259  
FXUS02 KWBC 180646  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
245 AM EDT THU APR 18 2019  
 
VALID 12Z SUN APR 21 2019 - 12Z THU APR 25 2019  
   
..OVERVIEW AND GUIDANCE PREFERENCES
 
 
INCREASINGLY ZONAL FLOW OVER THE CONUS BY EARLY NEXT WEEK WILL  
LEAD TO LOWER PREDICTABILITY OF GENERALLY WEAKER FRONTAL SYSTEMS  
NEXT WEEK. CONTINUED A BLENDED/CONSENSUS APPROACH TO MINIMIZE  
FUTURE SHIFTS IN SYSTEM TIMING/TRACK. ENSEMBLES GENERALLY AGREE  
THAT TROUGHING WILL SLOWLY EXIT THE SOUTHWEST/FOUR CORNERS REGION  
EARLY NEXT WEEK AND PUSH INTO THE SOUTHERN PLAINS AS THE NORTHERN  
STREAM ALONG THE US/CANADIAN BORDER WOBBLES DOWNSTREAM OF AN UPPER  
LOW IN THE GULF OF ALASKA. 12Z ECMWF WAS CLOSEST TO THE ENSEMBLE  
CONSENSUS, WHICH DIFFERED ON THE SPEED OF THE WESTERN TROUGH  
(ECMWF ENSEMBLES GENERALLY QUICKER THAN THE GEFS/CANADIAN  
MEMBERS). A DETERMINISTIC BLEND EARLY IN THE PERIOD GAVE WAY TO A  
BLEND OF THE ECMWF ENSEMBLE MEAN (WHICH HAS TRENDED SLOWER BY NEXT  
WED/THU TOWARD THE GEFS MEAN) WITH THE SLOWER 00Z ECMWF AND 18Z  
GEFS MEAN. QUESTIONS IN SPECIFICS (E.G., WILL LOW PRESSURE LIFT  
TOWARD THE GREAT LAKES NEXT WED OR STAY FLATTER?) WILL REMAIN  
UNANSWERED FOR NOW.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE OVERALL SHORTWAVE TROUGH ALOFT AFFECTING THE WESTERN/CENTRAL  
U.S. AND ASSOCIATED SURFACE FEATURES WILL SPREAD RAIN AND HIGH  
ELEVATION SNOW OVER CENTRAL LATITUDES OF THE WEST AND THEN  
RAINFALL OF VARYING INTENSITY OVER CENTRAL/SOUTHERN PARTS OF THE  
PLAINS AND POSSIBLY THE MISSISSIPPI VALLEY. CONFIDENCE IN  
SPECIFICS OF THIS PRECIPITATION AREA IS LOWER THAN DESIRED DUE TO  
THE GUIDANCE SPREAD FOR DETAILS ALOFT. THERE IS A SIGNAL FOR  
LOW-LEVEL UPSLOPE FLOW TO PROVIDE SOME PRECIPITATION ENHANCEMENT  
ALONG THE EASTERN SLOPES OF THE CENTRAL ROCKIES AROUND SUN (SNOW  
AT RELATIVELY HIGH ELEVATIONS). THEREAFTER ENSEMBLE GUIDANCE SHOWS  
RELATIVELY HIGHER PROBABILITIES FOR LOCALLY HEAVY RAINFALL OVER  
THE SOUTHERN PLAINS WHICH SHOULD SEE A MULTI-DAY FEED OF MOISTURE  
FROM THE GULF, THOUGH PLACEMENT DIFFERENCES (ESPECIALLY  
NORTH-SOUTH) EXIST BETWEEN THE FARTHER SOUTH ECMWF ENSEMBLES AND  
FARTHER NORTH GEFS ENSEMBLES. THE PACIFIC NORTHWEST SHOULD SEE  
PERIODS OF GENERALLY LIGHT PRECIPITATION FROM MON ONWARD AS  
MULTIPLE FRONTS APPROACH/CROSS THE REGION.  
 
BEHIND THE EXITING EASTERN SYSTEM A BRIEF PERIOD OF CHILLY  
TEMPERATURES ARE EXPECTED FOR THE MISSISSIPPI VALLEY/EAST ON  
SUNDAY. THEREAFTER, TEMPERATURES SHOULD OTHERWISE BE NEAR TO ABOVE  
NORMAL GIVEN THE FLATTER TREND OF FLOW ALOFT. EXCEPTION MAY BE  
OVER TEXAS LATER NEXT WEEK GIVEN EXTENSIVE CLOUD COVER AND  
RAINFALL. EXPECT THE HIGHEST WARM ANOMALIES OVER THE WEST AND INTO  
THE NORTHERN HIGH PLAINS WITH ONE OR MORE DAYS OF MAX AND/OR MIN  
READINGS 10-20F ABOVE NORMAL.  
 
FRACASSO/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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