032  
FXUS02 KWBC 241615  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1215 PM EDT TUE APR 24 2018  
 
VALID 12Z FRI APR 27 2018 - 12Z TUE MAY 01 2018  
   
..OVERVIEW AND GUIDANCE PREFERENCES
 
 
MODEL GUIDANCE THIS MORNING CONTINUES TO SUPPORT A PATTERN CHANGE  
TOWARD TROUGHING IN THE WESTERN U.S. WHILE RIDGING IS INDICATED  
FROM THE PLAINS EASTWARD. HOWEVER...THERE REMAINS NOTABLE  
DIFFERENCES REGARDING THE FORMATION/EVOLUTION OF SMALLER SCALE  
FEATURES THROUGH THE MEDIUM-RANGE PERIOD. THE FIRST FEATURE OF  
CONCERN IS THE POSSIBILITY OF A LOW PRESSURE WAVE DEVELOPING ALONG  
A STALLED FRONT OVER THE SOUTHEAST U.S. DAY 3/FRIDAY. BOTH THE  
GFS AND CANADIAN TAKE THIS LOW JUST OFF THE MID-ATLANTIC AND NEW  
ENGLAND ON SATURDAY. THE ECMWF HAS BEEN THE WEAKEST REGARDING  
THIS FEATURE BUT HAS TRENDED TOWARD A MORE DEVELOPED SOLUTION FOR  
THE LAST FEW RUNS. IT APPEARS THAT SOME FORM OF WAVE DEVELOPMENT  
IS CALLED FOR OVER THE SOUTHEAST U.S. SINCE THE SYSTEM CURRENTLY  
LOCATED IN THE NORTHERN PLAINS APPEARS A BIT ON THE COMPACT SIZE  
FOR THE MODELS TO RESOLVE. THE 06Z GFS SHOWS THE MOST DEVELOPED  
SOLUTION BUT ONLY A SMALL PERCENTAGE IS INCORPORATED INTO THE WPC  
BLEND...OUT OF RESPECT FOR CONTINUITY.  
 
OVER THE WESTERN U.S...THE GFS CONTINUES TO SHOW THE FORMATION OF  
AN UPPER CLOSED LOW NEAR THE CALIFORNIA COAST EARLY NEXT WEEK. IN  
CONTRAST...THE ECMWF REMAINS MUCH FLATTER WITH THIS FEATURE. THE  
06Z GFS AMPLIFIES THIS FEATURE EVEN MORE SO THAN THE 00Z GFS. THE  
GFS SOLUTION IS CONSIDERED AN OUTLIER AT THIS POINT.  
 
THEREFORE...THE WPC MORNING GRID PACKAGE WAS DERIVED MAINLY USING  
THE 00Z ECMWF AND EC MEAN WITH ONLY A SMALL PERCENTAGE OF THE 06Z  
GFS.  
   
..WEATHER/THREATS HIGHLIGHTS
 
 
MILD TEMPERATURES INITIALLY IN THE WEST LATE THIS WEEK WILL SLIDE  
EASTWARD INTO THE PLAINS BY SUNDAY AND INTO THE NORTHEAST NEXT  
TUESDAY. 70S WILL BE FAIRLY WIDESPREAD BY NEXT TUESDAY FROM THE  
OHIO VALLEY INTO PARTS OF NEW ENGLAND. CONVERSELY, THE WEST WILL  
TREND COOLER WITH TIME AS THE UPPER TROUGH SETTLES IN, WITH  
WIDESPREAD RAIN AND SOME HIGH MOUNTAIN SNOW TO WA/OR/ID/MT AND  
ACROSS NORTHERN CA/NV/UT. FARTHER EAST, RETURN FLOW FROM THE  
WESTERN GULF SHOULD BE SUFFICIENT TO SUPPORT MOSTLY  
LIGHT/SCATTERED RAIN OVER THE SOUTHERN ROCKIES INTO THE HIGH  
PLAINS BY THE WEEKEND/NEXT MONDAY. AREAS THAT STAND TO SEE THE  
MOST PRECIPITATION LIE ACROSS SOUTHERN OREGON INTO SOUTHERN  
CENTRAL MONTANA JUST TO THE NORTH OF THE UPPER LOW'S TRACK. OVER  
THE SOUTHEAST U.S....THERE IS AN INCREASING CHANCE OF  
PRECIPITATION FRIDAY AND SATURDAY AS THE POSSIBILITY OF A FRONTAL  
WAVE PASSAGE INCREASES.  
 
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  
 
KONG/FRACASSO  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page