772  
FXUS02 KWBC 271614  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1213 PM 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...  
 
...OVERVIEW AND ASSESSMENT OF MODEL/ENSEMBLE GUIDANCE AND  
PREDICTABILITY...  
 
A LARGE UPPER LOW LOCATED IN CENTRAL CANADA ON DAY 3/TUE WILL  
RETROGRADE WESTWARD THROUGH THE MEDIUM RANGE PERIOD, ENCROACHING  
UPON AN UPPER RIDGE SET UP IN ALASKA AND INTO THE ARCTIC.  
UNCERTAINTY REMAINS REGARDING THE ORIENTATION OF THE LOW AND VORT  
MAXES WITHIN IT, AS WELL AS THE AMOUNT OF ENERGY THAT COULD STREAM  
UNDERNEATH THE AFOREMENTIONED RIDGE. THE 00Z DETERMINISTIC ECMWF  
IS THE MOST BULLISH WITH THAT ENERGY BY DAY 6/FRI, WHICH  
SUPPRESSED RIDGING IN THE NORTHERN PACIFIC. THIS WAS UNSUPPORTED  
BY OTHER MODELS AND ENSEMBLES, SO LEANED AWAY FROM THAT SOLUTION  
FOR NOW.  
 
ACROSS THE CONUS, A GENERAL PATTERN OF UPPER TROUGHING WILL REMAIN  
ACROSS THE WEST THROUGH MIDWEEK, WHILE A SUBTROPICAL RIDGE  
PERSISTS OVER THE SOUTHEAST. A SHORTWAVE IS EXPECTED TO STRENGTHEN  
AND MOVE THROUGH THE MIDWEST BY THURSDAY. ADDITIONAL ENERGY MAY  
PUSH THROUGH THE SOUTHERN STREAM ACROSS THE SOUTHERN PLAINS/LOWER  
MISSISSIPPI VALLEY AT THAT POINT TOO, WITH THE 00Z AND 06Z GFS  
RUNS MORE BULLISH WITH THIS FEATURE THAN THE EC. NEVERTHELESS,  
EXPECT THE UPPER TROUGH TO PUSH EASTWARD LATE IN THE WEEK WITH  
THESE FEATURES, LEADING TO HIGH PRESSURE AT THE SURFACE FOR THE  
CENTRAL AND EASTERN PARTS OF THE COUNTRY BY FRI/SAT. MODEL  
DISAGREEMENT INCREASES BY DAY 6 AND ESPECIALLY DAY 7/SAT FOR AN  
UPPER LOW IN THE EASTERN PACIFIC APPROACHING THE WEST COAST; THE  
00Z EC KEEPS THE LOW IN THE SOUTHERN STREAM, WHILE PARTICULARLY  
THE 00Z GFS COMBINES THE NORTHERN AND SOUTHERN STREAMS AND LEADS  
TO A MORE PROGRESSIVE TROUGH IN THE WEST. AT THIS POINT, A  
COMPROMISE SEEMS REASONABLE, BUT LEANED TOWARD THE EC MEAN A BIT  
AS THE GFS HAS MORE RUN-TO-RUN VARIABILITY AND IS OFTEN TOO FAST.  
OVERALL, A MULTI-MODEL MAINLY DETERMINISTIC BLEND SEEMED LIKE THE  
BEST SOLUTION EARLY IN THE PERIOD, GRADUALLY TRANSITIONING TO  
FAVORING THE EC AND GEFS MEANS BY LATE IN THE WEEK.  
   
..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. THE MAIN THREAT IN THE MEDIUM RANGE,  
HOWEVER, IS FOR HEAVY RAINFALL DEVELOPING IN THE CENTER OF THE  
COUNTRY AS MOISTURE STREAMS IN AHEAD OF THE TROUGH AND COMBINES  
WITH A SLOW-MOVING/WAVY FRONT. MULTI-DAY TOTALS ARE EXPECTED TO BE  
SEVERAL INCHES FOR THE SOUTHERN PLAINS AND THE LOWER/MIDDLE  
MISSISSIPPI VALLEY AS MULTIPLE ROUNDS OF RAIN AND THUNDERSTORMS  
(POTENTIALLY SEVERE) WILL OCCUR. 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. THERE IS SOME POTENTIAL FOR HEAVY  
RAIN TO SPREAD OVER THE OHIO VALLEY AND GREAT LAKES REGION AT  
TIMES AS WELL. THE FRONT IS EXPECTED TO PUSH EASTWARD AHEAD OF THE  
TROUGH BY FRI/SAT, HELPING LESSEN THE HEAVY RAIN THREAT.  
 
TATE  
 
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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