007  
FXUS02 KWBC 300654  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
154 AM EST SUN DEC 30 2018  
 
VALID 12Z WED JAN 02 2019 - 12Z SUN JAN 06 2019  
   
..OVERVIEW
 
 
A POSITIVELY TILTED TROUGH STRETCHING FROM THE GREAT LAKES TO THE  
FOUR CORNERS REGION WILL MOVE EASTWARD TO THE SOUTHEAST AND  
TENNESSEE VALLEY BY THE END OF THE WEEK. A CLOSED MID-LEVEL LOW  
WILL BE OVER THE FOUR CORNERS ON WEDNESDAY--MOVING ACROSS THE  
SOUTHERN PLAINS BY THURSDAY BEFORE MAKING IT TO THE SOUTHEAST.  
DURING THIS TRANSITION, MOVING FROM THE PLAINS TO SOUTHEAST, WHERE  
MODEL DIFFERENCES BECOME APPARENT. MEANWHILE, AN UPPER RIDGE WILL  
BUILD ACROSS THE WESTERN U.S. DURING THIS TIME. BY THE WEEKEND,  
THE PATTERN WILL BECOME MORE ZONAL FOR THE EASTERN U.S. AS A  
TROUGH IN THE PACIFIC BEGINS TO APPROACH THE WEST COAST. OVERALL,  
EXPECT AN ACTIVE PATTERN FOR THE SOUTHEAST AND MID-ATLANTIC  
THROUGH THE FIRST PORTION OF THE WEEK--WHILE PRECIPITATION WILL  
INCREASE ACROSS THE WEST COAST BY THE WEEKEND.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
IN THE BEGINNING OF THE MEDIUM RANGE PERIOD, DAYS 3-4 (WED/THU),  
THE 12Z GFS, 12Z ECMWF, AND 18Z FV3-GFS ARE IN FAIR AGREEMENT. THE  
TIMING OF THE TROUGH MOVING ACROSS THE SOUTHERN PLAINS LINES UP  
WELL. THE 12Z UKMET WAS QUITE SLOW AND MUCH STRONGER WITH THE  
CLOSED LOW OVER THE FOUR CORNERS, WHEREAS THE 12Z CMC WAS TOO  
FAST--THUS BOTH OF THESE MODELS WERE NOT USED IN THE BLEND. BY DAY  
4/THU, THERE WERE ALREADY SOME DIFFERENCES WITH THE ECMWF AND  
GFS/FV3, WITH THE ECMWF SHOWING A CLOSED LOW OVER THE MISSISSIPPI  
VALLEY AND GFS/FV3 HAVING A MORE ELONGATED TROUGH. THE ECMWF HAS  
BEEN MORE CONSISTENT WITH THIS FEATURE ESPECIALLY COMPARED WITH  
THE GFS. BY DAY 5/FRI, THE GFS STILL SHOWS ENERGY WITH THE  
ELONGATED TROUGH OVER THE SOUTHEAST AS THE ECMWF LIFTS THE TROUGH  
NORTHWARD OVER THE MID-ATLANTIC. THE GFS IS ALSO MORE AMPLIFIED  
WITH THE UPPER RIDGE OVER THE INTERMOUNTAIN WEST/GREAT BASIN DUE  
TO AN INCOMING CLOSED MID-LEVEL LOW--IT KEEPS THE CLOSED LOW  
INTACT OFF THE COAST OF BRITISH COLUMBIA WHILE THE ECMWF HAS IT  
BECOMING AN OPEN WAVE MOVING ACROSS THE WESTERN CANADIAN  
PROVINCES. ONCE THE WEEKEND APPROACHES, DIFFERENCES ONCE AGAIN  
SHOW UP WITH THE INCOMING TROUGH IN THE PACIFIC IN BOTH DETAIL AND  
TIMING--WITH THE GFS FASTER AND THE ECMWF SHOWING A CLOSED LOW.  
THE 12Z ECMWF ENSEMBLE MEAN AND 18Z GEFS MEAN ARE MORE CONSISTENT  
WITH THE MAIN FEATURES OVERALL FROM DAY 5 AND BEYOND.  
 
A BLEND OF THE 12Z GFS/18Z FV3-GFS AND 12Z ECMWF WAS USED FOR DAYS  
3/4, WITH MORE WEIGHT ON THE ECMWF DUE TO ITS CONSISTENCY. FOR  
DAYS 5-7, USED A BLEND OF THE 12Z ECMWF ENSEMBLE MEAN AND 18Z GEFS  
MEAN ALONG WITH THE 12Z ECMWF AND A LITTLE BIT OF THE 12Z GFS.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
PRECIPITATION WILL BEGIN TO INCREASE ACROSS THE WESTERN AND  
CENTRAL GULF COAST BY MIDWEEK AS THE MID-LEVEL TROUGH APPROACHES  
THE PLAINS. AT THE SURFACE, A LOW WILL MOVE NORTHWARD ALONG WITH A  
WARM FRONT. THIS WILL PROMOTE CONVECTION ACROSS THE GULF COAST AND  
SOUTHEAST. BY THURSDAY, PRECIPITATION IS EXPECTED TO DECREASE  
ACROSS THE WESTERN GULF COAST WHILE CONTINUING ACROSS THE  
SOUTHEAST AND CENTRAL GULF COAST AS THE SURFACE LOW LIFTS INTO  
THESE REGIONS. WHEN THE FRONTAL SYSTEM MOVES NORTH AND EAST INTO  
THE MID-ATLANTIC AND NORTHEAST ON THURSDAY AND INTO FRIDAY,  
PRECIPITATION WILL FOLLOW. BY THE WEEKEND, PRECIPITATION SHOULD BE  
WINDING DOWN FOR THE EASTERN U.S. THE HIGHEST QPF TOTALS WILL  
STRETCH FROM WEST-CENTRAL MISSISSIPPI EASTWARD INTO THE CAROLINAS  
ON WEDNESDAY AND THURSDAY. FARTHER WEST, EXPECT AN INCREASE IN  
PRECIPITATION BY THURSDAY FOR THE PACIFIC NORTHWEST--WITH RAIN AND  
HIGHER ELEVATION SNOW FOR THE OLYMPICS/WASHINGTON CASCADES AND  
PORTIONS OF THE NORTHERN ROCKIES. ON SATURDAY AND SUNDAY, A  
FRONTAL SYSTEM ASSOCIATED WITH THE TROUGH OFF THE WEST COAST WILL  
BRING RAIN/HIGHER ELEVATION SNOW FOR CALIFORNIA AND THE FOUR  
CORNERS.  
 
THE SOUTHERN PLAINS WILL BE THE COOLEST AREA IN THE BEGINNING OF  
THE MEDIUM RANGE PERIOD--WITH HIGH TEMPERATURES BEING 15-20  
DEGREES BELOW NORMAL. THE NORTHERN PLAINS AND UPPER MIDWEST WILL  
BE ABOVE AVERAGE FOR WEDNESDAY/THURSDAY, WITH TEMPERATURES  
EXPECTED TO BE 15-20 DEGREES ABOVE AVERAGE. THE WARM CONDITIONS  
WILL SHIFT TO THE MISSISSIPPI VALLEY AND EASTERN U.S. BY THE  
WEEKEND, WITH TEMPERATURES NEARING 10-15 DEGREES ABOVE AVERAGE.  
THE WESTERN U.S. WILL STAY NEAR NORMAL THROUGH THE MEDIUM RANGE  
PERIOD.  
 
REINHART  
 
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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