778  
FXUS02 KWBC 301901  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 PM EDT SAT APR 30 2022  
 
VALID 12Z TUE MAY 03 2022 - 12Z SAT MAY 07 2022  
   
..OVERVIEW
 
 
A SERIES OF SYSTEMS WILL PRODUCE EPISODES OF PRECIPITATION FROM  
THE NORTHWEST U.S. AND NORTHERN-CENTRAL ROCKIES (RAIN AND HIGH  
ELEVATION SNOW) THROUGH THE CENTRAL-SOUTHERN PLAINS AND MUCH OF  
THE EAST. A SYSTEM TRACKING OUT OF THE MIDWEST EARLY TUESDAY  
ONWARD AND ANOTHER ONE TRACKING OUT OF THE WEST SHOULD BE THE LAST  
IN THE SERIES DURING THE CURRENTLY ESTABLISHED PATTERN CONSISTING  
OF DISCRETE TROUGHS/CLOSED LOWS, WHILE MEAN TROUGHING ALOFT  
SETTING UP NEAR THE WEST COAST LATE WEEK INTO THE WEEKEND WILL  
LIKELY BRING A COUPLE FRONTAL SYSTEMS AND ASSOCIATED PRECIPITATION  
FOCUS INTO THE WEST. THE MOST ACTIVE WEATHER SHOULD BE WITH THE  
SYSTEM EMERGING FROM THE WEST BY MIDWEEK WITH THE STORM PREDICTION  
CENTER INDICATING A THREAT OF SEVERE WEATHER OVER THE SOUTHERN  
PLAINS AND VICINITY AND WPC SHOWING AN EXPERIMENTAL MEDIUM RANGE  
"SLIGHT RISK" FOR EXCESSIVE RAINFALL OVER PARTS OF THE REGION AS  
WELL, WITH RUNOFF ISSUES POTENTIALLY ENHANCED DUE TO WET GROUND  
FROM RAINFALL EXPECTED IN THE SHORT RANGE TIME FRAME. THE MIDWEEK  
THREAT SIGNAL IS STRONGER THAN AVERAGE AS A CLOSED UPPER  
SYSTEM/LEAD UPPER DIFFLUENCE COMBINE WITH INCREASING INFLOW OF  
GULF MOISTURE INTO A WAVY FRONT. RAINFALL WILL CONTINUE SPREADING  
INTO/THROUGH THE EAST LATER IN THE WEEK.  
 
   
..MODEL GUIDANCE EVALUATION
 
 
GUIDANCE THROUGH THE 00Z/06Z CYCLES OFFERED SIGNIFICANT FORECAST  
CHALLENGES IN MULTIPLE RESPECTS. EVERY DAY OR SO THE MODELS KEEP  
CHANGING THE SPECIFICS OF FLOW ALOFT OVER EASTERN CANADA INTO THE  
EASTERN U.S., LEADING TO OSCILLATIONS IN STRENGTH/TRACK OF LOW  
PRESSURE TRACKING OUT OF THE MIDWEST EARLY TUESDAY ONWARD. LATEST  
CLUSTERING SUGGESTS SOMEWHAT LESS INTERACTION BETWEEN CANADA  
TROUGHING AND THE MIDWEST SHORTWAVE, GENERALLY YIELDING A  
WEAKER/SOUTHWARD SURFACE LOW AND THEN BY EARLY THURSDAY A WAVE  
OFFSHORE FROM THE NORTHEAST. MEANWHILE THE PRONOUNCED SPREAD  
CONTINUES FOR THE UPPER LOW TRACKING OUT OF THE WEST, WITH THE  
GFS/GEFS MEAN ON THE FAST SIDE AND THE ECMWF SLOWEST. FROM  
THURSDAY ONWARD THE 00Z ECMWF MEAN AND CMC/CMC MEAN OFFERED A  
COMPROMISE CLOSEST TO WHAT HAS HISTORICALLY BEEN THE BEST STARTING  
POINT IN THIS TYPE OF TIMING DISCREPANCY, ESPECIALLY INVOLVING A  
CLOSED LOW, WHICH IS A TWO-THIRDS LEAN TOWARD THE SLOWER SIDE OF  
THE ENVELOPE. GENERAL PREFERENCES ULTIMATELY LEANED CLOSEST TO THE  
00Z CMC/CMC MEAN AND ECMWF MEAN. WITH THE MEAN TROUGH SETTLING  
NEAR THE WEST COAST, THERE IS A GENERAL THEME OF A LEADING  
SHORTWAVE REACHING THE COAST THURSDAY AND THEN ANOTHER FEATURE  
ARRIVING AROUND SATURDAY. HOWEVER MODELS/ENSEMBLES HAVE VARIED  
WILDLY FOR AMPLITUDE OF THE LEADING SHORTWAVE. SOME GFS RUNS/GEFS  
ENSEMBLES HAVE BEEN QUITE AMPLIFIED WHILE ECMWF RUNS/ECMWF  
ENSEMBLES HAVE BEEN TRENDING NOTICEABLY FLATTER (WITH THE CMC/CMC  
MEAN A COMPROMISE). COMPARED TO THE VERY AMPLIFIED 00Z RUN, THE  
06Z AND THEN 12Z GFS RUNS HAVE MADE A PRONOUNCED FLATTER TREND  
CLOSER TO THE CONSENSUS.  
 
GUIDANCE PREFERENCES LED TO STARTING WITH A 06Z/00Z OPERATIONAL  
MODEL COMPOSITE FOR THE FIRST HALF OF THE PERIOD, EMPLOYING  
SLIGHTLY LESS THAN TYPICAL WEIGHT OF THE GFS COMPONENT. THEN THE  
FORECAST TRANSITIONED TO A MODEL/ENSEMBLE MEAN BLEND INCLUDING  
MORE CMC THAN ECMWF ALONG WITH REMAINING INPUT CONSISTING OF THE  
00Z ECMWF/CMC MEANS AND 06Z GEFS MEAN. NEW 12Z MODEL TRENDS  
(INCLUDING A FASTER ADJUSTMENT IN THE ECMWF) REMAIN SUPPORTIVE OF  
SLOWER TIMING THAN THE GFS FOR THE SYSTEM EMERGING FROM THE WEST,  
BUT FASTER THAN THE 00Z ECMWF.  
 
   
..SENSIBLE WEATHER/THREATS
 
 
OVER THE WEST, THE UPPER LOW FORECAST TO TRACK FROM NEAR SOUTHERN  
IDAHO THROUGH THE CENTRAL ROCKIES TUESDAY-WEDNESDAY AND ASSOCIATED  
SURFACE REFLECTION WILL SPREAD RAIN AND HIGHER ELEVATION SNOW  
ACROSS THE NORTHERN-CENTRAL ROCKIES AND HIGH PLAINS DURING THAT  
TIME. THIS SYSTEM COULD PRODUCE SOME LOCALLY ENHANCED TOTALS  
DEPENDING ON EXACT DETAILS. THEN AN AMPLIFIED UPPER TROUGH AND  
SURFACE FRONTAL SYSTEM FORECAST TO REACH THE WEST COAST AND  
PROGRESS INLAND NEXT THURSDAY-SATURDAY SHOULD BRING A RENEWED  
PRECIPITATION FOCUS INTO THE PACIFIC NORTHWEST AND THEN FARTHER  
EASTWARD. THE SOUTHERN EXTENT OF PRECIPITATION WILL DEPEND ON THE  
UPPER TROUGH'S PRECISE AMPLITUDE WHICH HAS BEEN QUITE UNCERTAIN SO  
FAR, BUT LATEST TREND SUGGEST THAT MOST MOISTURE SHOULD BE  
CONFINED TO THE NORTHERN HALF OF THE WEST. THE UPPER  
DYNAMICS/SURFACE FRONT COULD REACH FAR ENOUGH EAST TO START  
PRODUCING AT LEAST SCATTERED RAINFALL OVER THE NORTHERN HIGH  
PLAINS BY NEXT WEEKEND. THE PACIFIC NORTHWEST MAY SEE ADDITIONAL  
PRECIPITATION BY NEXT SATURDAY WITH ANOTHER FRONT.  
 
OVER THE CENTRAL/EASTERN U.S., THE INITIAL RAINFALL FOCUS WILL BE  
WITH A SYSTEM TRACKING OUT OF THE MIDWEST EARLY TUESDAY ONWARD.  
THIS LOW AND ASSOCIATED FRONTS SHOULD PRODUCE THE HIGHEST TOTALS  
OVER THE LOWER GREAT LAKES AND OHIO VALLEY WITH SOMEWHAT LIGHTER  
AMOUNTS EXTENDING EASTWARD THROUGH THE EAST COAST. THE NEXT SYSTEM  
IN THE SERIES WILL LIKELY EMERGE OVER THE PLAINS DURING THE DAY  
WEDNESDAY AND LEAD TO ANOTHER EPISODE OF POTENTIALLY HEAVY  
RAINFALL, WITH THE WPC EXPERIMENTAL EXCESSIVE RAINFALL OUTLOOK  
SHOWING A SLIGHT RISK OVER/NEAR PARTS OF THE SOUTH-CENTRAL PLAINS  
FOR WEDNESDAY INTO EARLY THURSDAY. THE STORM PREDICTION CENTER IS  
ALSO MONITORING SEVERE THREATS OVER AND JUST EAST OF THE SOUTHERN  
PLAINS WEDNESDAY-THURSDAY. RAIN SHOULD CONTINUE PUSHING EASTWARD  
FROM THE PLAINS THROUGH THE REST OF THE WEEK WITH SOME POCKETS OF  
MODERATE TO HEAVY AMOUNTS. SYSTEM DETAILS BY LATE IN THE WEEK ARE  
STILL FAIRLY UNCERTAIN BUT CURRENTLY THE MOST LIKELY AXIS OF  
HIGHEST RAINFALL TOTALS EXTENDS FROM THE MIDWEST THROUGH THE  
MID-ATLANTIC. OVER THE CENTRAL/EAST-CENTRAL U.S., RAIN THAT FALLS  
PRIOR TO THIS FINAL SYSTEM COULD INCREASE SENSITIVITY TO ADDED  
RAINFALL. FORTUNATELY THE GUIDANCE IS CONSISTENT IN KEEPING THIS  
SYSTEM'S MOISTURE SOUTH OF THE FAR NORTHERN PLAINS WHERE SOIL  
CONDITIONS ARE THE WETTEST.  
 
THE SYSTEM INITIALLY CROSSING THE WEST WILL SUPPORT HIGHS 10-15F  
BELOW NORMAL OVER THE NORTHERN ROCKIES INTO GREAT BASIN ON  
TUESDAY. THEN THIS SYSTEM'S PROGRESSION WILL REINFORCE THE CHILLY  
PATTERN OVER THE CENTRAL PLAINS/MIDWEST (HIGHS UP TO 10-15F BELOW  
NORMAL TUESDAY-THURSDAY) BEFORE TEMPERATURES MAY FINALLY MODERATE  
TOWARD THE END OF THE WEEK. WARMER READINGS WILL CROSS THE WEST  
MID-LATE WEEK WITH BEST POTENTIAL FOR HIGHS 10-15F ABOVE NORMAL ON  
WEDNESDAY-THURSDAY. A GRADUAL INCREASE OF CLOUDS/PRECIPITATION  
WILL BRING HIGHS DOWN TO MODERATELY BELOW NORMAL LEVELS OVER THE  
NORTHWEST FRIDAY-SATURDAY. THE NORTHERN TWO-THIRDS OF THE EAST  
WILL SEE ABOVE NORMAL TEMPERATURES INTO MIDWEEK, FOLLOWED BY A  
GRADUAL COOLING TREND THAT WILL EXPAND COVERAGE OF NEAR TO  
SOMEWHAT BELOW NORMAL HIGHS LATE IN THE WEEK.  
 
RAUSCH  
 
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL  
OUTLOOK, 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/#PAGE=ERO  
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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