717  
FXUS02 KWBC 291559  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1158 AM EDT MON APR 29 2019  
 
VALID 12Z THU MAY 02 2019 - 12Z MON MAY 06 2019  
 
...FLOODING/FLASH FLOODING THREAT IN THE SHORT RANGE CONTINUES  
INTO THURSDAY FOR THE SOUTHERN PLAINS/LOWER MISSISSIPPI VALLEY...  
   
..16Z UPDATE
 
 
THE OVERNIGHT MODEL GUIDANCE MAINTAINED A SIMILAR PATTERN AS  
DESCRIBED PREVIOUSLY WITH THE CLOSED UPPER LOW IN CANADA AND  
TROUGHING ACROSS THE CENTRAL U.S. REGARDING THE SOUTHERN STREAM  
UPPER LOW TRACKING THROUGH THE EASTERN PACIFIC AND INTO CALIFORNIA  
BY EARLY NEXT WEEK...THE EC RUNS HAVE BEEN CONSISTENTLY SLOWER  
THAN THE GFS RUNS FOR AT LEAST A COUPLE OF DAYS. HOWEVER, THE LAST  
COUPLE OF EC RUNS HAVE BEEN TRENDING JUST A BIT FASTER, AND THE  
00Z GFS AND MEAN TRENDED SLOWER, WHICH MADE FOR MUCH BETTER MODEL  
AGREEMENT. THUS, WAS ABLE TO INCORPORATE THE 00Z GFS SUITE IN THIS  
FORECAST, ALONG WITH THE 00Z EC/EC MEAN, AND THE 00Z UKMET  
(THROUGH DAY 5) AND 00Z CMC, WHICH ALL LINED UP WELL. THE 06Z GFS  
WENT AGAINST THE TREND, HOWEVER, MOVING THE LOW FARTHER EASTWARD  
AND BEGINNING TO PHASE IT WITH THE NORTHERN STREAM TROUGH IN THE  
WEST BY DAY 7/MON, SO EXCLUDED THAT RUN FROM THE FORECAST.  
 
FOR ADDITIONAL INFORMATION ON SENSIBLE WEATHER, PLEASE SEE THE  
PREVIOUS DISCUSSION.  
 
TATE  
   
..PREVIOUS DISCUSSION
 
 
...OVERVIEW AND ASSESSMENT OF MODEL/ENSEMBLE GUIDANCE AND  
PREDICTABILITY...  
 
IT REMAINS THE CASE THAT A LARGE CLOSED UPPER CIRCULATION SETTLES  
OVER WESTERN CANADA THIS WEEK AS A SERIES OF NORTHERN STREAM  
TROUGHS WITH HEIGHT FALLS AND SWATHS OF PRECIPITATION DIG INTO THE  
NORTHWEST AND EASTWARD OVER THE WINTRY ROCKIES THEN U.S. NORTHERN  
TIER. THERE REMAINS POTENTIAL FOR SOME DEGREE OF PHASING WITH A  
SOUTHERN STREAM FLOW OF IMPULSES/HEIGHT FALLS WORKING UNDERNEATH  
DURING THIS PERIOD FROM THE PACIFIC INLAND OVER THE U.S. SOUTHERN  
TIER. THE GFS/GEFS/FV3 HAVE TENDED TO BE ON THE PROGRESSIVE SIDE  
OF THE FULL ENVELOPE OF SOLUTIONS WHILE RECENT ECMWF RUNS AND TO A  
LESSER EXTENT ECMWF ENSEMBLES AND UKMET HAVE BEEN ON THE SLOWER  
SIDE OF THE FORECAST ENVELOPE. THE WPC MEDIUM RANGE PRODUCT SUITE  
WAS MAINLY DERIVED FROM A COMPOSITE OF THE ECMWF/ECMWF ENSEMBLE  
MEAN. THIS CONSIDERS BLOCKY UPSTREAM FLOW AND INHERENT SLOW NATURE  
OF INITIALLY CLOSED LOWS.  
   
..WEATHER HIGHLIGHTS/THREATS
 
 
DYNAMIC TROUGHING CROSSING THE N-CENTRAL U.S. AND COOLED  
TEMPERATURES FAVORS SOME EARLY MAY UPPER MIDWEST/GREAT LAKES  
SNOWS. A LEAD AND WAVY FRONTAL SYSTEM WILL PROGRESS LATE WEEK  
ACROSS THE CENTRAL THEN EASTERN U.S. DEEPENING INFLOW/MOISTURE  
FROM THE GULF OF MEXICO WILL FEED INTO CONVECTIVELY ACTIVE WARM  
SECTOR MESO-BOUNDARIES AS WELL AS A STARK BAROCLINIC ZONE OVERTOP.  
STRONG TO SEVERE THUNDERSTORMS WITH SOME HEAVY RAIN AND FLASH  
FLOODING/FLOODING POTENTIAL WILL THREATEN THE SOUTHERN PLAINS AND  
LOWER MISSISSIPPI/OHIO VALLEYS THURSDAY. FLOODING REMAINS POSSIBLE  
AS PARTICULARLY THE MISSISSIPPI VALLEY HAS HAD FLOODING CONCERNS  
FOR WEEKS, AND WITH THE CONVECTIVE NATURE OF THE PRECIPITATION  
FLASH FLOODING IS POSSIBLE AS WELL. LESS DEFINED ACTIVITY PRESSES  
OVER THE EAST AND SOUTH INTO FRIDAY/SATURDAY. THE FRONT SHIFTS AND  
STALLS MAINLY OFFSHORE FROM THE WEEKEND INTO EARLY NEXT WEEK IN A  
DRIER POST-FRONTAL PATTERN AS NEW UPSTREAM TROUGH ENERGIES WITH  
MORE LIMITED PRECIPITATION WORK BACK INTO THE WEST IN A CONTINUED  
SPLIT FLOW REGIME.  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page