460  
FXUS02 KWBC 181532  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1032 AM EST MON FEB 18 2019  
 
VALID 12Z THU FEB 21 2019 - 12Z MON FEB 25 2019  
 
...MULTI-DAY HEAVY RAIN EVENT FROM THE LOWER MISSISSIPPI/TENNESSEE  
VALLEYS TO SOUTHERN/CENTRAL APPALACHIANS...  
 
...WINTRY HEAVY PRECIPITATION THREAT FOR THE SOUTHWEST AND  
SOUTH-CENTRAL GREAT BASIN/ROCKIES THU INTO FRI...  
 
1530 UTC UPDATE...  
 
MODEL SOLUTIONS REMAIN RELATIVELY STABLE AND THE FORECAST WAS KEPT  
FAIRLY CLOSE TO CONTINUITY IN THE UPDATE THIS MORNING. A  
MULTI-MODEL DETERMINISTIC BLEND WAS USED AS A BASIS FOR THE  
FORECAST DURING DAYS 3-4 (THU-FRI). STARTING ON DAY 5 (SAT),  
PREFERRED THE SLOWER SOLUTIONS (00Z ECMWF/06Z GFS) TO BRING  
SHORTWAVE ENERGY INTO THE SOUTHERN PLAINS, WITH SUPPORT FROM THE  
CONSISTENT ECENS MEAN AND THE LATEST GEFS MEAN. DIFFERENCES EMERGE  
WITH RESPECT TO THIS SYSTEM ACROSS THE MIDWEST/GREAT LAKES BY SUN,  
BUT DECENT CLUSTERING WAS EVIDENT AMONG ENSEMBLE MEMBERS,  
WELL-CENTERED AROUND THE ECMWF. ALSO OF NOTE WAS A NEARLY  
UNIVERSAL TREND AMONG THE MODELS/ENSEMBLES TOWARD A QUICKER  
PROGRESSION OF SHORTWAVE ENERGY AND ASSOCIATED SURFACE FRONTAL  
SYSTEM REACHING THE PACIFIC NORTHWEST SAT - THIS WAS PROBABLY THE  
MOST SIGNIFICANT CHANGE TO THE FORECAST FROM OVERNIGHT. A BLEND OF  
THE ECMWF/GFS AND ECENS/GEFS MEANS WAS USED FOR DAYS 5-7, WITH  
MORE WEIGHT PLACED TOWARD THE ECMWF/ECENS SOLUTIONS GIVEN SOMEWHAT  
BETTER CLUSTERING AND CONSISTENCY. PREVIOUS DISCUSSION FROM  
OVERNIGHT FOLLOWS BELOW.  
 
RYAN  
 
PREVIOUS DISCUSSION (ISSUED AT 0552 UTC)...  
   
..PATTERN OVERVIEW AND WEATHER HIGHLIGHTS/HAZARDS
 
 
WHAT HAS PROVEN TO BE QUITE THE PERSISTENT AND WINTRY WESTERN U.S.  
MEAN UPPER TROUGH WILL AGAIN BE REINFORCED INTO THU-FRI, SPREADING  
AN ENHANCED PRECIPITATION THREAT TO INCLUDE HIGHER ELEVATION HEAVY  
SNOWS FROM SRN CA TO THE S-CENTRAL GREAT BASIN/ROCKIES. TROUGH  
ENERGY EJECTS OVER THE CENTRAL THEN EASTERN U.S. OVER THE WEEKEND,  
WORKING OVERTOP AN AMPLIFIED AND SLOW TO ERODE BAHAMAS UPPER  
RIDGE. A FAVORABLE CORRIDOR FOR A MULTI-DAY HEAVY RAIN/TRAINING  
EPISODE PERSISTS FROM THE LOWER MS/TN/OH VALLEYS TO THE  
SRN/CENTRAL APPALACHIANS AND MID-ATLANTIC. FLOODING/RUNOFF ISSUES  
WILL BE FUELED BY HIGHLY ANOMALOUS MOISTURE CHANNELING INTO A WAVY  
FRONTAL ZONE UNDER FAVORABLE JET SUPPORT. A THREAT FOR HEAVY  
SNOW/ICE DEVELOPS FROM THE N-CENTRAL PLAINS TO THE MIDWEST/GREAT  
LAKES/NORTHEAST AS ENHANCED BY LESS CERTAIN BUT POTENTIALLY DEEP  
SURFACE CYCLOGENESIS FRI-MON. UPSTREAM, WEAKER TROUGH ENERGIES DIG  
INTO A LESS UNSETTLED WEST IN TRANSITION TO LESS STORMY AND  
MODERATING LOWER 48 MEAN ZONAL FLOW.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
MODELS AND ENSEMBLES OVERALL CLUSTER PRETTY WELL INTO THU/FRI WITH  
THE LARGER SCALE FLOW EVOLUTION AND A FAVORED COMPOSITE SOLUTION  
OF THE GFS/ECMWF AND GEFS/ECMWF ENSEMBLE MEANS MAINTAINS GOOD WPC  
CONTINUITY IN A PATTERN WITH ABOVE NORMAL PREDICTABILITY. RECENT  
AMPLE RUN TO RUN MODEL VARIANCE PROMPTS A QUICK TRANSITION IN  
FAVOR OF THESE ENSEMBLE MEANS OVER THE WEEKEND INTO EARLY NEXT  
WEEK AMID GROWING UNCERTAINTY IN TRANSITIONAL FLOW.  
 
SCHICHTEL  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION AND WINTER WEATHER OUTLOOK  
PROBABILITIES ARE FOUND 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  
 

 
 
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