURES ACROSS THE  
GREAT LAKES REGION AND THE NORTHEAST. IN ADDITION, MOST GUIDANCE SUPPORTS A  
RAPID WARMUP IN SURFACE TEMPERATURES ACROSS THE SOUTHEASTERN QUARTER OF THE  
CONUS DURING WEEK-2, FOLLOWING THE RAPID RETREAT OF THE POLAR AIR.  
 
FOR THE WEEK-2 PRECIPITATION OUTLOOK, THE MAIN ADJUSTMENT MADE IN WEEK-2  
COMPARED TO THE 6-10 DAY PERIOD INVOLVES A WETTER SOLUTION OVER THE SOUTHEAST.  
AS NOTED EARLIER IN THE 6-10 DAY SECTION OF THE DISCUSSION, HIGH PRESSURE OFF  
THE SOUTHEAST COAST IS FORECAST TO STEER GULF MOISTURE NORTHWARD ACROSS THE  
CENTRAL GULF COAST REGION AND TENNESSEE VALLEY. SOME OF THE TOOLS SUGGESTED A  
CONNECTION (ALBEIT, TENUOUS) BETWEEN THIS NORTHWARD-MOVING AREA OF MOISTURE  
WITH THE ABOVE NORMAL PRECIPITATION EXPECTED OVER THE NORTHERN STATES.  
 
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, HISTORICAL ANALOGS, AND GEFS AND ECMWF CALIBRATED  
REFORECASTS.  
 
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: BELOW AVERAGE, 2 OUT OF 5, DUE TO  
INCREASING UNCERTAINTY RELATED TO A PREDICTED DEAMPLIFYING CIRCULATION PATTERN,  
AND 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:  
20071122 - 20021124 - 19591125 - 19561122 - 19761129  
 
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 - 19851221 - 20071120 - 20021128 - 19761129  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 14 - 18 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 A A IOWA A N MISSOURI A B  
ARKANSAS A B LOUISIANA A B WISCONSIN N A  
ILLINOIS N B MISSISSIPPI N B MICHIGAN B A  
INDIANA N N OHIO B N KENTUCKY N N  
TENNESSEE N B ALABAMA N B NEW YORK B N  
VERMONT B B NEW HAMP B B MAINE B B  
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 A  
 
 
 
8-14 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 16 - 22 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 N A WYOMING A N  
UTAH A B ARIZONA A B COLORADO A N  
NEW MEXICO A B N DAKOTA N A S DAKOTA N 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 N LOUISIANA A N WISCONSIN B A  
ILLINOIS N B MISSISSIPPI A A MICHIGAN B A  
INDIANA N N OHIO N A KENTUCKY N N  
TENNESSEE A A ALABAMA A A 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 N A  
MARYLAND N N DELAWARE N N VIRGINIA N N  
N CAROLINA A B S CAROLINA A N GEORGIA A N  
FL PNHDL A A FL PENIN A 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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