375  
FXUS02 KWBC 311604  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1203 PM EDT SUN MAR 31 2019  
 
VALID 12Z WED APR 03 2019 - 12Z SUN APR 07 2019  
   
..OVERVIEW
 
 
TODAY'S GUIDANCE REMAINS FAIRLY AGREEABLE AND CONSISTENT IN  
SHOWING A PROGRESSION OF SHORTWAVES FROM THE PACIFIC INTO AND  
ACROSS PORTIONS OF THE LOWER 48, WITH A CORRESPONDING SERIES OF  
SURFACE SYSTEMS. THE NORTHWEST PERIPHERY OF STRONG LOW PRESSURE  
OFF THE EAST COAST ON WED MAY HAVE SOME INFLUENCE ON NEW ENGLAND'S  
COASTAL AREAS AS THE SYSTEM TRACKS NORTHEASTWARD. THEN SHORTWAVE  
ENERGY OVER THE WEST ON WED WILL MAKE STEADY PROGRESS AND PUSH A  
WAVE/FRONTAL SYSTEM ACROSS THE CENTRAL/EASTERN STATES DURING THE  
LATTER HALF OF THE WEEK. THE NORTHERN PART OF INCOMING PACIFIC  
ENERGY THU-FRI SHOULD WEAKEN AS IT HEADS INTO A DEVELOPING WESTERN  
CANADA RIDGE BUT THE SOUTHERN PART WILL LIKELY CONTINUE ACROSS THE  
SOUTHERN U.S. AND NORTHERN MEXICO. THEN A FAIRLY STRONG SHORTWAVE  
SHOULD REACH THE WEST COAST AROUND SAT WITH CONTINUED PROGRESSION  
THEREAFTER, PERHAPS FOLLOWED BY YET MORE ENERGY BRUSHING THE  
PACIFIC NORTHWEST LATE NEXT WEEKEND. THE COMBINATION OF THESE  
SYSTEMS WILL LIKELY BRING PRECIPITATION TO MOST OF THE CONUS AT  
SOME POINT DURING THE WED-SUN PERIOD, WITH THE SOUTHERN THIRD OR  
QUARTER OF THE WEST THE MOST LIKELY AREA TO STAY DRY.  
 
   
..GUIDANCE ASSESSMENT/PREFERENCES
 
 
MODEL/ENSEMBLE CLUSTERING HAS IMPROVED DRAMATICALLY FOR THE STORM  
OFF THE EAST COAST AS OF EARLY WED WITH A LOCATION JUST SOUTHEAST  
OF THE 40/70 BENCHMARK. HOWEVER NOTE THERE ARE SOME SMALLER BUT  
LOCALLY SIGNIFICANT DIFFERENCES THAT PERSIST EVEN IN THE  
SHORT-RANGE TIME FRAME. OTHERWISE GUIDANCE CONTINUES TO AGREE  
FAIRLY WELL WITH THE EXISTENCE OF EACH FEATURE IN THE  
PACIFIC/CONUS STREAM BUT STILL DISPLAYS SPREAD/UNCERTAINTY FOR  
SPECIFICS. FAVORED KEEPING A CONSENSUS APPROACH THAT WAS OBTAINED  
THROUGH A BLEND OF THE DETERMINISTIC MODELS (00Z  
GFS/ECMWF/CANADIAN AND 06Z GFS/FV3-GFS) ALONG WITH CONTINUITY  
DURING THE PERIOD. THIS MATCHED QUITE WELL WITH THE ENSEMBLE  
CONSENSUS BUT WITH A BIT MORE DETAIL.  
 
THE SHORTWAVE AND ASSOCIATED LOW PRESSURE REACHING THE PLAINS  
AROUND THU AGREES FAIRLY WELL IN THE GUIDANCE UP TO THAT TIME.  
SOLUTIONS THEN DIFFER ON EXACTLY HOW ENERGY WILL BE DISTRIBUTED  
WITHIN THE OVERALL TROUGH ALOFT--ALONG WITH STRENGTH AND TRACK OF  
BEST-DEFINED SURFACE LOW PRESSURE. FAST MOVING NORTHERN TIER  
ENERGY MAY ALSO FEED INTO THE UPPER TROUGH AS IT REACHES THE  
EASTERN U.S., PROVIDING ADDED COMPLEXITY TO THE FORECAST. THIS  
TYPE OF EVOLUTION TENDS NOT TO BE EASILY RESOLVED IN THE EXTENDED  
TIME FRAME. MIDDLE GROUND SOLUTION WAS EMPLOYED. BY EARLY FRI  
ENSEMBLE MEMBERS ARE STILL VARIED NORTH-SOUTH BUT HAVE TRENDED  
TOWARD A CONSENSUS POSITION NEAR SOUTHERN INDIANA BETWEEN THE MORE  
SOUTHERLY ECMWF ENSEMBLES AND MORE NORTHERLY GEFS ENSEMBLES. THAT  
SYSTEM SHOULD EXIT OFF THE COAST NEAR THE NY BIGHT PER THE BEST  
MULTI-ENSEMBLE OVERLAP.  
 
FARTHER UPSTREAM COMPOSITE BLEND REPRESENTS ESTABLISHED CONSENSUS  
WITH LITTLE CONTINUITY CHANGE FOR THE SOUTHERN STREAM PACIFIC  
SHORTWAVE THAT EVENTUALLY HEADS INTO THE SOUTHERN PLAINS, AS WELL  
AS FOR THE VIGOROUS SHORTWAVE REACHING THE WEST COAST AROUND EARLY  
SAT. ESTABLISHMENT OF PACIFIC TROUGHING SOUTH OF ALASKA WILL  
TEMPER HEIGHT FALLS A BIT INTO THE PACIFIC NORTHWEST.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE SERIES OF SYSTEMS AFFECTING THE WEST WILL BRING AT LEAST TWO  
OR THREE PERIODS OF ENHANCED RAIN AND HIGH ELEVATION SNOW. EXPECT  
HIGHEST TOTALS FOR THE FIVE-DAY PERIOD TO BE ALONG FAVORED TERRAIN  
FROM NORTHERN CALIFORNIA/SIERRA NEVADA THROUGH THE PACIFIC  
NORTHWEST. MOISTURE WILL EXTEND THROUGH THE INTERMOUNTAIN WEST  
AND NORTHERN-CENTRAL ROCKIES, WITH SOME SIGNIFICANT PRECIPITATION  
OVER THESE AREAS AS WELL BUT WITH LESS EXTREME TOTALS RELATIVE TO  
AREAS NEAR THE COAST. THE SYSTEM EMERGING INTO THE PLAINS ON WED  
AND REACHING THE EAST COAST TOWARD THE END OF THE WEEK WILL SPREAD  
A BROAD SHIELD OF PRECIPITATION ACROSS THE EASTERN HALF OF THE  
COUNTRY WITH EMBEDDED CONVECTION. SPC HAS NOTED A 15% CHANCE OF  
SEVERE THUNDERSTORMS ON WED/THU OVER OK/LOWER MS VALLEY,  
RESPECTIVELY. THERE IS STILL LESS THAN DESIRED AGREEMENT ON AREAS  
OF HEAVIEST RAINFALL BUT AT LEAST LOCALIZED POCKETS OF MODERATE TO  
HEAVY RAINFALL MAY BE POSSIBLE OVER PARTS OF THE SENSITIVE EASTERN  
PLAINS/MISSISSIPPI VALLEY REGION AND THEN INTO THE NORTHEAST. THE  
NORTHERN PERIPHERY OF THE MOISTURE SHIELD MAY CONTAIN SNOW WITH  
BEST POTENTIAL FROM THE NORTH-CENTRAL PLAINS INTO NEW ENGLAND.  
TODAY'S GUIDANCE IS SHOWING A STRONGER SIGNAL FOR HEAVY RAINFALL  
POTENTIAL OVER PARTS OF THE SOUTHERN PLAINS AND POSSIBLY INTO THE  
LOWER MISSISSIPPI VALLEY FROM ABOUT FRI NIGHT THROUGH THE WEEKEND.  
THIS ACTIVITY SHOULD BE ENCOURAGED BY THE COMBINATION OF AN  
APPROACHING SOUTHERN STREAM SHORTWAVE ALOFT AND LOW LEVEL GULF  
INFLOW INTERACTING WITH A FRONT EXPECTED TO STALL NEAR THE GULF  
COAST. DURING THE DAY WED MOST PRECIPITATION WITH THE WESTERN  
ATLANTIC STORM SHOULD BE MOSTLY CONFINED TO AREAS NEAR THE NEW  
ENGLAND COAST.  
 
STEADY PROGRESSION OF SYSTEMS ACROSS THE LOWER 48 WILL PROVIDE  
SOME DAY-TO-DAY VARIABILITY OF TEMPERATURES. WITHIN THIS PATTERN  
THE GENERAL EVOLUTION OF MEAN FLOW WILL LIKELY BE TOWARD MORE  
ABOVE AVERAGE HEIGHTS ALOFT WITH TIME, CORRESPONDING TO INCREASING  
COVERAGE OF ABOVE AVERAGE TEMPERATURES FROM MIDWEEK THROUGH THE  
WEEKEND. THE AREAS OF CLOUDS AND PRECIPITATION ACCOMPANYING EACH  
SYSTEM WILL TEND TO FAVOR GREATER WARM EXTREMES FOR MORNING LOWS  
WITH SOME AREAS OF PLUS 10-20F ANOMALIES. IN TERMS OF FIVE-DAY  
AVERAGES THE INTERIOR WEST INTO THE PLAINS SHOULD SEE WARMEST  
TEMPERATURES RELATIVE TO CLIMATOLOGY. PLUS 10F OR GREATER  
ANOMALIES FOR HIGHS ARE MOST LIKELY OVER THE PARTS OF THE PLAINS  
FRI-SUN.  
 
FRACASSO/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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