293  
FXUS02 KWBC 060701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT MON MAY 06 2019  
 
VALID 12Z THU MAY 09 2019 - 12Z MON MAY 13 2019  
   
..ACTIVE SPRINGTIME PATTERN FOR PARTS OF THE LOWER 48
 
 
   
..OVERVIEW
 
 
SIGNIFICANT PRECIPITATION WILL BE IN THE FORECAST ACROSS PORTIONS  
OF THE SOUTHERN AND EASTERN U.S. DURING THE PERIOD. A STORM  
SYSTEM REACHING THE MIDWEST BY THE START OF THE PERIOD EARLY THU  
AND TRACKING NORTHEAST WITH TIME WILL BRING ONE AREA OF ENHANCED  
RAINFALL ACROSS THE GREAT LAKES/NORTHEAST LATE THIS WEEK, ALONG  
WITH A THREAT OF STRONG TO SEVERE CONVECTION IN THE WARM SECTOR.  
MEANWHILE THERE IS STILL A PRONOUNCED SIGNAL FOR HEAVY RAINFALL  
POTENTIAL FROM EASTERN TEXAS THROUGH THE LOWER MISSISSIPPI VALLEY  
AND TO SOME DEGREE EXTENDING FARTHER NORTHEASTWARD. THIS THREAT  
CORRESPONDS TO GUIDANCE CONTINUING TO SHOW THE MIDWEST STORM'S  
TRAILING FRONT STALLING NEAR AND NORTHEAST FROM THE WESTERN GULF  
COAST, WITH SOME DEGREE OF LOW LEVEL GULF INFLOW PROVIDING  
MOISTURE WHILE IMPULSES PROGRESS ALONG IN SOUTHWESTERLY FLOW  
ALOFT. AT THE SAME TIME UPPER TROUGHING OVER THE WEST WILL BRING  
MULTIPLE DAYS OF PRECIPITATION TO LOCATIONS FROM CENTRAL-SOUTHERN  
CALIFORNIA INTO THE SOUTHERN HALF OF THE ROCKIES WITH HIGHEST  
TOTALS OVER AREAS WITH FAVORABLE TERRAIN ENHANCEMENT.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE MAJORITY OF GUIDANCE SHOWS A SIMILAR THEME FOR THE EVOLUTION  
OF MEAN FLOW ALOFT, AN EASTERN PACIFIC RIDGE BUILDING INTO THE  
NORTHWEST STATES WHILE SPLIT FLOW PREVAILS TO THE SOUTHEAST--A  
MEAN TROUGH SETTLING OVER EAST-CENTRAL CANADA INTO THE UPPER  
MIDWEST/GREAT LAKES AND A DEVELOPING UPPER LOW TRACKING NEAR THE  
WESTERN U.S.-MEXICO BORDER. THE RELATIVE AGREEMENT IN MEAN FLOW  
CONCEALS SIGNIFICANT DIFFERENCES/UNCERTAINTY IN SOME DAY-TO-DAY  
DETAILS.  
 
GREATEST DIFFERENCES OVER THE PAST COUPLE DAYS HAVE INVOLVED  
NORTHERN STEAM FLOW, BOTH WITHIN THE MEAN TROUGH OVER SOUTHERN  
CANADA AND NORTHERN U.S. AS WELL AS NORTH PACIFIC FLOW HEADING  
TOWARD/INTO NORTH AMERICA. THE MOST NOTICEABLE MULTI-DAY TREND  
HAS BEEN FOR STRONGER RIDGING TO BUILD OVER THE NORTHWEST AND TO  
PERSIST FOR A LONGER TIME. UNCERTAIN DETAILS OF NORTH PACIFIC  
FLOW ROUNDING THE RIDGE CONTINUE TO CAUSE DIFFICULTY IN RESOLVING  
THE TIMING AND AMPLITUDE OF A POTENTIAL SURFACE LOW/FRONTAL SYSTEM  
DROPPING FROM CANADA INTO THE NORTHERN U.S. LATE WEEK ONWARD.  
BASED ON THE FULL ARRAY OF GUIDANCE GFS RUNS MAY BE SOMEWHAT  
STRONG/FAST WITH THE SYSTEM BUT THE 12Z ECMWF/ECMWF MEAN ARE  
SLOWEST/WEAKEST. THE OLD 00Z ECMWF WAS SOMEWHAT CLOSER TO OTHER  
GUIDANCE. ACROSS THIS EXPANSE OF NORTHERN LATITUDES A  
BLEND/COMPROMISE APPROACH PROVIDES REASONABLE CONTINUITY WHILE  
REFLECTING LATEST TRENDS FOR THE NORTHWEST RIDGE ALOFT.  
 
GUIDANCE STILL SHOWS A COMPLEX EVOLUTION TAKING PLACE ALONG AND TO  
THE SOUTH OF THE CALIFORNIA COAST, AS INTERIOR WEST ENERGY PUSHES  
SOUTHWEST TO INTERACT WITH AN OFFSHORE UPPER LOW MOVING EASTWARD  
ALONG 30N LATITUDE. THERE WILL BE VARIOUS WAYS THAT THIS  
EVOLUTION COULD ULTIMATELY STRAY FROM CONSENSUS BUT SO FAR THE  
MAJORITY/INTERMEDIATE SOLUTION HAS BEEN CONSISTENT IN SHOWING THE  
CENTER OF THE UPPER LOW REACHING NEAR THE SOUTHERN ARIZONA BORDER  
BY SUN. GIVEN THE RIDGE BUILDING OVER THE NORTHWEST, SUSPECT THE  
ECMWF/ECMWF MEAN MAY BE TOO QUICK TO OPEN UP/EJECT THE FEATURE  
AFTER SUN. THE NEW 00Z GFS/GEFS MEAN MAINTAIN SUPPORT FOR SLOWER  
TIMING VERSUS ECMWF-BASED SOLUTIONS BY MON.  
 
FOR THE STORM TRACKING NORTHEAST FROM THE MIDWEST, UKMET RUNS ARE  
NOTABLE FOR BEING ON THE STRONG/NORTHWEST FRINGE OF THE MODEL  
SPREAD. OTHERWISE CONSENSUS HAS TRENDED A BIT WEAKER FROM PRIOR  
CYCLE BUT TO A DEGREE THAT IS GENERALLY WITHIN THE NOISE RANGE.  
MOST SOLUTIONS CONTINUE TO SHOW A TRIPLE POINT WAVE OFF NEW  
ENGLAND BY EARLY SAT. ALONG THE TRAILING FRONT THAT WILL BECOME  
THE FOCUS FOR HEAVY RAINFALL OVER THE SOUTH, SOME UNCERTAINTY IN  
WAVINESS/FRONTAL POSITION ARISES TOWARD SUN-MON IN RESPONSE TO  
DETAILS OF THE UPPER TROUGH TO THE NORTH.  
 
FOR THE FULL FORECAST DOMAIN A GENERAL MODEL BLEND EARLY IN THE  
PERIOD TRENDING TOWARD A BLEND AMONG THE 18Z GFS/GEFS MEAN AND 12Z  
ECMWF/ECMWF MEAN PROVIDED A REASONABLE STARTING POINT FOR  
REPRESENTING THE DESIRED CONSENSUS OR INTERMEDIATE SOLUTION FOR  
FEATURES OF INTEREST. THIS APPROACH PROVIDED FAIRLY GOOD  
CONTINUITY WHILE AWAITING ANY POSSIBLE ADJUSTMENTS OVER AREAS OF  
GREATEST UNCERTAINTY.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE STORM TRACKING NORTHEAST FROM THE MIDWEST THU-FRI WILL PRODUCE  
AN AREA OF RAINFALL THAT MAY BE HEAVY AT TIMES OVER THE GREAT  
LAKES/NORTHEAST AS WELL AS THUNDERSTORMS (SOME STRONG TO SEVERE)  
IN THE WARM SECTOR FROM THE SOUTHEASTERN PLAINS/LOWER MISSISSIPPI  
VALLEY INTO THE OHIO VALLEY/LOWER GREAT LAKES, AND POSSIBLY  
EXTENDING FARTHER EASTWARD WITH TIME. CONSULT STORM PREDICTION  
CENTER PRODUCTS FOR LATEST INFO ON THE SEVERE WEATHER FORECAST.  
IN THE NORTHERN PART OF THE PRECIP SHIELD THERE MAY BE LOCALIZED  
AREAS OF SNOW AT TIMES, WITH BEST POTENTIAL (THOUGH WITH FAIRLY OW  
PROBABILITY IN ABSOLUTE TERMS) OVER THE WESTERN UP OF MICHIGAN AND  
EXTREME NORTHERN WISCONSIN.  
 
THE FAVORABLE SETUP OF A STALLING FRONT, LOW LEVEL GULF INFLOW,  
AND IMPULSES ALOFT CARRIED BY SOUTHWESTERLY MEAN FLOW, ARE  
MAINTAINING THE THREAT FOR HEAVY RAIN ACROSS PARTS OF THE SOUTH.  
THE BEST POTENTIAL FOR HIGHEST 5-DAY TOTALS STILL EXISTS OVER  
EASTERN TEXAS THROUGH LOUISIANA WITH SIGNIFICANT TOTALS EXTENDING  
FARTHER NORTHEASTWARD. GUIDANCE CONTINUES TO SHOW THE POSSIBILITY  
FOR AT LEAST 5-10" ACCUMULATIONS AT SOME LOCATIONS. THE FRONT MAY  
DRIFT A LITTLE SOUTHEASTWARD LATE IN THE PERIOD TO TONE DOWN THE  
HEAVY RAINFALL THREAT.  
 
WITHIN THE AREA OF TERRAIN-ENHANCED PRECIPITATION FROM  
CENTRAL-SOUTHERN CALIFORNIA EASTWARD INTO THE ROCKIES, THE BEST  
POTENTIAL FOR HIGHER ELEVATION SNOW WILL BE CENTERED OVER THE  
ROCKIES OF COLORADO THU INTO FRI BEFORE HEIGHTS ALOFT RISE OVER  
THAT AREA. THERE IS STILL UNCERTAINTY OVER DETAILS OF THE UPPER  
LOW THAT MAY TRACK ALONG THE SOUTHWESTERN U.S./NORTHERN MEXICO  
BORDER BUT THE FAVORED AVERAGE OF GUIDANCE DURING THE WEEKEND INTO  
EARLY NEXT WEEK YIELDS A FAIRLY CONSISTENT FORECAST FOR THE TIME  
BEING. RAINFALL MAY INCREASE IN COVERAGE/INTENSITY OVER THE  
SOUTHERN HIGH PLAINS EARLY NEXT WEEK AS THE FEATURE APPROACHES.  
 
THE UPPER RIDGE BUILDING INTO THE NORTHWEST WILL BRING MULTIPLE  
DAYS OF WELL ABOVE NORMAL TEMPERATURES--GENERALLY PLUS 10-20F  
ANOMALIES AND MAYBE LOCALLY HIGHER. SOME DAILY RECORDS FOR  
HIGHS/WARM LOWS WILL BE POSSIBLE. ON THE OTHER HAND MUCH BELOW  
NORMAL HIGHS (MINUS 15-25F ANOMALIES) WILL PUSH DOWN THROUGH THE  
CENTRAL/SOUTHERN HIGH PLAINS LATE THIS WEEK AND SLOWLY MODERATE  
THEREAFTER. TO A LESS EXTREME EXTENT THE SOUTHWEST WILL SEE COOL  
DAYTIME HIGHS AS WELL. THE EAST WILL BE WARM LATE THIS WEEK AHEAD  
OF THE MIDWEST SYSTEM, FOLLOWED BY A TREND TOWARD MORE NORMAL  
READINGS.  
 
RAUSCH  
 
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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