775  
FXUS02 KWBC 091600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1059 AM EST THU NOV 09 2017  
 
VALID 12Z SUN NOV 12 2017 - 12Z THU NOV 16 2017  
   
..PATTERN OVERVIEW/MODEL EVALUATION/UNCERTAINTIES/PREFERENCES
 
 
MULTI-DAY MEANS AGREE WELL THAT THE PATTERN DURING THE DAYS 3-7  
SUN-THU PERIOD WILL BE DOMINATED BY NORTH-CENTRAL  
PACIFIC/ALEUTIANS/BERING SEA RIDGING AND NORTHEAST PACIFIC  
TROUGHING, WHICH WILL FAVOR LOW AMPLITUDE FLOW ACROSS MUCH OF THE  
LOWER 48. THE MEAN CLOSED LOW EXPECTED OVER THE CANADIAN  
ARCHIPELAGO ALSO TENDS TO CORRESPOND TO PROGRESSIVE CONUS FLOW.  
TO THE SOUTH OF THIS RELATIVELY FLAT FLOW, RIDGING WILL LIKELY  
PREVAIL OVER/NEAR MEXICO. THIS PATTERN SHOULD FOCUS THE MOST  
IMPACTFUL WEATHER ACROSS THE NORTHWEST STATES.  
 
THROUGH AT LEAST THE FIRST HALF OF THE PERIOD THERE IS REASONABLE  
AGREEMENT ON EMBEDDED FEATURES BUT SOME LINGERING UNCERTAINTY ON  
THE DETAILS. CURRENT CONSENSUS SHOWS A LEADING SHORTWAVE CROSSING  
THE EASTERN HALF OF THE LOWER 48 SUN-MON NIGHT REMAINING FAIRLY  
OPEN, LEADING TO ASSOCIATED WESTERN ATLANTIC LOW PRESSURE  
DEVELOPING SOME DISTANCE OFFSHORE. HOWEVER THERE HAVE BEEN  
ISOLATED OPERATIONAL RUNS SUCH AS THE 00Z UKMET AND 12Z/08 ECMWF  
WITH A MORE CONCENTRATED UPPER SYSTEM AND WRAPPED UP LOW PRESSURE  
NEAR THE EAST COAST. SUCH SOLUTIONS ARE IN THE WESTERN FRINGE OF  
THE FULL ENSEMBLE SPREAD AND SEEM TO HAVE RELATIVELY LOWER  
PROBABILITY GIVEN THE PROGRESSIVE TENDENCY OF THE MEAN PATTERN,  
BUT CANNOT BE FULLY DISMISSED. POTENTIAL FOR SOUTHERN CANADA  
ENERGY TO INTERACT WITH THIS SYSTEM BY TUE-WED ADDS SOME  
COMPLEXITY TO THE FORECAST NEAR THE CANADIAN MARITIMES. UPSTREAM  
THERE IS REASONABLE AGREEMENT ON A VIGOROUS EAST PACIFIC SYSTEM  
THAT SHOULD TRACK INTO SOUTHWEST CANADA AROUND MON AND THEN  
CONTINUE ONWARD WHILE PULLING A FRONT ACROSS THE CENTRAL U.S..  
 
WHILE THERE IS DECENT CONFIDENCE IN THE MEAN PATTERN LATE IN THE  
PERIOD, DETAILS BECOME MORE AMBIGUOUS TOWARD DAYS 6-7 WED-THU--  
PRIMARILY AS SOLUTIONS DIVERGE FOR SHORTWAVE ENERGY REACHING THE  
GREAT LAKES/ONTARIO BY EARLY WED AND FOR UPSTREAM SHORTWAVE ENERGY  
EJECTING INTO WESTERN NORTH AMERICA FROM THE PACIFIC. THE MOST  
COMMON MODEL/ENSEMBLE SIGNALS ARE FOR THE EASTERN SHORTWAVE TO  
BECOME MORE DIFFUSE THUS LEADING TO A WEAKENING SURFACE REFLECTION  
WHILE EJECTING PACIFIC ENERGY SUPPORTS A SURFACE WAVE OVER OR JUST  
NORTH OF THE NORTHERN PLAINS BY EARLY DAY 7 THU. ON AVERAGE LOW  
PRESSURE WOULD PERSIST TO THE NORTHWEST OF THE WASHINGTON COAST  
WITH SOME MODEL/ENSEMBLE SOLUTIONS SUGGESTING A LOW CENTER COULD  
TRACK CLOSER TO THE STATE.  
 
THE FIRST HALF OF THE PERIOD EMPHASIZES OPERATIONAL GUIDANCE  
(00Z-06Z GFS/00Z ECMWF AND LESSER WEIGHT OF THE 00Z CMC) GIVEN  
REASONABLE AGREEMENT AND PREFERENCE FOR INTERMEDIATE  
STRENGTH/TIMING WHERE DIFFERENCES EXIST. THEN THE FORECAST  
INCREASES 06Z GEFS-00Z ECMWF MEAN WEIGHTING WITH TIME AS  
OPERATIONAL RUNS DIVERGE FOR SOME DETAILS. THE RESULT YIELDS GOOD  
CONTINUITY IN PRINCIPLE WITH DETAIL ADJUSTMENTS LIMITED TO TYPICAL  
RUN TO RUN VARIABILITY.  
 
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
EXPECT A PERIOD OF ACTIVE WEATHER OVER THE PACIFIC  
NORTHWEST/NORTHERN CALIFORNIA AND EXTENDING TO SOME EXTENT INTO  
THE NORTHERN ROCKIES. THERE SHOULD BE MULTIPLE EPISODES OF HEAVY  
RAINFALL AND HIGHER ELEVATION SNOW ALONG WITH PERIODS OF STRONG  
WINDS. HIGHEST TOTALS FOR THE 5-DAY PERIOD WILL LIKELY EXTEND  
FROM THE COASTAL RANGES/CASCADES OF THE PACIFIC NORTHWEST INTO  
FAVORED NORTHERN CALIFORNIA TERRAIN. THE NORTHERN ROCKIES SHOULD  
ALSO SEE A RELATIVE MAXIMUM OF PRECIP BUT WITH TOTALS SOMEWHAT  
LESS THAN SEEN CLOSER TO THE WEST COAST. FARTHER EAST, A WEAK  
SYSTEM WILL BE ACCOMPANIED BY MOSTLY LIGHT PRECIP EARLY IN THE  
PERIOD. NORTHERN AREAS MAY BE COLD ENOUGH FOR SOME SNOW.  
SUBSEQUENT ATLANTIC DEVELOPMENT WILL LIKELY CONFINE ASSOCIATED  
PRECIP OFFSHORE BUT THERE ARE LOWER PROBABILITY SCENARIOS THAT  
COULD HAVE MORE SIGNIFICANT INFLUENCE ON THE EAST COAST. AN  
UPSTREAM SYSTEM EJECTING FROM THE PACIFIC WILL BRING ANOTHER  
FRONTAL SYSTEM THROUGH THE PLAINS AND INTO PARTS OF THE EAST  
TUE-THU. ASSOCIATED PRECIP (MOSTLY RAIN) IS MOST LIKELY TO FOCUS  
FROM THE EASTERN PLAINS TO WEST OF THE APPALACHIANS. SOME OF THIS  
RAIN MAY REACH AT LEAST MODERATE INTENSITY.  
 
FOR MOST OF THE PERIOD THE LOW AMPLITUDE MEAN FLOW ALOFT WITH  
EMBEDDED PACIFIC-ORIGIN SYSTEMS SHOULD YIELD ABOVE NORMAL  
TEMPERATURES FOR MID-NOVEMBER FROM THE ROCKIES EASTWARD TO THE MS  
RIVER VALLEY. GREATEST ANOMALIES FOR TEMPS EXCEEDING PLUS 10F ARE  
MOST LIKELY FOR ONE OR MORE DAYS FROM THE GREAT BASIN/CENTRAL  
SOUTHERN ROCKIES AND THEN INTO PARTS OF THE PLAINS SUN-TUE AHEAD  
OF A PACIFIC FRONT REACHING THE PLAINS/ROCKIES BY TUE. A COUPLE  
COOL HIGH PRESSURE CENTERS OVER THE EAST, ONE AT THE START OF THE  
PERIOD SUN AND ANOTHER BUILDING IN BY TUE WILL TEND TO KEEP TEMPS  
BELOW NORMAL OVER THE EASTERN STATES. THE PERSISTENCE OF CLOUD  
COVER AND PRECIP WILL KEEP CONDITIONS ON THE COOL SIDE FOR THE  
PACIFIC NORTHWEST DURING MOST OF THE PERIOD.  
 
RAUSCH  
 

 
 
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