143  
FXUS02 KWBC 180557  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
157 AM EDT MON MAR 18 2019  
 
VALID 12Z THU MAR 21 2019 - 12Z MON MAR 25 2019  
   
..OVERVIEW AND GUIDANCE ASSESSMENT/PREFERENCES
 
 
SPLIT FLOW PATTERN IS EXPECTED TO PERSIST ACROSS NORTH AMERICA  
DURING THE EXTENDED PERIOD. ENSEMBLE GUIDANCE SHOWS GOOD CONSENSUS  
THAT A STRONG AND BLOCKING UPPER-LEVEL RIDGE AXIS INITIALLY ACROSS  
THE HIGH PLAINS OF THE U.S. AND CANADA WILL VERY SLOWLY SHIFT  
EASTWARD OVER THE NEXT WEEK. WITH THE STRONGEST POSITIVE HEIGHT  
ANOMALIES REMAINING CENTERED ACROSS NORTH CENTRAL CANADA, THIS  
WILL CONTINUE TO SPLIT INCOMING ENERGY FROM THE PACIFIC INTO  
NORTHERN STREAM COMPONENTS DIRECTED NORTHWARD TOWARD ALASKA, AND  
SOUTHERN STREAM COMPONENTS THAT TRAVERSE THE SOUTHERN/CENTRAL  
U.S., UNDERCUTTING THE RIDGE. DOWNSTREAM OF THE RIDGE, THE  
NORTHEAST WILL BE SUBJECT TO CONTINUED MEAN TROUGHING, REINFORCED  
BY A SERIES OF ENERGETIC SHORTWAVES. SOME GUIDANCE SUGGESTS THAT  
PERHAPS THIS NORTHERN STREAM AMPLIFIED RIDGE/TROUGH PATTERN MAY  
BEGIN TO WEAKEN BY EARLY NEXT WEEK, BUT CONFIDENCE IN THAT IS  
RELATIVELY LOW AT THIS TIME GIVEN INCREASED SPREAD AMONG THE  
ENSEMBLE GUIDANCE AS TO THE INTENSITY AND DURATION OF THE UPPER  
RIDGE.  
 
MODEL DEPICTIONS ARE NOW RELATIVELY SIMILAR WITH RESPECT TO THE  
UPPER LOW/TROUGH CROSSING THE FOUR CORNERS THU-FRI AND EXITING  
INTO THE PLAINS FRI NIGHT-SAT. FARTHER EAST, SOLUTIONS DIFFER MORE  
SIGNIFICANTLY WITH RESPECT TO SMALL SCALE NORTHERN STREAM  
SHORTWAVE ENERGY TRAVERSING THE LARGER MEAN TROUGH, AND THE  
POTENTIAL FOR DEVELOPMENT OF A SURFACE LOW OFF THE EASTERN  
SEABOARD THU NIGHT-FRI. THE MAJORITY OF SOLUTIONS KEEP ANY WAVE OF  
LOW PRESSURE RELATIVELY WEAK OFF THE U.S. EAST COAST, DELAYING  
SIGNIFICANT INTENSIFICATION UNTIL THE FEATURE NEARS THE CANADIAN  
MARITIMES WHERE IT POTENTIALLY INTERACTS WITH ADDITIONAL SHORTWAVE  
ENERGY. FINALLY, MODELS SHOW GENERAL CONSENSUS THAT AN ANOTHER  
SHORTWAVE/FRONTAL SYSTEM SHOULD REACH THE WEST COAST FRI-SAT, WITH  
RELATIVELY MINOR TIMING AND AMPLITUDE DIFFERENCES THROUGH SAT.  
BASED ON THESE FACTORS AND AN ASSESSMENT OF MODERATE CONFIDENCE, A  
BLEND OF THE ECMWF/GFS/UKMET WAS USED A BASIS FOR THE FORECAST  
DURING DAYS 3-5.  
 
TIMING DIFFERENCES BECOME MORE SIGNIFICANT AS THE SECOND PACIFIC  
SHORTWAVE MOVES INLAND BY SUN, WITH THE GFS PERSISTING IN A MUCH  
QUICKER PROGRESSION RELATIVE TO THE SLOWER ECMWF/CMC AND ENSEMBLE  
MEANS. THE SAME HOLDS TRUE REGARDING YET ANOTHER POTENTIAL SYSTEM  
APPROACHING THE WEST COAST. THE GFS CONTINUES TO BE QUICKER THAN  
THE CONSENSUS OF OTHER GUIDANCE IN BRINGING ANOTHER AMPLIFIED  
TROUGH/UPPER LOW TO THE WEST COAST BY SUN NIGHT-MON. GIVEN THESE  
DIFFERENCES, THE GFS WAS EXCLUDED FROM THE FORECAST DURING DAYS  
6-7, WITH THE FORECAST BASED ON A BLEND OF THE ECMWF AND THE  
ECENS/GEFS ENSEMBLE MEANS.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
RAIN AND HIGH ELEVATION SNOWS ARE EXPECTED ACROSS THE  
SOUTHERN/CENTRAL ROCKIES THU-FRI AS THE LEADING PACIFIC SYSTEM  
PASSES THE REGION. INCREASING MOISTURE RETURN AHEAD OF THE SYSTEM  
WILL INCREASE COVERAGE OF SHOWERS AND SOME THUNDERSTORMS ACROSS  
THE SOUTHERN/CENTRAL HIGH PLAINS BY FRIDAY. THE NEXT SYSTEM WILL  
BRING ANOTHER ROUND OF RAIN/SNOW TO PACIFIC NORTHWEST TO THE  
ROCKIES FRI-SAT, WITH FURTHER INCREASED POTENTIAL FOR RAIN AND  
THUNDERSTORMS, SOME OF WHICH COULD BE HEAVY, FROM THE  
SOUTHERN/CENTRAL PLAINS TO THE MISSISSIPPI VALLEY THROUGH THE  
WEEKEND. AS THE UPPER RIDGE MOVES SLOWLY EAST, ABOVE AVERAGE  
TEMPERATURES ARE EXPECTED TO DEVELOP BY LATE THIS WEEK ACROSS THE  
MIDWEST, GRADUALLY SPREADING EAST ACROSS THE GREAT LAKES TO THE  
EASTERN SEABOARD THROUGH THE WEEKEND. MAXIMUM TEMPERATURES RANGING  
FROM 5 TO 15 DEG F ABOVE AVERAGE ARE FORECAST, WITH MINIMUM  
TEMPERATURES APPROACHING 20 DEG ABOVE AVERAGE FOR SOME AREAS  
ACROSS THE MIDWEST AND MISSISSIPPI VALLEY.  
 
RYAN  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page