002  
FXUS02 KWBC 161535  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1134 AM EDT THU MAY 16 2019  
 
VALID 12Z SUN MAY 19 2019 - 12Z THU MAY 23 2019  
 
1530 UTC UPDATE...  
 
MODELS SHOWED BROAD AGREEMENT ON THE LARGE SCALE FEATURES  
THROUGHOUT THE MEDIUM RANGE, WITH DIFFERENCES PRIMARILY CONFINED  
TO TIMING AND AMPLITUDE OF VARIOUS FEATURES. THIS SETUP WAS  
WELL-SUITED FOR USE OF A MULTI-MODEL DETERMINISTIC BLEND (00Z  
ECMWF/CMC AND 06Z GFS/FV3) THROUGH MUCH OF THE PERIOD, WITH A  
GRADUAL TREND TOWARD HEAVIER ENSEMBLE WEIGHTING (ECENS/NAEFS  
MEANS) THROUGH TIME. OVERALL, CHANGES TO FORECAST CONTINUITY WERE  
RELATIVELY SMALL. HEMISPHERIC STANDARDIZED 500 HPA ANOMALIES SHOW  
THE LONG WAVE PATTERN BECOMING MORE AMPLIFIED AND LOCKED IN PLACE  
TOWARD LATE IN THE MEDIUM RANGE, WITH A MEAN TROUGH IN THE WEST  
AND A STRENGTHENING RIDGE ANCHORED ACROSS THE SOUTHEAST,  
SUPPORTING A CONTINUED STORMY SETUP FROM THE WEST TO THE CENTRAL  
U.S. AND MIDWEST.  
 
RYAN  
 
PREVIOUS DISCUSSION (ISSUED AT 0606 UTC)...  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE INITIAL CYCLONE THIS WEEKEND IS FORECAST TO CROSS FROM THE  
UPPER MS VALLEY TO THE GREAT LAKES SUNDAY AND ACROSS THE NORTHEAST  
AND INTO THE CANADIAN MARITIMES MON INTO TUE. THE OVERALL TREND  
WAS FOR SLIGHTLY FASTER MOTION THAN PRIOR FORECASTS.  
GIVEN GOOD AGREEMENT AMONG THE 12Z ECMWF AND ITS ENSEMBLE MEAN,  
THE PROGS GAVE MORE WEIGHTING TO THESE SOLUTIONS. THE 12Z UKMET  
WAS THE SOUTHERN MOST SOLUTION AND GIVEN THE LEAST WEIGHTING.  
MODEL AND ENSEMBLE SOLUTIONS CONTINUE TO SHOW ABOVE NORMAL  
FORECAST SPREAD WITH RESPECT TO NORTHEASTERN U.S. FLOW THROUGH  
THIS WEEKEND.  
 
THE ANTICIPATED UPPER TROUGH MOVES ONSHORE SUN IN THE PACIFIC  
NORTHWEST/CA,  
WITH THE SURFACE REFLECTION CROSSING THE GREAT BASIN SUN AND MON.  
AS A WAVE EMERGES AS THE SYSTEM CROSSES THE SOUTHERN ROCKIES, LEE  
CYCLONE DEVELOPMENT OCCURS MON WITH THE NEW SYSTEM MOVING ACROSS  
THE SOUTHERN AND CENTRAL PLAINS MON INTO TUE, CONTINUING NORTH  
NORTHEAST ACROSS THE PLAINS TO THE UPPER MS VALLEY BY WED 22 MAY.  
THE 12Z ECMWF/18Z GFS OFFER GOOD FORECAST AGREEMENT WITH THEIR  
ENSEMBLE MEANS AND CANADIAN GLOBAL TRACKING THE MID-UPPER LOW  
FURTHER NORTHWEST.  
THE NEXT IN THE SERIES OF 500 MB WAVE MAY MOVE ONSHORE INTO CA THU  
23 MAY, ACCORDING TO THE 12Z ECMWF/GFS/CANADIAN ENSEMBLE MEANS.  
 
DOWNSTREAM FROM THE SERIES OF CYCLONES DEVELOPING WITHIN THE  
WESTERN US TROUGH, A DEVELOPING MID LEVEL ANTICYCLONE IS FORECAST  
OVER THE SOUTHEAST US, WHICH GRADUALLY BECOMES STRONGER IN THE  
MIDDLE OF NEXT WEEK. EXCELLENT CLUSTERING OF SOLUTIONS EXIST, SO  
CONFIDENCE IS ABOVE NORMAL IN THE DEVELOPING ANTICYCLONE.  
 
THE WPC PRODUCT SUITE FOR TEMPERATURES, DEWPOINTS, ETC. WAS  
DERIVED FROM A BLEND GIVING MORE WEIGHT TO THE 12Z ECMWF/ECMWF  
ENSEMBLE MEAN WITH LOWER WEIGHTING TO THE 18Z GEFS MEAN AND 18Z  
OPERATIONAL GFS.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
SEVERAL ROUNDS OF SHOWERS/STORMS ARE EXPECTED IN THE CENTRAL US,  
WITH SAT-SUN TARGETING THE EASTERN SOUTHERN TO CENTRAL PLAINS TO  
THE UPPER MS VALLEY , THEN INTO THE UPPER GREAT LAKES AND LOWER MS  
VALLEY SUN. LOCALLY HEAVY RAIN IS POSSIBLE IN THESE AREAS. THE  
NEXT SYSTEM ENTERING THE SOUTHERN PLAINS MON TRIGGERS THE NEXT  
ROUND OF SHOWERS/STORMS. SEE THE STORM PREDICTION CENTER SEVERE  
WEATHER OUTLOOKS FOR EACH DAY'S SEVERE CONVECTIVE POTENTIAL. AS  
THE SYSTEM MOVES NORTH THE ACTIVITY SPREADS FROM THE CENTRAL INTO  
NORTHERN PLAINS TUE AND INTO THE MS VALLEY BEFORE MOVING  
DOWNSTREAM INTO THE UPPER GREAT LAKES WED 22 MAY.  
 
UPSTREAM, A DYNAMIC MID-UPPER LEVEL TROUGH WILL PRODUCE RAINFALL  
IN CA/PACIFIC NORTHWEST TO THE GREAT BASIN OVER THE WEEKEND. ON  
MONDAY THE SLOW MOVING FRONTAL SYSTEM TARGETS THE RANGES OF  
EASTERN NV ACROSS UT/CO/WY/ID WITH VALLEY SHOWERS AND MIXED  
RAIN/SNOWS AT HIGHER ELEVATIONS. ON TUE THE PRECIPITATION IS  
FOCUSED IN THE PACIFIC NORTHWEST TO NORTHERN CA INLAND INTO THE  
NORTHERN GREAT BASIN AND NORTHERN ROCKIES.  
ON WED THE FOCUS OF VALLEY SHOWERS AND MIXED PRECIP AT HIGHER  
ELEVATIONS MOVES INTO THE NORTHERN ROCKIES AND HIGH PLAINS, THEN  
GRADUALLY SPREADING INTO THE NORTHERN PLAINS AND UPPER MS VALLEY.  
 
THE BUILDING MID LEVEL RIDGE IN THE SOUTHEAST LEADS TO GROWING  
CONFIDENCE ABOUT HOT TEMPERATURES DEVELOPING IN THE SOUTHEAST.  
THE FIRST FORECAST 100 DEGREE READINGS POPPED UP IN BOTH THE 12Z  
ECMWF AND ECMWF ENSEMBLE MEAN IN SOUTHERN GA NEXT WED 22 MAY AND  
THU 23 MAY, MARKING AN EARLY SEASON DEVELOPING HEAT WAVE. THERE IS  
POTENTIAL FOR RECORD SETTING HEAT IN THE SOUTHEAST AND SOUTHERN  
APPALACHIANS THE LATTER HALF OF NEXT WEEK. ALONG WITH THE HEAT  
COMES A DRY SPELL IN AL/GA AND THE CAROLINAS, WITH BELOW NORMAL  
CHANCES OF RAIN.  
 
PERSISTENT COLD IS FORECAST IN THE WEST TO THE NORTHERN PLAINS  
THIS WEEKEND THRU THE MIDDLE OF NEXT WEEK. LARGE AREAS OF -10 TO  
-20 DEGREE ANOMALIES FOR DAILY HIGH TEMPERATURES REMAIN FORECAST  
ACROSS THE GREAT BASIN AND NORTHERN PLAINS SUN, CONTINUING INTO  
THE EARLY AND MIDDLE PORTIONS OF NEXT WEEK. OVERNIGHT MINIMUM  
ANOMALIES ARE NOT AS HIGH A MAGNITUDE BUT STILL BELOW NORMAL OVER  
LARGE PORTIONS OF THE WEST TO THE NORTHERN PLAINS.  
 
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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