539  
FXUS02 KWBC 030658  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
157 AM EST SUN MAR 3 2019  
 
VALID 12Z WED MAR 6 2019 - 12Z SUN MAR 10 2019  
   
..WEATHER PATTERN DESCRIPTION
 
 
THE FLOW ACROSS THE CONUS WILL BEGIN THE MEDIUM RANGE IN A RATHER  
AMPLIFIED SETUP, AND THEN GRADUALLY TREND MORE ZONAL AND  
PROGRESSIVE BY THE MID TO LATTER PORTION OF THE FORECAST PERIOD.  
SHORTWAVE ENERGY EJECTING FROM A MEAN UPPER TROUGH OFF THE WEST  
COAST WILL CROSS THE COUNTRY EVERY COUPLE DAYS. MEANWHILE, A BROAD  
UPPER TROUGH INITIALLY IN PLACE ACROSS THE GREAT LAKES/NORTHEAST  
SHOULD GRADUALLY LIFT OUT BY THE MIDDLE TO END OF THE UPCOMING  
WORK WEEK.  
 
   
..MODEL GUIDANCE EVALUATION AND PREFERENCES
 
 
THE MEDIUM RANGE FORECAST PERIOD BEGINS ON WEDNESDAY WITH A WEST  
COAST TROUGH AND BROAD CYCLONIC FLOW ENCOMPASSING THE EASTERN HALF  
OF THE NATION, WITH A BROAD UPPER RIDGE OVER THE ROCKIES.  
NOTEWORTHY MODEL DIFFERENCES APPEAR AS EARLY AS DAY 4 (THURSDAY)  
WITH THE BREAK DOWN OF THE RIDGE AS PACIFIC ENERGY LOWERS HEIGHTS  
AND A QUASI-ZONAL FLOW PATTERN RETURNS. THE FV3, ECMWF, AND UKMET  
WERE IN REASONABLY GOOD AGREEMENT ON THE PASSAGE OF SHORTWAVE  
ENERGY ACROSS THE HIGH PLAINS AND UPPER MIDWEST THROUGH THURSDAY  
AND FRIDAY, WHILE THE GFS WAS MORE AMPLIFIED. EVEN GREATER MODEL  
DIFFERENCES RESIDE ACROSS THE WEST COAST REGION FOR FRIDAY AND  
BEYOND, WITH THE CMC MUCH SLOWER WITH THE TROUGH AXIS PROGRESSION.  
THIS LARGE SCALE TROUGH AND EVENTUAL EVOLUTION INTO A CLOSED  
UPPER LOW WILL EVENTUALLY SPAWN THE DEVELOPMENT OF A STRONG  
SURFACE LOW ACROSS THE CENTRAL U.S. ALTHOUGH THE CHANCES ARE GOOD  
THAT A STRONG STORM SYSTEM WILL DEVELOP, THERE ARE MAJOR  
DIFFERENCES IN THE PLACEMENT AND TRACK OF THE LOW, SO FUTURE  
FORECASTS ARE LIKELY TO CHANGE SIGNIFICANTLY IN THE COMING DAYS  
SINCE CONFIDENCE IS BELOW AVERAGE IN THIS PORTION OF THE FORECAST.  
 
GIVEN THESE CONSIDERATIONS, THE FORECAST WAS INITIALLY BASED ON A  
MULTI-MODEL DETERMINISTIC BLEND (12Z ECMWF/UKMET/FV3) DURING DAYS  
3-5 (WEDNESDAY THROUGH FRIDAY). FOR NEXT WEEKEND, THE FORECAST WAS  
MAINLY DERIVED FROM ENSEMBLE MEAN (ECENS AND NAEFS) WEIGHTING,  
WITH SOME CONTINUED EMPHASIS ON THE 12Z ECMWF/FV3 SOLUTIONS AS  
WELL.  
 
   
..SENSIBLE WEATHER AND POTENTIAL HAZARDS
 
 
ALTHOUGH THE COLDEST TEMPERATURES WILL BE PRIOR TO THE START OF  
THIS FORECAST PERIOD, IT WILL STILL BE VERY COLD BY EARLY MARCH  
STANDARDS ACROSS MUCH OF THE CENTRAL AND EASTERN U.S. ON WEDNESDAY  
AND THURSDAY. A LARGE ARCTIC HIGH WILL ENCOMPASS MUCH OF THE U.S.  
EAST OF THE ROCKIES, AND TEMPERATURES ONLY SLOWLY MODERATE BY THE  
END OF THE WEEK WITH ANOMALIES OF 15 TO 30 DEGREES BELOW NORMAL  
THROUGH THURSDAY, AND A SECOND SURGE OF COLD TEMPERATURES IS  
EXPECTED FOR THE NORTHERN PLAINS AND UPPER MIDWEST THROUGH NEXT  
WEEKEND, KEEPING READINGS ABOUT 20 DEGREES BELOW NORMAL. HOWEVER,  
MUCH OF THE SOUTHERN AND EASTERN U.S. WARMS UP TO NEAR AVERAGE  
LEVELS BY THE WEEKEND AS A STORM SYSTEM GATHERS STRENGTH ACROSS  
THE PLAINS.  
 
HEAVY RAIN AND MOUNTAIN SNOW RETURN TO THE WESTERN U.S. BY TUESDAY  
NIGHT AS AN ATMOSPHERIC RIVER EVENT ACCOMPANIES A STRONG PACIFIC  
LOW HEADED TOWARDS CALIFORNIA. THE SIERRA NEVADA WILL LIKELY GET  
AN ADDITIONAL 1 TO 3 FEET OF SNOW, THUS ADDING TO ITS EXTENSIVE  
SNOW PACK. SIGNIFICANT SNOW IS FORECAST FOR THE CENTRAL AND  
NORTHERN ROCKIES ON WEDNESDAY AND THURSDAY AS THE MOISTURE PLUME  
ADVECTS INLAND, ALBEIT NOT TO THE SAME DEGREE AS CALIFORNIA.  
 
WITH A LARGE STORM SYSTEM POSSIBLY AFFECTING THE CENTRAL U.S. NEXT  
WEEKEND, WIDESPREAD RAIN IS EXPECTED TO DEVELOP FROM PORTIONS OF  
THE LOWER/MID-MISSISSIPPI VALLEY TO THE OHIO VALLEY AND  
APPALACHIANS AS A RICH SUPPLY OF GULF MOISTURE SURGES NORTHWARD.  
DEPENDING ON WHERE THE SURFACE LOW DEVELOPS, A BAND OF HEAVY SNOW  
AND WINDY CONDITIONS ARE POSSIBLE ACROSS PARTS OF THE NORTHERN  
PLAINS, UPPER MIDWEST, AND WESTERN GREAT LAKES REGION.  
 
D. HAMRICK  
 
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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