353  
FXUS02 KWBC 121549  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1148 AM EDT THU OCT 12 2017  
 
VALID 12Z SUN OCT 15 2017 - 12Z THU OCT 19 2017  
   
..OVERVIEW
 
 
A PROGRESSIVE/WAVY FLOW PATTERN EARLY NEXT WEEK WILL EVENTUALLY  
TRANSLATE TO INCREASED WESTERN US TROUGHING AND BUILDING HEIGHTS  
IN THE EASTERN STATES. A COLD FRONT MOVING OUT OF THE GREAT  
LAKES/OHIO VALLEY/LOWER MS VALLEY ON SUNDAY WILL USHER IN MORE  
TYPICAL FALL TEMPERATURES TO THE EASTERN HALF OF THE LOWER 48  
SUN-WED AND PUSH THE RAIN CHANCES OFF THE COAST AND INTO FLORIDA.  
IN THE NORTHWEST, AN UPPER LOW SETTLING INTO ALASKA WILL SLOWLY  
PUSH THE STORM TRACK SOUTHWARD -- INITIALLY INTO BRITISH COLUMBIA  
EARLY IN THE WEEK AND THEN INTO WA/OR AND THE INTERIOR WEST BY  
NEXT THURSDAY AND BEYOND. THIS MAY START A RATHER STORM PERIOD FOR  
THE NORTHWEST LATE NEXT WEEK (SEE THE LATEST CPC OUTLOOKS FOR MORE  
INFORMATION). OTHERWISE, THE REST OF THE COUNTRY LATER NEXT WEEK  
WILL SEE DRY CONDITIONS AND NEAR TO ABOVE AVERAGE TEMPERATURES.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
MODELS CONTINUE TO STRUGGLE WITH HOW THE PATTERN EVOLVES (I.E.,  
SYSTEM TIMING, TRACK, AND DEPTH) ESPECIALLY THROUGH SOUTHERN  
CANADA BUT ALL EVENTUALLY AGREE ON INCREASED TROUGHING INTO THE  
WEST BY THE END OF THE FORECAST NEXT THU (THOUGH THE GEFS  
ENSEMBLES WERE GENERALLY ABOUT 12-24 HRS QUICKER THAN THE ECMWF  
ENSEMBLES). LEAD SYSTEM EXITING THE GREAT LAKES ON SUNDAY (WITH  
ATTENDANT COLD FRONT PUSHING THROUGH THE EAST/SOUTHEAST/LOWER MS  
VALLEY) HAS TRENDED A BIT QUICKER WITH THE 00Z/06Z GUIDANCE WHICH  
WAS ALREADY TRENDING FASTER. CONSENSUS OF THE LATEST  
GFS/ECMWF/UKMET OFFERED A GOOD STARTING POINT SUN/MON AS THE FRONT  
MOVES OFF THE NORTHEAST/MID-ATLANTIC COAST AND INTO THE GULF AND  
HIGH PRESSURE FOLLOWS IN ITS WAKE. 00Z CANADIAN AND ITS ENSEMBLE  
MEAN SEEMED TOO FAR DISPLACED FROM THE OTHERWISE GOOD CONSENSUS TO  
USE.  
 
FOR NEXT TUE-THU, 00Z/06Z GFS RUNS APPEARED TOO QUICK THROUGH  
CENTRAL CANADA WITH A SYSTEM PUSHING EASTWARD WHILE ITS 06Z  
ENSEMBLE MEAN WAS CLOSER TO THE 00Z ECMWF/UKMET AND ECMWF ENSEMBLE  
MEAN. FARTHER WEST, MODELS CONTINUED TO WAVER ON HOW MUCH, AND  
WHERE, TO DEVELOP A SFC WAVE ALONG A FRONT THAT MAY MOVE INTO  
BRITISH COLUMBIA TUESDAY -- 00Z ECMWF REPRESENTED A PLAUSIBLE  
SOLUTION IN BETWEEN THE QUICKER 00Z GFS AND SLOWER 06Z GFS THOUGH  
PERHAPS A BIT FARTHER SOUTH THAN THE ENSEMBLE CONSENSUS. FOR THE  
LAST COUPLE DAYS OF THE PERIOD, OPTED TO USE JUST THE 00Z ECMWF  
WITH ITS ENSEMBLE MEAN IN CONJUNCTION WITH THE 06Z GEFS MEAN AND  
WPC CONTINUITY WHICH ONLY SLIGHTLY MODIFIED THE FRONTAL  
PROGRESSION.  
 
FRACASSO  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE COLD FRONT MOVING FROM THE MS VALLEY TO THE EASTERN SEABOARD  
SUN-MON WILL SUPPORT SCATTERED AREAS OF PRECIPITATION. THE  
HEAVIEST AMOUNTS SHOULD REMAIN MOSTLY NORTH OF THE U.S. CANADIAN  
BORDER ACROSS ONTARIO/QUEBEC CLOSEST TO THE BEST LOW/MID-LEVEL  
FORCING. THE BEST POTENTIAL FOR ANY HEAVY RAIN ASSOCIATED WITH  
THIS SYSTEM WOULD BE ACROSS NORTHERN NEW ENGLAND -- NORTHERN MAINE  
IN PARTICULAR AS THE WARM FRONT LIFTS THROUGH. BEHIND THE FRONT  
DRY CONDITIONS ARE EXPECTED TO PREVAIL ACROSS MOST OF THE CENTRAL  
AND EASTERN U.S. FOR THE DURATION OF THE MEDIUM RANGE PERIOD WITH  
THE CYCLONE TRACK GENERALLY ALONG/NORTH OF THE CANADIAN BORDER.  
SCATTERED TO NUMEROUS SHOWERS AND STORMS ARE EXPECTED TO LINGER  
ACROSS FLORIDA, HOWEVER, AS THE TRAILING END OF THE SURFACE COLD  
FRONT ENTERS THE STATE AND THEN STALLS ACROSS SOUTH FLORIDA NEXT  
WEEK. FARTHER WEST, DRY CONDITIONS WILL ALSO PREVAIL UNTIL A  
SERIES OF PACIFIC FRONTAL SYSTEMS IMPACTS THE NORTHWEST TUE-THU.  
RAIN SHOULD BECOME WIDESPREAD BY THE MIDDLE OF NEXT WEEK ACROSS  
THE NORTHWEST WITH HEAVY RAIN POSSIBLE ESPECIALLY IN FAVORED  
TERRAIN AREAS. SNOW LEVELS SHOULD BE RELATIVELY HIGH (8,000-10,000  
FT) GIVEN THE PERSISTENT ONSHORE FLOW, BUT THEN LOWER LATE IN THE  
WEEK TO PERHAPS 6000FT BEHIND THE FRONT LATE THURSDAY.  
 
TEMPERATURES ARE EXPECTED TO BE WELL ABOVE AVERAGE ACROSS MUCH OF  
THE EASTERN THIRD OF THE NATION AHEAD OF THE COLD FRONT SUN-MON,  
WITH HIGH TEMPERATURES 5 TO 15 DEG F ABOVE AVERAGE COMMON. AS THE  
FRONT PASSES, TEMPERATURES WILL DROP TO SLIGHTLY BELOW SEASONAL  
NORMS. IN THE WEST, TEMPERATURES SHOULD GRADUALLY WARM THROUGH THE  
PERIOD TO NEAR OR SLIGHTLY ABOVE AVERAGE VALUES. BY MID-WEEK,  
CLOUDS AND PRECIPITATION SHOULD LOWER MAX TEMPS TO 5 TO 10 DEG  
BELOW NORMAL ACROSS THE NORTHWEST AND CONTINUE TO FALL THROUGH THE  
END OF THE PERIOD AS COOLER AIR PUSHES IN.  
 
RYAN  
 

 
 
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