380  
FXUS02 KWBC 150528  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
128 AM EDT WED MAY 15 2019  
 
VALID 12Z SAT MAY 18 2019 - 12Z WED MAY 22 2019  
   
..GUIDANCE ASSESSMENT AND WEATHER HIGHLIGHTS/THREATS
 
 
...SYSTEM MOVING FROM THE PLAINS SAT/SUN TO UPPER MS VALLEY/GREAT  
LAKES MON/NORTHEAST TUE...  
 
THE LATEST DETERMINISTIC MODELS (18 UTC GFS AND 12 UTC  
ECMWF/UKMET/CANADIAN)  
HAVE GOOD CLUSTERING OF THE SURFACE LOW FORECAST TO BE IN NEBRASKA  
SAT MORNING, WITH GRADUAL WEAKENING OF THIS LOW FOLLOWED BY  
DEVELOPMENT OF A SECOND LOW 00Z SUN OVER KS THAT MOVES NORTH TO  
NEAR THE NE/IA BORDER BY 12Z SUN MORNING. THE SLOW FRONTAL MOVEMENT  
LEADS TO POTENTIAL FOR MULTIPLE ROUNDS OF SHOWERS/STORMS AND  
LOCALLY HEAVY RAIN FROM THE SOUTHERN TO THE CENTRAL PLAINS. SEE  
THE STORM PREDICTION CENTER OUTLOOKS FOR THE PROBABILITY OF SEVERE  
CONVECTIVE WEATHER.  
 
THE WPC PRODUCT SUITE PRIMARILY WAS DERIVED FROM A COMPOSITE  
ENSEMBLE MEAN SOLUTION WITH GREATER WEIGHTING ON THE ECMWF  
ENSEMBLE MEAN AS ITS POSITION IS CLOSE TO THE MULTI-MODEL  
CONSENSUS 12Z SUN. BY 12Z MON 20 MAY, EXCELLENT OVERLAP OF THE 12Z  
ECMWF ENSEMBLE MEAN AND 18Z GEFS MEAN WITH THE LOW PRESSURE CENTER  
SUPPORTS A MEAN SOLUTION. GREATER WEIGHTING ON THE MEANS REMAINS  
THROUGH MID WEEK AS THE MODELS/MEANS DIVERGENCE AS THE SYSTEM  
CROSSES INTO THE UPPER MS VALLEY/GREAT LAKES/NORTHEAST AND INTO  
THE COASTAL AND OFFSHORE WATERS BY THE MIDDLE OF NEXT WEEK.  
 
...DEVELOPING WESTERN US MEAN TROUGH OVER THE WEEKEND INTO THE  
MIDDLE OF NEXT WEEK...  
THE MODELS SHOW A NEGATIVELY TILTED UPPER TROUGH POISED TO MOVE  
INTO THE WESTERN US OVER THE WEEKEND AND REMAIN IN PLACE THROUGH  
THE MIDDLE OF NEXT WEEK. THERE IS POTENTIAL FOR A CLOSED LOW TO  
DEVELOP AT THE BASE OF THE TROUGH IN THE SOUTHWEST BUT THE 12Z  
ECMWF/18Z GFS/12Z CANADIAN GLOBAL MODELS ARE HUNDREDS OF MILES  
APART ON THE LOW TRACK/POSITION BY THE MIDDLE OF NEXT WEEK,  
LENDING DECREASING CONFIDENCE TO THE FORECAST. THE 12Z ECMWF WAS  
ON THE SOUTHEASTERN EDGE OF THE SUITE OF SOLUTIONS IN THE SOUTHERN  
PLAINS WITH ITS 500 MB LOW POSITION, SO MORE WEIGHTING TO THE  
BETTER CLUSTERED 12Z ECMWF/18Z GEFS ENSEMBLE MEANS WAS USED  
INSTEAD.  
 
MUCH OF THE WESTERN US TO THE NORTHERN HIGH PLAINS WILL TURN  
COLDER, WITH PERSISTENT AREAS OF 10-20 EGRESS BELOW NORMAL FOR  
HIGH TEMPERATURES EXPECTED IN THE CENTRAL TO NORTHERN GREAT BASIN  
TO THE NORTHERN HIGH PLAINS. AS A RESULT OF COLD TEMPERATURES,  
TERRAIN ENHANCED SNOWS ARE POSSIBLE IN THE RANGES IN THE PACIFIC  
NORTHWEST/NORTHERN CA/GREAT BASIN/NORTHERN TO CENTRAL ROCKIES.  
 
DOWNSTREAM, THE PERSISTENCE OF WESTERN CYCLONIC CIRCULATIONS  
INDUCES A MID LEVEL ANTICYCLONE OVER THE LOWER MS VALLEY TO THE  
SOUTHEAST. UNDERNEATH THE UPPER RIDGE, MUCH OF THE LOWER MS VALLEY  
EASTWARD ACROSS THE SOUTHEAST, INCLUDING THE CAROLINAS, TURN MORE  
SUMMER LIKE WITH ABOVE NORMAL TEMPERATURES THIS WEEKEND INTO THE  
MIDDLE OF NEXT WEEK. A STALLED FRONT LEADS TO THE PERSISTENCE OF  
SHOWERS/STORMS SAT OVER THE FL KEYS.  
 
PETERSEN  
 
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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