050  
FXUS02 KWBC 221549  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1049 AM EST WED NOV 22 2017  
 
VALID 12Z SAT NOV 25 2017 - 12Z WED NOV 29 2017  
 
...GUIDANCE/UNCERTAINTY ASSESSMENT AND PATTERN/WEATHER THREAT  
HIGHLIGHTS...  
 
AN ACTIVE MOIST PATTERN WILL REMAIN IN PLACE FOR THE PACIFIC  
NORTHWEST/NRN CA AND THE NRN INTER-MOUNTAIN WEST/ROCKIES THROUGH  
THE UPCOMING WEEKEND, AS A SERIES OF ERN PACIFIC IMPULSES ALONG  
MULTIPLE STREAMS LIFT INLAND FROM THE SOUTH AND WEST. THEN ON  
CYBER MONDAY, A VERY PRONOUNCED AMPLIFIED UPPER TROUGH WILL FOLLOW  
UP THESE FEATURES ALOFT AND SPREAD THROUGH THE WEST TO REACH THE  
INTER-MOUNTAIN REGION AND FRONT RANGE OF THE ROCKIES. MEANWHILE,  
THE UPPER RIDGE INITIALLY OVER THE WEST SAT MORNING, STRETCHING  
FROM BAJA CA NORTH THROUGH THE INTER-MOUNTAIN WEST... WILL  
GRADUALLY PRESS DOWNSTREAM FROM THE INFLUENCE OF HEIGHT FALLS  
SPREADING INTO THE WEST TO REACH THE MIDDLE TO EASTERN THIRD OF  
THE COUNTRY. THIS MEANS THE INITIAL AMPLIFIED COLD UPPER TROUGH  
OVER EAST OF THE MS RIVER WILL SWEEP OFF THE EAST COAST, AS  
HEIGHTS ATTEMPT TO REBOUND SOME.  
 
BY NEXT TUES AND WED, THE PROGRESSING BUT AMPLIFIED UPPER TROUGH  
EJECTS OUT INTO THE PLAINS/MS VALLEY BUT INCREASING SPREAD KEEPS  
SOME UNCERTAINTY ON WHETHER A RATHER DEEP CYCLONE FORMS OR WHETHER  
THE SYSTEM REMAINS PROGRESSIVE WITH JUST SOME LEFTOVER UPPER  
DYNAMICS POSSIBLY CLOSING OFF TOWARDS NORTHERN MEXICO. THE ECMWF  
IS TRENDING TOWARD A DEEPER SOLUTION, WHILE THE GFS RUNS FLIP FLOP  
BACK AND FORTH. THE MEANS OF BOTH GLOBAL MODELS PRETTY MUCH  
SUPPORT THE LATEST OPERATIONAL SOLUTIONS.  
 
WPC AS A WHOLE FOLLOWED A BLEND OF THE 00Z ECMWF/EC MEAN WITH THE  
00Z GFS AND 06Z GFS/GEFS MEAN, WITH THE LARGEST WEIGHT ON THE 00Z  
ECMWF, THROUGH NEXT MONDAY. THEN NEXT TUES, A BLEND OF THE 00Z  
ECMWF/GFS/EC MEAN WAS USED AND FINALLY NEXT WED, A BLEND MOSTLY ON  
THE EC MEAN WITH SMALL PERCENTAGES OF THE 00Z ECMWF/GFS OR A TREND  
TO A DEEPER AND SLOWER CYCLONE OVER THE MIDDLE TO UPPER PORTION OF  
THE COUNTRY.  
 
PRECIPITATION CHANCES FOR OVER THE WEEKEND THROUGH NEXT MONDAY  
WILL SOLELY OVER THE WEST WITH THE HEAVIEST QPF ANTICIPATED FROM  
COASTAL WA/OR INTO THE CASCADES AND ACROSS NORTHERN CA AND SIERRA  
SPINE. ENHANCED OROGRAPHICS WILL ALSO BE LIKELY TO INCREASE QPF  
AMOUNTS IN THESE LOCALES AND HELP PINPOINT THE FAVORED TERRAIN  
EAST OF THE RAIN SHADOW AND THROUGH THE INTER-MOUNTAIN WEST TO THE  
NORTHERN/CENTRAL ROCKIES. ALSO DURING THIS THREE DAY PERIOD OR  
MAINLY MON, A STREAK OF LIGHT TO MODERATE OVERRUNNING QPF WILL BE  
ANTICIPATED FROM EASTERN MT/NERN WY THROUGH THE DAKOTAS TO  
NORTHERN MN. THEN NEXT TUES AND WED, THE FOCUS WILL BE ACROSS THE  
UPPER MIDWEST/MS VALLEY WHERE AN AXIS OF HEAVIER QPF IS  
ANTICIPATED WITH THE THREAT OF FROZEN ACCUMULATIONS, ESPECIALLY  
ACROSS MN INTO WI. ALSO NEXT TUES/WED, WARM SECTOR SHOWERS/STORMS  
WILL BE POSSIBLE FROM THE GULF COAST/SOUTH TO OH VALLEY/GREAT  
LAKES BUT MOISTURE RETURN FROM THE GULF OF MEXICO WILL BE SOMEWHAT  
LIMITED.  
 
TEMPERATURES OVER THE 5 DAYS, THE WPC MEAN MAX TEMP ANOMALY  
SUGGESTS BASICALLY AVG TO ABOVE AVG HIGHS FOR THE COUNTRY. ABOVE  
AVG HIGHS WILL BE COMMON OVER MUCH OF THE WEST INTO THE PLAINS/MS  
VALLEY WITH HIGHS 10 TO 20 DEG ABOVE AVG DURING THE PERIOD FROM  
PARTS OF THE FOUR CORNERS REGION INTO EASTERN MT/WY AND MUCH OF  
THE NORTHERN/CENTRAL PLAINS. IN FACT, A FEW RECORD HIGHS COULD BE  
POSSIBLE OVER PARTS OF CA/NV INTO THE DESERT SOUTHWEST AND FOUR  
CORNERS REGION SAT - MON. OVER THE EAST, HIGHS DURING THIS 5 DAY  
STRETCH WILL BE NEAR AVG FOR THE MOST PART.  
 
MUSHER  
 

 
 
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