382  
FXUS02 KWBC 201600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1159 AM EDT SAT APR 20 2019  
 
VALID 12Z TUE APR 23 2019 - 12Z SAT APR 27 2019  
   
..OVERVIEW AND GUIDANCE PREFERENCES
 
 
GUIDANCE SPREAD AND VARIABILITY FOR DETAILS OF FLOW ACROSS THE  
PACIFIC AND EXTENDING INTO/ACROSS THE NORTHERN LOWER 48 AND  
SOUTHERN CANADA CONTINUE TO KEEP CONFIDENCE FAIRLY LOW FOR MANY  
ASPECTS OF THE FORECAST. THE ONE PART OF THE FORECAST THAT HAS  
BETTER CONFIDENCE IS THE SLOWER MOVING SOUTHERN STREAM TROUGH THAT  
PROGRESSES FROM THE SOUTHWESTERN U.S./NORTHWESTERN MEXICO INTO THE  
SOUTHERN PLAINS TUE-THU. THERE ARE STILL SOME DIFFERENCES AND  
RUN-TO-RUN ADJUSTMENTS IN THIS TIME FRAME BUT A STRONG SIGNAL  
PERSISTS FOR ASSOCIATED HEAVY RAINFALL OVER THE SOUTHERN PLAINS  
AND LIKELY EXTENDING AT LEAST INTO THE LOWER MISSISSIPPI VALLEY.  
AFTER EARLY THU THE CHARACTER OF NORTHERN STREAM FLOW WILL BECOME  
INCREASINGLY IMPORTANT TO THE TIMING/PROGRESSION OF THE SOUTHERN  
TROUGH.  
 
THE LATEST FORECAST UPDATE REFLECTS A BLEND OF THE PAST TWO  
12-HOURLY ECMWF/6-HOURLY GFS RUNS ALONG WITH MINORITY INPUT FROM  
THE 06Z GEFS/00Z ECMWF MEANS DURING THE TUE INTO THU TIME FRAME.  
THE REST OF THE FORECAST ELIMINATES THE GFS RUNS, HOLDS ONTO  
ECMWF/ECMWF MEAN/GEFS MEAN INPUT, AND INTRODUCES SOME WPC  
CONTINUITY.  
 
THE PREFERRED BLEND REFLECTS GRADUALLY IMPROVING CONSENSUS TOWARD  
FAIRLY SLOW DEPARTURE OF THE INITIAL NEW ENGLAND UPPER LOW, BUT  
NOT AS SLOW/AMPLIFIED AS THE 00Z CMC BECOMES. BEHIND THIS LOW THE  
BLEND REMAINS CLOSE TO CONTINUITY (AN INTERMEDIATE SOLUTION) FOR  
SOUTHEASTERN CANADA SHORTWAVE ENERGY--DEPICTED IN THE GUIDANCE AS  
ANYTHING FROM A WEAK OPEN WAVE TO A CONCENTRATED CLOSED UPPER LOW.  
THUS FAR MODELS AND MEANS HAVE HELD ONTO OR EVEN FURTHERED A BIT  
YESTERDAY'S FASTER TREND FOR THE FRONT CROSSING SOUTHERN CANADA  
AND THE NORTHERN TIER OF THE U.S. BY LATE NEXT WEEK PREFER TO  
STAY CLOSER TO ECMWF-BASED CONTINUITY WHICH REFLECTS GREATER  
STREAM SEPARATION OVER THE EAST VERSUS THE AGGRESSIVE NORTHERN  
STREAM AMPLIFICATION (AND WESTERN ATLANTIC OR NEW ENGLAND STORM  
DEVELOPMENT) DEPICTED IN THE GFS/CMC RUNS. EVOLUTION OF RECENT  
SYSTEMS WOULD ALSO FAVOR MORE STREAM SEPARATION.  
 
FARTHER WESTWARD ONE FAVORABLE TREND IN THE GUIDANCE IS BETTER  
CLUSTERING AMONG GFS/ECMWF RUNS AND THEIR MEANS TOWARD  
NORTHEASTERN PACIFIC CYCLONIC FLOW DURING THE LATTER HALF OF THE  
PERIOD--AS SUPPORTED BY TELECONNECTIONS RELATIVE TO THE UPPER LOW  
OVER NORTHERN CANADA. BASED ON THIS CLUSTER/TELECONNECTION  
RELATIONSHIP, RIDGING IN THE 00Z CMC MEAN LOOKS RATHER SUSPECT.  
THE FORECAST LOOKS AS UNCERTAIN AS EVER FARTHER SOUTH OVER THE  
EASTERN PACIFIC. THE 00Z ECMWF AND SOME ECMWF ENSEMBLES QUICKLY  
PULL OFF ENERGY FROM A SHORTWAVE AROUND 140-145W BY THU WHILE A  
GREATER PROPORTION OF MODELS/ENSEMBLES BRING MORE OF THE SHORTWAVE  
ENERGY TOWARD THE WEST COAST. THUS A MORE EVEN BLEND OF GFS/GEFS  
AND ECMWF-BASED GUIDANCE MAY BE MORE SUITABLE OVER THIS REGION AT  
LEAST INTO DAY 6 FRI.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE SYSTEM FORECAST TO AFFECT THE SOUTHERN PLAINS TUE-WED SHOULD  
PRODUCE WIDESPREAD SHOWERS AND THUNDERSTORMS, WITH  
MODELS/ENSEMBLES SHOWING A STRONG SIGNAL FOR HEAVY RAINFALL  
POTENTIAL OVER TEXAS AND OKLAHOMA. SOME CONVECTION MAY BE STRONG  
TO SEVERE AS WELL. THE STORM PREDICTION CENTER CURRENTLY  
INDICATES BEST CHANCES FOR SEVERE WEATHER IN THE EARLY WED-EARLY  
THU TIME FRAME. CHECK LATEST SPC PRODUCTS FOR FURTHER  
INFORMATION. EXPECT SCATTERED TO NUMEROUS SHOWERS AND  
THUNDERSTORMS TO ACCOMPANY THE SYSTEM EASTWARD INTO THE LOWER  
MISSISSIPPI VALLEY AND SOUTHEAST LATER IN THE WEEK BUT INCREASING  
UNCERTAINTY IN SYSTEM STRENGTH AND TIMING REDUCE CONFIDENCE IN  
DURATION AND INTENSITY OF RAINFALL TO THE EAST OF THE PLAINS.  
CURRENT PREFERENCE FOR A SOMEWHAT SLOWER SOLUTION WOULD MAINTAIN  
DECENT POTENTIAL FOR LOCALLY HEAVY RAINFALL INTO PORTIONS OF THE  
GULF COAST AND SOUTHEAST.  
 
WAVINESS EXTENDING FROM THE MIDWEST/GREAT LAKES INTO NEW ENGLAND  
AND ASSOCIATED FRONT(S) EARLY IN THE PERIOD WILL PROVIDE A FOCUS  
FOR RAINFALL OVER PARTS OF THE EAST. STILL EXPECT SNOW TO BE  
CONFINED TO LOCATIONS NORTH OF THE CANADIAN BORDER EXCEPT PERHAPS  
FOR NORTHERN MAINE. A FRONT PUSHING INTO THE NORTHWEST AND THEN  
CONTINUING EASTWARD MAY GENERATE SOME RAINFALL BUT MOST ACTIVITY  
SHOULD BE IN THE LIGHT-MODERATE RANGE. PRECIPITATION MAY PERSIST  
FOR A TIME OVER PARTS OF THE INTERIOR WEST/ROCKIES AS THE WESTERN  
PART OF THE FRONT STALLS. SOME MOISTURE MAY REACH THE NORTHWEST  
LATE IN THE PERIOD BUT TIMING/EXTENT ARE UNCERTAIN GIVEN THE WIDE  
SPREAD IN GUIDANCE FOR DETAILS OF FLOW ALOFT AT THAT TIME.  
 
THERE WILL BE A BROAD AREA OF ABOVE AVERAGE TEMPERATURES WITH PLUS  
10-20F ANOMALIES OVER THE WEST, WITH SOME OF THIS WARMTH EXTENDING  
INTO THE NORTHERN AND THEN CENTRAL PLAINS. DAILY RECORDS  
(ESPECIALLY FOR WARM LOWS) ARE MOST LIKELY ON WED-THU AND SOME ARE  
POSSIBLE ON FRI AS WELL. THE FRONT PUSHING INTO THE NORTHWEST  
WILL PRODUCE A COOLING TREND OVER NORTHERN PARTS OF THE WEST.  
BELOW NORMAL HIGHS WILL PREVAIL OVER THE SOUTHERN PLAINS  
ESPECIALLY ON TUE-WED. PARTS OF THE NORTHERN TIER SHOULD TREND A  
LITTLE BELOW NORMAL FOR HIGHS BY FRI-SAT.  
 
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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