752  
FXUS02 KWBC 181555  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1155 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. INTO ALBERTA/SASKATCHEWAN WILL MEANDER  
IN PLACE OVER THE NEXT WEEK. 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 COMPACT/ROBUST SURFACE LOW OFF THE  
EASTERN SEABOARD THU NIGHT-FRI. TREND IN THE ENSEMBLE GUIDANCE HAS  
BEEN TOWARD A BIT SLOWER/DEEPER AND CLOSER TO THE COAST SOLUTION,  
FORMING A MIDDLE GROUND BETWEEN THE DEEPER 00Z ECMWF AND 06Z  
FV3-GFS AND WEAKER/QUICKER 00Z/06Z GFS AND 00Z CANADIAN/UKMET.  
THIS BLEND SUFFICED FOR THE WEST/CENTRAL STATES AS WELL GIVEN SOME  
OVERALL MINOR DETAIL DIFFERENCES. 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.  
 
TIMING DIFFERENCES BECOME MORE SIGNIFICANT SAT-MON IN THE WEST AS  
SUBSEQUENT PACIFIC SHORTWAVES MOVE INLAND. IN GENERAL, THE 00Z GFS  
CONTINUED TO BE QUICKER THAN THE CONSENSUS OF OTHER GUIDANCE AND  
WAS EXCLUDED FROM THE FORECAST. 06Z GFS AND 06Z FV3-GFS WERE  
SLOWER LIKE THE ECMWF AND ITS ENSEMBLE MEAN, WHICH HAVE BEEN MUCH  
MORE CONSISTENT WITH THE CROSS-CONTINENTAL FLOW OVER THE PAST  
SEVERAL RUNS COMPARED TO THE GEFS. USED A BLEND OF THOSE SLOWER  
SOLUTIONS WITH CONTINUITY FOR A STARTING POINT WHICH ONLY RESULTED  
IN A FEW MINOR CHANGES TO THE FRONTS, BUT PERHAPS MORE CHANGES TO  
THE POPS GIVEN TIMING UNCERTAINTIES OF RETURN FLOW FROM THE GULF  
THIS WEEKEND.  
 
   
..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 EXPAND 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 THE PACIFIC NORTHWEST AND 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. ABOVE AVERAGE TEMPERATURES ARE EXPECTED TO DEVELOP BY  
LATE THIS WEEK ACROSS THE UPPER MIDWEST AND THEN GRADUALLY SPREAD  
EASTWARD ACROSS THE GREAT LAKES TO THE EASTERN SEABOARD THROUGH  
THE WEEKEND AS SURFACE HIGH PRESSURE MOVES OFFSHORE. 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.  
COOLER THAN AVERAGE TEMPERATURES IN THE SOUTHWEST WILL MODERATE A  
BIT LATE THIS WEEKEND AHEAD OF THE PACIFIC SYSTEM JUST OFFSHORE  
NEXT MONDAY.  
 
FRACASSO/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  
 

 
 
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