670  
FXUS02 KWBC 221600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT FRI MAR 22 2019  
 
VALID 12Z MON MAR 25 2019 - 12Z FRI MAR 29 2019  
   
..OVERVIEW
 
 
THE 00Z AND 06Z SUITE OF MODELS CONTINUED TO PORTRAY GENERAL  
AGREEMENT IN THE OVERALL PATTERN OF AN UPPER LOW IN THE EASTERN  
PACIFIC (OFF THE U.S. WEST COAST), RIDGING INTO THE WESTERN AND  
CENTRAL CONUS, AND A DEEP UPPER LOW IN EASTERN CANADA THAT CREATES  
TROUGHING IN THE EASTERN CONUS ON DAY 3 (MON). THIS PATTERN WILL  
BE SLOW-MOVING ON DAYS 3-5 (MON-WED), BEFORE THE UPPER LOW IN THE  
EASTERN PACIFIC BEGINS BREAKING DOWN AND SENDS ENERGY INTO THE  
WESTERN CONUS BY THU AND THE CENTRAL CONUS ON FRI.  
   
..GUIDANCE ASSESSMENT/PREFERENCES
 
 
DAYS 3-5 IN THE MEDIUM RANGE WERE MARKED BY GENERAL MODEL  
AGREEMENT BETWEEN THE 00Z/06Z GFS, 00Z GEFS, 00Z ECMWF/ITS  
ENSEMBLE, AND THE 00Z UKMET, SO WAS ABLE TO INCLUDE COMPONENTS OF  
ALL THESE MODELS IN THE BLEND, RATHER THAN ATTEMPTING TO SELECT  
WHICH MODEL'S SMALL-SCALE FEATURES WOULD PREVAIL. DID EXCLUDE THE  
CMC FROM THE BLEND AS IT BROKE DOWN THE EASTERN PACIFIC UPPER LOW  
MORE QUICKLY THAN THE OTHER MODELS, BY DAY 5/WED. MODEL SPREAD  
INCREASES QUITE A BIT AS THE UPPER LOW MOVES INTO THE WEST AND  
WEAKENS/BECOMES ASSOCIATED WITH A DEEP TROUGH IN CENTRAL CANADA,  
AS EACH MODEL HANDLES SHORTWAVES EMBEDDED IN THE TROUGH  
DIFFERENTLY. THUS BY DAY 6-7 WE LEANED TOWARD THE 00Z GEFS AND EC  
MEANS, WITH A LOWER PERCENTAGE OF THE OPERATIONAL ECMWF FROM 00Z.  
THE 00Z GFS STRENGTHENED A TROUGH IN THE CENTRAL CONUS MORE THAN  
OTHER MODELS, WHILE THE 06Z GFS FOCUSED ON A TROUGH ORIENTED  
DIFFERENTLY IN THE WESTERN U.S. THE 00Z ECMWF SEEMED LIKE A  
COMPROMISE OF THESE FEATURES AND SEEMED SIMILAR ENOUGH TO THE  
MEANS TO INCORPORATE SOME OF IT, AND WANTED TO STAY AWAY FROM THE  
INCONSISTENCY OF THE GFS RUNS.  
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
THIS MEDIUM RANGE PERIOD STARTS MONDAY/TUESDAY AS A SOUTHERN  
STREAM FRONT WITH SEVERAL MOISTURE/ENHANCED PRECIPITATION FOCUSING  
WAVES EJECTS ACROSS THE SOUTH/SOUTHEAST/AND MID-ATLANTIC. THESE  
WAVES CUT UNDERNEATH/INTERACT WITH A COOLING NORTHERN STREAM  
FRONTAL DRAPE WHOSE POST-FRONTAL HIGH PRESSURE BUILDS DOWN THROUGH  
THE CENTRAL AND EASTERN U.S.  
 
MEANWHILE, A PROTRACTED SERIES OF PACIFIC SYSTEMS WITH ASSOCIATED  
HEIGHT FALLS AND ENHANCED PRECIPITATION SWATHS WILL TRACK ONSHORE  
AND ACROSS MUCH OF THE WEST EARLY THROUGH MID NEXT WEEK IN ADVANCE  
OF AN MEAN CLOSED LOW/TROUGH REINFORCED JUST OFF WEST COAST.  
EXPECT HEAVIEST PRECIPITATION/HEAVY MOUNTAIN SNOWS THREATS FROM  
NORTHERN CALIFORNIA/OREGON TO THE NORTHERN ROCKIES. INDICATION  
THAT THE BULK OF PACIFIC TROUGH ENERGY WILL EJECT THROUGH THE WEST  
WED/THU TO EMERGE OVER THE PLAINS LATER NEXT WEEK TO INDUCE  
CYCLO/FRONTOGENESIS. THIS MAY OCCUR JUST AS A RENEWED NORTHERN  
STREAM MAY FORCE COOL AIR DOWN INTO THE UNSETTLED N-CENTRAL  
STATES. THIS AIRMASS WOULD PROVE TO BE IN STARK CONTRAST TO A  
RAPIDLY WARMING AIRMASS SPREADING OVER THE E-CENTRAL U.S. WHERE  
MOIST GULF RETURN FLOW MAY FUEL AN EXPANDING RISK OF ENHANCING  
RAINS/CONVECTION CHANNELING BETWEEN THE SURGING FRONTS AND  
RETREATING EASTERN U.S. HIGH PRESSURE. THUS, HEAVY RAIN IS  
POSSIBLE SOMEWHERE IN THE MISSISSIPPI VALLEY/MIDWEST (WHERE  
FLOODING IS ONGOING) BY LATE IN THE MEDIUM RANGE PERIOD, BUT  
UNCERTAINTY REMAINS HIGH REGARDING RAINFALL AMOUNTS AND PLACEMENT  
OF THE HEAVIEST RAINFALL.  
 
TATE/SCHICHTEL  
 
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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