532  
FXUS02 KWBC 191944  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
343 PM EDT FRI APR 19 2019  
 
VALID 12Z MON APR 22 2019 - 12Z FRI APR 26 2019  
   
..OVERVIEW AND GUIDANCE PREFERENCES
 
 
EXPECT TWO PRONOUNCED STREAMS ALOFT TO PREVAIL ACROSS NORTH  
AMERICA NEXT WEEK. A FAIRLY SLOW-MOVING SOUTHERN STREAM WILL  
FEATURE A TROUGH/UPPER LOW THAT SHOULD PROMOTE A HEAVY RAINFALL  
THREAT OVER THE SOUTHERN PLAINS/MISSISSIPPI VALLEY, WHILE A  
PROGRESSIVE NORTHERN STREAM ACROSS SOUTHERN CANADA AND NORTHERN  
U.S. WILL CONTAIN SHORTWAVES WHOSE SCALE AND SPEED WILL LEAD TO  
BELOW AVERAGE PREDICTABILITY. QUESTIONS OF WHETHER ANY STREAM  
INTERACTION MAY OCCUR AT SOME POINT DURING THE FORECAST PERIOD  
PRODUCE FURTHER UNCERTAINTY IN FORECAST DETAILS.  
 
OVER THE PAST DAY THE SOUTHERN STREAM UPPER TROUGH (WITH EMBEDDED  
CLOSED LOW AT TIMES) DRIFTING FROM THE WESTERN U.S. INTO THE  
PLAINS/MISSISSIPPI VALLEY HAS SHOWN THE BEST RELATIVE STABILITY  
OVER THE PAST DAY. THAT SAID, THERE HAS STILL BEEN A RECENT  
TENDENCY TOWARD GREATER SOUTHWESTWARD DIGGING OF ENERGY WITHIN THE  
TROUGH DURING THE EARLY PART OF THE WEEK BEFORE THE SYSTEM  
CONTINUES EASTWARD. THERE IS STILL CONSIDERABLE UNCERTAINTY OVER  
SPECIFICS OF INDIVIDUAL SHORTWAVES SO OVERALL CONFIDENCE IN THE  
EXACT FORECAST REMAINS FAIRLY LOW. AT THE VERY LEAST THE DOMINANT  
CLUSTER OF GUIDANCE SUGGESTS THE 06Z GFS IS TOO QUICK TO SHEAR THE  
UPPER TROUGH LATER IN THE WEEK.  
 
MODEL/ENSEMBLE SPAGHETTI PLOTS BECOME CHAOTIC ACROSS THE NORTH  
PACIFIC EARLY IN THE PERIOD AND THIS SPREAD CONTINUES QUICKLY  
EASTWARD WITH TIME. GUIDANCE CONTINUITY HAS ALSO BEEN POOR FOR  
INDIVIDUAL SHORTWAVES ACROSS SOUTHERN CANADA AND NORTHERN U.S.,  
WITH SIGNIFICANT CORRESPONDING VARIABILITY IN PROGRESSION OF  
SURFACE WAVES/FRONTS ACROSS THE NORTHERN AND EASTERN U.S. A  
SLOWER/STRONGER SHORTWAVE IN LATEST GUIDANCE HAS RESULTED IN A  
BETTER DEFINED WAVE TRACKING FROM THE MIDWEST INTO NEW ENGLAND  
DURING MON-WED. FOR A TIME THIS ADJUSTMENT SLOWS DOWN FRONTAL  
PROGRESSION INTO THE EAST BUT WITH THE WAVE'S PASSAGE THE FRONT  
PUSHES BACK DOWN TOWARD THE PREVIOUS CYCLE'S CONSENSUS--BUT WELL  
SOUTHWARD OF WHAT YESTERDAY'S 00-06Z GUIDANCE WAS ADVERTISING.  
THE OTHER MAJOR CHANGE IN LATEST GUIDANCE IS FASTER PROGRESSION OF  
NORTH PACIFIC FLOW ACROSS NORTH AMERICA. AS A RESULT THE  
OVERWHELMING MAJORITY OF CURRENT 00-06Z GUIDANCE BRINGS A FRONT  
MUCH FARTHER SOUTHEAST INTO THE NORTHERN STATES VERSUS PREVIOUS  
CYCLE. BY THE END OF THE PERIOD MODELS/ENSEMBLES SHOW COMPLETELY  
OPPOSITE SOLUTIONS OVER THE NORTHEASTERN PACIFIC, THE ECMWF/ECMWF  
MEAN WITH TROUGHING AND THE CMC/CMC MEAN PLUS THE GFS TO SOME  
EXTENT WITH RIDGING. THE UPPER LOW OVER NORTHERN CANADA  
TELECONNECTS TO CYCLONIC FLOW OVER THE NORTHEASTERN PACIFIC SO IT  
SEEMS REASONABLE TO LEAN AWAY FROM THE RIDGE SOLUTIONS.  
 
THE UPPER LOW DEPARTING FROM THE NORTHEAST CONTINUES TO DISPLAY  
SIGNIFICANT TIMING DIFFERENCES. THE 00Z GFS CONTINUES TO BE ON  
THE FAST SIDE WHILE THE 06Z VERSION ACTUALLY BECOMES SLOWER THAN  
THE ECMWF AFTER EARLY TUE. AN AVERAGE AMONG THE 06Z GFS AND 00Z  
ECMWF/CMC LOOKS REASONABLE AT THIS TIME.  
 
BASED ON THE CURRENT ARRAY OF GUIDANCE THE UPDATED FORECAST  
STARTED WITH A BLEND OF THE 06Z GFS/00Z ECMWF/00Z CMC FOR THE  
EARLY WEEK FORECAST, FOLLOWED BY A GRADUAL INCREASE OF THE 06Z  
GEFS/00Z ECMWF MEANS TO 70 PERCENT TOTAL WEIGHT BY NEXT FRI.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE MOST PROMINENT WEATHER THREAT NEXT WEEK SHOULD BE WITH HEAVY  
RAINFALL FROM WIDESPREAD SHOWERS/THUNDERSTORMS ACROSS THE SOUTHERN  
PLAINS AND EVENTUALLY INTO THE LOWER MISSISSIPPI VALLEY FROM MON  
NIGHT/TUE ONWARD. THERE WILL BE MULTIPLE INGREDIENTS TO SUPPORT  
THIS EVENT: THE UPPER SYSTEM TRACKING OUT OF THE SOUTHWEST, A  
LEADING SLOW-MOVING WAVY FRONT, AND A MULTI-DAY FEED OF LOW LEVEL  
MOISTURE FROM THE GULF OF MEXICO. ENSEMBLE GUIDANCE SHOWS BEST  
POTENTIAL OF HIGHEST RAINFALL TOTALS DURING THE PERIOD OVER TEXAS  
AND OKLAHOMA. EARLY IN THE WEEK EXPECT PRECIPITATION OVER THE  
EASTERN GREAT BASIN AND CENTRAL-SOUTHERN ROCKIES. HIGHEST  
ELEVATIONS IN COLORADO MAY SEE SOME SNOW. MEANWHILE A WAVE  
TRACKING FROM THE MIDWEST TO NEW ENGLAND MAY FOCUS MEANINGFUL  
RAINFALL NEAR ITS TRACK. ANY SNOW SHOULD BE CONFINED TO AREAS  
NORTH OF THE CANADIAN BORDER EXCEPT PERHAPS FOR NORTHERN MAINE. A  
FRONT MOVING INTO/ACROSS THE NORTHWEST AND ONWARD ACROSS THE  
NORTHERN TIER STATES WILL BE ACCOMPANIED BY MOSTLY LIGHT RAIN AND  
POSSIBLY A LITTLE VERY HIGH ELEVATION SNOW.  
 
THE WESTERN U.S. WILL SEE A BROAD AREA OF PLUS 10-20F TEMPERATURE  
ANOMALIES WITH SOME OF THIS WARMTH EXTENDING INTO THE NORTHERN AND  
EVENTUALLY CENTRAL PLAINS. A COLD FRONT MOVING INTO THE NORTHWEST  
WILL BRING A COOLING TREND TO THAT PART OF THE WEST DURING THE  
LATTER HALF OF THE WEEK. DAILY RECORDS APPEAR MOST LIKELY FOR  
WARM LOWS OVER CALIFORNIA AND THE INTERIOR WEST WED-THU BUT A FEW  
RECORD HIGHS MAY BE POSSIBLE AS WELL. PARTS OF THE EAST WILL SEE  
A PERIOD OF ABOVE NORMAL TEMPERATURES IN THE WARM SECTOR OF THE  
MIDWEST TO NEW ENGLAND WAVE MON-WED. ON THE OTHER SIDE OF THE  
SPECTRUM THE CENTRAL-SOUTHERN PLAINS WILL BE THE PRIMARY FOCUS FOR  
BELOW NORMAL HIGHS DURING THE PERIOD.  
 
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  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST, THE LOWER  
MISSISSIPPI VALLEY, AND THE SOUTHERN PLAINS, TUE-FRI, APR 23-APR  
26.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE MID-ATLANTIC, THE  
MISSISSIPPI VALLEY, THE CENTRAL/SOUTHERN APPALACHIANS, THE  
NORTHERN PLAINS, THE TENNESSEE VALLEY, THE NORTHEAST, THE  
SOUTHEAST, THE GREAT LAKES, AND THE OHIO VALLEY.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE  
MISSISSIPPI VALLEY, THE NORTHERN PLAINS, AND THE OHIO VALLEY.  
- FLOODING LIKELY ACROSS PORTIONS OF THE NORTHEAST, THE NORTHERN  
PLAINS, AND THE NORTHERN GREAT BASIN.  
 
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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