364  
FXUS02 KWBC 152101  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
500 PM EDT MON APR 15 2019  
 
VALID 12Z THU APR 18 2019 - 12Z MON APR 22 2019  
 
16Z UPDATE: THE DETERMINISTIC MODELS REMAIN IN ABOVE AVERAGE  
AGREEMENT ACROSS THE CONTINENTAL U.S. THROUGH SATURDAY WITH AN  
AMPLIFIED UPPER LEVEL PATTERN IN PLACE. THE 6Z FV3 GFS SOLUTION  
IS CLOSER TO THE ENSEMBLE MEANS WITH THE MAIN SURFACE LOW ACROSS  
THE GREAT LAKES FOR THE END OF THE WEEK, WHEREAS THE OPERATIONAL  
GFS IS FARTHER SOUTH WITH THE CLOSED LOW OVER THE TENNESSEE RIVER  
VALLEY, SO MORE OF THE FV3 WAS INCORPORATED INTO THE FORECAST.  
THE OPERATIONAL ECMWF HAS INDICATED BETTER RUN-TO-RUN CONTINUITY  
WITH THE EAST COAST STORM SYSTEM COMPARED TO THE OTHER GUIDANCE,  
AND WAS ALSO PART OF THE FORECAST PROCESS. THE MORE UNCERTAIN  
ASPECT TO THIS FORECAST RELATES TO THE LIKELY DEVELOPMENT OF A  
SECONDARY LOW OFF THE EAST COAST BY SUNDAY, AND THE MODELS ARE  
STILL RESOLVING THIS POTENTIAL FEATURE. BY THE END OF THE  
FORECAST PERIOD NEXT MONDAY, A NEW SURFACE LOW WILL LIKELY EVOLVE  
ACROSS THE HIGH PLAINS IN RESPONSE TO THE NEXT PACIFIC TROUGH  
MOVING ACROSS THE WESTERN U.S., WITH THE OPERATIONAL GFS AMONG THE  
MOST AMPLIFIED SOLUTIONS. THIS STORM SYSTEM MAY BE THE NEXT  
SIGNIFICANT WEATHER EVENT GOING INTO THE BEGINNING OF NEXT WEEK.  
THE PREVIOUS OVERNIGHT DISCUSSION IS APPENDED BELOW FOR REFERENCE.  
 
HAMRICK  
   
..OVERVIEW
 
 
PROGRESSIVE BUT AMPLIFIED PATTERN WILL SUPPORT A DYNAMIC SYSTEM  
MOVING THROUGH THE CENTRAL STATES THU/FRI INTO THE EAST BY THE  
WEEKEND BUT POSSIBLY TAKING UNTIL NEXT WEEK TO FULLY MOVE  
OFFSHORE. THE WEST WILL SEE A FRONT MOVE INTO WASHINGTON/OREGON  
EARLY FRIDAY AND THEN PROGRESS EASTWARD AND SOUTHWARD INTO THE  
PLAINS AND SOUTHERN ROCKIES LATE THIS WEEKEND INTO NEXT MONDAY.  
 
   
..GUIDANCE PREFERENCES
 
 
BLEND OF THE 18Z GFS/GEFS AND 12Z ECMWF/ECMWF ENSEMBLE MEAN  
OFFERED A REASONABLE STARTING POINT TO THE MEDIUM RANGE PERIOD,  
WITH A DETERMINISTIC-CENTERED BLEND INCLUDING THE UKMET/CANADIAN  
TO START AND A 2/5THS ENSEMBLE WEIGHTING BY NEXT MONDAY. THIS  
MAINTAINED GOOD CONTINUITY OVERALL AS THE PATTERN REMAINS FAIRLY  
WELL-HANDLED BY THE ENSEMBLES AFTER EARLIER UNCERTAINTIES. STILL,  
QUESTIONS REMAIN IN HOW THE EASTERN SYSTEM EVOLVES DEPENDING ON  
THE STRENGTH/TRACK OF MID-LEVEL SHORTWAVES NOT EASILY RESOLVED AT  
THIS LEAD TIME. ENSEMBLE CLUSTERING SUGGESTED A SLOWING OF THE  
FRONT ALONG OR JUST OFF THE EAST COAST WITH A NEW SURFACE LOW/WAVE  
DEVELOPING NEAR THE MID-ATLANTIC BEFORE TURNING NORTHEASTWARD.  
RESIDENCE TIME NEAR NEW ENGLAND SHOULD BE LIMITED DUE TO THE  
APPROACHING SYSTEM FROM THE WEST BY THAT TIME.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
MULTI-INCH RAINFALL TOTALS WITH LOCAL FLOODING ARE PROBABLE  
(ENHANCED IN EMBEDDED CONVECTION) ALONG/AHEAD OF THE FRONT OVER  
THE LOWER MISSISSIPPI VALLEY (POSSIBLY INTO PARTS OF THE SOUTHEAST  
AND MID-ATLANTIC) WITH LESSER AMOUNTS IN A LOCAL MAX AREA TO THE  
NORTH/NORTHEAST OF THE SURFACE LOW ACROSS WISCONSIN. CONSULT SPC  
FOR THE LATEST ON THE SEVERE WEATHER RISK. MILD TEMPERATURES WILL  
PRECEDE THE FRONT (10-15F ABOVE AVERAGE) TO BE REPLACED BY COOLER  
THAN AVERAGE TEMPERATURES AFTER ITS PASSAGE. THE NORTHWEST WILL  
SEE GENERALLY LIGHT PRECIPITATION ALONG A FRONT PUSH THROUGH THE  
GREAT BASIN AND CENTRAL ROCKIES THIS WEEKEND INTO NEXT MONDAY.  
 
FRACASSO  
 
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  
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE MIDDLE/LOWER MISSISSIPPI  
VALLEY, THE TENNESSEE VALLEY, THE SOUTHERN APPALACHIANS, THE  
SOUTHEAST, AND THE OHIO VALLEY, THU-FRI, APR 18-APR 19.  
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL APPALACHIANS, THE  
MID-ATLANTIC, THE SOUTHERN APPALACHIANS, THE SOUTHEAST, THE GREAT  
LAKES, AND THE OHIO VALLEY, FRI-SAT, APR 19-APR 20.  
- SEVERE WEATHER ACROSS PORTIONS OF THE MIDDLE/LOWER MISSISSIPPI  
VALLEY, THE TENNESSEE VALLEY, THE MID-ATLANTIC, THE SOUTHERN  
APPALACHIANS, THE SOUTHEAST, THE GREAT LAKES, AND THE OHIO VALLEY,  
THU, APR 18.  
- SEVERE WEATHER ACROSS PORTIONS OF THE SOUTHEAST, THE  
CENTRAL/SOUTHERN APPALACHIANS, AND THE MID-ATLANTIC, FRI, APR 19.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN/CENTRAL  
PLAINS, THE NORTHEAST, THE NORTHERN GREAT BASIN, THE MID-ATLANTIC,  
THE UPPER MISSISSIPPI VALLEY, THE SOUTHEAST, AND THE GREAT LAKES.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE LOWER  
MISSISSIPPI VALLEY, THE NORTHERN PLAINS, THE UPPER/MIDDLE  
MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND THE OHIO VALLEY.  
- FLOODING LIKELY ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY  
AND THE NORTHERN PLAINS.  
- HIGH WINDS ACROSS PORTIONS OF THE CENTRAL PLAINS AND THE  
SOUTHERN PLAINS, SUN-MON, APR 21-APR 22.  
 
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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