216  
FXUS02 KWBC 031907  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
307 PM EDT FRI MAY 03 2019  
 
VALID 12Z MON MAY 06 2019 - 12Z FRI MAY 10 2019  
   
..OVERVIEW
 
 
MUCH OF THE SOUTHERN AND CENTRAL U.S. WILL REMAIN IN A MOSTLY  
UNSETTLED AND WET PATTERN AS THE FLOW ALOFT AMPLIFIES TOWARD THE  
LATTER HALF OF NEXT WEEK ALLOWING A LONGWAVE TROUGH TO BECOME  
REINFORCED OVER THE WESTERN U.S. AN UPPER LEVEL LOW APPROACHING  
THE CALIFORNIA WILL TRACK THROUGH THE SOUTHERN GREAT  
BASIN/SOUTHWEST THROUGH THE EXTENDED PERIOD AND WILL NORTHEASTWARD  
OVER AND BEYOND THE ROCKIES. THIS MAY LEAD TO ADDITIONAL HEAVY  
RAINFALL OVER PARTS OF THE CENTRAL U.S. THAT HAVE ALREADY RECEIVED  
SIGNIFICANT ACCUMULATIONS RECENTLY, WHICH WILL KEEP THE RISK FOR  
FLASH FLOODING ELEVATED DURING THIS PERIOD. FLAT RIDGING ALOFT  
SHOULD SETTLE OVER THE EAST COAST/WESTERN ATLANTIC BY NEXT  
WEDNESDAY-FRIDAY.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
MODEL GUIDANCE HAVE STRUGGLED A BIT WITH A SHORTWAVE FEATURE THAT  
WILL TRACK SOUTH/SOUTHEAST FROM THE SOUTHERN TIER OF CANADA INTO  
THE NORTHERN U.S. STATES. AS NOTED FROM THE PREVIOUS FORCAST, THE  
GFS/GEFS MEAN WERE 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. THE  
REST OF THE DETERMINISTIC AND MEANS DEPICTED FLATTER AND FASTER  
FLOW IN VARYING WAYS, RESULTING IN A MORE SUPPRESSED WAVY FRONT  
OVER THE NORTHEAST QUADRANT OF THE U.S. NEXT TUESDAY-THURSDAY. THE  
LATEST RUNS SHOW A SLIGHT IMPROVEMENT WITH THE DETAILS OF THIS  
FEATURE, HOWEVER THERE IS UNCERTAINTY.  
 
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. CLUSTERING WAS BETTER WITH  
THE LATEST GUIDANCE AND IS SUGGESTING THAT IT WILL TRACK  
SOUTHWEST/SOUTH OF THE GREAT BASIN; THE EJECTING SHORTWAVE WILL  
LIKELY PRODUCE A RAINFALL-ENHANCING FRONTAL WAVE TRACKING THROUGH  
THE SOUTHERN HIGH PLAINS AND INTO THE MISSISSIPPI VALLEY AND  
BEYOND BY MIDWEEK.  
 
THE PREFERRED BLEND FOR THE BEGINNING OF THE EXTENDED FORECAST  
CONSISTED OF THE ECWMF AND ITS ENSEMBLE MEAN, THE GFS, UKMET AND  
THE CANADIAN MODEL. WEIGHTING OF THE OPERATIONAL MODELS DECREASED  
WITH TIME AS THE WEIGHTING OF THE ECWMF ENSEMBLE MEAN AND GEFS  
MEANS INCREASED.  
 
   
..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.  
 
CAMPBELL/RAUSCH  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN PLAINS, MON, MAY 6.  
- HEAVY RAIN FROM PORTIONS OF THE SOUTHERN PLAINS TO THE LOWER  
OHIO VALLEY, WED-FRI, MAY 8-MAY 10.  
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS AND THE MIDDLE  
MISSISSIPPI VALLEY, MON-WED, MAY 6-MAY 8.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL PLAINS, THE  
MIDDLE MISSISSIPPI VALLEY, THE LOWER MISSISSIPPI VALLEY, THE  
SOUTHERN PLAINS, AND THE UPPER MISSISSIPPI VALLEY.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE CENTRAL  
PLAINS, THE LOWER MISSISSIPPI VALLEY, THE NORTHERN PLAINS, THE  
GREAT LAKES, THE MIDDLE MISSISSIPPI VALLEY, THE UPPER MISSISSIPPI  
VALLEY, THE SOUTHERN PLAINS, AND THE OHIO VALLEY.  
- FLOODING LIKELY ACROSS PORTIONS OF THE CENTRAL PLAINS, THE GREAT  
LAKES, THE MIDDLE MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND THE  
OHIO VALLEY.  
 
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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