653  
FXUS02 KWBC 180644  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
243 AM EDT SAT MAY 18 2019  
 
VALID 12Z TUE MAY 21 2019 - 12Z SAT MAY 25 2019  
   
..OVERALL WEATHER PATTERN
 
 
THE UPPER LEVEL PATTERN ACROSS THE CONTINENTAL U.S. WILL CONTINUE  
TO BE RATHER AMPLIFIED AND SLOW TO CHANGE NEXT WEEK. THE UPPER  
LEVEL RIDGE OVER THE SOUTHEAST U.S. BECOMES ANCHORED OVER THE  
REGION AND GRADUALLY BECOMES STRONGER FOR THE SECOND HALF OF THE  
UPCOMING WORK WEEK. ACROSS THE WESTERN U.S., A LARGE SCALE TROUGH  
WILL BE DOMINANT AS MULTIPLE SHORTWAVE PERTURBATIONS KEEP  
CONDITIONS COOL AND UNSETTLED. THIS WILL ALSO BE SLOW TO MOVE  
GIVEN THE EXPECTED DEVELOPMENT OF AN OMEGA BLOCK PATTERN OVER THE  
EASTERN PACIFIC. THE MAIN WEATHER FEATURE OF INTEREST WILL BE A  
STRONG LOW PRESSURE SYSTEM ACROSS THE PLAINS AND UPPER MIDWEST FOR  
THE TUESDAY AND WEDNESDAY TIME PERIOD, AND THEN FOLLOWED BY A  
WEAKER LOW AND FRONTAL BOUNDARY FOR THE END OF THE WEEK.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE MODELS AND ENSEMBLE MEANS INDICATE THE GREATEST AGREEMENT WITH  
RESPECT TO THE BUILDING UPPER LEVEL RIDGE OVER THE SOUTHEASTERN  
U.S., WITH THE ECMWF AND THE EC MEAN SUPPORTING THE STRONGEST  
SOLUTIONS. THE GREATEST DIFFERENCES INVOLVE THE EVOLUTION AND  
TRACK OF INDIVIDUAL CLOSED LOWS WITHIN THE WESTERN U.S. TROUGH.  
THESE BECOME EVIDENT AT THE BEGINNING OF THE FORECAST PERIOD ON  
TUESDAY, WITH THE 00Z UKMET NOTABLY MORE AMPLIFIED WITH THE UPPER  
LOW OVER NEW MEXICO, AND ITS SURFACE LOW TRACKS WELL TO THE WEST  
OF THE MODEL CONSENSUS. THE CMC BECOMES MORE PROGRESSIVE WITH THE  
NEXT CLOSED LOW OVER THE DESERT SOUTHWEST AND THIS BECOMES MORE  
APPARENT BY THURSDAY. EVEN GREATER DIFFERENCES EXIST WITH THE  
SURFACE LOW THAT EVENTUALLY REACHES THE UPPER MIDWEST AND SOUTHERN  
CANADA BY THURSDAY MORNING, WITH THE ECMWF AND EC MEAN OVER  
ONTARIO AND THE GFS MUCH MORE DELAYED IN BRINGING THE LOW OUT OF  
THE UPPER MIDWEST. THE TRACK OF THE ECMWF BEST FITS CONTINUITY  
AND RECENT STORM TRACKS. TOWARDS THE END OF THE FORECAST PERIOD,  
THERE IS AN INCREASING MODEL SIGNAL FOR A THIRD TROUGH AXIS TO  
CLOSE OFF NEAR THE CALIFORNIA COAST BY FRIDAY AND SATURDAY, WITH  
SUPPORT FROM THE GFS, FV3, AND ECMWF. TAKING THESE FACTORS INTO  
ACCOUNT, THE WPC FORECAST WAS BASED ON A BLEND OF THE  
ECMWF/GFS/FV3/ENSEMBLE MEANS, ALONG WITH SOME OF THE PREVIOUS WPC  
FORECAST FOR CONTINUITY.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
NUMEROUS SHOWERS AND THUNDERSTORMS CONTINUE TO BE IN THE FORECAST  
THROUGH THE MIDDLE OF NEXT WEEK FROM THE CENTRAL PLAINS TO THE  
UPPER MIDWEST. MULTIPLE ROUNDS OF MCS ACTIVITY ARE LIKELY WITH  
BOTH OF THE LOW PRESSURE SYSTEMS THAT ARE PROGGED TO TRACK ACROSS  
THE PLAINS. THIS WILL HAVE THE POTENTIAL TO PRODUCE VERY HEAVY  
RAINFALL CAPABLE OF PRODUCING FLASH FLOODING, AND SEVERE WEATHER  
IS ALSO LIKELY ACROSS MUCH OF THE MIDWEST STATES BASED ON RECENT  
SPC FORECASTS. ADDITIONAL HEAVY RAIN IS ALSO POSSIBLE FROM THE  
NEXT STORM SYSTEM TRACKING EASTWARD FROM THE INTERMOUNTAIN WEST  
LATER IN THE WEEK, ALTHOUGH DETAILS ON TIMING AND PLACEMENT  
CONTINUE TO REMAIN UNCLEAR AT THIS TIME.  
 
THERE WILL ALSO BE A DICHOTOMY OF TEMPERATURE ANOMALIES GIVEN THE  
AMPLIFIED FLOW PATTERN IN PLACE. TEMPERATURES ARE EXPECTED TO BE  
WELL ABOVE NORMAL ACROSS MUCH OF THE SOUTHEASTERN U.S. OWING TO  
THE STRENGTH OF THE UPPER RIDGE, AND THIS WILL ALSO SERVE TO KEEP  
RAINFALL CHANCES MINIMAL. AFTERNOON HIGH TEMPERATURES MAY  
APPROACH 100 DEGREES FOR PARTS OF GEORGIA AND SOUTH CAROLINA BY  
LATER IN THE WEEK. THE OPPOSITE WILL BE THE CASE ACROSS MUCH OF  
THE WESTERN U.S. AND ALSO THE NORTHERN PLAINS WITH READINGS ON THE  
ORDER OF 10 TO 20 DEGREES BELOW CLIMATOLOGY, WHICH WILL BE UNDER  
THE INFLUENCE OF THE UPPER LEVEL TROUGH AND TO THE NORTH OF THE  
LOW TRACKS. HEAVIER LATE SEASON SNOWS ARE ALSO LIKELY FOR THE  
SIERRA NEVADA TO THE NORTHERN ROCKIES FOR THE MIDDLE OF THE WEEK.  
 
D. HAMRICK  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page