055  
FXUS02 KWNH 220540  
PREEPD  
 
PRELIMINARY EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
140 AM EDT SUN APR 22 2018  
 
VALID 12Z WED APR 25 2018 - 12Z SUN APR 29 2018  
   
..OVERVIEW AND GUIDANCE PREFERENCES
 
 
MODELS AND ENSEMBLES CONTINUE TO SHOW PERSISTENT TROUGHING IN THE  
EAST AND A CLOSED LOW OFF THE CALIFORNIA COAST EVENTUALLY COMING  
ASHORE LATE IN THE WEEK INTO NEXT WEEKEND WITH RIDGING IN BETWEEN,  
CENTERED OVER THE ROCKIES. A LEAD AND TRAILING SYSTEM WILL PUSH  
THROUGH THE EAST WED-THU WITH A THIRD ON ITS HEELS FRI-SAT, THOUGH  
THERE WAS INCREASED TIMING SPREAD WITHIN THE GUIDANCE -- GFS  
GENERALLY QUICKER THAN THE ECMWF/UKMET WITH THE ENSEMBLE MEANS IN  
BETWEEN. OPTED TO RELY MORE ON THE ENSEMBLE GUIDANCE WITH TIME TO  
HELP MITIGATE FUTURE CHANGES TO FRONTAL TIMING. TO THE WEST,  
CLOSED LOW APPEARS MUCH BETTER HANDLED UNTIL ABOUT FRIDAY WHEN  
THERE BECOMES A N-S DIFFERENCE IN TRACK (THROUGH OREGON OR INTO  
CALIFORNIA PER THE ECMWF VS CANADIAN VS FARTHER SOUTH GFS).  
ENSEMBLES WERE CLUSTERED NEARER TO THEIR DETERMINISTIC PARENT AND  
GIVEN THE MULTI-DAY CHANGES A POSITION IN BETWEEN THE ECMWF/GFS  
ENSEMBLE MEANS OFFERED A PRUDENT POSITION, TAKING THE UPPER LOW  
THROUGH NORTHERN CALIFORNIA INTO SE OREGON NEXT WEEKEND.  
 
   
..WEATHER/THREATS HIGHLIGHTS
 
 
EXITING LEAD AND TRAILING UPPER/SFC LOWS WILL SPREAD RAINS THROUGH  
THE NORTHEAST AND THEN THROUGH THE SOUTHEAST NEXT WED-FRI WITH  
ANOTHER ROUND WITH THE THIRD SYSTEM NEXT FRI/SAT BEFORE THE FRONT  
EXITS THE NORTHEAST BY SUNDAY. TEMPERATURES WILL GENERALLY BE  
BELOW AVERAGE WITH THE EXCEPTION OF MAINE.  
 
IN THE WEST, UPPER RIDGING WILL ENSURE WELL ABOVE AVERAGE  
TEMPERATURES (+10 TO +20F ABOVE CLIMO) WITH SOME RECORDS POSSIBLE  
UNTIL THE CLOSED LOW FINALLY PUSHES INLAND. PRECIPITATION WILL  
GRADUALLY INCREASE ALONG THE COAST OF NORTHERN CALIFORNIA INTO  
OREGON LATE IN THE WEEK THEN THROUGH THE NORTHERN SIERRAS INTO THE  
GREAT BASIN WITH AMOUNTS DEPENDING ON THE TRACK OF THE UPPER LOW.  
FAVOR THE CONSENSUS SLOWER THAN THE GFS BY NEXT SUNDAY WHICH WOULD  
KEEP MOST/ALL OF THE PRECIPITATION WEST OF THE DIVIDE THROUGH THE  
CENTRAL ROCKIES.  
 
ASSOCIATED WPC MEDIUM RANGE FORECASTS OF 500 MB HEIGHTS...SURFACE  
SYSTEMS...WEATHER GRIDS...QUANTITATIVE PRECIPITATION FORECASTS  
(QPF)...AND WINTER WEATHER OUTLOOK SNOW/SLEET PROBABILITIES CAN BE  
FOUND AT...  
 
HTTP://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTP://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTP://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTP://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTP://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
 
FRACASSO  
 

 
 
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