386  
FXUS02 KWBC 261640  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1140 AM EST MON NOV 26 2018  
 
VALID 12Z THU NOV 29 2018 - 12Z MON DEC 03 2018  
   
..MULTI-FACETED STORM FROM THE PLAINS EASTWARD THIS WEEKEND
 
 
   
..OVERVIEW
 
 
A BLOCKING UPPER HIGH NEAR THE DAVIS STRAIT WILL WEAKEN LATER THIS  
WEEK AS UPSTREAM RIDGING OVER THE NORTHEASTERN PACIFIC INTO  
EASTERN ALASKA BECOMES THE NEW DOMINANT UPPER FEATURE. THIS FAVORS  
TROUGHING OVER THE CENTRAL CONUS AND AN ATTEMPT AT SUBTROPICAL  
RIDGING TO PUSH INTO FLORIDA. THIS UPPER TROUGH WILL SUPPORT A  
ROBUST STORM SYSTEM LATE THIS WEEK THROUGH THE WEEKEND LIFTING OUT  
OF THE SOUTHERN PLAINS INTO THE GREAT LAKES REGION.  
 
   
..MODEL GUIDANCE EVALUATION
 
 
START OF THE PERIOD ON THURSDAY WILL FEATURE A STORM MOVING INTO  
CALIFORNIA WHERE THE MODELS CLUSTERED FAIRLY WELL (00Z UKMET WAS  
SLOWER THAN THE REST BUT NOT OUTSIDE THE ENSEMBLE SPREAD). THIS  
WILL MOVE THROUGH THE FOUR CORNERS REGION FRIDAY AND INTO THE  
PLAINS BY SATURDAY. BY THAT POINT, THE MODELS/ENSEMBLES DIVERGE IN  
THE AMPLITUDE AND SPEED OF THE DEVELOPING SURFACE LOW -- GFS AND  
GEFS WERE GENERALLY QUICKER/WEAKER THAN THE ECMWF AND ITS ENSEMBLE  
MEAN WITH THE CANADIAN A BIT IN BETWEEN. PREFERRED THE ECMWF AND  
ITS ENSEMBLE MEAN DUE TO ITS BETTER CONSISTENCY OVER THE PAST FEW  
RUNS AS THE GEFS HAS ALTERNATED BETWEEN FAVORING A STRONGER/WEAKER  
STORM IN ITS 12Z/00Z RUNS, RESPECTIVELY, THE PAST TWO DAYS. THIS  
WOULD TAKE THE SURFACE LOW INTO THE CENTRAL/EASTERN GREAT LAKES ON  
SUNDAY AND OUT THROUGH QUEBEC NEXT MONDAY. BACK TO THE WEST,  
ANOTHER SYSTEM IS FORECAST TO MOVE INTO OREGON ON SATURDAY THOUGH  
THE 00Z ECMWF WAS DIFFERENT THAN THE REST IN ITS HANDLING OF TWO  
INCOMING SYSTEMS FROM THE WEST AND NORTHWEST. BLENDED SOLUTION  
SHOULD SUFFICE THERE AS THERE HAS BEEN LESS CONSISTENCY OVERALL  
AMONG THE GUIDANCE. THAT SYSTEM WILL MOVE THROUGH THE INTERIOR  
WEST ON SUNDAY AND DOWN INTO THE SOUTHERN PLAINS NEXT MONDAY AS  
BROAD TROUGHING ALONG 100W IS FLANKED BY RIDGING UP/DOWNSTREAM PER  
THE ENSEMBLES -- MORE AMPLIFIED IN THE ECMWF ENSEMBLE MEAN  
(PREFERRED) THAN THE GEFS MEAN.  
 
   
..WEATHER HIGHLIGHTS
 
 
FIRST ROUND OF PRECIPITATION IN THE MEDIUM RANGE PERIOD FOR THE  
WEST IS EXPECTED THURSDAY AS THE STRONG PACIFIC LOW MOVES ASHORE.  
THIS SHOULD BRING PRECIPITATION INTO SOUTHERN CALIFORNIA GIVEN A  
SOUTHEASTERLY TRACK OF THE SYSTEM WITH ENHANCEMENT ALONG  
WESTERN-FACING COASTAL RANGES. SEVERAL INCHES TO OVER A FOOT OF  
SNOW IS POSSIBLE FOR THE SIERRAS AND ALSO IN THE MOUNTAINS OUTSIDE  
LOS ANGELES (E.G., SAN GABRIEL, SAN BERNADINO, SAN JACINTO  
MOUNTAINS). THIS SYSTEM WILL REORGANIZE IN THE SOUTHERN PLAINS  
FRIDAY WHERE THE STORM PREDICTION CENTER HAS OUTLINED A CHANCE OF  
SEVERE WEATHER FOR NORTHEASTERN TEXAS EASTWARD (ARKLATEX TO THE  
ARKLAMISS). CONVECTION WILL LIKELY CONTINUE EASTWARD ON SATURDAY  
AS THE FRONT MOVES EASTWARD. WARM FRONT ALONG THE GULF COAST WILL  
LIFT NORTHWARD BUT PERHAPS ONLY SLOWLY EAST OF THE APPALACHIANS  
UNTIL ENOUGH SOUTHERLY FLOW WILL TAKE IT NORTHWARD. WIDESPREAD  
MODEST RAINFALL IS LIKELY ALONG/AHEAD OF THE FRONT WITH A STRONG  
MOISTURE INFLUX. TO THE NORTH/NORTHWEST OF THE SURFACE LOW, ENOUGH  
COLD AIR SHOULD BE IN PLACE FOR SOME SNOW OR MIXED PRECIP FROM  
NE/SD NORTHEASTWARD PERHAPS INTO NORTHERN NEW ENGLAND WHERE ICING  
COULD BE IN THE MIX AS WELL GIVEN THE SURGE OF WARM AIR ALOFT BUT  
MARGINALLY COLD AIR AT THE SURFACE. ALONG THE PAC NW COAST ON  
SATURDAY, THE NEXT SYSTEM WILL BRING IN RAIN/SNOW TO THE WEST  
AGAIN, BUT LIKELY FARTHER NORTH THAN THE PREVIOUS ONE.  
 
TEMPERATURES WILL BE ABOVE AVERAGE (ABOUT +5 TO +15F ANOMALIES)  
AHEAD OF THE WESTERN SYSTEM THURSDAY THROUGH SUNDAY, FIRST IN THE  
SOUTHERN PLAINS THEN INTO THE MS/OHIO/TN VALLEYS THEN INTO THE  
EAST. COOLER/COLDER AIR WILL FILTER IN BEHIND IT AS TROUGHING  
SETTLES INTO THE CENTRAL STATES. TEMPERATURES MAY BE 10-20F BELOW  
AVERAGE IN THE INTERIOR WEST BY NEXT WEEK.  
 
FRACASSO  
 
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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