491  
FXUS02 KWBC 090515  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
114 AM EDT TUE APR 09 2019  
 
VALID 12Z FRI APR 12 2019 - 12Z TUE APR 16 2019  
   
..MAJOR WINTER STORM TRACKING ACROSS THE UPPER GREAT LAKES FRI
 
 
...HEAVY RAINFALL THREAT FROM EASTERN TEXAS/LOWER MISSISSIPPI  
VALLEY NORTHEASTWARD DURING THE WEEKEND TO MONDAY...  
   
..OVERVIEW AND GUIDANCE ASSESSMENT/PREFERENCES
 
 
THE MEDIUM RANGE PERIOD STARTS WITH THE TAIL END OF THE CENTRAL US  
MAJOR CYCLONE MOVING THROUGH THE UPPER GREAT LAKES FRI AND THEN  
ACROSS THE BORDER INTO CANADA FRI NIGHT, WHEN THE EVENT WINDS DOWN  
OVER THE US. THE MODELS AND ENSEMBLES REMAIN CLUSTERED SO A  
CONSENSUS BASED APPROACH CONTINUES TO BE PREFERRED.  
 
ALSO ON FRI, THE SYSTEM THAT WILL BECOME A PRODUCER OF WIDESPREAD  
PRECIPITATION IN THE LOWER MS VALLEY WITH FLOODING POTENTIAL DIGS  
SOUTH ACROSS THE GREAT BASIN TOWARDS THE SOUTHWEST, WITH A CLOSED  
500 MB LOW POSSIBLY NEAR THE NM/AZ BORDER AT 12Z SAT.  
THE SYSTEM MOVES EAST AFTERWARD ON TO THE SOUTHERN PLAINS AND  
LOWER MS VALLEY BY SUN MORNING, A BIT FASTER THAN THE PRIOR  
CYCLE'S DOMINANT CLUSTER OF SOLUTIONS.  
LOW PRESSURE FORMS AT THE SURFACE AND MOVES STEADILY NORTHEAST  
TOWARDS THE OHIO VALLEY, WITH THE SYSTEM OCCLUDING AND A NEW LOW  
FORMING NEAR THE MID ATLANTIC COAST AND PROCEEDING NORTHEAST NEAR  
OR OFF THE NEW ENGLAND COAST EARLY NEXT WEEK.  
 
THE 12Z ECMWF/12Z ECMWF MEAN SOLUTIONS SHOW A SLOWER PROGRESSION  
OF THE UPPER TROUGH THAN THE GFS RUNS THIS WEEKEND INTO EARLY NEXT  
WEEK AND REMAIN PREFERRED.  
THE 18Z GEFS MEAN WAS AN INTERMEDIATE SOLUTION AND GIVEN A  
MINORITY WEIGHTING TO HEDGE THE TIMING.  
 
THE GUIDANCE SHOWS THE ARRIVAL OF UPSTREAM PACIFIC ENERGY INTO THE  
NORTHWEST BY AROUND DAY 5 SUN AND INTO THE NORTHERN ROCKIES ON DAY  
6 MON, POSSIBLY REACHING THE HIGH PLAINS DAY 7 TUE 16 APR. THE  
12Z ECMWF/12Z CANADIAN/18Z GFS MODELS ALL SHOW DIFFERING TIMING  
AND PHASING OF THE UPPER TROUGH, SO MUCH GREATER WEIGHTING WAS  
GIVEN TO THE RESPECTIVE ENSEMBLE MEANS, ALTHOUGH GREATER WEIGHTING  
WAS GIVEN TO THE ECMWF ENSEMBLE MEAN FOR THIS FORECAST CYCLE.  
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
CONSENSUS STILL DISPLAYS A HIGH POTENTIAL FOR HEAVY SNOWFALL AND  
STRONG WINDS--LEADING TO A PERIOD OF BLOWING SNOW AND POSSIBLE  
BLIZZARD CONDITIONS INTO THE UPPER GREAT LAKES FRI. SOME STRONG  
TO SEVERE CONVECTION WILL BE POSSIBLE FARTHER SOUTH/SOUTHEAST IN  
THE WARM SECTOR IN THE OHIO VALLEY THU. THE LATE WEEK/EARLY  
WEEKEND SYSTEM DIGGING INTO THE WEST WILL SPREAD LIGHT VALLEY RAIN  
AND HIGH ELEVATION SNOW ACROSS THE REGION.  
 
THIS SYSTEM WILL LEAD TO A HEAVY RAINFALL THREAT FROM EASTERN  
TEXAS AND THE LOWER MISSISSIPPI VALLEY REGION INTO THE  
APPALACHIANS, MID-ATLANTIC AND SOUTHERN NEW ENGLAND, AND POSSIBLY  
INCLUDING THE OHIO VALLEY. THE HIGHEST FORECAST RAINFALL AMOUNTS  
ARE CENTERED OVER THE LOWER MS VALLEY.  
 
THE PACIFIC NORTHWEST AND NORTHERN ROCKIES SHOULD SEE ADDITIONAL  
PRECIPITATION AFTER THE LATE WEEK SYSTEM IN ASSOCIATION WITH  
FRONTAL SYSTEMS MOVING ONSHORE AND INLAND.  
 
THE COLD TEMPERATURE ANOMALIES WILL BE OVER THE ROCKIES/PLAINS  
FRI-SAT, BEHIND THE INITIAL GREAT LAKES STORM (PEAKING 20-25  
DEGREES BELOW NORMAL IN THE CENTRAL TO NORTHERN CENTRAL PLAINS.  
ALSO DURING FRI-SAT EXPECT ABOVE NORMAL TEMPERATURES OVER THE  
EAST, ESPECIALLY FOR MORNING LOWS WHICH MAY BE 10-20F ABOVE NORMAL  
IN THE UPPER OHIO VALLEY/APPALACHIANS FRI AND COASTAL MID ATLANTIC  
TO SOUTHERN NEW ENGLAND SAT. EXPECT READINGS TO MODERATE OVER  
MUCH OF THE LOWER 48 EARLY NEXT WEEK, WITH SLIGHTLY BELOW NORMAL  
TEMPS UNDER THE ROCKIES UPPER TROUGH AND ABOVE NORMAL IN RETURN  
FLOW IN THE SOUTHERN TO CENTRAL PLAINS.  
 
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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