617  
FXUS02 KWBC 281945  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
344 PM EDT THU APR 28 2022  
 
VALID 12Z SUN MAY 01 2022 - 12Z THU MAY 05 2022  
   
..OVERVIEW
 
 
LATEST GUIDANCE FOR THE SUNDAY-THURSDAY PERIOD MAINTAINS THE THEME  
OF AN ACTIVE PATTERN WITH A SERIES OF PACIFIC SYSTEMS (EACH  
SUPPORTED BY AN UPPER TROUGH THAT MAY CONTAIN A CLOSED LOW FOR A  
PERIOD OF TIME) ENTERING AND PROGRESSING ACROSS THE LOWER 48.  
THESE SYSTEMS WILL SPREAD RAIN AND HIGH ELEVATION SNOW ACROSS THE  
PACIFIC NORTHWEST AND NORTHERN HALF OF THE ROCKIES, AND THEN  
MOSTLY RAIN OVER A LARGE PART OF THE CENTRAL/EASTERN U.S. SOME  
AREAS OF PRECIPITATION MAY BE HEAVY. THIS PATTERN WILL LIKELY  
LEAVE THE SOUTHERN HALF OR THIRD OF THE WEST, THE NORTHERN PLAINS  
NEAR THE CANADIAN BORDER, AND THE GULF COAST AS THE RELATIVELY  
DRIER AREAS DURING THE FORECAST PERIOD. AS FOR INDIVIDUAL  
FEATURES, A LEADING SYSTEM WILL WEAKEN AS IT TRACKS NORTHEAST FROM  
THE UPPER MISSISSIPPI VALLEY SUNDAY ONWARD WHILE ANOTHER OVER THE  
WEST BY EARLY SUNDAY SHOULD REACH THE MIDWEST/GREAT LAKES BY  
TUESDAY AND THE NEXT ONE ENTERING THE WEST BY MONDAY MAY REACH AS  
FAR EAST AS THE MISSISSIPPI VALLEY BY NEXT THURSDAY. A LARGER  
SCALE UPPER TROUGH APPROACHING THE WEST COAST NEXT THURSDAY MAY  
ALSO BRING SOME MOISTURE INTO THE NORTHWEST.  
 
   
..MODEL GUIDANCE EVALUATION
 
 
MODELS AND ENSEMBLE MEANS STILL KEY ON THE SAME INDIVIDUAL SYSTEMS  
BUT CONTINUE TO EXHIBIT A COMBINATION OF MEANINGFUL SPREAD AND/OR  
RUN-TO-RUN VARIABILITY/TRENDING. SOME OF THE DIFFICULTY IN THE  
FORECAST IS THAT SPECIFICS WILL DEPEND ON NOT ONLY THE DETAILS OF  
EACH SYSTEM AS IT TRACKS OVER THE LOWER 48 BUT ALSO THE CHARACTER  
OF CENTRAL INTO EASTERN CANADA MEAN TROUGHING WHOSE SOUTHERN  
PERIPHERY MAY INTERACT WITH AT LEAST THE LEADING TWO FEATURES.  
 
THE SYSTEM FORECAST TO BE OVER THE UPPER MISSISSIPPI VALLEY AS OF  
EARLY SUNDAY IS STILL WELL CLUSTERED AT THAT TIME BUT THEN  
UNCERTAINTIES OF SOUTHERN CANADA FLOW QUICKLY COME INTO PLAY AS IT  
LIFTS THROUGH AND AWAY FROM THE GREAT LAKES. BY TUESDAY THE MOST  
NOTABLE TREND IS OVER THE NORTHEAST WHERE A MORE PERSISTENT  
SURFACE RIDGE LEADS TO EARLIER DISSIPATION OF THE FRONT  
APPROACHING FROM THE WEST ON MONDAY.  
 
FOR THE NEXT SYSTEM THAT REACHES THE WEST JUST BEFORE THE START OF  
THE PERIOD EARLY SUNDAY, THERE HAS BEEN DECENT CLUSTERING AND  
CONTINUITY THROUGH ABOUT LATE MONDAY WHEN THE SYSTEM REACHES THE  
PLAINS. FROM THERE GUIDANCE SHOWS INCREASING DIVERGENCE AND SOME  
TRENDING FOR HOW FLOW ALOFT NEAR THE U.S.-CANADIAN BORDER MAY  
INFLUENCE THE SYSTEM. IN GENERAL THE TREND OVER THE PAST DAY IS  
FOR GREATER INTERACTION WHICH LEADS TO A STRONGER SURFACE LOW WITH  
FARTHER NORTHWEST TRACK. IF ANYTHING, NEW 12Z GUIDANCE HAS  
INCREASED THE SPREAD AS THE UKMET HAS BECOME AN AMPLIFIED EXTREME  
WITH NORTHERN STREAM FLOW (YIELDING A DEEP/NORTHERN SURFACE LOW)  
WHILE THE CMC SHOWS LITTLE STREAM INTERACTION (TO PRODUCE A WEAKER  
AND SLOWER SURFACE LOW).  
 
THROUGH THE 00Z/06Z CYCLES, NOT MUCH HAS CHANGED FOR THE FORECAST  
OF THE THIRD SYSTEM WHICH SHOULD REACH THE WEST ON MONDAY. THE  
00Z ECMWF REMAINS A SOUTHERN EXTREME WITH THE UPPER LOW TRACKING  
INTO THE WEST AND REMAINS ON THE SOUTHWESTERN SIDE OF THE ENVELOPE  
FOR THE REST OF THE PERIOD. WITH TIME THE GFS MAINTAINS ITS  
POSITION IN THE FASTER PART OF THE SPREAD. GEFS MEAN RUNS HAVE  
TENDED TO BE SIMILAR TO OR SOMEWHAT SLOWER THAN THE OPERATIONAL  
GFS WHILE THE UKMET/CMC HAVE GENERALLY BEEN BETWEEN THE TWO  
EXTREMES--THOUGH THE NEW 12Z CMC IS ABOUT AS SLOW AS THE 00Z ECMWF  
BY DAY 7 THURSDAY. PREFER TO MAINTAIN AN INTERMEDIATE SOLUTION  
WHILE AWAITING BETTER CONVERGENCE AMONG THE GUIDANCE.  
 
MOST MODELS AND MEANS HAVE BEEN FAIRLY WELL BEHAVED THUS FAR FOR  
THE UPPER TROUGH NEARING THE WEST COAST NEXT THURSDAY. GFS RUNS  
HAVE BEEN MORE INCONSISTENT, OCCASIONALLY PULLING MORE ENERGY OFF  
THE SOUTHERN PERIPHERY OF THE TROUGH (MOST PRONOUNCED IN THE 00Z  
RUN).  
 
THE UPDATED FORECAST STARTED WITH A COMPOSITE OF 00Z/06Z  
OPERATIONAL MODELS FOR ABOUT THE FIRST HALF OF THE PERIOD AND THEN  
INCORPORATED VARYING WEIGHTS OF 06Z GEFS/00Z ECMWF MEANS ALONG  
WITH SOME INPUT FROM THE MODELS AND WPC CONTINUITY. THIS APPROACH  
MAINTAINED A SOLUTION CLOSE TO CONTINUITY WHERE GUIDANCE WAS  
CONSISTENT OR SIGNIFICANT SPREAD PERSISTS, WHILE REPRESENTING SOME  
TRENDS WHERE SUFFICIENTLY AGREEABLE.  
 
   
..SENSIBLE WEATHER/THREATS
 
 
OVER THE NORTHWEST AND NORTHERN ROCKIES, ONE SYSTEM SHOULD BE  
PRODUCING RAIN/MOUNTAIN SNOW OVER THE ROCKIES ON SUNDAY WHILE  
ANOTHER SYSTEM RIGHT BEHIND IT WILL SPREAD MOISTURE FROM THE  
PACIFIC NORTHWEST THROUGH THE ROCKIES DURING SUNDAY INTO TUESDAY.  
DEPENDING ON EXACT SYSTEM DETAILS, THE SECOND ONE COULD PRODUCE  
SOME ENHANCED TOTALS OVER OR NEAR THE NORTHERN ROCKIES. THE UPPER  
TROUGH APPROACHING THE WEST COAST BY THURSDAY MAY START TO BRING  
LIGHT PRECIPITATION INTO THE PACIFIC NORTHWEST AT THAT TIME.  
 
OVER THE CENTRAL/EASTERN U.S., THE LEADING SURFACE LOW TRACKING  
OUT OF THE UPPER MISSISSIPPI VALLEY ON SUNDAY AND ASSOCIATED  
FRONTS WILL SPREAD PRECIPITATION ACROSS MUCH OF THE EASTERN U.S.  
WITH GENERALLY LIGHT TO MODERATE RAIN. POTENTIAL EXISTS FOR  
POCKETS OF LOCALLY HEAVIER ACTIVITY THOUGH. THE TRAILING COLD  
FRONT WILL STALL OVER THE SOUTHERN PLAINS WHILE THE NEXT SYSTEM  
EMERGES FROM THE WEST, WITH THIS SYSTEM CURRENTLY EXPECTED TO  
TRACK THROUGH THE PLAINS/MIDWEST EARLY NEXT WEEK. CURRENTLY THERE  
APPEARS TO BE DECENT POTENTIAL FOR SOME AREAS OF MODERATE TO HEAVY  
RAINFALL FROM PORTIONS OF THE CENTRAL/SOUTHERN PLAINS  
NORTHEASTWARD, BUT IT WILL TAKE ADDITIONAL TIME TO REFINE MORE  
PRECISE THREAT AREAS WITHIN THIS AREA. SOME SEVERE WEATHER IS  
ALSO POSSIBLE, WITH THE STORM PREDICTION CENTER CURRENTLY  
INDICATING THE BEST POTENTIAL FOR SEVERE THUNDERSTORMS ACROSS THE  
SOUTHERN PLAINS SUNDAY AND MONDAY. THE NEXT SYSTEM IN THE SERIES  
MAY PRODUCE YET ANOTHER AREA OF SIGNIFICANT RAINFALL OVER AND EAST  
OF THE NORTH-CENTRAL THROUGH SOUTHERN PLAINS. EVEN MORE WITH THIS  
SYSTEM, CONFIDENCE IS FAIRLY LOW FOR DETAILS OF COVERAGE AND  
TIMING. A SYSTEM ON THE DEEPEST SIDE OF THE SPREAD COULD PRODUCE  
SOME SNOW IN THE NORTHERN PERIPHERY, BUT THIS HAS FAIRLY LOW  
PROBABILITY AT THE MOMENT. SOME AREAS OVER THE CENTRAL U.S. NEED  
TO MONITOR FORECASTS OF THESE SYSTEMS GIVEN THE POTENTIAL TO  
PRODUCE SIGNIFICANT WEATHER AND SENSITIVITY TO ADDITIONAL  
RAINFALL. AT LEAST FOR THE TIME BEING, THE MAJORITY OF FORECASTS  
PRODUCE MOST PRECIPITATION TO THE SOUTH OF THE FAR NORTHERN PLAINS  
WHERE SOIL CONDITIONS ARE THE WETTEST.  
 
THE NORTHERN HALF OF THE PLAINS AND UPPER MIDWEST WILL SEE THE  
MOST PERSISTENT BELOW NORMAL TEMPERATURES DURING THE PERIOD. SOME  
AREAS WITHIN THIS REGION MAY SEE HIGHS AT LEAST 15-20F BELOW  
NORMAL ON SUNDAY-MONDAY AND THEN REMAIN 10-15F BELOW NORMAL  
TUESDAY THROUGH THURSDAY. SYSTEM PROGRESSION OVER THE WEST WILL  
BRING VARIABLE READINGS ACROSS THE REGION LATE WEEKEND INTO EARLY  
NEXT WEEK. A RIDGE MOVING INTO AND OVER THE WEST WILL BRING A  
BROADER AREA OF PLUS 5-15F ANOMALIES FOR HIGHS NEXT  
WEDNESDAY-THURSDAY. THE EAST WILL TEND TO SEE ABOVE NORMAL  
TEMPERATURES, WITH MORNING LOWS TENDING TO HAVE MORE COVERAGE OF  
PLUS 10F OR GREATER ANOMALIES THAN DAYTIME HIGHS. SOME LOCATIONS  
IN THE NORTHEAST COULD SEE SLIGHTLY BELOW NORMAL TEMPERATURES  
EARLY 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  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE MIDDLE/LOWER MISSISSIPPI  
VALLEY, AND THE SOUTHERN PLAINS,  
SUN-MON, MAY 1-MAY 2.  
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL/SOUTHERN PLAINS AND  
THE MIDDLE/LOWER MISSISSIPPI  
VALLEY, WED, MAY 4.  
- SEVERE WEATHER ACROSS PORTIONS OF THE SOUTHERN PLAINS, SUN, MAY  
1.  
- SEVERE WEATHER ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,  
AND THE SOUTHERN PLAINS, MON, MAY  
2.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE UPPER MISSISSIPPI  
VALLEY AND THE NORTHERN PLAINS.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE  
LOWER/UPPER MISSISSIPPI VALLEY, AND THE  
NORTHERN PLAINS.  
- FLOODING LIKELY ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY  
AND THE NORTHERN PLAINS.  
- ENHANCED WILDFIRE RISK ACROSS PORTIONS OF THE SOUTHERN ROCKIES,  
THE SOUTHERN PLAINS, AND THE  
SOUTHWEST, SUN, MAY 1.  
- FLOODING POSSIBLE ACROSS PORTIONS OF MAINLAND ALASKA, SUN-THU,  
MAY 1-MAY 5.  
 
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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