451  
FXUS02 KWBC 150542  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
142 AM EDT FRI MAR 15 2019  
 
VALID 12Z MON MAR 18 2019 - 12Z FRI MAR 22 2019  
   
..OVERVIEW
 
 
A BLOCKING MID/UPPER-LEVEL RIDGE INITIALLY CENTERED FROM THE  
PACIFIC NORTHWEST TO WESTERN CANADA EARLY NEXT WEEK IS EXPECTED TO  
VERY SLOWLY SHIFT EASTWARD THROUGH THE FORECAST PERIOD. WITH THE  
RIDGE AXIS ACROSS WESTERN NORTH AMERICA EARLY NEXT WEEK, A MEAN  
TROUGH WILL BE IN PLACE ACROSS THE GREAT LAKES/NORTHEAST, WITH  
NUMEROUS SMALL SCALE SHORTWAVES TRAVERSING THE LARGER TROUGH.  
STRONG WESTERLY FLOW ACROSS THE NORTH CENTRAL PACIFIC WILL SPLIT  
AS IT ENCOUNTERS THE RIDGE, WITH SOME SHORTWAVE ENERGY DIRECTED  
NORTH INTO THE HIGHER LATITUDES OF CANADA, AND SOME SEPARATING  
INTO THE SOUTHERN STREAM. BY THE LATTER PORTION OF NEXT WEEK AS  
THE WESTERN RIDGE AXIS SHIFTS EAST, THIS MAY ALLOW FOR STRONGER  
HEIGHT FALLS FROM THE NORTH PACIFIC TO APPROACH THE PACIFIC  
NORTHWEST.  
 
   
..GUIDANCE ASSESSMENT/PREFERENCES
 
 
IN GENERAL A BLEND OF DETERMINISTIC MODELS (ECMWF/GFS/CMC/UKMET)  
SERVED AS A GOOD FORECAST STARTING POINT DURING DAYS 3-5  
(MON-WED). OVERALL, SPREAD WAS RELATIVELY LOW DURING THIS TIME  
FRAME. MODELS DIFFERED ON THE AMPLITUDE OF A NORTHERN STREAM  
TROUGH DIGGING INTO THE CENTRAL U.S. TUE-WED, BUT NO CLEAR  
OUTLIERS WERE EVIDENT AND A CONSENSUS APPROACH WAS PREFERRED.  
MODELS WERE ALSO INITIALLY VERY SIMILAR WITH HANDLING OF AN  
AMPLIFIED SOUTHERN STREAM SHORTWAVE/UPPER LOW APPROACHING  
CALIFORNIA BY WED. DIFFERENCES IN AMPLITUDE EMERGE AS THE SYSTEM  
APPROACHES THE COAST, WITH THE GFS WEAKER AND FASTER THAN THE  
CONSENSUS OF THE ECMWF/UKMET/CMC WHICH SHOW A DEEPER SYSTEM AND  
SLOWER PROGRESSION. FOR THIS REASON, THE GFS FROM 12Z THU (WHICH  
WAS CLOSER TO THE MODEL/ENSEMBLE CONSENSUS) WAS USED IN THE BLEND  
OVER THE LATER RUNS. BY DAYS 6-7 (THU-FRI), SPREAD GRADUALLY  
INCREASES AS THE SOUTHERN STREAM SYSTEM MOVES EAST INTO THE FOUR  
CORNERS REGION AND STRONGER HEIGHT FALLS APPROACH THE PACIFIC  
NORTHWEST. WEIGHTING OF THE ECENS AND NAEFS ENSEMBLE MEANS WAS  
BOOSTED DURING THIS TIME PERIOD TO ACCOUNT FOR THE INCREASED SPREAD  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
A LINGERING FRONTAL BOUNDARY SOUTH OF THE FLORIDA PENINSULA (WITH  
A WAVE OF LOW PRESSURE DEVELOPING ALONG IT) WILL SUPPORT  
WIDESPREAD AND POTENTIALLY HEAVY RAINS FOR THE SOUTHERN HALF OF  
THE FLORIDA PENINSULA MON-TUE. THE SOUTHERN STREAM TROUGH/UPPER  
LOW WILL SPREAD RAIN AND MOUNTAIN SNOW INTO THE SIERRA NEVADA, THE  
GREAT BASIN, AND THE CENTRAL/SOUTHERN ROCKIES BY THE MIDDLE TO  
LATTER PORTION OF NEXT WEEK. PRECIPITATION SHOULD INCREASE IN  
COVERAGE ACROSS THE PACIFIC NORTHWEST BY LATE THE WEEK AS THE  
UPPER-LEVEL TROUGH APPROACHES. TEMPERATURES WILL INITIALLY BE 5 TO  
10 DEG F BELOW AVERAGE EARLY NEXT WEEK ACROSS THE EASTERN THIRD OF  
THE U.S. UNDER THE INFLUENCE OF THE GREAT LAKES/NORTHEAST UPPER  
TROUGH, BUT TEMPERATURES ACROSS THESE AREAS WILL GRADUALLY  
MODERATE TO NEAR SEASONAL AVERAGES BY THE MID-LATTER PORTION OF  
THE WEEK AS THE TROUGH LIFTS OUT. MUCH OF THE WEST WILL START NEXT  
WEEK 5 TO 10 DEG ABOVE AVERAGE, AND THE WARM TEMPERATURES WILL  
GRADUALLY SHIFT EAST THROUGH THE WEEK ALONG WITH THE UPPER RIDGE.  
TEMPERATURES ACROSS THE MIDWEST COULD REACH 15 DEG ABOVE AVERAGE  
BY LATE NEXT WEEK.  
 
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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