126  
FXUS02 KWBC 290700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT FRI MAR 29 2019  
 
VALID 12Z MON APR 01 2019 - 12Z FRI APR 05 2019  
   
..OVERVIEW
 
 
A RIDGE OVER MAINLAND ALASKA AS OF EARLY MON WILL LIKELY SPLIT  
WITH A PART COLLAPSING TO THE SOUTHEAST AND THE REST REBUILDING  
NORTHWEST TOWARD THE BERING STRAIT AND EASTERN RUSSIA. EVEN WITH  
THIS TRANSITION THERE IS SOME SUPPORT FOR MAINTAINING CYCLONIC  
MEAN FLOW OVER CANADA INTO THE NORTHERN LOWER 48. MEANWHILE  
PERIODIC PACIFIC SHORTWAVES WILL BRING PRECIPITATION TO AREAS  
ACROSS THE WESTERN U.S. AS WELL AS PARTS OF THE CENTRAL/EASTERN  
STATES.  
 
   
..GUIDANCE ASSESSMENT/PREFERENCES
 
 
WITHIN THE FAIRLY AGREEABLE MEAN PATTERN THERE ARE SOME  
SIGNIFICANT ISSUES WITH SPECIFICS. DIFFERENCES IN HANDLING THE  
INITIAL ALASKA RIDGE PLAY AT LEAST A PARTIAL ROLE IN THE  
DIVERGENCE OF SOLUTIONS FOR FLOW ACROSS SOUTHERN CANADA AND  
NORTHERN U.S. THROUGH THE 12-18Z CYCLES THERE ARE TWO GENERAL  
CLUSTERS, ONE INCLUDING THE ECMWF/ECMWF MEAN AND CMC/UKMET WHICH  
SHOW MORE TROUGHING IN WESTERN CANADA AND HIGHER HEIGHTS OVER  
EASTERN CANADA, VERSUS THE GFS/GEFS WHICH KEEP TROUGHING AWAY FROM  
SOUTHWEST CANADA AND BRING A MORE AMPLIFIED TROUGH ACROSS THE  
UPPER MISSISSIPPI VALLEY/GREAT LAKES INTO NEW ENGLAND TUE-WED.  
THE 00Z UKMET HAS ADJUSTED SOMEWHAT CLOSER TO THE GFS UP TO THE  
POINT OF THE TROUGH REACHING THE GREAT LAKES--AFTER WHICH POINT  
THE UKMET TRENDS LESS AMPLIFIED THAN GFS RUNS.  
 
AT THE SAME TIME GUIDANCE SUGGESTS A SHORTWAVE REACHING THE  
SOUTHERN PLAINS BY MON WILL CONTINUE ONWARD AND GENERATE LOW  
PRESSURE ALONG OR OFFSHORE THE SOUTHEASTERN COAST BY TUE. THE  
ECMWF IS IN THE SLOWER PART OF THE SPREAD AND GFS RUNS IN THE  
MIDDLE TO FASTER SIDE OF THE ENVELOPE. BY MID-LATE WEEK, WHAT  
HAPPENS WITH SOUTHERN CANADA/NORTHERN U.S. FLOW WILL AFFECT THE  
FORECAST OF THE SOUTHERN STREAM SYSTEM. FOR NOW GFS RUNS AND SOME  
GEFS MEMBERS ARE IN THE MINORITY WITH THEIR MORE PHASED SCENARIO  
THAT WOULD BRING THE SYSTEM RAPIDLY NORTHWARD INTO/THROUGH THE  
CANADIAN MARITIMES INSTEAD OF SPENDING A LONGER TIME OVER THE  
WESTERN ATLANTIC--ALBEIT WITH VERY UNCERTAIN DURATION OF EFFECTS  
ALONG THE EAST COAST. BASED ON DATA THROUGH THE 18Z CYCLE,  
FORECAST PREFERENCES ENCOMPASSING THESE FEATURES END UP LEANING  
2/3 AWAY FROM THE GFS FOR SOUTHERN CANADA/NORTHERN U.S. FLOW AND  
AN INTERMEDIATE SOLUTION FOR THE SOUTHERN STREAM SYSTEM. HOWEVER  
AN EARLY LOOK AT THE NEW 00Z ECMWF SHOWS A SHIFT TOWARD THE GFS  
SCENARIO WITH BOTH FEATURES SO NEEDLESS TO SAY THERE IS HIGH  
SENSITIVITY IN THIS PATTERN.  
 
LOOKING FARTHER WESTWARD, MOST SOLUTIONS EXPECT ENERGY OFFSHORE  
BRITISH COLUMBIA TO COMBINE WITH A SEPARATE SYSTEM TRACKING TOWARD  
THE WEST COAST AND PRODUCE AN UPPER TROUGH THAT PROGRESSES THROUGH  
THE WEST AROUND MIDWEEK AND THE PLAINS/MISSISSIPPI VALLEY THU-FRI.  
THERE IS STILL POTENTIAL THESE FEATURES MAY NOT MERGE THOUGH. AT  
THE SURFACE LOW PRESSURE WILL LIKELY TRACK INTO THE NORTHWEST  
EARLY IN THE WEEK AND THEN A WAVY FRONTAL SYSTEM SHOULD REACH THE  
CENTRAL/EAST-CENTRAL STATES WED-FRI. NOT SURPRISINGLY THE  
OPERATIONAL MODELS DEVELOP SIGNIFICANT DIFFERENCES WITH SOME  
SPECIFICS AT THE SURFACE AND ALOFT BY THE LATTER HALF OF THE  
PERIOD--FAVORING GREATER EMPHASIS ON THE MEANS AT THAT TIME.  
 
IN THE WAKE OF THIS SYSTEM EXPECT A MODEST RIDGE TO BUILD INTO THE  
WEST COAST/INTERIOR WEST WHILE MORE TROUGH ENERGY PUSHES INTO THE  
EASTERN PACIFIC. THUS FAR GFS RUNS HAVE TENDED TO BE A BIT ON THE  
AGGRESSIVE SIDE OF THE ENVELOPE WITH BRINGING THE ENERGY INTO THE  
RIDGE THOUGH THE 12Z ECMWF STARTS TO BECOME QUESTIONABLY AMPLIFIED  
WITH ITS TROUGH BY LATE FRI. THE ENSEMBLE MEANS ARE FAIRLY CLOSE  
(JOINED IN PRINCIPLE BY THE 18Z FV3 GFS) AND MERIT THE GREATEST  
WEIGHT IN THE FORECAST BY LATE IN THE PERIOD.  
 
...WEATHER HIGHLIGHTS/HAZARDS  
 
EXPECT RAIN/HIGHER ELEVATION SNOW TO SPREAD THROUGH THE NORTHERN  
HALF TO TWO-THIRDS OF THE WEST IN THE MON-WED PERIOD, FOLLOWED BY  
ADDITIONAL PRECIPITATION REACHING THE WEST COAST LATE IN THE WEEK.  
SOME MOISTURE MAY HAVE A CONNECTION TO LOWER LATITUDES. HIGHEST  
PRECIPITATION TOTALS ARE MOST LIKELY OVER NORTHERN  
CALIFORNIA/SIERRA NEVADA WITH ENHANCED ACTIVITY REACHING INTO THE  
NORTHERN/CENTRAL ROCKIES. LOCATIONS ACROSS THE SOUTH AND EAST  
COAST REGIONS MAY SEE A PERIOD OF RAIN (AND POSSIBLY SOME SNOW  
OVER HIGHER ELEVATIONS) WITH THE SYSTEM FORECAST TO TRACK INTO THE  
ATLANTIC. WIDE GUIDANCE SPREAD FOR TRACK AND TIMING KEEPS  
CONFIDENCE LOW WITH RESPECT TO PRECIPITATION COVERAGE AND  
INTENSITY. POCKETS OF LOCALLY MODERATE/HEAVY RAINFALL MAY BE  
POSSIBLE. THE SYSTEM EMERGING FROM THE WEST MAY SPREAD  
PRECIPITATION ALONG A WAVY FRONTAL SYSTEM INTO THE  
PLAINS/MISSISSIPPI VALLEY REGION DURING THE LATTER HALF OF THE  
WEEK. THUS FAR SIGNALS FOR SIGNIFICANT AMOUNTS ARE NOT AGREEABLE  
ENOUGH TO PROVIDE MEANINGFUL CONFIDENCE IN SPECIFICS.  
TEMPERATURES WILL VARY IN ACCORDANCE WITH SYSTEM PROGRESSION. THE  
SOUTH AND EAST WILL BE ON THE CHILLY SIDE EARLY IN THE WEEK WITH  
SOME AREAS OF MINUS 10-20F ANOMALIES. THEN ABOVE NORMAL READINGS  
(MOSTLY PLUS 5-15F ANOMALIES) SHOULD PROGRESS FROM THE WEST AND  
INTO THE CENTRAL/EASTERN STATES OVER THE COURSE OF THE WEEK.  
 
RAUSCH  
 
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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