945  
FXUS02 KWBC 210557  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
156 AM EDT THU MAR 21 2019  
 
VALID 12Z SUN MAR 24 2019 - 12Z THU MAR 28 2019  
   
..OVERVIEW AND GUIDANCE ASSESSMENT/PREFERENCES
 
 
ANOMALOUS UPPER-LEVEL RIDGING EXTENDING FROM WESTERN CANADA INTO  
THE NORTH CENTRAL U.S. THIS WEEKEND IS FORECAST BY GRADUALLY BREAK  
DOWN DURING THE EARLY TO MIDDLE PORTION OF NEXT WEEK. SOME DEGREE  
OF RIDGING APPEARS LIKELY TO BECOME REESTABLISHED FROM THE GULF  
OF ALASKA NORTH ACROSS ALASKA - A POSITION MUCH MORE COMMON IN  
RECENT MONTHS. MEAN TROUGHING SHOULD PERSIST ACROSS THE NORTH  
CENTRAL PACIFIC, BRINGING A CONTINUATION OF THE RECENTLY SEEN  
PATTERN WITH PACIFIC SHORTWAVE ENERGY CROSSING THE CONUS EVERY  
COUPLE DAYS. THE RECONFIGURATION OF FLOW AT THE HIGHER LATITUDES  
WILL HAVE SOME IMPLICATIONS FARTHER SOUTH, WITH LESS SPLIT FLOW  
AND GREATER LIKELIHOOD OF PHASED SYSTEMS ACROSS THE CENTRAL U.S.  
BY MID TO LATE NEXT WEEK. IN THE MEANTIME, ONE SIGNIFICANT  
SOUTHERN STREAM SYSTEM REMAINS DURING THE MEDIUM RANGE, AFFECTING  
THE SOUTH CENTRAL AND SOUTHEASTERN U.S. SUN-TUE.  
 
MODELS CONTINUE TO STRUGGLE WITH THE SYSTEM CROSSING THE SOUTHERN  
U.S. FROM SUN ONWARD, AND THE POTENTIAL EVOLUTION OF A COASTAL LOW  
ALONG/OFF THE EASTERN SEABOARD EARLY-MID NEXT WEEK. IN GENERAL,  
GUIDANCE OVER THE PAST DAY HAS TRENDED TOWARD A QUICKER EASTWARD  
PROGRESSION, AND SOMEWHAT LESS LIKELIHOOD OF A SIGNIFICANT LOW  
ALONG THE SOUTHEAST/MID-ATLANTIC COAST EARLY NEXT WEEK. ENSEMBLE  
SPREAD REMAINS QUITE LARGE, HOWEVER. AT 12Z ON TUE, FOR EXAMPLE,  
ENSEMBLE MEMBERS RANGE FROM A LOW STILL OVER THE MISSISSIPPI  
RIVER, TO OTHERS HAVING ENERGY ALREADY TRANSFERRED TO A NEW LOW  
OFF THE SOUTHEAST COAST. WHILE THE CONSENSUS OF SOLUTIONS HAS  
SHIFTED FASTER, SPREAD ALSO SEEMS TO HAVE INCREASED OVER THE PAST  
FEW ENSEMBLE CYCLES. THUS, CONFIDENCE IS LOW, AND WOULD EXPECT  
CONTINUED RUN-TO-RUN VARIABILITY. OPTED TO TWEAK THE FORECAST  
TOWARD A FASTER PROGRESSION RATHER THAN MAKING A DRAMATIC CHANGE  
GIVEN THE LOW CONFIDENCE. THIS RESULTED IN A BLEND WEIGHTED A BIT  
MORE TOWARD THE SLOWER SOLUTIONS (12Z ECMWF/CMC) AND NOT MUCH  
WEIGHT ON THE GFS WHICH CONTINUES TO LEAD THE PACK IN TERMS OF  
EASTWARD PROGRESSION OF THE SYSTEM AND QUICKLY MOVING ANY LOW OUT  
INTO THE OPEN ATLANTIC EARLY NEXT WEEK. GIVEN SIGNIFICANT  
UNCERTAINTY AS TO HOW QUICKLY ANY LOW ALONG THE SOUTHEAST COAST BY  
THE MIDDLE OF NEXT WEEK MOVES OUT TO SEA OR, PERHAPS UP THE COAST  
AS THE 12Z CMC AND A HANDFUL OF ENSEMBLE MEMBERS SHOW, MAINTAINED  
AT LEAST LOW POPS FOR PORTIONS OF THE SOUTHEAST/MID-ATLANTIC INTO  
MIDWEEK.  
 
ELSEWHERE, MODELS SHOW BETTER CONSENSUS THAT ONE WEAKENING  
SHORTWAVE SHOULD REACH THE WEST COAST LATE MON, WITH A MORE  
SIGNIFICANT WAVE ARRIVING LATE TUE, MOVING INTO THE GREAT BASIN OR  
ROCKIES WED NIGHT-THU. MODELS HANDLE THE FIRST WAVE SIMILARLY, BUT  
SOME LARGER DIFFERENCES EMERGE BY THE MIDDLE OF NEXT WEEK WITH THE  
SECOND SYSTEM. SOME TIMING DIFFERENCES EMERGE WITH THE SECOND  
SYSTEM WED-THU. DIFFERENCES ALSO EXIST AS TO STRUCTURE OF THE  
NORTH PACIFIC RIDGE, WITH IMPACTS ON HOW/IF THE SECOND SHORTWAVE  
INTERACTS WITH ADDITIONAL NORTHERN STREAM ENERGY. IN GENERAL, A  
MORE ENSEMBLE-BASED APPROACH WAS TAKEN TO THE FORECAST BY WED-THU,  
WITH INCREASED WEIGHT ON THE ECENS AND NAEFS ENSEMBLE MEANS.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
THE SOUTHERN STREAM SYSTEM IS EXPECTED TO BRING RAIN AND  
THUNDERSTORMS FROM PORTIONS OF THE SOUTHERN PLAINS AND  
LOWER/MID-MISSISSIPPI VALLEY TO THE SOUTHEAST. LOCALLY HEAVY RAIN  
IS POSSIBLE, BUT NO STRONG SIGNAL FOR EXCESSIVE RAINS IS EVIDENT  
IN THE GUIDANCE AT THIS POINT GIVEN THE TREND TOWARD INCREASED  
FORWARD SPEED OF THE SYSTEM. COLD TEMPERATURES ON THE NORTHERN END  
OF THE PRECIPITATION SHIELD MAY MARGINALLY SUPPORT SNOW OR A  
RAIN/SNOW MIX FOR SOME AREAS FROM THE CENTRAL APPALACHIANS AND  
MID-ATLANTIC, AND PERHAPS INTO THE NORTHEAST. MEANWHILE, THE WEST  
WILL SEE A COUPLE ROUNDS OF PRECIPITATION FROM THE INCOMING  
PACIFIC SYSTEMS, BRINGING RAIN AND MOUNTAIN SNOWS TO MUCH OF THE  
CENTRAL/NORTHERN ROCKIES AND FROM CENTRAL CALIFORNIA TO THE  
PACIFIC NORTHWEST. THE ARRIVAL OF THE MORE SIGNIFICANT SYSTEM BY  
THE MIDDLE OF NEXT WEEK PRODUCES A STRONGER SIGNAL FOR POTENTIALLY  
HEAVY PRECIP (RAIN AND MOUNTAIN SNOW) ACROSS PORTIONS OF CENTRAL  
AND NORTHERN CALIFORNIA. GIVEN THE INCREASINGLY PROGRESSIVE FLOW  
PATTERN ACROSS THE CONUS, TEMPERATURES WILL BE HIGHLY VARIABLE,  
WITH MUCH OF THE COUNTRY SEEING BOTH ABOVE AND BELOW AVERAGE  
TEMPERATURES AT DIFFERENT POINTS DURING THE EXTENDED PERIOD.  
 
RYAN  
 
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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