926  
FXUS02 KWBC 181959  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
359 PM EDT THU APR 18 2019  
 
VALID 12Z SUN APR 21 2019 - 12Z THU APR 25 2019  
   
..OVERVIEW AND GUIDANCE PREFERENCES
 
 
MEAN FLOW ALOFT ACROSS THE LOWER 48 WILL BECOME SOMEWHAT LESS  
ENERGETIC WITH HIGHER HEIGHTS AFTER THE DEPARTURE OF THE DEEP BUT  
GRADUALLY WEAKENING SYSTEM OVER THE EAST SUN INTO MON.  
 
TELECONNECTIONS RELATIVE TO A PERSISTENT UPPER LOW IN NORTHERN  
CANADA FAVOR RELATIVELY FLAT FLOW--OR AT LEAST DECENT PROGRESSION  
OF ANY AMPLIFIED FEATURES--BUT OVER THE PAST DAY GUIDANCE HAS  
GRAVITATED TOWARD GFS/GEFS/UKMET SOLUTIONS THAT HAVE BEEN FAIRLY  
SLOW AND AMPLIFIED WITH THE INITIAL WESTERN U.S. UPPER TROUGH  
DRIFTING INTO THE CENTRAL STATES. IN GENERAL A MODEL/MEAN BLEND  
REFLECTS LATEST CONSENSUS WELL AND MITIGATES DETAIL UNCERTAINTIES  
WITHIN THE TROUGH ALOFT AND CORRESPONDING WAVY SURFACE FRONT.  
 
FARTHER UPSTREAM THERE IS REASONABLE AGREEMENT ON STRONG FLOW  
COMING INTO SOUTHWESTERN CANADA FROM EARLY IN THE WEEK ONWARD,  
WITH THE SOUTHERN PERIPHERY OF THIS FLOW GRADUALLY SAGGING  
SOUTHWARD INTO THE EXTREME NORTHWESTERN U.S. 00Z CMC/CMC  
ENSEMBLES ARE MORE AGGRESSIVE TO BRING HEIGHT FALLS INTO WESTERN  
NORTH AMERICA VERSUS OTHER GUIDANCE THAT AGREES AMONG EACH OTHER  
RATHER WELL. CMC ISSUES MAY ADVERSELY IMPACT ITS FORECAST  
DOWNSTREAM AS WELL.  
 
OVER THE EAST, RECENT TRENDS HAVE BEEN SLOWER FOR THE UPPER LOW  
DEPARTING SUN-MON--FAVORING PROGRESSION CLOSER BUT MAYBE NOT  
COMPLETELY TO THE 06Z FV3 GFS/00Z ECMWF OR A COMPROMISE WITH THE  
00Z CMC. THE 00Z GFS BECOMES A FAST EXTREME VERY EARLY IN THE  
PERIOD WHILE THE 06Z RUN HAS ADJUSTED TO A COMPROMISE. DEPENDENCE  
ON SMALLER SCALE DETAILS WILL LIMIT CONFIDENCE IN DETAILS OF A  
WAVY FRONT DROPPING INTO THE REGION DURING THE LATTER HALF OF THE  
PERIOD. LATEST MAJORITY SOLUTION HAS BACKED AWAY SOMEWHAT ON THE  
FRONT'S SOUTHWARD EXTENT.  
 
BASED ON THE CURRENT ARRAY OF GUIDANCE THE UPDATED FORECAST  
EMPHASIZED THE 06Z GFS/FV3 GFS AND 00Z ECMWF/UKMET DURING THE  
FIRST HALF OF THE FORECAST WITH MINOR EDITS FOR THE DEPARTING  
EASTERN SYSTEM. THEN THE BLEND TRANSITIONED TO AN ENSEMBLE  
MEAN/MODEL COMPOSITE OF THE 06Z GEFS/00Z ECMWF MEAN AND  
AFOREMENTIONED GFS/ECMWF RUNS TO MITIGATE INCREASING DETAIL  
UNCERTAINTIES WITHIN AN OVERALL AGREEABLE PATTERN EVOLUTION BY  
DAYS 6-7 WED-THU.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE SYSTEM INITIALLY CROSSING THE WEST WILL BRING RAIN AND SOME  
HIGH ELEVATION SNOW TO PARTS OF THE GREAT BASIN AND NORTH-CENTRAL  
INTO CENTRAL ROCKIES. A PERIOD OF LOW LEVEL UPSLOPE FLOW MAY  
ENHANCE PRECIPITATION OVER SOME NORTHWARD AND EASTWARD FACING  
SLOPES OF THE ROCKIES DURING THE FIRST HALF OF THE PERIOD. FROM  
ABOUT MON NIGHT ONWARD THE MOST PROMINENT THREAT WILL BE FOR HEAVY  
RAINFALL OVER PORTIONS OF THE SOUTHERN HALF OF THE PLAINS AS THE  
UPPER TROUGH APPROACHES/REACHES THE AREA WHILE PERSISTENT LOW  
LEVEL GULF INFLOW INTERACTS WITH A SLOW MOVING AND WAVY FRONT.  
IMPROVED MODEL AGREEMENT FOR THE LARGE SCALE EVOLUTION COMPARED TO  
YESTERDAY IS HELPING TO INCREASE CONFIDENCE IN THE OVERALL EVENT  
BUT IMPORTANT SMALLER SCALE DETAILS WILL LIKELY TAKE INTO THE  
SHORT RANGE TIME FRAME TO BE RESOLVED BETTER. CURRENTLY EXPECT  
HIGHEST RAINFALL TOTALS THROUGH THE END OF THE PERIOD TO BE OVER  
TEXAS. RAIN OF VARYING INTENSITY SHOULD EXTEND NORTHEASTWARD  
ALONG A FRONT THAT REACHES THE EASTERN STATES. AHEAD OF THIS  
MOISTURE, THE DEPARTING EASTERN SYSTEM MAY PRODUCE A DAY OR SO OF  
SHOWERY WEATHER OVER THE MID-ATLANTIC/NORTHEAST SUN-MON. A SERIES  
OF FRONTS WILL BRING MOISTURE TO THE NORTHWEST BUT WITH MOSTLY  
LIGHT TO MODERATE AMOUNTS. THE BEST DEFINED FRONT SHOULD PUSH  
INTO THE REGION WED-THU WITH A CORRESPONDING BAND OF MOISTURE  
DRIFTING EAST/SOUTHEAST WITH TIME.  
 
CLOUDS AND PRECIPITATION ON THE COOL SIDE OF THE CENTRAL U.S.  
FRONT WILL TEND TO FOCUS LOWEST ANOMALIES FOR HIGH TEMPERATURES  
OVER THE HIGH PLAINS. EXPECT WARMEST ANOMALIES OVER THE WEST  
TUE-THU AS UPPER RIDGING BUILDS OVER THE REGION, WITH FAIRLY BROAD  
COVERAGE OF MORNING LOWS AND DAYTIME HIGHS 10-20F ABOVE NORMAL.  
AT LEAST A FEW DAILY RECORDS MAY BE POSSIBLE. MEANWHILE ANOTHER  
AREA OF WARMTH WILL PROGRESS FROM THE CENTRAL U.S. INTO THE EAST  
WITH SOME PLUS 10F OR GREATER ANOMALIES POSSIBLE.  
 
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  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL/SOUTHERN PLAINS, AND  
THE MIDDLE/LOWER MISSISSIPPI VALLEY, TUE-THU, APR 23-APR 25.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE MID-ATLANTIC, THE  
MISSISSIPPI VALLEY, THE CENTRAL/SOUTHERN APPALACHIANS, THE  
NORTHERN PLAINS, THE TENNESSEE VALLEY, THE GREAT LAKES, THE  
NORTHEAST, THE SOUTHEAST, THE SOUTHERN PLAINS, AND THE OHIO VALLEY.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE  
MISSISSIPPI VALLEY, THE NORTHERN PLAINS, THE TENNESSEE VALLEY, THE  
NORTHEAST, AND THE OHIO VALLEY.  
- FLOODING LIKELY ACROSS PORTIONS OF THE NORTHEAST, THE NORTHERN  
PLAINS, AND THE NORTHERN GREAT BASIN.  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page