771  
FXUS02 KWBC 030700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 AM EDT FRI MAY 03 2019  
 
VALID 12Z MON MAY 06 2019 - 12Z FRI MAY 10 2019  
   
..OVERVIEW
 
 
THE PATTERN EVOLUTION EXPECTED FOR NEXT WEEK MAY LEAD TO  
ADDITIONAL HEAVY RAINFALL OVER PARTS OF THE CENTRAL U.S. THAT HAVE  
ALREADY RECEIVED SIGNIFICANT ACCUMULATIONS RECENTLY. UNSETTLED TO  
ACTIVE WEATHER WILL ALSO BE POSSIBLE ACROSS OTHER PORTIONS OF THE  
LOWER 48 FOR AT LEAST PART OF THE PERIOD. GUIDANCE SUGGESTS FLOW  
ALOFT WILL AMPLIFY TOWARD THE LATTER HALF OF NEXT WEEK, WITH A  
BUILDING EASTERN PACIFIC RIDGE HELPING TO DEVELOP A WESTERN U.S.  
TROUGH. FLAT RIDGING ALOFT SHOULD SETTLE OVER THE EAST  
COAST/WESTERN ATLANTIC BY NEXT WED-FRI. THE OTHER MAJOR FEATURE  
OF NOTE WILL BE AN UPPER LOW THAT SHOULD REACH CALIFORNIA AT THE  
START OF THE WEEK AND THEN OPEN UP/EJECT NORTHEASTWARD OVER AND  
BEYOND THE ROCKIES.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
ONE OF THE LESS CONFIDENT ASPECTS OF THE FORECAST INVOLVES  
SHORTWAVE ENERGY PROGRESSING ACROSS SOUTHERN CANADA AND THE  
NORTHERN U.S. FROM DAY 3 MON ONWARD. AMONG 12-18Z GUIDANCE, THE  
GFS/GEFS MEAN WERE ON THEIR OWN IN BEING SLOWER AND STRONGER WITH  
THE UPPER DYNAMICS--LEADING TO SURFACE LOW PRESSURE TRACKING  
THROUGH THE UPPER MIDWEST/UPPER GREAT LAKES AND WRAPPING UP OVER  
CANADA. REMAINING SOLUTIONS WERE FLATTER AND FASTER IN VARYING  
WAYS, RESULTING IN A MORE SUPPRESSED WAVY FRONT OVER THE NORTHEAST  
QUADRANT OF THE U.S. NEXT TUE-THU. CONTINUITY/CLUSTERING HAVE NOT  
BEEN VERY GOOD OVER THE PAST COUPLE DAYS, PLUS EITHER SCENARIO IS  
PLAUSIBLE FROM THE MULTI-DAY MEAN POINT OF VIEW. PREFERRED TO  
BLEND TOWARD THE MAJORITY SCENARIO, WHICH ALSO HAD SUPPORT FROM  
THE 18Z FV3 GFS. MOST OF THE NEW 00Z SOLUTIONS STILL FAVOR THE  
NON-GFS IDEA WITH THE GEFS MEAN SHOWING A PARTIAL TREND IN THAT  
DIRECTION AS WELL.  
 
WITHIN THE AMPLIFYING WESTERN U.S. TROUGH THERE HAVE BEEN SIGNALS  
FOR AN EMBEDDED CLOSED LOW BY THE LATTER HALF OF THE WEEK BUT WITH  
A FAIR AMOUNT OF SPREAD FOR LOCATION. BASED ON THE TROUGH AXIS IN  
THE ENSEMBLE MEANS AND AVERAGE OF THE PAST COUPLE ECMWF RUNS (THE  
MOST COMPATIBLE GUIDANCE), IT APPEARS THE MOST LIKELY PATH OF AN  
UPPER LOW WOULD BE OVER OR JUST SOUTHWEST OF THE GREAT BASIN.  
 
THE UPPER LOW MOVING THROUGH THE SOUTHWEST WILL OPEN UP AND EJECT  
NORTHEASTWARD AS THE WESTERN TROUGH BEGINS TO AMPLIFY. THE  
EJECTING SHORTWAVE WILL LIKELY PRODUCE A RAINFALL-ENHANCING  
FRONTAL WAVE TRACKING THROUGH AND BEYOND THE PLAINS MID-LATE WEEK.  
CLUSTERING HAS BEEN FAIRLY GOOD THOUGH THE NEW 00Z GFS BECOMES  
SLOWER THAN MOST OTHER SOLUTIONS AFTER EARLY TUE.  
 
BASED ON ABOVE CONSIDERATIONS THE FIRST HALF OF THE PERIOD STARTED  
WITH AN OPERATIONAL MODEL BLEND (INCLUDING TWO ECMWF RUNS GIVEN  
THE LACK OF CONFIDENCE WITH NORTHERN STREAM DETAILS AND ASSOCIATED  
SURFACE FORECAST). THEN THE FORECAST RAPIDLY ADJUSTED TO A BLEND  
OF THE 18Z GEFS/12Z ECMWF MEANS WITH MINORITY INPUT FROM THE TWO  
ECMWF RUNS THROUGH DAY 7 FRI AND THE 18Z GFS THROUGH DAY 6 THU  
(AFTER WHICH TIME THE GFS EJECTED PART OF THE WESTERN TROUGH  
FASTER THAN DESIRED).  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
PORTIONS OF THE PLAINS AND MISSISSIPPI VALLEY SHOULD SEE THE  
HIGHEST POTENTIAL FOR HEAVIEST TOTAL RAINFALL DURING THE 5-DAY  
PERIOD, ESPECIALLY ACROSS SOUTHERN AREAS. A WAVE EMBEDDED WITHIN  
A NORTH-CENTRAL U.S. FRONT SHOULD PROMOTE ONE AREA OF ENHANCED  
RAIN/THUNDERSTORM ACTIVITY OVER THE PLAINS/MIDWEST DURING THE  
FIRST HALF OF THE WEEK WITH LESSER AMOUNTS OF MOISTURE EXTENDING  
FARTHER EAST. MEANWHILE MOIST FLOW FROM THE GULF WILL INTERSECT A  
FRONT INITIALLY DRAPED NEAR GULF COAST, AND THEN THE EJECTING  
SOUTHWEST U.S. FEATURE WILL BRING A SURFACE WAVE AND TRAILING  
FRONT INTO THE SOUTHERN PLAINS. THE THREAT FOR HEAVY RAINFALL MAY  
PERSIST OVER/NEAR THE SOUTHERN PLAINS THROUGH FRI AS THE SOUTHERN  
PLAINS FRONT LIKELY DECELERATES/STALLS AS IT BECOMES PARALLEL WITH  
FLOW ALOFT WHILE LOW LEVEL MOISTURE CONTINUES TO FEED IN FROM THE  
GULF. THE COMBINATION OF FRONTS/WAVES MAY BRING SOME SIGNIFICANT  
RAINFALL AMOUNTS TO THE NORTHEAST/MID-ATLANTIC BUT LIKELY WITH  
LOWER TOTALS THAN EXPECTED OVER THE CENTRAL U.S.  
 
THE WESTERN STATES WILL SEE A BROAD AREA OF PRECIPITATION (FROM  
CALIFORNIA THROUGH THE GREAT BASIN/NORTHERN ARIZONA AND INTO MOST  
OF THE ROCKIES) IN ASSOCIATION WITH THE UPPER LOW TRACKING THROUGH  
THE SOUTHWEST EARLY IN THE WEEK AND THE UPPER TROUGH/POSSIBLE  
EMBEDDED UPPER LOW DEVELOPING OVER THE WEST LATER IN THE WEEK.  
SOME OF THE PRECIPITATION MAY BE IN THE FORM OF SNOW OVER HIGH  
ELEVATIONS OF THE NORTHERN-CENTRAL ROCKIES. EXPECT HIGHEST PRECIP  
TOTALS TO BE OVER FAVORED TERRAIN OF THE GREAT BASIN AND CENTRAL  
ROCKIES. SNOW POTENTIAL COULD EXTEND INTO THE EXTREME NORTHERN  
PLAINS EARLY IN THE WEEK.  
 
THE GREATEST TEMPERATURE ANOMALIES DURING THE PERIOD SHOULD BE  
WITH COOL AIR PUSHING SOUTH FROM THE NORTHERN HIGH PLAINS, LEADING  
TO DECENT COVERAGE OF HIGHS 10-20F BELOW NORMAL BY WED-THU.  
HIGHEST WARM ANOMALIES, OF SIMILAR MAGNITUDE, SHOULD BE FOR  
MORNING LOWS IN THE WARM SECTOR FROM THE EASTERN/SOUTHEASTERN  
PLAINS TO MID-ATLANTIC TUE ONWARD AND FOR HIGHS OVER THE PACIFIC  
NORTHWEST.  
 
RAUSCH  
 
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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