639  
FXUS02 KWBC 290656  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
155 AM EST THU NOV 29 2018  
 
VALID 12Z SUN DEC 2 2018 - 12Z THU DEC 6 2018  
   
..GENERAL PATTERN OVERVIEW
 
 
THE FORECAST PERIOD FROM SUNDAY THROUGH THURSDAY MORNING WILL  
FEATURE A PATTERN CHANGE ACROSS THE CONTINENTAL U.S. AS A LARGE  
SCALE UPPER LEVEL TROUGH ENCOMPASSES MUCH OF THE CENTRAL AND  
WESTERN U.S. WITH A DISTINCT SOUTHERN STREAM AND NORTHERN STREAM  
FLOW. THE UPPER RIDGE OVER THE EASTERN U.S. WILL BE DISPLACED  
OFFSHORE BY NEXT WEEK AS THE TROUGH BUILDS IN FROM THE WEST. THE  
FIRST STORM SYSTEM OVER THE GREAT LAKES ON SUNDAY, FOLLOWED BY A  
WEAKER LOW ALONG THE MAIN FRONTAL BOUNDARY, WILL HERALD MUCH  
COOLER TEMPERATURES COURTESY OF CANADIAN HIGH PRESSURE BUILDING  
INTO THE REGION. BY THE MIDDLE OF NEXT WEEK, A NEW PACIFIC STORM  
SYSTEM IS EXPECTED TO SLOWLY APPROACH THE CALIFORNIA COAST WITH A  
RETURN TO RAIN/SNOW FOR THAT REGION.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
MODELS AND ENSEMBLE MEANS ARE IN RELATIVELY GOOD AGREEMENT ON  
SUNDAY ACROSS MOST OF THE CONTINENTAL U.S., INCLUDING THE  
REPRESENTATION OF THE TWO MAIN STORM SYSTEMS THAT WILL AFFECT THE  
U.S. THROUGH TUESDAY. HOWEVER, MODEL SPREAD INCREASES BY MONDAY  
REGARDING THE EVOLUTION OF THE SECOND LOW PRESSURE SYSTEM OVER THE  
GULF COAST REGION ALONG THE TRAILING COLD FRONT FROM THE FIRST  
STORM SYSTEM. THE GFS AND GEFS MEAN CONTINUE TO FAVOR A MORE  
AMPLIFIED SURFACE LOW OVER THE SOUTHEAST U.S., WHILST THE UKMET  
AND ECMWF ARE MORE SUPPRESSED AND ARE MORE INDICATIVE OF A SUBTLE  
WAVE ALONG THE FRONT. THE 12Z ECMWF RUN ON WEDNESDAY WAS CLOSER  
TO THE MODEL CONSENSUS COMPARED TO THE 12Z RUN ON TUESDAY, WHICH  
DEPICTED CONSIDERABLY MORE UPPER LEVEL RIDGING OVER THE  
SOUTHWESTERN U.S. COMPARED TO THE MODEL CONSENSUS. THE PREFERENCE  
WITH THIS SYSTEM IS TO STAY CLOSE TO PREVIOUS WPC CONTINUITY ALONG  
WITH A BLEND OF THE GFS/ECMWF/MEANS, WITH THE LOW LIKELY TRACKING  
NEAR THE GULF COAST AND EXITING OFF THE SOUTHEAST COAST.  
 
REGARDING THE WEST COAST SYSTEM FOR THE MIDDLE OF NEXT WEEK, THE  
TREND HAS BEEN FOR A SLIGHTLY FASTER PROGRESSION COMPARED TO  
YESTERDAY. THE GEFS AND EC MEANS ARE RELATIVELY CLOSE TOGETHER  
NEAR THE NORTHERN COAST OF CALIFORNIA BY WEDNESDAY MORNING, AND  
THE ECMWF IS SLIGHTLY FARTHER SOUTH THAN THE GFS. THE CMC IS A  
WESTERN OUTLIER AND NOT SUPPORTED BY THE ENSEMBLE MEANS, SO IT WAS  
NOT PART OF THE FORECAST BLEND.  
 
THE FIRST HALF OF THE FORECAST INCORPORATED MAINLY A BLEND OF THE  
ECMWF, UKMET, AND GFS, AND THE SECOND HALF LEANING MORE TOWARD THE  
EC AND GEFS MEANS FOR PLACEMENT OF MAIN FEATURES. GIVEN THE  
LINGERING UNCERTAINTY REGARDING THE SECOND LOW PRESSURE SYSTEM  
OVER THE SOUTHEAST U.S. EARLY NEXT WEEK, ADDITIONAL REVISIONS TO  
THE FORECAST ARE LIKELY AS MODELS CONTINUE TO RESOLVE THIS FEATURE.  
 
   
..SENSIBLE WEATHER AND HAZARDS
 
 
AN ACTIVE WEATHER PATTERN IS EXPECTED ACROSS THE SOUTHEASTERN U.S.  
TO END THE WEEKEND WITH HEAVY RAIN AND SOME STRONG STORMS NEAR THE  
GULF COAST AND INTO THE SOUTHEAST STATES IN ASSOCIATION WITH THE  
WAVE OF LOW PRESSURE ALONG THE FRONT, BUT GIVEN THE UNCERTAINTY IN  
THE EVOLUTION OF THIS SYSTEM, PREDICTABILITY REMAINS LIMITED  
REGARDING THE MAGNITUDE AND PLACEMENT OF THE HEAVIEST  
PRECIPITATION. THE NEXT SYSTEM APPROACHING CALIFORNIA BY THE END  
OF THE FORECAST PERIOD NEXT WEDNESDAY SHOULD BRING ANOTHER ROUND  
OF HEAVY RAIN AND MOUNTAIN SNOW FOR MUCH OF CALIFORNIA. LAKE  
EFFECT SNOW WILL BE LIKELY DOWNWIND OF THE GREAT LAKES EARLY-MID  
NEXT WEEK COURTESY OF STRONG COLD AIR ADVECTION BEHIND THE  
DEPARTING LOW SUNDAY NIGHT.  
 
IN TERMS OF TEMPERATURES, READINGS ARE EXPECTED TO BE ON THE ORDER  
OF 10 TO 15 DEGREES ABOVE NORMAL AHEAD OF THE WEEKEND STORM SYSTEM  
FROM THE GULF COAST TO THE MID-ATLANTIC REGION ON SUNDAY. MUCH  
COLDER WEATHER WILL SETTLE IN ACROSS THE CENTRAL AND WESTERN U.S.  
COURTESY OF THE BUILDING UPPER LEVEL TROUGH, WITH ANOMALIES ON THE  
ORDER OF 10 TO 20 DEGREES BELOW NORMAL TO BEGIN THE WORK WEEK,  
LEADING TO SOME SUBZERO OVERNIGHT LOWS IN THE NORMALLY COLDER  
LOCATIONS OF THE INTERMOUNTAIN WEST. AN ARCTIC FRONT REACHING THE  
UPPER MIDWEST BY NEXT THURSDAY WILL BRING AN EVEN COLDER SURGE,  
WITH SOME HIGH TEMPERATURES STRUGGLING TO REACH 10 DEGREES ACROSS  
PARTS OF NORTH DAKOTA AND MINNESOTA. WITH THE EXCEPTION OF  
FLORIDA, MOST OF THE CONTINENTAL U.S. SHOULD HAVE BELOW AVERAGE  
TEMPERATURES BY THE MIDDLE OF NEXT WEEK.  
 
D. HAMRICK  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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