076  
FXUS02 KWBC 280607  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
207 AM EDT SUN APR 28 2019  
 
VALID 12Z WED MAY 01 2019 - 12Z SUN MAY 05 2019  
 
...STRONG TO SEVERE THUNDERSTORMS WITH HEAVY RAINS AND FLASH  
FLOODING/FLOODING POTENTIAL WILL THREATEN THE SOUTHERN PLAINS AND  
LOWER/MIDDLE MISSISSIPPI VALLEY WEDNESDAY INTO THURSDAY...  
 
...OVERVIEW AND ASSESSMENT OF MODEL/ENSEMBLE GUIDANCE AND  
PREDICTABILITY...  
 
A LARGE CLOSED UPPER CIRCULATION WILL RETROGRESS AND SETTLE OVER  
WESTERN CANADA THIS WEEK. THIS OCCURS AS A SERIES OF NORTHERN  
STREAM TROUGHS, HEIGHT FALLS, AND PRECIPITATION SWATHS DIG INTO  
THE NORTHWEST THEN EASTWARD OVER THE U.S. NORTHERN TIER. THERE IS  
POTENTIAL FOR SOME DEGREE OF PHASING WITH A SOUTHERN STREAM FLOW  
OF IMPULSES/HEIGHT FALLS WORKING UNDERNEATH DURING THIS PERIOD  
FROM THE EASTERN PACIFIC INLAND OVER THE U.S. SOUTHERN TIER. THE  
GFS/GEFS AND TO A LESSER EXTENT THE FV3 HAVE TENDED TO BE ON THE  
PROGRESSIVE SIDE OF THE FULL ENVELOPE OF SOLUTIONS WITH RECENT  
ECMWF RUNS AND TO A LESSER EXTENT ECMWF ENSEMBLES AND THE  
UKMET/CANADIAN LIE ON THE SLOWER SIDE OF THE FORECAST ENVELOPE.  
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM  
COMPOSITE SOLUTIONS INCLUDING THE NATIONAL BLEND OF MODELS  
INCREASINGLY TOWARD ECMWF ENSEMBLE MEAN GUIDANCE OVER TIME. THIS  
IS WITH CONSIDERATION OF THE OVERALL BLOCKY FLOW UPSTREAM OVER THE  
PACIFIC, UNCERTAINTY WITH EMBEDDED FEATURE TIMING AND PHASING IN  
TWO MAIN STREAM FLOWS, AND THE INHERENTLY SLOW NATURE OF CLOSED  
LOWS TO EJECT INTO THE FLOW.  
   
..WEATHER HIGHLIGHTS/THREATS
 
 
WITH THE TROUGHING IN THE WEST EARLY IN THE PERIOD, TEMPERATURES  
WILL BE COLD ENOUGH TO SUPPORT SNOW MAINLY IN THE NORTHERN/CENTRAL  
ROCKIES, THOUGH LATE SEASON LIGHT SNOWS ARE POSSIBLE IN THE  
NORTHERN/CENTRAL PLAINS. A RESULTANT LEAD AND WAVY FRONTAL SYSTEM  
WILL PROGRESS MID-LATE WEEK OVER THE CENTRAL THEN EASTERN U.S.  
DEEPENING INFLOW/MOISTURE FROM THE GULF OF MEXICO CONSISTINT WITH  
ULTIMATE FRONTAL WAVE DEVELOPMENTS WILL FEED INTO CONVECTIVELY  
ACTIVE WARM SECTOR MESO-BOUNDARIES AS WELL AS A STARK BAROCLINIC  
ZONE OVERTOP. FLOODING REMAINS POSSIBLE AS PARTICULARLY THE  
MISSISSIPPI VALLEY HAS HAD FLOODING CONCERNS FOR WEEKS, AND WITH  
THE CONVECTIVE NATURE OF THE PRECIPITATION, FLASH FLOODING IS  
POSSIBLE AS WELL. STRONG TO SEVERE THUNDERSTORMS WITH HEAVY RAINS  
AND FLASH FLOODING/FLOODING POTENTIAL WILL FOCUS/THREATEN THE  
SOUTHERN PLAINS AND LOWER/MIDDLE MISSISSIPPI VALLEY WEDNESDAY INTO  
THURSDAY. THE BULK OF ACTIVITY WILL PROGRESS ACROSS THE EAST AND  
SOUTH INTO FRIDAY BEFORE SHIFTING OFFSHORE BY NEXT WEEKEND AS NEW  
UPSTREAM NORTHERN AND SOUTHERN STREAM TROUGH ENERGIES/HEIGHT FALLS  
AND MODEST PRECIPITATION LIKELY WORKS BACK INTO THE WEST IN  
CONTINUED SPLIT FLOW.  
 
SCHICHTEL  
 
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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