626  
FXUS02 KWBC 061601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST MON NOV 06 2017  
 
VALID 12Z THU NOV 09 2017 - 12Z MON NOV 13 2017  
   
..PATTERN OVERVIEW/MODEL GUIDANCE/UNCERTAINTIES/PREFERENCES
 
 
THE MEDIUM RANGE PERIOD FEATURES A FAIRLY ACTIVE WEATHER PATTERN  
WITH A SPLIT FLOW REGIME IN PLACE. TO BEGIN...ON THURSDAY/DAY  
3...SHORTWAVE ENERGY IN THE SOUTHERN STREAM WILL BE TRAVERSING  
THROUGH THE SOUTHEASTERN STATES WHILE AN IMPRESSIVE LONGWAVE  
TROUGH DESCENDS FROM HUDSON BAY TOWARD THE GREAT  
LAKES/NORTHEASTERN U.S.. EXPECT THIS TROUGH TO ATTAIN A NEGATIVE  
TILT OVER SOUTHERN QUEBEC THURSDAY NIGHT WHICH WOULD ALLOW FOR THE  
FORMATION OF A RATHER DEEP CYCLONE AT THE SURFACE WHICH LIFTS  
FARTHER INTO EASTERN CANADA BY DAY 5/SATURDAY. OUT WEST...AN  
INITIAL DEEP UPPER LOW SHOULD BE APPROACHING THE NORTHERN  
CA/PACIFIC NORTHWEST COAST EARLY THURSDAY WHICH QUICKLY EVOLVES  
INTO AN OPEN WAVE AND SLIDES DOWNSTREAM TOWARDS THE GREAT  
PLAINS/MISSISSIPPI RIVER VALLEY BY THE WEEKEND. BEHIND  
THIS...ANOTHER SHORTWAVE EVENTUALLY MOVES INTO THE WESTERN EDGE OF  
THE MAP LATE IN THE FORECAST PERIOD WHICH SHOULD KEEP THE PACIFIC  
NORTHWEST IN AN ACTIVE/WET PATTERN INTO EARLY NEXT WEEK. WHILE  
MUCH OF THE CONTIGUOUS U.S. SEES AN ACTIVE MEDIUM RANGE  
PERIOD...UPPER RIDGING SHOULD DOMINATE THE RIO GRANDE VALLEY AND  
DOWN INTO MEXICO.  
 
REGARDING THE AVAILABLE MODEL GUIDANCE...THE 00Z CMC/UKMET  
CONTINUE TO BE ON THE FASTER SIDE OF THE GUIDANCE WITH THE  
SHORTWAVE TRAVERSING THE DEEP SOUTH EARLY ON. THE 06 GFS/00Z ECMWF  
AND RESPECTIVE ENSEMBLE MEANS ARE NOTABLY SLOWER TO DRAG BOTH THE  
SHORTWAVE AND WEAK WAVE OF LOW PRESSURE OFF THE COAST BY THE  
WEEKEND. TO THE NORTH...MODELS SEEM TO HAVE COME INTO MUCH BETTER  
AGREEMENT WITH THE DIGGING LONGWAVE TROUGH AND DESCENDING ARCTIC  
AIR MASS INTO THE NORTHEAST BY THE END OF THE WEEK WITH SOME MINOR  
TIMING DIFFERENCES ARISING AS THE ASSOCIATED DEEP SURFACE CYCLONE  
LIFTS INTO CANADA DAY 4 AND BEYOND. TO THE WEST...DIFFERENCES  
BEGIN TO ARISE AMONGST THE OPERATIONAL MODELS AS THE SHORTWAVE  
MOVES INTO THE GREAT PLAINS ON DAY 5 WITH THE 00Z CMC ON THE  
FASTER SIDE...AND THE ECMWF SHOWING THE SLOWEST SOLUTION. THE  
ENSEMBLE MEANS SHOW GOOD SUPPORT FOR A SOLUTION SOMEWHERE IN THE  
MIDDLE...OR CLOSEST TO THAT OF THE 06 GFS...ALBEIT SLIGHTLY WEAKER  
AND FLATTER. DEPENDING ON THE AMPLIFICATION OF THIS  
SHORTWAVE...SOME MODELS/ENSEMBLES CONTINUE HINT AT A POSSIBLE  
COASTAL LOW OFF THE NORTHEAST COAST BY DAY 6/7 BUT THERE REMAINS  
SIGNIFICANT SPREAD AND UNCERTAINTY ON THIS...BOTH BETWEEN THE  
OPERATIONAL MODELS AND THE INDIVIDUAL ENSEMBLE MEMBERS. AND  
FINALLY...OPERATIONAL MODELS AND ENSEMBLES SHOW FAIRLY GOOD  
AGREEMENT ON BOTH TIMING AND AMPLIFICATION OF RENEWED TROUGHING  
ALONG THE NORTHWEST COAST ON DAY 7.  
 
THIS CYCLE OF THE WPC MEDIUM RANGE PROGS FAVORS A BLEND OF THE  
LATEST OPERATIONAL GFS/ECMWF (WITH DECREASING AMOUNTS OF THE 00Z  
CMC) DAYS 3 AND 4. BY DAY 5...INCREASING AMOUNTS OF THE GEFS/EC  
MEAN WERE ADDED TO THE BLEND TO HELP MITIGATE SOME DIFFERENCES  
DISCUSSED ABOVE...BUT FAIRLY GOOD AGREEMENT IN THE OPERATIONAL  
GFS/ECMWF MEANT 40 PERCENT OPERATIONAL MODEL GUIDANCE WAS STILL  
USABLE EVEN ON DAY 7.  
 
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
WHILE AN IMPRESSIVE SHOT OF MODIFIED ARCTIC AIR ENTERS THE PICTURE  
DURING THE THURSDAY THROUGH SATURDAY TIME FRAME ACROSS THE  
NORTHEAST...VERY FEW DAILY TEMPERATURE RECORDS ARE EXPECTED TO BE  
BROKEN. DESPITE THIS...EXPECT DEPARTURES FROM NORMAL ON THE ORDER  
OF 10 TO 20 DEGREES BELOW AVERAGE TO BE THE NORM FROM THE NORTHERN  
PLAINS THROUGH THE UPPER MIDWEST AND INTO THE GREAT LAKES/OH  
VALLEY/NORTHEASTERN U.S.. SOME OVERNIGHT LOWS MAY PUSH BELOW ZERO  
DEGREES ON FRIDAY MORNING ACROSS FAR NORTHERN NORTH  
DAKOTA/MINNESOTA. THE AIR MASS WILL MODIFY IN TIME WHILE ADVANCING  
EASTWARD BUT MAY BRING THE FIRST FREEZE TO MANY LOCATIONS FARTHER  
EAST. GRADUALLY TEMPERATURES ACROSS THE COUNTRY WILL MODERATE SOME  
AS THE FLOW TURNS A BIT MORE ZONAL IN NATURE BY THE END OF THE  
WEEKEND.  
 
REGARDING PRECIPITATION...UNSETTLED CONDITIONS ARE LIKELY FROM  
NORTHERN CA UP INTO WESTERN OR/WA GIVEN STRONG AMPLE ONSHORE  
FLOW...AND FAVORABLE UPSLOPING ALONG THE TERRAIN. THROUGH EARLY  
FRIDAY...MODERATE TO LOCALLY HEAVY PRECIPITATION IS LIKELY FROM  
THE SHASTA/NORTHERN SIERRA NEVADA RANGES NORTHWARD TO THE  
OLYMPICS/CASCADES. SOME OF THIS WILL FALL IN THE FORM OF SNOWFALL  
ACROSS THE HIGHER ELEVATIONS AS WELL AS MORE INLAND LOCALES LIKE  
THE BITTERROOTS...SAWTOOTH...AND TETONS. THE WEST COAST WILL  
BRIEFLY DRY OUT OVER THE WEEKEND BEFORE THE NEXT TROUGH BRINGS A  
BOUT OF RAIN/SNOW BY LATE IN THE PERIOD. ACROSS THE EASTERN  
U.S...LINGERING SHOWERS ALONG A COLD FRONT ARE LIKELY ACROSS THE  
SOUTHEAST AND CENTRAL/EASTERN GULF COAST ON THURSDAY WHILE SOME  
ACTIVITY IS POSSIBLE OVER THE GREAT LAKES GIVEN STEEPENING LAPSE  
RATES ACCOMPANYING THE STRONG UPPER TROUGH. SOME SNOW IS ALSO  
POSSIBLE OVER THE INTERIOR NORTHEAST ALTHOUGH MOISTURE SHOULD BE  
SOMEWHAT SCANT. EVENTUALLY SOME WARM ADVECTION ACTIVITY IS  
POSSIBLE BY SATURDAY ACROSS THE GREAT PLAINS/MS RIVER VALLEY WITH  
THE PROGRESSIVE SHORTWAVE MOVING THROUGH. IF ENOUGH COLD AIR  
LINGERS ACROSS THE UPPER MIDWEST/GREAT LAKES...SOME PRECIPITATION  
MAY FALL AS SNOW OVER THE WEEKEND. EVENTUALLY ALL OF THE UNSETTLED  
WEATHER WILL MOVE TOWARD THE EASTERN SEABOARD BY NOVEMBER 12/13  
WITH ANY DISCERNIBLE COASTAL WAVE AUGMENTING LOCAL AMOUNTS.  
 
SANTORELLI  
 

 
 
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