369  
FXUS02 KWBC 071601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST TUE NOV 07 2017  
 
VALID 12Z FRI NOV 10 2017 - 12Z TUE NOV 14 2017  
   
..PATTERN OVERVIEW...MODEL UNCERTAINTIES AND PREFERENCES
 
 
MODELS CONTINUE TO DEPICT A PROGRESSIVE PATTERN THROUGH NEXT  
TUESDAY...WITH THREE APPRECIABLE SYNOPTIC UPPER-LEVEL WAVES HAVING  
AN INFLUENCE ON PRECIPITATION ACROSS THE CONUS. THE MEDIUM-RANGE  
PERIOD STARTS OFF WITH VERY GOOD MODEL AGREEMENT OVER NEW ENGLAND  
WITH AN AMPLIFYING TROUGH ON FRIDAY...WHICH WILL RAPIDLY MOVE EAST  
INTO THE CANADIAN MARITIMES ON SATURDAY AS AN OUTBREAK OF COLD AIR  
OVERSPREADS THE NORTHEASTERN U.S. DURING THE WEEKEND.  
MEANWHILE...A PACIFIC FRONT SHOULD TEND TO WEAKEN AS IT PENETRATES  
THE INTERIOR MOUNTAINS OF THE WESTERN U.S. ON FRIDAY BEFORE MOVING  
ACROSS THE PLAINS DURING THE WEEKEND. THE GFS HAS BEEN  
CONSISTENTLY INDICATING A LOW TO FORM ALONG THE FRONT AND MOVES  
NORTHEASTWARD INTO THE GREAT LAKES ON SUNDAY. THE ECMWF HOWEVER  
WAS INDICATING A STRONGER ZONAL FLOW ALONG THE U.S-CANADIAN BORDER  
AND LITTLE OR NO INDICATIONS OF A SURFACE LOW OVER THE GREAT LAKES  
ON SUNDAY BUT THE MOST RECENT ECMWF RUN BEGAN TO SHOW A COMPARABLE  
WAVE FORMING ALONG THE FRONT MORE IN LINE WITH WHAT THE GFS  
DEPICTS. BY EARLY NEXT WEEK...THE OLDER ECMWF RUNS HAD BEEN  
INDICATING CYCLOGENESIS OFF THE SOUTHEAST COAST EARLY NEXT WEEK AS  
IT CARRIES THE FRONTAL WAVES OFF THE EAST COAST. THE MOST RECENT  
ECMWF RUN HAS SPED UP THE PROGRESSION OF THIS WAVE LEADING TO A  
SLOWER ONSET OF THE CYCLOGENESIS FARTHER OFFSHORE. IN  
CONTRAST...THE GFS HAS LITTLE INDICATIONS OF SUCH CYCLOGENESIS  
SINCE IT HAS BEEN TAKING THE WAVE OFFSHORE MUCH FASTER THAN THE  
ECMWF. WITH THE ECMWF TRENDING FASTER...THE FASTER GFS SOLUTIONS  
ARE PREFERRED. LASTLY...ANOTHER PACIFIC SYSTEM IS SHOWN TO MOVE  
ACROSS THE WESTERN U.S. EARLY NEXT WEEK WITH PRETTY GOOD MODEL  
AGREEMENT. A PREFERENCE IS GIVEN TO THE 00Z GEFS RATHER THAN THE  
06Z GEFS OR THE 00Z EC MEAN. THEREFORE...THE MORNING WPC  
MEDIUM-RANGE PRESSURE AND WIND GRIDS WERE DERIVED STARTING FROM A  
50-50 BLEND OF THE 06Z GFS WITH THE 00Z ECMWF FOR  
FRIDAY...GRADUALLY TRENDING TOWARD A 30%-70% BLEND OF THE 00Z  
ECMWF/EC MEAN WITH THE 06Z GFS AND THE 00Z GEFS WITH MORE WEIGHTS  
GIVEN TO THE MEANS BY DAY 7.  
 
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
IT WILL BE A COLD START TO THE PERIOD ACROSS MOST LOCATIONS EAST  
OF THE ROCKIES GIVEN THE AMPLIFIED FLOW SWEEPING THROUGH THE GREAT  
LAKES/NORTHEASTERN U.S. IT SHOULD BE QUITE COOL AND AT TIMES  
BREEZY ON FRIDAY/SATURDAY WITH A STRONG SURFACE RIDGE SETTING UP  
OVER THE REGION AS THE DEEP CYCLONE EXITS INTO EASTERN CANADA. THE  
LARGEST DEPARTURES FROM NORMAL WILL BE ACROSS THE GREAT LAKES/OH  
VALLEY/MID-ATLANTIC/NEW ENGLAND WITH 10 TO 20 DEGREES BELOW  
AVERAGE BEING LIKELY. HIGH TEMPERATURES IN THE 40S WILL BE LIKELY  
AS FAR SOUTH AS UPSTATE NC WHILE BELOW FREEZING OVERNIGHT  
TEMPERATURES COULD REACH DOWN INTO THE INTERIOR CAROLINAS. WHILE  
NO DAILY TEMPERATURE RECORDS SHOULD BE BROKEN DOWN IN THE  
CAROLINAS...EXPECT SOME RECORD LOWS POSSIBLE ON SATURDAY MORNING  
OVER THE MID-ATLANTIC INTO LOWER NEW ENGLAND. FOR THE REST OF THE  
COUNTRY...TEMPERATURES SHOULD BE ON THE MILDER SIDE GIVEN THE  
LOWER AMPLITUDE FLOW REGIME. EXPECT READINGS CLOSER TO CLIMATOLOGY  
TO ABOVE BY AROUND 5 TO 10 DEGREES FROM THE FOUR CORNERS EASTWARD  
INTO THE GREAT PLAINS. COOLER WEATHER CAN BE EXPECTED LATER IN THE  
FORECAST ACROSS THE PACIFIC NORTHWEST GIVEN THE RETURN OF MULTIPLE  
SHORTWAVES.  
 
ACROSS THE GREAT PLAINS/MS RIVER VALLEY/GREAT LAKES...WARM  
ADVECTION PRECIPITATION WILL LIKELY BE EXPANDING IN COVERAGE OVER  
THE WEEKEND. THE BEST FORCING WILL RESIDE ACROSS THE NORTHERN TIER  
STATES WHERE A SURFACE WAVE WILL ACCELERATE TOWARD THE GREAT  
LAKES. REMNANT COLD AIR FROM THE ARCTIC BLAST MAY KEEP SURFACE  
TEMPERATURES COLD ENOUGH FOR SNOW OVER THE GREAT LAKES THIS  
WEEKEND WITH FURTHER CHANCES DOWNSTREAM OVER THE INTERIOR  
NORTHEASTERN U.S. OUT WEST...IT SHOULD BE QUITE UNSETTLED  
THROUGHOUT MUCH OF THE FORECAST ALTHOUGH THERE WILL BE A BRIEF  
LULL IN THE ACTIVITY IN BETWEEN SYSTEMS. THE LONGWAVE TROUGH  
APPROACHING ON SUNDAY HAS AN IMPRESSIVE HEAVY PRECIPITATION SIGNAL  
FROM NORTHERN CA UP INTO THE PACIFIC NORTHWEST WITH OROGRAPHICALLY  
FAVORED LOCATIONS SEEING A BRUNT OF THE RAIN/SNOW. EVENTUALLY THE  
ACTIVITY WILL SHIFT INTO THE UPPER INTERMOUNTAIN WEST WITH  
RAIN/SNOW EXPECTED INTO THE BITTERROOTS...SAWTOOTH...AND TETONS.  
 
KONG/RUBIN-OSTER  
 

 
 
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