102  
FXUS02 KWBC 270626  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
226 AM EDT SAT APR 27 2019  
 
VALID 12Z TUE APR 30 2019 - 12Z SAT MAY 04 2019  
 
...HEAVY RAIN AND THE POTENTIAL FOR FLOODING AND FLASH FLOODING  
ARE EXPECTED FOR PARTS OF THE SOUTHERN PLAINS AND LOWER/MIDDLE  
MISSISSIPPI VALLEY TO OHIO VALLEY...  
 
...OVERVIEW AND ASSESSMENT OF MODEL/ENSEMBLE GUIDANCE AND  
PREDICTABILITY...  
 
A REASONABLY PERSISTENT FLOW PATTERN DEVELOPS NEXT WEEK OVER THE  
U.S.AS A DEEP NORTH-CENTRAL CANADIAN UPPER LOW GRADUALLY  
RETROGRADES TO WESTERN CANADA. NORTHERN STREAM TROUGHING DIGS  
UNDERNEATH INTO A WINTRY NORTHWESTERN U.S. AS AN INITIALLY CLOSED  
SOUTHERN STREAM E-PACIFIC LOW EJECTS WITH VARIOUS TIMINGS INLAND  
INTO THE SOUTHWEST. PREFER A SOUTHERN STREAM PROGRESSION ON THE  
SLOWER SIDE OF THE FULL ENVELOPE OF SOLUTIONS CONSIDERING THE  
INITIALLY CLOSED NATURE OF THE LOW, WITH THE GFS MORE PROGRESSIVE  
THAN THE ECMWF/UKMET/CANADIAN. A SERIES OF TROUGHS SUBSEQUENTLY  
EJECT NORTHEASTWARD FROM THE PLAINS THROUGH THE MS/OH VALLEYS TO  
THE NORTHEAST TO SUPPORT WET LOW DEVELOPMENT ON A SLOW MOVING  
FRONT. THIS OCCURS OVERTOP A SUBTROPICAL RIDGE FORECAST TO BUILD  
OVER THE SOUTHEAST THROUGH MIDWEEK BEFORE PUSHING OUT BY FRIDAY.  
THE OVERALL PATTERN SEEMS TO BE GENERALLY WELL HANDLED BY THE  
MODELS, WITH TYPICAL UNCERTAINTY IN THE TIMING AND PLACEMENT OF  
SHORTWAVES FROM A GENERAL TROUGHING PATTERN IN THE WEST AND  
CENTRAL U.S. WPC USED A MULTI-MODEL DETERMINISTIC COMPOSITE BLEND  
TUE-THU, WITH TRANSITION TO THE GEFS/ECMWF ENSEMBLE MEANS LATER  
WEEK CONSISTENT WITH GROWING UNCERTAINTY AND RUN TO RUN  
INCONSISTENCY.  
   
..WEATHER HIGHLIGHTS/THREATS
 
 
PASSAGE OF MULTIPLE SHORTWAVES/HEIGHT FALLS IN BOTH NORTHERN AND  
SOUTHERN STREAMS WILL GENERATE SOME ENHANCED RAINS AND MOUNTAIN  
SNOWS FOR PORTIONS OF THE CENTRAL/NORTHERN ROCKIES EARLY NEXT  
WEEK. THESE SYSTEMS WILL PROGRESS DOWNSTREAM AND A MAIN WEATHER  
FOCUS WILL DEVELOP OVER THE CENTRAL U.S. MOISTURE INFLOW/POOLING  
INTO A PERSISTENT/SLOW MOVING/WAVY FRONT WILL FOCUS MULTIPLE  
ROUNDS OF SHOWERS AND THUNDERSTORMS, WITH SOME POTENTIAL FOR  
SEVERE WEATHER AND AREAS OF HEAVY RAINFALL. THE STRONGEST SIGNAL  
FOR HEAVY RAINFALL OF MULTIPLE INCHES WILL BE FROM THE  
SOUTHERN/CENTRAL PLAINS TO THE LOWER/MID-MISSISSIPPI VALLEY, WITH  
SOME POTENTIAL FOR HEAVY RAIN TO SPREAD OVER THE OHIO VALLEY AND  
NORTHERN MID-ATLANTIC/LOWER GREAT LAKES REGION. FLOODING REMAINS  
POSSIBLE AS PARTICULARLY THE MISSISSIPPI VALLEY HAS HAD FLOODING  
CONCERNS FOR WEEKS, AND WITH THE CONVECTIVE ELEMENT OF THE  
PRECIPITATION, FLASH FLOODING IS POSSIBLE AS WELL. ON THE NORTHERN  
FRINGE THE PRECIPITATION, SUFFICIENT COLD AIR MAY BE IN PLACE TO  
SUPPORT SOME SNOWS FOR PORTIONS OF THE NORTHERN HIGH PLAINS WITH  
LOW GENESIS AND APPROACH.  
 
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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