926  
FXUS02 KWBC 170659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
258 AM EDT FRI MAY 17 2019  
 
VALID 12Z MON MAY 20 2019 - 12Z FRI MAY 24 2019  
   
..OVERALL WEATHER PATTERN
 
 
A STORMY AND UNSETTLED WEATHER PATTERN IS EXPECTED ACROSS MUCH OF  
THE CENTRAL U.S. DURING THE MEDIUM RANGE PERIOD WITH A LARGE SCALE  
UPPER TROUGH BECOMING ESTABLISHED OVER THE INTERMOUNTAIN WEST AND  
A BUILDING UPPER LEVEL RIDGE OVER THE SOUTHEASTERN STATES. THREE  
WELL DEFINED STORM SYSTEMS ARE EXPECTED NEXT WEEK, WITH THE FIRST  
AFFECTING THE NORTHEASTERN U.S. ON MONDAY. THE SECOND STORM  
GATHERS STRENGTH ACROSS THE PLAINS ON TUESDAY AND TRACKS TOWARDS  
THE GREAT LAKES, AND THE THIRD ONE DEVELOPS OVER THE INTERMOUNTAIN  
WEST MIDWEEK AND REACHES THE PLAINS BY THE END OF THE WEEK.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODELS AND ENSEMBLE MEANS INDICATE DECENT OVERALL AGREEMENT ON THE  
SYNOPTIC SCALE ON MONDAY. BY TUESDAY, THE 00Z UKMET BEGINS TO  
DIFFER WITH THE SURFACE LOW WELL TO THE SOUTH OF THE MODEL  
CONSENSUS ACROSS THE SOUTHERN PLAINS, AND FARTHER NORTH WITH THE  
NEXT LOW OVER THE EASTERN PACIFIC. BY THE MIDDLE OF THE WEEK,  
NOTEWORTHY DIFFERENCES ARE APPARENT WITH THE NEXT UPPER LEVEL  
TROUGH CROSSING THE WEST COAST REGION, WITH THE ECMWF/EC MEAN  
SLOWER WITH THE PROGRESSION OF THE CLOSED LOW, AND THE 00Z GFS  
MORE AMPLIFIED AND FASTER ACROSS THE DESERT SOUTHWEST. THE  
FEATURE WITH THE GREATEST PREDICTABILITY WILL BE THE UPPER LEVEL  
RIDGE OVER THE SOUTHEAST, WHERE A GENERAL MODEL BLEND SUFFICES.  
ELSEWHERE, THE FORECAST WAS DERIVED FROM A BLEND OF THE  
ECMWF/GFS/PARALLEL GFS AND INCREASING PERCENTAGES OF THE GEFS AND  
EC MEAN FOR THE SECOND HALF OF THE FORECAST PERIOD.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
NUMEROUS SHOWERS AND THUNDERSTORMS CONTINUE TO BE IN THE FORECAST  
GOING INTO NEXT WEEK ACROSS THE CENTRAL/SOUTHERN PLAINS AND  
EXTENDING 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 FLASH FLOODING, AND SEVERE  
WEATHER IS ALSO LIKELY FROM NORTHERN TEXAS TO THE MIDWEST BASED ON  
RECENT SPC FORECASTS. THE GREATEST CHANCE OF FLOODING WOULD BE  
FROM THE TEXAS PANHANDLE REGION TO IOWA WITH THE STRONG LOW  
PRESSURE SYSTEM FOR THE EARLY TO MIDDLE PART OF THE WEEK.  
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 ARE LESS CERTAIN.  
 
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. THE OPPOSITE WILL BE THE CASE ACROSS  
MUCH OF THE WESTERN U.S. AND ALSO THE NORTHERN PLAINS THAT WILL BE  
UNDER THE INFLUENCE OF THE UPPER LEVEL TROUGH AND TO THE NORTH OF  
THE LOW TRACKS. LATE SEASON SNOW IS LIKELY FOR THE SIERRA NEVADA  
AND THE NORTHERN ROCKIES.  
 
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  
 

 
 
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