436  
FXUS02 KWBC 250558  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
158 AM EDT THU APR 25 2019  
 
VALID 12Z SUN APR 28 2019 - 12Z THU MAY 02 2019  
   
..OVERVIEW AND GUIDANCE PREFERENCES
 
 
AN EXPANSIVE REX BLOCK ACROSS THE NORTH/CENTRAL PACIFIC, EXTENDING  
FROM HAWAII TO ALASKA, WILL SUPPORT A DOWNSTREAM MEAN UPPER TROUGH  
CENTERED ACROSS THE NORTHERN ROCKIES THROUGH THE EXTENDED FORECAST  
PERIOD. A PERSISTENT UPPER LOW CENTERED WEST OF HUDSON BAY, AND  
SLOWLY RETROGRADING THROUGH THE PERIOD, WILL SUPPORT SOUTHWARD  
TRANSPORT OF CHILLY POLAR AIR INTO THE NORTH CENTRAL U.S. FARTHER  
EAST, THE SUBTROPICAL RIDGE IS EXPECTED TO GRADUALLY EXERT ITS  
INFLUENCE NORTHWARD INTO THE SOUTHEAST AND SOUTHERN MID-ATLANTIC  
EARLY NEXT WEEK.  
 
PREFERRED A MULTI-MODEL BLEND APPROACH INITIALLY DURING DAYS 3-5  
(SUN-TUE), INCORPORATING THE 12Z ECMWF/CMC AND 18Z GFS (WITH  
HEAVIEST WEIGHT PLACE TOWARD THE ECMWF). THIS BLEND LEANED TOWARD  
THE SLOWER SOLUTIONS (WHICH WERE WELL SUPPORTED BY ENSEMBLE MEMBER  
CLUSTERING) WITH THE SHORTWAVE/SURFACE LOW CROSSING THE OHIO  
VALLEY/NORTHEAST ON SUN. ADDITIONAL NORTHERN STREAM SHORTWAVES,  
ONE CROSSING THE NORTH CENTRAL U.S., AND ANOTHER DIVING INTO THE  
PACIFIC NORTHWEST SUN-MON WERE HANDLED SIMILARLY BY THESE  
PREFERRED SOLUTIONS. FARTHER SOUTH, A CUTOFF SOUTHERN STREAM UPPER  
LOW APPROACHING SOUTHERN CALIFORNIA LATE SUN-MON CONTINUED TO SHOW  
SOME TIMING DIFFERENCES, AND THE SLOWER ECMWF WAS PREFERRED OVER  
THE SOMEWHAT FASTER GFS TIMING (CAUSING THE GFS SOLUTION BE  
FURTHER DEEMPHASIZED BY MON).  
 
DURING DAYS 6-7 (WED), TIMING DIFFERENCES WITH THE SOUTHERN STREAM  
FEATURE CONTINUE TO GROW AS THE FEATURE MOVES INTO THE CENTRAL  
U.S. BY WED, WITH THE GFS AT LEAST 18 HOURS FASTER THAN THE  
ECMWF/CMC. FARTHER NORTH, MODEL CONSENSUS HAS IMPROVED A BIT THAT  
THE ARRIVAL OF ADDITIONAL SHORTWAVE ENERGY INTO THE PACIFIC  
NORTHWEST EARLY-MID NEXT WEEK SHOULD SERVE TO FURTHER AMPLIFY A  
BROAD UPPER TROUGH AXIS CENTERED OVER THE NORTHERN GREAT  
BASIN/NORTHERN ROCKIES, WITH A CONSOLIDATED AREA OF SHORTWAVE  
ENERGY PERHAPS LIFTING OUT INTO THE NORTHERN PLAINS BY THU.  
ENSEMBLE MEANS SHOWED GENERAL AGREEMENT ON THIS IDEA DESPITE  
INCREASING SPREAD. THUS, THE FORECAST BY WED-THU PLACED INCREASING  
WEIGHT ON ECENS/GEFS ENSEMBLE MEANS, WITH SOME CONTINUED USE OF  
THE DETERMINISTIC ECMWF THROUGH THE END OF THE PERIOD.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
SHOWERS AND PERHAPS A FEW THUNDERSTORMS ARE EXPECTED TO ACCOMPANY  
THE LOW PRESSURE SYSTEM MOVING FROM THE OHIO VALLEY/LOWER GREAT  
LAKES TO THE NORTHEAST ON SUN. AFTER THAT, THE FOCUS SHIFTS TO THE  
CENTRAL U.S., WHERE A PERSISTENT STALLED FRONTAL BOUNDARY ALONG  
WITH A FEW PASSING UPPER SHORTWAVES WILL FOCUS MULTIPLE ROUNDS OF  
SHOWERS AND THUNDERSTORMS, WITH THE POTENTIAL FOR AREAS OF HEAVY  
RAINFALL. THE STRONGEST SIGNAL IN THE GUIDANCE FOR HEAVY RAIN WAS  
SEEN FROM PORTIONS OF THE SOUTHERN/CENTRAL PLAINS TO THE  
MID-MISSISSIPPI VALLEY FROM MON THROUGH THE MIDDLE OF NEXT WEEK,  
WITH QPF GUIDANCE SUGGESTING THE POTENTIAL FOR MULTI-INCH RAINFALL  
TOTALS OVER THE COURSE OF A FEW DAYS. ON THE NORTHERN FRINGE OF  
THIS AREA OF PRECIPITATION IN THE CENTRAL U.S. SUFFICIENT COLD AIR  
MAY BE IN PLACE TO SUPPORT SOME SNOW ON SUN ACROSS PORTIONS OF THE  
NORTHERN PLAINS. A SECOND ROUND OF POTENTIAL SNOW OR RAIN/SNOW MIX  
WILL BE POSSIBLE ACROSS PORTIONS OF THE NORTHERN HIGH PLAINS  
TUE-WED. FARTHER WEST, LOWERING HEIGHTS AND THE PASSAGE OF  
MULTIPLE SHORTWAVES WILL GENERATE RAIN AND MOUNTAIN SNOW FOR  
PORTIONS OF THE GREAT BASIN AND CENTRAL/NORTHERN ROCKIES THROUGH  
THE PERIOD.  
 
BELOW AVERAGE TEMPERATURES ARE EXPECTED FROM SUN INTO NEXT WEEK,  
FROM THE NORTHERN ROCKIES TO THE GREAT LAKES. THE GREATEST  
ANOMALIES ARE EXPECTED SUN-WED FROM THE NORTHERN ROCKIES TO THE  
NORTHERN HIGH PLAINS, WHERE HIGH TEMPERATURES MAY BE 10-20 DEG F  
BELOW AVERAGE. WARMING TEMPERATURES ARE EXPECTED ACROSS THE  
SOUTHEAST AND SOUTHERN MID-ATLANTIC BY EARLY NEXT WEEK AS THE  
SUBTROPICAL RIDGE BUILDS. HIGHS ACROSS THESE AREAS MAY REACH 10 TO  
15 DEG ABOVE AVERAGE TUE-THU.  
 
RYAN  
 
ADDITIONAL 3-7 DAY HAZARDS INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDICES ARE 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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