387  
FXUS02 KWBC 260658  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
258 AM EDT SAT APR 26 2025  
 
VALID 12Z TUE APR 29 2025 - 12Z SAT MAY 03 2025  
 
 
...HEAVY RAINFALL THREAT OVER THE SOUTHERN HALF OF THE PLAINS  
TUESDAY-WEDNESDAY...  
   
..OVERVIEW
 
 
A COLD FRONT PUSHING ACROSS THE NORTHEASTERN QUADRANT OF THE LOWER  
48 WILL HANG BACK OVER THE PLAINS WHILE AWAITING EJECTION OF A  
SOUTHWEST U.S. SHORTWAVE. THIS FEATURE AND DYNAMICS COMING IN  
BEHIND IT SHOULD ULTIMATELY GENERATE A SURFACE LOW THAT BRINGS A  
FRONT THROUGH MORE OF THE EAST BY THE END OF THE WEEK AS UPPER  
TROUGHING AMPLIFIES. THE TUESDAY-WEDNESDAY PATTERN WILL FAVOR  
EPISODES OF HEAVY RAINFALL OVER AND NEAR THE SOUTHERN HALF OF THE  
PLAINS BEFORE SYSTEM PROGRESSION SPREADS LESS PRONOUNCED RAINFALL  
TOTALS ACROSS THE EAST. A TRAILING UPPER RIDGE SHOULD MOVE INTO THE  
NORTHWEST AFTER EARLY WEDNESDAY, REACHING THE PLAINS BY THE START  
OF THE WEEKEND, WHILE A PACIFIC UPPER TROUGH SHOULD REACH THE WEST  
COAST AROUND SATURDAY WITH SOME PRECIPITATION OVER THE NORTHWEST.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
GUIDANCE IS SIMILAR IN PRINCIPLE FOR THE FORECAST OVER THE CENTRAL  
AND EASTERN U.S. BUT WITH SOME TYPICAL DIFFERENCES AND MINORITY  
STRAY SOLUTIONS. THERE ARE STILL SOME TIMING DIFFERENCES AS LOW  
PRESSURE CROSSING SOUTHEASTERN CANADA TUESDAY-WEDNESDAY PUSHES A  
TRAILING COLD FRONT THROUGH THE GREAT LAKES/NORTHEAST, WITH AN  
AVERAGE PROVIDING A REASONABLE STARTING POINT. THEN AS SOUTHWEST  
U.S. SHORTWAVE ENERGY EJECTS NORTHEASTWARD, SOLUTIONS STILL VARY  
FOR DETAILS OF DEVELOPING LOW PRESSURE THAT TRACKS NORTHEASTWARD.  
AT LEAST THE SURFACE LOW'S POSITION OVER THE CENTRAL-EASTERN GREAT  
LAKES BY THURSDAY NIGHT-FRIDAY IN THE MAJORITY CLUSTER HAS HELD UP  
RATHER WELL OVER THE PAST DAY. IN ADDITION THE LATEST MACHINE  
LEARNING (ML) MODELS SEEM TO BE GAINING SOME DEFINITION FOR THIS  
WAVINESS COMPARED TO 24 HOURS AGO. THROUGH THURSDAY OR SO, THE 12Z  
CMC STARTED TO STRAY ON THE FAST SIDE WHILE THE 12Z UKMET LAGGED  
OTHER GUIDANCE FOR THE EJECTING SOUTHWEST UPPER FEATURE. THE 00Z  
SOLUTIONS HAVE TRIMMED THE EXTREME SIDES OF THE ENVELOPE. HOWEVER  
TOWARD THE END OF THE WEEK THERE IS A FAIR AMOUNT OF  
SPREAD/VARIABILITY FOR HOW THE OVERALL EASTERN NORTH AMERICA UPPER  
TROUGH WILL EVOLVE IN BOTH THE DYNAMICAL AND ML GUIDANCE, LOWERING  
CONFIDENCE IN SPECIFICS. THIS FAVORS A BLENDED/ENSEMBLE MEAN  
APPROACH LATE IN THE PERIOD.  
 
OVER THE WEST, SOME WEAK SHORTWAVE/UPPER LOW ENERGY MAY BRIEFLY  
REACH THE SOUTHWEST BEFORE AN AMPLIFIED UPPER TROUGH WITH LEADING  
COLD FRONT REACHES THE WEST COAST BY EARLY SATURDAY. RECENT GFS  
TRENDS HAVE LED TO IMPROVED CLUSTERING INTO FRIDAY, THOUGH WITH  
CONSENSUS AS A WHOLE ADJUSTING A BIT SLOWER COMPARED TO YESTERDAY.  
BY EARLY SATURDAY THE LATEST DYNAMICAL/ML MAJORITY SUGGESTS THE  
UPPER TROUGH WILL REMAIN FAIRLY PHASED, VERSUS SOME EARLIER MODEL  
RUNS THAT HAD VARIOUS IDEAS FOR HOW FLOW COULD SEPARATE. HOWEVER  
MULTIPLE SOLUTIONS SHOW SEPARATION BY LATER SATURDAY OR SUNDAY.  
 
GUIDANCE COMPARISONS BASED ON 12Z/18Z GUIDANCE LED TO EMPHASIZING  
THE 18Z GFS/12Z ECMWF ALONG WITH A LITTLE 12Z CMC TUESDAY-  
WEDNESDAY, FOLLOWED BY A TRANSITION TOWARD AN EVEN WEIGHT OF THE  
GFS/ECMWF AND THEIR CORRESPONDING ENSEMBLE MEANS BY NEXT SATURDAY.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
DURING TUESDAY-WEDNESDAY, LOW PRESSURE LIFTING AWAY FROM LAKE  
SUPERIOR WILL PUSH A COLD FRONT ACROSS THE NORTHEASTERN QUADRANT OF  
THE LOWER 48 WHILE THE TRAILING PART OVER THE PLAINS STALLS AND  
DEVELOPS A WAVE AS A SOUTHWEST U.S. SHORTWAVE EJECTS NORTHEASTWARD.  
THIS PATTERN COMBINED WITH ANOMALOUS MOISTURE AND SUFFICIENT  
INSTABILITY WILL FAVOR A HEAVY RAINFALL THREAT OVER AND NEAR THE  
SOUTHERN HALF OF THE PLAINS IN THIS TIME FRAME. THE DAY 4/TUESDAY  
EXCESSIVE RAINFALL OUTLOOK MAINTAINS A MARGINAL RISK AREA FROM  
PARTS OF TEXAS INTO THE LOWER OHIO VALLEY. THERE STILL SEEMS TO BE  
ENOUGH GUIDANCE SPREAD WITHIN THIS AREA TO FAVOR WAITING FOR  
IMPROVED CLUSTERING BEFORE INTRODUCING AN EMBEDDED SLIGHT RISK.  
MODELS/ENSEMBLES AND FIRST-GUESS FIELDS GENERALLY STRENGTHEN THE  
HEAVY RAINFALL SIGNAL ON DAY 5/WEDNESDAY. THUS THE DAY 5 ERO  
INTRODUCES A SLIGHT RISK AREA ENCOMPASSING PARTS OF TEXAS/OKLAHOMA  
AND NUDGING INTO FAR WESTERN ARKANSAS. THE SURROUNDING MARGINAL  
RISK COVERS A SIMILAR AREA AS THE DAY 4 ERO. THE STORM PREDICTION  
CENTER IS ALSO MONITORING FOR SEVERE THREATS ON TUESDAY FROM THE  
EASTERN GREAT LAKES AND VICINITY SOUTHWEST INTO NORTHERN TEXAS.  
CHECK THE SPC OUTLOOKS FOR THE LATEST INFO ON SEVERE THREATS.  
 
AFTER EARLY WEDNESDAY, CONTINUED PROGRESS OF LOW PRESSURE AND ITS  
TRAILING COLD FRONT SHOULD PUSH RAINFALL ACROSS MUCH OF THE EAST  
BUT WITH LESSER TOTALS THAN FORECAST OVER THE CENTRAL U.S. FARTHER  
WEST, SHORTWAVE ENERGY AND A FRONTAL SYSTEM SHOULD SPREAD RAIN AND  
SOME HIGH ELEVATION SNOW FROM THE NORTHWEST THROUGH THE NORTHERN  
AND CENTRAL ROCKIES TUESDAY-THURSDAY. BY THE END OF THE WEEK SOME  
RAIN MAY DEVELOP OVER THE SOUTHERN HIGH PLAINS WITH THE HELP OF  
EASTERLY LOW LEVEL FLOW. AN UPPER TROUGH/COLD FRONT REACHING THE  
WEST COAST BY FRIDAY-SATURDAY SHOULD BRING RAIN AND HIGH ELEVATION  
SNOW INTO THE NORTHWEST.  
 
EXPECT UNSEASONABLY WARM TEMPERATURES OVER THE EASTERN U.S. ON  
TUESDAY AHEAD OF AN ADVANCING COLD FRONT. PLUS 10-20F ANOMALIES  
WILL EQUATE TO HIGHS REACHING INTO THE 80S OVER THE OHIO VALLEY.  
MORNING LOWS WILL BE EVEN A LITTLE MORE ANOMALOUS. NORTHERN PARTS  
OF THE EAST WILL TREND COOLER BY MIDWEEK BUT LOCATIONS FARTHER  
SOUTH SHOULD REMAIN SOMEWHAT ABOVE NORMAL THROUGH FRIDAY. A MORE  
AMPLIFIED UPPER TROUGH WILL LIKELY PUSH THE NEXT COLD FRONT FARTHER  
SOUTH, BRINGING TEMPERATURES OVER THE EAST TO WITHIN A FEW DEGREES  
ON EITHER SIDE OF NORMAL BY SATURDAY. MEANWHILE AN UPPER RIDGE  
DRIFTING FROM THE NORTHWEST INTO THE PLAINS AFTER WEDNESDAY WILL  
SUPPORT CORRESPONDING EASTWARD PROGRESS OF AN AREA OF HIGHS 10-20F  
ABOVE NORMAL.  
 
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 FORECAST (QPF), EXCESSIVE RAINFALL  
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT  
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:  
 
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  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page