447  
FXUS02 KWBC 111601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT WED OCT 11 2017  
 
VALID 12Z SAT OCT 14 2017 - 12Z WED OCT 18 2017  
   
..OVERVIEW
 
 
MODEL GUIDANCE THIS MORNING IS DEPICTING A COUPLE OF  
SYNOPTIC-SCALE FEATURES FORECAST TO AFFECT THE U.S. MAINLAND  
THROUGH THE MEDIUM-RANGE PERIOD. THE FIRST FEATURE WILL BE THE  
LIKELIHOOD OF CYCLOGENESIS ALONG A BAROCLINIC ZONE DURING THE  
WEEKEND FROM THE MIDWEST INTO THE GREAT LAKES AND THEN ACROSS NEW  
ENGLAND ON MONDAY. THE FOCUS WILL THEN SHIFT WESTWARD INTO THE  
PACIFIC NORTHWEST WHERE INCREASINGLY FAST UPPER-LEVEL FLOW WITH  
MULTIPLE SHORTWAVE ENERGY FROM THE NORTHEAST PACIFIC WILL BRING  
INCREASINGLY UNSETTLED WEATHER TOWARD THE REGION.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
MODEL SOLUTIONS ARE COMING INTO MUCH BETTER AGREEMENT WITH REGARD  
TO THE SPEED AND TRACK OF THE CYCLONE THAT IS FORECAST TO MOVE  
ACROSS THE MIDWEST INTO THE GREAT LAKES DURING THE WEEKEND. THE  
GFS HAS BEEN QUITE CONSISTENT IN PLACING THE CYCLONE CENTER OVER  
THE CENTRAL GREAT LAKES SUNDAY MORNING WHEREAS THE ECMWF'S MUCH  
SLOWER AND MORE INTENSE SOLUTION A COUPLE OF DAYS AGO HAS  
GRADUALLY TRENDED FASTER AND BECOMES SIMILAR TO THE GFS SOLUTION  
THIS MORNING. THE GFS CONTINUES TO KEEP THE CYCLONE LESS  
AMPLIFIED AS IT TRACKS ACROSS NEW ENGLAND A FASTER EASTWARD MOTION  
THAN THE ECMWF ACROSS NEW ENGLAND ON MONDAY.  
 
INCREASINGLY FAST UPPER-LEVEL FLOW OVER THE NORTHEAST PACIFIC IS  
DEPICTED ON GLOBAL MODELS FOR EARLY TO MIDDLE OF NEXT WEEK. MODEL  
SPREAD IS HIGH ACROSS THE PACIFIC NORTHWEST IN THIS REGIME AS  
EXPECTED. THE GFS SOLUTIONS APPEAR TO BE MORE CONSISTENT THAN THE  
ECMWF SOLUTIONS IN THE PAST COUPLE OF DAYS AS THE ECMWF NOW  
DEPICTS A LARGE CYCLONE APPROACHING THE WEST COAST OF CANADA AND  
THE PACIFIC NORTHWEST BY NEXT WEDNESDAY IN AGREEMENT WITH THE GFS.  
 
GIVEN THE MORE CONSISTENT GFS SOLUTIONS...THE WPC MORNING  
SEA-LEVEL PRESSURE FIELDS WERE DERIVED BASED ON 60% OF THE 06Z GFS  
AND 40% OF 00Z ECMWF WITH MORE WEIGHTS GIVEN TO THEIR ENSEMBLE  
MEANS TOWARD DAY 7.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
MODELS/ENSEMBLE CONTINUE TO HINT AT THE POTENTIAL FOR A ROUND OF  
HEAVY CONVECTION ACROSS THE MIDWEST/GREAT LAKES SAT-SUN AS A AN  
UPPER SHORTWAVE APPROACHES AND THE ASSOCIATED SURFACE FRONT MOVES  
INTO THE REGION AND THEN STALLS WHILE ADDITIONAL WAVES DEVELOP  
ALONG IT. DEVELOPMENT OF A HEALTHY LOW-LEVEL JET SHOULD TRANSPORT  
SUFFICIENT MOISTURE/INSTABILITY NORTHWARD INTO THE FRONT TO  
SUPPORT CONVECTION WITH POTENTIALLY HEAVY RAINFALL. DESPITE SOME  
UNCERTAINTY AMONG DETERMINISTIC GUIDANCE SURROUNDING THE MASS  
FIELDS, THE ECENS/GEFS ENSEMBLES HAVE BEEN STEADFAST AND  
REMARKABLY SIMILAR IN THEIR DEPICTION OF A BAND OF HEAVY RAINFALL  
ALONG/JUST NORTH OF THE FRONT. FARTHER SOUTH, THE FLORIDA  
PENINSULA WILL REMAIN WET THROUGH THE PERIOD. AN ELONGATED  
TROUGH/EASTERLY WAVE MOVING FROM THE BAHAMAS ACROSS THE FL  
PENINSULA WILL SUPPORT SCATTERED TO NUMEROUS SHOWERS AND STORMS  
FRI-SUN. BY EARLY NEXT WEEK ANOTHER SURFACE FRONT WILL PUSH INTO  
THE PENINSULA BRINGING A CONTINUATION OF WET CONDITIONS. MOST OF  
THE WEST WILL INITIALLY BE DRY BEFORE RAPID SUCCESSION SHORTWAVES  
APPROACH THE REGION BY TUE-WED. THUS, THE NORTHWEST WILL GET  
INCREASINGLY WET BY EARLY TO MID NEXT WEEK, WITH HEAVIEST AMOUNTS  
FOCUSED ON FAVORED TERRAIN AREAS AND HIGH ELEVATION SNOWS  
POSSIBLE.  
 
TEMPERATURES ARE EXPECTED TO BE WELL ABOVE AVERAGE ACROSS MUCH OF  
THE CENTRAL AND EASTERN U.S. AHEAD OF THE COLD FRONT SAT-MON, WITH  
HIGH TEMPERATURES 5 TO 15 DEG F ABOVE AVERAGE COMMON. AS THE FRONT  
PASSES, TEMPERATURES WILL DROP BUT ONLY TO NEAR OR SLIGHTLY BELOW  
SEASONAL NORMS. IN THE WEST, TEMPERATURES WILL INITIALLY BE 5 TO  
15 DEG BELOW NORMAL ON SAT BEFORE UPPER TROUGHING MOVES EAST, BUT  
SHOULD RECOVER TO NEAR NORMAL LEVELS FROM SUN ONWARD AS HEIGHTS  
RISE AHEAD OF THE NEXT INCOMING SHORTWAVES.  
 
KONG/RYAN  
 

 
 
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