354  
FXUS02 KWBC 161600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1159 AM EDT TUE APR 16 2019  
 
VALID 12Z FRI APR 19 2019 - 12Z TUE APR 23 2019  
   
..HEAVY RAIN THREAT FOR PARTS OF THE EAST FRIDAY
 
 
   
..16Z UPDATE
 
 
THE NARROW TROUGH MOVING ACROSS MISSISSIPPI VALLEY ON DAY 3  
APPEARED TO BE BETTER HANDLED BY THE 00Z AND 06Z GFS THAN IN  
PREVIOUS RUNS. DETERMINISTIC MODELS AND MEANS ACROSS KEEP ONE  
TROUGH IN BOTH THE NORTHERN AND SOUTHERN STREAM AT DAY 3, WITH THE  
VORT MAX THEN SPINNING INTO AN UPPER LOW IN THE SOUTHERN STREAM BY  
DAY 4. THUS THE MEDIUM RANGE FORECAST USED A MULTI-MODEL BLEND  
THROUGH DAY 3-4. THIS PATTERN STILL SUPPORTS HEAVY RAIN ACROSS THE  
EAST EARLY IN THE PERIOD.  
 
SPLIT FLOW REMAINS AN ISSUE WITH THE LATEST GUIDANCE ACROSS THE  
WESTERN/CENTRAL U.S., AND ONCE AGAIN LEANED AWAY FROM THE  
OPERATIONAL GFS DURING THE LATER FORECAST PERIOD AS IT STRENGTHENS  
AND SLOWS DOWN A TROUGH IN THE WESTERN U.S., UNLIKE CONSENSUS AND  
SUGGESTION FROM TELECONNECTIONS. FAVORED THE EC/NAEFS/GEFS MEANS  
WITH SOME ELEMENT OF THE OPERATIONAL 00Z ECMWF.  
 
FOR DETAILS ON SENSIBLE WEATHER, PLEASE SEE THE PREVIOUS  
DISCUSSION.  
 
TATE  
   
..PREVIOUS DISCUSSION
 
 
   
..OVERVIEW
 
 
QUASI-PROGRESSIVE PATTERN FOR THE MEDIUM RANGE AS ATMOSPHERIC  
SPINDOWN CONTINUES DURING THIS TRANSITION SEASON. DEEP  
TROUGH/CLOSED UPPER LOW WILL PUSH EAST OF THE MISSISSIPPI LATE  
THIS WEEK AND PERHAPS CUT OFF FROM THE FLOW OFF THE  
MID-ATLANTIC/NEW ENGLAND COAST AS WESTERN TROUGHING (FROM BOTH THE  
SUBTROPICS AND THE MID-LATITUDES) PUSH OUT OF THE ROCKIES AND ONTO  
THE PLAINS NEXT MON/TUE. HEAVY RAIN THREAT AT THE END OF THE SHORT  
RANGE WILL SHIFT TO THE APPALACHIANS --> COASTAL PLAIN ON FRIDAY  
INTO EARLY SATURDAY.  
 
   
..GUIDANCE PREFERENCES
 
 
MODELS AND ENSEMBLES CONTINUED TO STRUGGLE WITH EXACTLY HOW THE  
EASTERN SYSTEM EVOLVES DURING THIS PERIOD, CONTINGENT UPON THE  
DEGREE OF NORTHERN/SOUTHERN STREAM SEPARATION AND EXACT TRACK OF  
THE UPPER FEATURES. 12Z/18Z GFS RUNS SEEMED TO DEPART MOST FROM  
THE OTHERWISE MODEST CLUSTERING OF THE ENSEMBLES AND 12Z  
ECMWF/UKMET/CANADIAN WITH THE TRACK OF THE UPPER LOW (GFS WAS  
FARTHER NORTH AND THUS QUICKER TO BRING THE SYSTEM BACK INTO THE  
WESTERLIES THAN THE ECMWF-LED CLUSTER). PREFERRED TO SIDE WITH THE  
NON-GFS GUIDANCE GIVEN THE TREND IN ESPECIALLY THE ECMWF ENSEMBLES  
BUT ALSO THE GEFS MEMBERS. NATURE OF THE FLOW DOES NOT INSTILL  
HIGH CONFIDENCE IN THE DETAILS GIVEN THE SENSITIVITY TO SHIFTS IN  
THE SHORT RANGE FORECAST, SO THE GFS WAS STILL WITHIN THE REALM OF  
POSSIBILITIES.  
 
TO THE WEST, ENSEMBLE CONSENSUS HAS PROVEN ITS WORTH IN MINIMIZING  
SHIFTS IN THE FORECAST OVER THE PAST SEVERAL DAYS. AGAIN HERE, THE  
GFS DEPARTED FROM THE MAJORITY CONSENSUS WITH THE TROUGH IN THE  
SOUTHWEST LATE SUNDAY (SLOWER VS A QUICKER CONSENSUS). WITH SPLIT  
FLOW OUT OF THE NORTHEASTERN PACIFIC, UNCERTAINTY INCREASES IN THE  
FORECAST, NECESSITATING AN INCREASE IN THE ENSEMBLES.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
DETERMINISTIC MODELS CONTINUE TO PAINT STRIPES OF MODEST/HEAVY  
RAINFALL NORTHEASTWARD ALONG AND EAST OF THE APPALACHIANS AS THE  
FLOW BECOMES INCREASINGLY MERIDIONAL. THIS SHOULD FOCUS A  
RELATIVELY NARROW BUT INTENSE PLUME OF MOISTURE FROM THE  
SUBTROPICS (YUCATAN/CUBA/GREATER ANTILLES) ALONG/AHEAD OF A COLD  
FRONT. WITH PW ANOMALIES +3 TO +4, RAINFALL COULD BE LEAD TO  
FLOODING CONCERNS, ESPECIALLY IN URBAN AREAS. SEVERE WEATHER  
THREAT WILL ACCOMPANY THE FRONT, LIKELY FOCUSED SOUTH OF THE  
MASON-DIXON LINE (PLEASE CONSULT THE SPC OUTLOOKS FOR MORE  
INFORMATION). GEFS MEAN QPF CONTINUES TO BE MUCH HIGHER THAN  
TYPICAL VALUES FOR THIS LEAD TIME IN MID-APRIL, SUGGESTING A  
HIGHER LIKELIHOOD OF AN ANOMALOUS EVENT.  
 
MILD TEMPERATURES WILL PRECEDE THE FRONT (10-15F ABOVE AVERAGE)  
BUT WILL BE REPLACED BY COOLER THAN AVERAGE TEMPERATURES AFTER ITS  
PASSAGE. THAT WILL BE SHORT-LIVED (1-2 DAYS) AS MILDER AIR IN THE  
WEST FRIDAY PUSHES THROUGH THE PLAINS THIS WEEKEND AND INTO THE  
EAST EARLY NEXT WEEK.  
 
FRACASSO  
 
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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