470  
FXUS02 KWBC 060602  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
201 AM EDT SAT APR 06 2019  
 
VALID 12Z TUE APR 09 2019 - 12Z SAT APR 13 2019  
   
..OVERVIEW AND GUIDANCE ASSESSMENT/PREFERENCES
 
 
ON DAY 3, THE EASTERN UPPER TROUGH INDICATE HEIGHT FALLS OVER THE  
NORTHEAST LEADING TO LOW PRESSURE DEVELOPMENT ON THE FRONT AS IT  
MOVES OFF THE NEW ENGLAND COAST, WITH A TRAILING TROUGH ACROSS THE  
REGION. THE SOUTHERN PORTION OF THE FRONT SLOWLY PROGRESSES  
ACROSS THE SOUTHEAST ON TUE BEFORE MOVING OFF THE COAST WED.  
THE ECMWF WAS ON THE FAST EDGE OF THE CLUSTER OF SOLUTIONS WITH  
THE UPPER TROUGH PROGRESSION, WITH THE 12Z ECMWF ENSEMBLE MEAN  
SEVERAL HOURS SLOWER AND CLUSTERING WELL WITH THE GEFS MEAN, SO  
THE MEANS WERE GIVEN MORE WEIGHTING GIVEN BETTER OVERLAP.  
 
ATTENTION TURNS WEST WITH THE THE FIRST OF THE WESTERN TROUGHS  
CROSSING THE GREAT BASIN TO THE WY/CO ROCKIES. LOW PRESSURE  
DEVELOPS ON THE HIGH PLAINS BY WED MORNING AND CONTINUES MOVING  
NORTHEAST TOWARDS THE MID MS VALLEY THU AND GREAT LAKES FRI WHILE  
OCCLUDING. ON SAT A TRIPLE POINT LOW DEVELOPS NEAR THE NEW  
ENGLAND COAST AND EVENTUALLY DEPART INTO THE CANADIAN MARITIMES.  
FOR THIS SYSTEM, THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS HOLD GOOD  
RUN TO RUN CONTINUITY AND OVERLAP WITH ONE ANOTHER , AS THE  
OPERATION THE 12Z ECMWF/18Z GFS WERE BOOKENDS ON EITHER SIDE OF  
THE MEANS (ECMWF/GFS SOUTH).  
 
THE NEXT IN THE SERIES OF UPPER-LEVEL WAVES SHOULD AMPLIFY ALONG  
THE WEST COAST THU-FRI AND CONTINUE INTO THE GREAT BASIN AND  
SOUTHWEST FRI WITH A SURFACE FRONTAL SYSTEM DEVELOPS IN THE  
SOUTHWEST. THE 12Z ECMWF HAS THE HIGHEST AMPLITUDE/SHORTER  
WAVELENGTH UPPER RIDGE APPROACHING THE PACIFIC NORTHWEST, LEADING  
TO HIGHER AMPLITUDE/SLOWER MOVING TROUGH ACROSS THE SOUTHWEST.  
MOST ECMWF ENSEMBLE MEMBERS HAVE A LOWER AMPLITUDE COUPLED  
NORTHEAST PACIFIC RIDGE AND DOWNSTREAM SOUTHWEST TROUGH, SO MORE  
WEIGHTING WAS GIVEN TOWARDS THE MEAN SOLUTION, AGAIN WITH SUPPORT  
FROM THE 18Z GEFS MEAN.  
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
SHOWERS AND THUNDERSTORMS WITH LOCALLY HEAVY RAINS ARE POSSIBLE IN  
THE SOUTHEAST TO SOUTHERN MID ATLANTIC TUE AS THE FIRST SOUTHERN  
STREAM SHORTWAVE/LOW PRESSURE SYSTEM MOVES SLOWLY ACROSS THE  
REGION.  
 
THE SECOND AND MOST SIGNIFICANT SOUTHERN STREAM SYSTEM DURING THE  
PERIOD SHOULD PRODUCE WIDESPREAD RAINS AND MOUNTAIN SNOWS (SOME  
POTENTIALLY HEAVY) ACROSS THE CENTRAL/NORTHERN ROCKIES TUE. AS THE  
SYSTEM REACHES THE CENTRAL U.S. BY THE MIDDLE OF NEXT WEEK, A BAND  
OF PRECIPITATION ALONG THE L0OW LEVEL FRONTOGENESIS MAXIMA IS  
EXPECTED TO DEVELOP FROM THE CENTRAL TO NORTHERN HIGH PLAINS TO  
THE MIDWEST AND GREAT LAKES.  
A BAND OF MODERATE TO HEAVY SNOW APPEARS PROBABLE NORTH AND WEST  
OF THE SURFACE LOW TRACK, WITH A TRANSITION ZONE AND AREAS OF  
MODERATE TO HEAVY RAIN AS WELL.  
SEE THE STORM PREDICTION CENTER OUTLOOKS FOR SEVERE CONVECTIVE  
WEATHER POTENTIAL.  
ONCE THE SYSTEM MOVES INTO THE LAKES, THE PRECIP SHOULD PROGRESSES  
ACROSS THE GREAT LAKES TO THE MID ATLANTIC AND NORTHEAST NEXT  
FRI-SAT 13 APR.  
 
THE NEXT WEST COAST TROUGH BRINGS VALLEY SHOWERS AND MOUNTAIN SNOW  
SHOWERS ACROSS THE GREAT BASIN TO THE CENTRAL ROCKIES FRI INTO SAT  
13 APR.  
 
WARM TEMPERATURES ARE EXPECTED ACROSS MUCH OF THE CENTRAL AND  
EASTERN U.S. DURING THE EARLY TO MIDDLE PORTION OF NEXT WEEK. HIGH  
TEMPERATURES RANGING FROM 10 TO 20 DEG F ABOVE AVERAGE ARE  
POSSIBLE MON-WED OVER A LARGE AREA, WITH THE GREATER ANOMALIES  
ACROSS THE SOUTHERN PLAINS TO LOWER MS VALLEY TUE-WED. COLDER AIR  
AND FURTHER AMPLIFICATION OF UPPER TROUGHING ACROSS THE WEST IN  
THE WAKE OF THE MID-WEEK SYSTEM WILL SUPPORT BELOW AVERAGE  
TEMPERATURES, WITH HIGHS 5 TO 15 DEG BELOW AVERAGE ACROSS MUCH OF  
THE INTERIOR WEST WED AND INTO THE CENTRAL/NORTHERN PLAINS  
THU-SAT. VERY LITTLE OF THE COUNTRY IS FORECAST TO BE ABOVE  
NORMAL SAT 13 APR, MAINLY FOCUSED ON FL AND NORTHWEST WA.  
 
PETERSEN  
 
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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