628  
FXUS02 KWBC 010700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 AM EDT MON APR 01 2019  
 
VALID 12Z THU APR 04 2019 - 12Z MON APR 08 2019  
   
..OVERVIEW
 
 
THE FORECAST OF THE OVERALL PATTERN HAS CHANGED LITTLE OVER RECENT  
DAYS, WITH A STEADY PROGRESSION OF PACIFIC FEATURES INTO THE WEST  
AND CONTINUING ONWARD PRODUCING ONE OR MORE EPISODES OF ACTIVE  
WEATHER OVER A DECENT PORTION OF THE LOWER 48. HEAVIEST  
PRECIPITATION DURING THE THU-MON PERIOD SHOULD EXTEND FROM THE  
CENTRAL/NORTHERN WEST COAST INTO THE NORTHERN ROCKIES AS WELL AS  
OVER AND SLIGHTLY EAST OF THE SOUTHERN PLAINS/LOWER MISSISSIPPI  
VALLEY. THE SOUTHERN THIRD OF THE WEST HAS THE BEST POTENTIAL TO  
STAY DRY DURING THE PERIOD. PARTS OF THE HIGH PLAINS MAY SEE  
LITTLE PRECIPITATION AS WELL.  
 
   
..GUIDANCE ASSESSMENT/PREFERENCES
 
 
LATEST MODELS AND ENSEMBLES HAVE BEEN REMARKABLY STUBBORN IN  
MAINTAINING THEIR SPREAD FOR THE EXACT DETAILS OF DIFFUSE  
SHORTWAVE ENERGY ALOFT AND ASSOCIATED SURFACE LOW PRESSURE  
TRACKING ACROSS THE EASTERN HALF OF THE COUNTRY LATE THIS WEEK  
INTO THE START OF THE WEEKEND. AS HAS BEEN THE CASE IN RECENT  
DAYS THERE IS DECENT CLUSTERING FOR LOW PRESSURE OVER THE  
SOUTH-CENTRAL PLAINS AS OF EARLY THU. THEN INDIVIDUAL  
MODELS/ENSEMBLE MEMBERS RAPIDLY DIVERGE FOR THE LATITUDE OF  
BEST-DEFINED LOW PRESSURE FARTHER EAST. IN FORECASTS VALID EARLY  
FRI THE ONE TREND OF NOTE IS A REDUCTION OF ENSEMBLE MEMBERS IN  
THE NORTHERN PART OF THE SPREAD IN THE GREAT LAKES. ON THE OTHER  
HAND THE 12Z ECMWF/CMC ARE IN THE SOUTHERN PART OF THE SPREAD. BY  
EARLY SAT THERE IS STILL THE POTENTIAL FOR LOW PRESSURE TO BE  
ANYWHERE FROM NORTHERN NEW ENGLAND TO SOUTHERN MID-ATLANTIC.  
CONFIDENCE REMAINS LOW FOR SYSTEM SPECIFICS DUE TO THE SENSITIVITY  
TO SMALL SCALE DETAILS ALOFT THAT INCLUDE A COMBINATION OF INITIAL  
PLAINS SHORTWAVE AND NORTHERN TIER ENERGY THAT COULD INTERACT BY  
FRI. PREFERENCE IS TO MINIMIZE CONTINUITY CHANGES UNTIL A BETTER  
CONSENSUS EMERGES, YIELDING A SURFACE WAVE TRACKING THROUGH THE  
OHIO VALLEY AND NORTHERN MID-ATLANTIC. IN SPITE OF THE MODEL  
SPREAD, A MULTI-MODEL BLEND ENDED UP PROVIDING A REASONABLE  
TEMPLATE FOR THE DESIRED EVOLUTION.  
 
FARTHER WESTWARD THE GUIDANCE HAS BEEN FAIRLY CONSISTENT IN  
WEAKENING SHORTWAVE ENERGY THAT CROSSES THE NORTHWEST AND HEADS  
INTO A DOWNSTREAM RIDGE, WHILE A SOUTHERN STREAM SHORTWAVE CROSS  
THE SOUTHWEST U.S./NORTHERN MEXICO AND THEN THE SOUTHERN PLAINS  
INTO MISSISSIPPI VALLEY. A FAIRLY STRONG NORTHEASTERN PACIFIC  
STORM SHOULD BRING A DECENT FRONT (WITH VIGOROUS UPPER SHORTWAVE  
SUPPORT) INTO THE WEST BY SAT, POTENTIALLY FOLLOWED A DAY LATER BY  
ANOTHER SYSTEM TRACKING NEAR/NORTHWEST OF VANCOUVER ISLAND AND  
BRINGING A FRONT/ENERGY ALOFT INTO THE NORTHWEST. BY THE LATTER  
HALF OF THE PERIOD THERE IS STILL A RAPID INCREASE IN SPREAD FOR  
DETAILS OF FLOW ALOFT FROM THE PACIFIC INTO THE WESTERN U.S. IN  
FORECASTS VALID NEXT MON THE GFS/GEFS SHOW THE MOST UPPER RIDGING  
OVER THE INTERIOR WEST WHILE THE PAST COUPLE ECMWF RUNS AND 12Z  
CMC DEPICT FLAT OR EVEN SLIGHTLY CYCLONIC FLOW. THE 12Z ECMWF/CMC  
MEANS SHOW A MODEST RIDGE. TELECONNECTIONS RELATIVE TO A NEGATIVE  
HEIGHT ANOMALY CENTER OVER THE WEST-CENTRAL PACIFIC IN D+8 CHARTS  
AND A POSITIVE CENTER EAST OF NORTHERN GREENLAND HINT AT A SPLIT  
FLOW TYPE OF PATTERN OVER WESTERN NORTH AMERICA. THE ESTABLISHED  
PATTERN OF EASTERN PACIFIC TROUGHING AND RELATIVE AGREEMENT AMONG  
THE MEANS FOR A WESTERN RIDGE ULTIMATELY LEAD TO A PREFERENCE  
CLOSE TO THE MEANS. INCLUDING SOME WEIGHT OF THE DIFFERING 18Z  
GFS/12Z ECMWF FOR THE FULL FORECAST DOMAIN ESSENTIALLY BALANCES  
OUT NEAR THE DESIRED SCENARIO OVER THE WEST. THE SPECIFICS OF  
FLOW OVER PACIFIC/WESTERN U.S. LATE IN THE PERIOD WILL AFFECT HOW  
ENERGY HEADING INTO THE WEST ON SAT WILL ULTIMATELY INTERACT WITH  
THE SOUTHERN STREAM SHORTWAVE REACHING THE PLAINS DURING THE  
WEEKEND. IT WILL LIKELY TAKE A WHILE TO RESOLVE THIS ASPECT OF  
THE FORECAST. CURRENTLY THE EVENTUAL COMBINATION OF SHORTWAVES IS  
MOST LIKELY TO SUPPORT A SURFACE WAVE TRACKING FROM THE SOUTHERN  
PLAINS INTO MIDWEST DURING SUN-MON.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
ASIDE FROM THE TYPICALLY VARIABLE FINER DETAILS, THERE IS GOOD  
CONTINUITY IN THE FORECAST OF MULTIPLE PERIODS OF SIGNIFICANT  
RAINFALL/HIGHER ELEVATION SNOW FROM NORTHERN CALIFORNIA/SIERRA  
NEVADA AND PACIFIC NORTHWEST INTO THE NORTHERN ROCKIES. HIGHEST  
FIVE-DAY TOTALS WILL LIKELY BE OVER FAVORED TERRAIN IN THE WEST  
COAST STATES WITH SOMEWHAT LESS MOISTURE REACHING THE ROCKIES.  
HEAVIEST PRECIPITATION SHOULD OCCUR ALONG THE WEST COAST DURING  
FRI-SUN. MEANWHILE THE SYSTEM TRACKING OUT OF THE PLAINS THU  
ONWARD WILL SPREAD A DECENT MOISTURE SHIELD ACROSS THE EASTERN  
HALF OF THE COUNTRY BUT WITH CONTINUED LACK OF CONFIDENCE IN  
SPECIFICS. TODAY THERE IS SOMEWHAT MORE OF A SIGNAL FOR HEAVY  
RAINFALL POTENTIAL OVER THE LOWER MISSISSIPPI VALLEY/GULF COAST  
REGION, AND SOME CONVECTION OVER THIS AREA COULD BE STRONG TO  
SEVERE. CHECK SPC OUTLOOKS FOR LATEST INFO ON SEVERE THREATS.  
SOME SNOW MAY BE POSSIBLE FROM THE CENTRAL GREAT LAKES INTO NEW  
ENGLAND. BEHIND THIS SYSTEM, MOST GUIDANCE CONTINUES TO SUGGEST A  
HEAVY RAINFALL THREAT NEXT WEEKEND OVER THE SOUTHERN PLAINS/LOWER  
MISSISSIPPI VALLEY. THIS ACTIVITY WILL BE ENCOURAGED BY THE  
APPROACHING SOUTHERN STREAM SHORTWAVE ALOFT AND A HEALTHY FLOW OF  
GULF MOISTURE INTERACTING WITH A STALLED FRONT THAT SHOULD RETURN  
NORTH AS A WARM FRONT. RAINFALL OF VARYING INTENSITY SHOULD ALSO  
SPREAD FARTHER NORTHWARD ACROSS THE CENTRAL AND EVENTUALLY EASTERN  
U.S.  
 
TEMPERATURES WILL VARY WITH THE PROGRESSION OF INDIVIDUAL SYSTEMS  
BUT THERE WILL BE A NOTICEABLE TREND OVER TIME TOWARD GREATER  
COVERAGE OF ABOVE NORMAL READINGS ACROSS THE LOWER 48. THE ONE  
EXCEPTION SHOULD BE OVER THE NORTHERN AND CENTRAL PARTS OF THE  
WEST WHERE CLOUDS AND PRECIPITATION WILL TEND TO KEEP HIGHS NEAR  
TO BELOW NORMAL. HIGHEST ANOMALIES (PLUS 10-20F WITH SOME HIGHER  
VALUES ESPECIALLY FOR MIN TEMPS) WILL BE MOST LIKELY FROM THE  
NORTHERN HALF OF THE PLAINS INTO EAST-CENTRAL U.S. DURING SAT-MON.  
A LARGE PART OF THE WEST SHOULD SEE PLUS 5-15F ANOMALIES FOR MIN  
TEMPS AS WELL.  
 
RAUSCH  
 
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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