442  
FXUS02 KWBC 050657  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
256 AM EDT FRI APR 05 2019  
 
VALID 12Z MON APR 08 2019 - 12Z FRI APR 12 2019  
   
..OVERVIEW AND GUIDANCE ASSESSMENT
 
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS DERIVED FROM A BLEND OF THE  
12 UTC ECMWF AND 12Z ECMWF/GEFS ENSEMBLE MEANS. THESE GUIDANCE  
OPTIONS WERE WELL CLUSTERED WITH THE FORECAST EVOLUTION OF THE  
LARGER SCALE SYSTEMS. A COMPOSITE BLEND PROVIDED GOOD RUN TO RUN  
CONTINUITY AND ADDRESSES MINOR TIMING/INTENSITY DIFFERENCES.  
   
..WESTERN AND CENTRAL US
 
 
THE MODELS SHOW TWO PRIMARY UPPER LEVEL TROUGHS THAT MOVE ONSHORE  
ACROSS THE WEST COAST FROM THE EASTERN PACIFIC AND SPREAD INLAND.  
THE INITIAL TROUGH IS OFFSHORE OVER THE NORTHEAST PACIFIC 12Z MON,  
AND MOVES ONSHORE AFTER 00Z, AN DIN MOST SOLUTIONS ONSHORE BY 12Z  
TUE 09 APR. THE MODELS SHOW STEADY FORWARD PROGRESSION ACROSS THE  
ROCKIES AND THEN HIGH PLAINS BY 12Z WED.  
 
THE 12Z ECMWF AND 18Z GFS RUNS CONTINUE TO SHOW ONCE THE UPPER  
TROUGH REACHES THE HIGH PLAINS,  
THE LOW REFORMS IN THE HIGH CENTRAL PLAINS AND INTENSIFIES INTO A  
STRONG CYCLONE WED AS THE CYCLONE MOVES NORTHEAST, REACHING THE MS  
VALLEY BY 12Z THU AND THEN THE GREAT LAKES BY 12Z FRI 12 APR. THE  
12Z ECMWF WAS ON THE NORTHWEST FRINGE OF THE SUITE OF FORECAST  
MODELS/MEMBERS  
 
UPSTREAM, AN UPPER LEVEL TROUGH ENERGY REACHING THE NORTHEASTERN  
PACIFIC IS EXPECTED TO REACH THE WEST COAST THU 11 APR, AMPLIFYING  
AS IT CONTINUES INLAND ON FRI 12 APR. THERE IS BETTER THAN AVERAGE  
AGREEMENT AMONG THE 18Z GEFS MEAN/12Z ECMWF ENSEMBLE MEAN, AND 12Z  
ECMWF TO WARRANT A CONSENSUS OF THESE SOLUTIONS TO BE USED IN THE  
FORECAST (FOR EXAMPLE, THE 12Z FRI SURFACE LOW POSITIONS OVER  
SOUTHERN NV NEAR THE AZ BORDER ARE CLOSE AMONG THE 12Z  
ECMWF/19-00Z GFS MODELS AND THE 12Z ECMWF AND 18Z GEFS ENSEMBLE  
MEANS).  
   
..EASTERN US
 
 
A LEADING UPPER TROUGH OVER THE GREAT LAKES MON WITH A SURFACE LOW  
AND TRAILING WAVY COLD FRONT PROGRESS SLOWLY EAST WITH MODELS  
MODELS INDICATING TRIPLE POINT LOW DEVELOPMENT ALONG THE NEW  
ENGLAND COAST EARLY TUE AND THEN MOVING OFFSHORE THEREAFTER. THE  
TRAILING COLD FRONT MOVES OFF THE SOUTHEAST COAST ON WED WITH  
BUILDING HIGH PRESSURE IN THE LAKES PRODUCING COLD AIR ADVECTION  
ACROSS THE NORTHEAST AND MID ATLANTIC.  
 
THE NEXT CLOSED LOW COMING OUT OF THE CENTRAL US ON DAY 6 IS  
FORECAST TO MOVE TOWARDS THE GREAT LAKES DAY 7. THE RESPECTIVE  
ENSEMBLE MEANS FROM THE 18Z GEFS AND 12Z ECMWF PRODUCED A LOW  
POSITION IN BETWEEN THE OPERATIONAL 12Z ECMWF AND 18Z GFS,  
PROVIDING AN INTERMEDIATE SOLUTION THAT IS WHERE WE WOULD USUALLY  
INDICATE A PREFERRED CYCLONE POSITION IN BETWEEN THE 12Z ECMWF AND  
18Z GFS FORECASTS IN MOST CASES. THE LOW WOULD INDUCE A WARM  
FRONT TO MOVE NORTH ACROSS THE MID ATLANTIC TOWARDS LONG ISLAND  
AND SOUTHERN NEW ENGLAND FRI 12 APR.  
THE 00Z GFS HAS COME IN WITH A FORWARD PROGRESSION THAT IS MUCH  
FASTER, AND APPEARS TO BE AN OUTLIER SOLUTION, SO IS CONSIDERED  
LOW PROBABILITY, PARTICULARLY GIVEN .  
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
AREAS OF TERRAIN-ENHANCED RAIN AND HIGHER ELEVATION SNOW ARE  
FORECAST FROM NORTHERN CALIFORNIA AND OREGON INTO IDAHO, SOUTHERN  
MONTANA, AND WYOMING EARLY NEXT WEEK. CURRENT GUIDANCE SUGGESTS  
BEST POTENTIAL FOR HEAVIEST ACTIVITY WILL BE CENTERED ALONG THE  
WEST COAST NEAR THE CALIFORNIA/OREGON BORDER AND THE OREGON  
CASCADES.  
 
CONTINUED PROGRESSION OF THIS SYSTEM SHOULD SPREAD PRECIPITATION  
ACROSS THE NORTH-CENTRAL ROCKIES, PLAINS, MID-UPPER MISSISSIPPI  
VALLEY, AND EVENTUALLY OHIO VALLEY AND GREAT LAKES. SOME ACTIVITY  
MAY BE HEAVY AND AREAS WITH ONGOING FLOODING CONCERNS WILL NEED TO  
MONITOR THIS SYSTEM. IN ADDITION THERE IS POTENTIAL FOR STRONG  
WINDS TO BE AN ISSUE NORTH OF THE LOW PRESSURE CENTER AS IT TRACKS  
FROM THE CENTRAL PLAINS TOWARDS THE LAKES. THERE IS ALSO A THREAT  
OF SNOW IN THE NORTHERN PERIPHERY OF THE PRECIP SHIELD FROM THE  
N-CENTRAL PLAINS TO THE UPPER MIDWEST.  
 
THE EASTERN HALF OF THE COUNTRY WILL SEE A BROAD AREA OF  
PRECIPITATION WITH THE SYSTEM PROGRESSING EASTWARD FROM THE LOWER  
MISSISSIPPI VALLEY AND CENTRAL GULF COAST REGION AND SOUTHERN  
APPALACHIANS EARLY NEXT WEEK. CONVECTION MAY BE STRONG TO SEVERE  
OVER SOUTHERN AREAS. CHECK THE SPC OUTLOOKS FOR THE LATEST  
PROBABILITIES. SIGNIFICANT RAINFALL IS ALSO POSSIBLE FROM THE  
OHIO VALLEY INTO NORTHERN MID-ATLANTIC/NORTHEAST. SNOW SHOULD BE  
CONFINED MOSTLY TO NORTHERN NEW ENGLAND MON-WED IN THIS PATTERN AS  
MOISTURE ADVECTS NORTHWARD INTO A COOLED/RECEDING SURFACE RIDGE.  
 
THE WARM SECTOR OF THE CENTRAL-EASTERN U.S. SYSTEM MON WILL  
PROVIDE MUCH ABOVE NORMAL TEMPERATURES. MORNING LOWS WILL BE  
PARTICULARLY ANOMALOUS WITH MANY LOCATIONS 15-25F ABOVE NORMAL MON  
IN THE OHIO VALLEY TO CENTRAL APPALACHIANS AND DAILY RECORD WARM  
LOW VALUES MAY BE CHALLENGED. ON TUE THE ANOMALIES OF 15-20F  
ABOVE NORMAL FOR THE MIN TEMPERATURES SHIFT TO THE MID ATLANTIC  
STATES, AND IN SOUTHERN NV TO WESTERN AZ. AS THE WESTERN SYSTEM  
MOVES EAST, THOSE SOUTHWEST WARM TEMPS SHIFT INTO THE SOUTHERN  
PLAINS FOR WED MORNING, AND THEN LOWER MS VALLEY FOR THU MORNING,  
FOLLOWED BY THE APPALACHIANS TO EAST COAST FRI MORNING 12 APR.  
 
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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