746  
FXUS02 KWBC 231601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT SAT MAR 23 2019  
 
VALID 12Z TUE MAR 26 2019 - 12Z SAT MAR 30 2019  
   
..OVERVIEW
 
 
AN UPPER LOW IN THE EASTERN PACIFIC ON DAY 3/TUE WILL APPROACH THE  
WESTERN CONUS ON DAY 4/WED, WITH TROUGHING TRAVERSING THE  
WESTERN/CENTRAL U.S. DAYS 5-7. AT THE SURFACE, FRONTS IN THE WEST  
WILL HELP CREATE HEAVY PRECIPITATION EARLY IN THE PERIOD, AND LOW  
DEVELOPMENT IN THE PLAINS AND MOVEMENT INTO THE MS VALLEY/MIDWEST  
COULD CAUSE HEAVY PRECIPITATION IN THOSE AREAS BY DAY 6-7, BUT  
UNCERTAINTY REMAINS HIGH.  
   
..GUIDANCE ASSESSMENT/PREFERENCES
 
 
FOR DAYS 3-4, A MULTI-MODEL BLEND WORKED WELL FOR THE LARGE-SCALE  
FEATURES WHILE DE-EMPHASIZING THE SMALL-SCALE DIFFERENCES IN THE  
FORECAST--MODELS WERE IN GENERAL AGREEMENT FOR THE UPPER LOW IN  
THE EASTERN PACIFIC MOVING EASTWARD INTO THE CONUS. BY DAY 4-5,  
THE 00Z CMC BECAME MUCH DEEPER WITH THE TROUGH THAN OTHER MODELS,  
AND SENT UPPER-LEVEL ENERGY AROUND THE UPPER HIGH IN THE GULF OF  
ALASKA IN A MANNER THAT SEEMED UNLIKELY, SO DID NOT UTILIZE THE  
CMC FOR THIS FORECAST. ADDITIONALLY, THE OPERATIONAL 00Z ECMWF  
BEGAN EXHIBITING DIFFERENCES FROM ITS MEAN AND OTHER MODELS AT DAY  
5, MOVING THE LARGE UPPER LOW IN CENTRAL CANADA EASTWARD MORE  
QUICKLY. MOVING INTO DAY 6-7, THIS MEANT THAT THE TROUGH IN THE  
CONUS WAS CUT OFF FROM THE NORTHERN STREAM FLOW, AND THUS WAS  
MOVING EASTWARD MORE SLOWLY AND MUCH STRONGER COMPARED TO OTHER  
MODELS, WHICH AFFECTED SURFACE LOW PLACEMENT AS WELL. THERE IS  
PLENTY OF SPREAD IN THE ENSEMBLES IN THE DEGREE OF SEPARATION OF  
THESE FEATURES AND OTHER ASPECTS OF THE CONUS TROUGH'S EVOLUTION,  
BUT PREFERRED TO STAY AWAY FROM THE DETERMINISTIC ECMWF SOLUTION  
FOR NOW IN FAVOR OF THE MEANS. USED THE GEFS AND EC MEANS AT DAY 7  
WITH SOME WPC CONTINUITY, WITH A SLIGHT EMPHASIS ON THE GEFS MEAN  
DUE TO HOW IT HANDLED THE TRANSITIONING PATTERN IN ALASKA.  
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
WITH THE UPPER LOW APPROACHING THE WEST, A COUPLE OF FRONTS WILL  
MAKE THEIR WAY THROUGH THE WEST, AND HEAVY PRECIPITATION IS  
EXPECTED FOR DAY 3-5. HEAVY VALLEY RAIN/MOUNTAIN SNOWS WILL  
THREATEN NORTHERN CALIFORNIA/OREGON THROUGH THE NORTHERN ROCKIES.  
AS THE TROUGH ENERGY EJECTS OUT THROUGH THE WEST, IT IS EXPECTED  
TO INDUCE CYCLO/FRONTOGENESIS IN THE PLAINS, AND THIS PLUS ANOTHER  
COLD FRONT DROPPING SOUTHWARD OUT OF CANADA, AS WELL AS DEEPENING  
RETURN FLOW FROM THE GULF OF MEXICO, WOULD ALL FUEL AN EXPANDING  
RISK OF ENHANCING RAINS/CONVECTION. THE EMERGING HEAVY RAIN AREA  
THREATENS AREAS OF THE MISSISSIPPI VALLEY/MIDWEST (WHERE FLOODING  
IS ONGOING) HEADING INTO NEXT WEEKEND. UNCERTAINTY REMAINS  
REGARDING HEAVIEST RAINFALL AMOUNTS/PLACEMENT, BUT THE GUIDANCE  
SIGNAL FOR DEVELOPMENT CONTINUES TO GROW.  
 
THE COLD FRONT MOVING QUICKLY SOUTHWARD THROUGH THE PLAINS AND  
MISSISSIPPI VALLEY IS EXPECTED TO CHANGE THE ONGOING REGIME OF  
ABOVE AVERAGE TEMPERATURES THERE IN THE SHORT/EARLY MEDIUM RANGE  
PERIOD TO BELOW NORMAL BY DAY 6-7 (FRI-SAT). AHEAD OF THIS FRONT,  
THE EASTERN SEABOARD IS EXPECTED TO BE WARMER THAN AVERAGE BY SAT  
AFTER THE COLD HIGH PRESSURE DOMINATES MIDWEEK.  
 
TATE  
 
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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