948  
FXUS02 KWBC 100641  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
240 AM EDT FRI MAY 10 2019  
 
VALID 12Z MON MAY 13 2019 - 12Z FRI MAY 17 2019  
 
 
TONIGHT'S FORECASTS WERE DERIVED FROM A BLEND OF THE LATEST  
DETERMINISTIC 12/18Z GFS /12Z ECMWF EQUALLY WEIGHTED WITH THE 12Z  
ECMWF/18Z GEFS ENSEMBLE MEANS DAYS 3-7.  
MODELS REMAINS SPLIT ON THE LATITUDE OF THE LOW DEVELOPING OFF THE  
MID-ATLANTIC COASTLINE SUN NIGHT-MON. THE 12Z ECMWF/ECMWF ENSEMBLE  
MEAN REMAIN FARTHER NORTH THAN MUCH OF THE OTHER GUIDANCE. THE 12Z  
UKMET WAS IN BETWEEN THE ECMWF AND FURTHER SOUTH GFS FORECASTS  
MON-TUE 14 MAY, AND THE FORECAST IS CLOSEST TO THE 12Z UKMET AS AN  
INTERMEDIATE SOLUTION.  
 
THE MODELS SHOW AN UPPER LEVEL LOW NEAR THE AZ/NM BORDER WITH  
MEXICO 12Z MON THAT SLOWLY MOVES EAST AND SHEARS INTO AN UPPER  
TROUGH AS IT PROGRESSES ACROSS THE SOUTHERN PLAINS/LOWER  
MISSISSIPPI VALLEY THROUGH THE PERIOD. MINOR TIMING DIFFERENCES  
WITH THE LOW/WAVE LED TO A CONSENSUS-BASED FORECAST, WITH THE GFS  
TYPICALLY FASTER. BLENDING WITH THE SLOWER 12Z ECMWF AND ECMWF  
ENSEMBLE MEAN PROVIDED A DESIRED MIDDLE GROUND.  
 
ELSEWHERE, MODELS HAVE TYPICAL TIMING/AMPLITUDE DIFFERENCES WITH  
NORTHERN STREAM ENERGY DIVING FROM THE UPPER MS VALLEY INTO THE  
MIDWEST/GREAT LAKES TUE NIGHT TO WED AND CROSSING THE CENTRAL  
APPALACHIANS/MID ATLANTIC/COASTAL WATERS WED-THU, WITH POTENTIAL  
LOW PRESSURE DEVELOPMENT OFF THE COAST FRI 17 MAY IN THE 12Z  
ECMWF/12-18Z GFS. THE LESS AMPLIFIED ECMWF ENSEMBLE MEAN AND 18Z  
GEFS MEAN HIGHLIGHT DIFFERENCES TO BE RESOLVED. AN INTERMEDIATE  
SOLUTION WAS USED UNTIL BETTER AGREEMENT DEVELOPS.  
 
BROAD AGREEMENT AMONGST THE MODELS/ENSEMBLES SUPPORTS AN AMPLIFIED  
UPPER TROUGH REACHING THE WEST COAST BY WED 15 MAY, WITH A  
SECONDARY TROUGH REACHING THE WEST COAST THU 16 MAY, WHICH THEN  
MOVES INLAND INTO THE GREAT BASIN AND TOWARDS THE PACIFIC  
NORTHWEST COAST FRI 17 MAY. MODELS DIFFER ON THE EXACT TIMING AND  
PHASING OF THE TROUGH, BUT IT IS EVIDENT IN EACH OF THE  
ECMWF/GFS/CANADIAN MODELS AND THEIR MEANS. A BLEND SHOULD SMOOTH  
OUT DIFFERENCES.  
   
..WEATHER HIGHLIGHTS/THREATS
 
 
EXPECT SHOWERS OVER THE NORTHERN MID ATLANTIC TO NEW ENGLAND AS  
CONSOLIDATION OF LOW PRESSURE OFF THE NORTHEASTERN COAST OCCURS,  
WITH THE SYSTEM MOVING SLOWLY. CONFIDENCE IN SPECIFICS REMAINS  
LOWER THAN DESIRED IN LIGHT OF PERSISTENT MODEL SPREAD. SOME OF  
THE PRECIPITATION COULD FALL IN THE FORM OF SNOW OVER HIGHEST  
ELEVATIONS OF NORTHERN NEW HAMPSHIRE AND WESTERN MAINE AS THE CORE  
OF THE UPPER TROUGH PASSES THROUGH.  
 
A COLD FRONT DROPPING SOUTHEAST FROM THE NORTHERN PLAINS MAY  
SPREAD SHOWERS FROM THE UPPER MS VALLEY, UPPER MIDWEST/GREAT  
LAKES/OHIO VALLEY DURING THE EARLY TO MIDDLE PORTIONS OF NEXT WEEK.  
 
THE UPPER LOW TRACKING FROM THE WESTERN U.S.-MEXICO BORDER INTO  
THE SOUTHERN PLAINS WILL BE RESPONSIBLE FOR LOCALLY ENHANCED AREAS  
OF SHOWERS/STORMS OVER THE SOUTHERN PLAINS AND WESTERN GULF COAST  
IN THE EARLY TO MIDDLE PORTIONS OF NEXT WEEK. SHOWERS/STORM ALSO  
DEVELOP IN THE VICINITY OF A STATIONARY FRONT LINGERING OVER THE  
FL PENINSULA IN THE MIDDLE OF NEXT WEEK.  
 
THE UPPER TROUGH NEARING THE WEST COAST SHOULD BRING INCREASED  
CLOUDS/PRECIPITATION TO THE PACIFIC NORTHWEST AND CA WED 15 MAY  
AND CONTINUING INLAND INTO THE GREAT BASIN AND NORTHERN ROCKIES  
THU 16 MAY.  
 
SHORT-RANGE WARMTH OVER THE NORTHWEST WILL CONTINUE INTO THE FIRST  
HALF OF NEXT WEEK,  
WITH HIGHS OF 10-20F ABOVE NORMAL OVER THE INTERIOR NORTHWEST AND  
NORTHERN ROCKIES MON-TUE. THE WARM CORE MOVES EAST INTO THE  
ROCKIES AND CENTRAL PLAINS IN THE MIDDLE OF THE WEEK WITH COOLING  
OVER THE NORTHWEST. WITH THE APPROACHING TROUGH, CA/OR/WA WILL SEE  
A REVERSAL TO COOLER THAN NORMAL TEMPERATURES IN THE MIDDLE TO  
LATTER PORTIONS OF NEXT WEEK.  
 
THE SYSTEM AFFECTING THE MID ATLANTIC, GREAT LAKES, AND NORTHEAST  
MON-TUE WILL KEEP HIGHS 10-15F OR SO BELOW NORMAL, WITH GRADUAL  
MODERATION AS THE TROUGH MOVES OFFSHORE  
WED AND THU 16 MAY.  
 
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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