674  
FXUS02 KWBC 221900  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT THU MAY 22 2025  
 
VALID 12Z SUN MAY 25 2025 - 12Z THU MAY 29 2025  
 
 
...HEAVY RAIN AND FLASH FLOODING CONCERNS CONTINUE IN THE OZARKS  
AND VICINITY SUNDAY...  
 
   
..OVERVIEW
 
 
A PATTERN SUPPORTING HEAVY RAIN AND THUNDERSTORMS WILL BE IN PLACE  
AS THE PERIOD BEGINS SUNDAY, AS AN UPPER TROUGH ATOP THE ROCKIES  
SUNDAY MOVES EAST WITH AMPLE MOISTURE AND INSTABILITY STREAMING  
INTO A FRONTAL SYSTEM IN THE CENTRAL U.S. AHEAD OF IT. FLASH  
FLOODING IS EXPECTED IN THE OZARKS AND VICINITY AS PART OF A  
POTENTIALLY SIGNIFICANT MULTI-DAY HEAVY RAINFALL EVENT. THIS TROUGH  
TRACKING EAST WILL COMBINE WITH ANOTHER TROUGH STRETCHING FROM THE  
EAST WESTWARD ACROSS THE GREAT LAKES, CAUSING THE TROUGH TO DIG  
ATOP THE EAST- CENTRAL U.S. AND FINALLY PRESS THE FRONT AND THE  
RESULTANT RAINFALL SOUTHEAST ACROSS THE SOUTHERN TIER INTO THE  
APPALACHIANS AND EVENTUALLY THE EASTERN SEABOARD. THE ROUNDS OF  
TROUGHING ALOFT WILL CAUSE COOLER THAN NORMAL TEMPERATURES IN PARTS  
OF THE CENTRAL AND EASTERN U.S., WHILE UPPER RIDGING BUILDING IN  
THE INTERMOUNTAIN WEST SHOULD ALLOW FOR WARMER THAN AVERAGE  
TEMPERATURES THERE.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE LATEST MODEL GUIDANCE SHOWS AN INITIALLY BLOCKY PATTERN  
HEADING INTO THE WEEKEND WITH A LINGERING UPPER-LOW OVER THE  
NORTHEASTERN U.S./GREAT LAKES, STRONG RIDGE ANCHORED NORTH INTO  
SOUTH-CENTRAL CANADA, AND ANOTHER UPPER-LOW OVER THE NORTHEASTERN  
PACIFIC. A LINGERING QUASI-STATIONARY FRONTAL BOUNDARY FROM THE  
PASSAGE OF THIS NORTHEASTERN U.S. UPPER-LOW WILL BE DRAPED ACROSS  
THE SOUTHEAST WEST THROUGH THE MISSISSIPPI VALLEY INTO THE SOUTHERN  
PLAINS, PROVIDING THE FOCUS FOR MULTIPLE DAYS OF WIDESPREAD  
SHOWER/STORM DEVELOPMENT. ALL OF THE GUIDANCE IS IN GENERALLY GOOD  
AGREEMENT DEPICTING A SOMEWHAT COMPLEX EVOLUTION OF SOUTHERN STREAM  
SHORTWAVE ENERGY THAT WILL BREAKTHROUGH UNDER THE PREVAILING  
UPPER-RIDGE AND SLOWLY PROGRESS EASTWARD FROM THE WESTERN U.S. AND  
OVER THE PLAINS SUNDAY INTO MONDAY, POTENTIALLY COMBINING WITH  
ADDITIONAL LINGERING UPPER-ENERGY FROM THE UPPER-LOW OVER THE  
NORTHEASTERN U.S. THIS SHOULD EVENTUALLY LEAD TO LEE CYCLOGENESIS  
OVER THE PLAINS AND HELP TO USHER THE FRONTAL SYSTEM EASTWARD  
THROUGH EARLY TO MID-NEXT WEEK. THERE IS SOME DISCREPANCY WITH THE  
EXACT EVOLUTION OF THIS SYSTEM AS IT LIFTS NORTHEASTWARD THROUGH  
THE MISSISSIPPI AND INTO THE OHIO VALLEY BEFORE APPROACHING THE  
EAST COAST WITH REGARD TO SECONDARY COASTAL LOW DEVELOPMENT, THOUGH  
THE GUIDANCE TENDS TO FAVOR THIS DEVELOPMENT AT SOME POINT MID-  
NEXT WEEK WHICH WILL HAVE IMPACTS ON RAINFALL POTENTIAL/AMOUNTS  
EXTENDING INTO THE MID-ATLANTIC/NORTHEAST.  
 
THERE IS GREATER DISAGREEMENT IN THE PATTERN TO THE WEST EARLY TO  
MID-NEXT WEEK AS SHORTWAVE ENERGY EJECTS FROM THE NORTHEASTERN  
PACIFIC LOW. THE 00Z ECMWF/CMC/UKMET (AS WELL AS THE ENSEMBLE  
MEANS) GENERALLY AGREE THAT THIS WAVE WILL MAKE SLOW PROGRESS AS  
THE UPPER-RIDGE OVER SOUTH-CENTRAL CANADA AND INTO THE INTERIOR  
WEST REMAINS ENTRENCHED TO ITS EAST BEFORE EVENTUALLY, POTENTIALLY  
WEAKENING AND LIFTING NORTHEASTWARD. THE FRONTAL SYSTEM REFLECTION  
AT THE SURFACE IS EXPECTED TO EVENTUALLY DISSIPATE GIVEN THE  
RIDGING TO THE EAST, WITH MODEST SENSIBLE WEATHER IMPACTS EXPECTED.  
THE LINGERING UPPER-ENERGY MAY ALSO EVENTUALLY MERGE WITH  
ADDITIONAL SOUTHERN STREAM ENERGY APPROACHING FROM THE PACIFIC. ON  
THE OTHER HAND, THE 00Z GFS WAS WEAKER WITH THIS UPPER  
-RIDGE, AND THE 06Z HAD A MUCH DIFFERENT SOLUTION DEPICTING THE  
UPPER-WAVE HELPING TO BREAKDOWN THE RIDGING BY MERGING WITH UPPER  
ENERGY FROM LINGERING UPPER-TROUGH ACROSS THE GREAT  
LAKES/NORTHEAST, AND EVENTUALLY MOVING EASTWARD OVER THE  
NORTHERN/CENTRAL PLAINS. THIS WOULD LEAD TO MUCH MORE  
PRECIPITATION ACROSS THE NORTH-CENTRAL U.S. TO GREAT LAKES. THE  
LATEST 12Z UPDATE FOR THE GFS ALSO SHOWS UPPER-TROUGHING LINGERING  
LONGER WESTWARD OVER THE NORTH-CENTRAL U.S., POTENTIALLY  
REINFORCED BY ADDITIONAL ENERGY FROM THE WEST, THAT WOULD LEAD TO  
MORE ADDITIONAL HEAVY PRECIPITATION CHANCES OVER THE  
PLAINS/MISSISSIPPI VALLEY.  
 
THE UPDATED WPC FORECAST BLEND INCLUDES A COMPOSITE OF THE  
AVAILABLE 00Z GUIDANCE (FAVORING THE 00Z GFS GIVEN THE NOTED  
DIFFERENCES IN THE 06Z) GIVEN GENERALLY SIMILAR SOLUTIONS. A  
CONTRIBUTION FROM THE MEANS IS INCLUDED WITH A REDUCED CONTRIBUTION  
FROM THE 00Z GFS/CMC LATER IN THE PERIOD GIVEN NATURALLY GROWING  
DIFFERENCES, WITH LARGER DIFFERENCES SPECIFICALLY WITH THE 00Z GFS.  
THIS BLEND PROVIDES FOR GOOD CONTINUITY WITH THE PRIOR WPC  
FORECAST.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
A WAVY WEST-EAST ORIENTED FRONT WILL BE IN PLACE OVER THE SOUTH-  
CENTRAL PLAINS AND MISSISSIPPI VALLEY ON SUNDAY. MOISTURE  
(PRECIPITABLE WATER) VALUES LIKELY OVER THE 90TH PERCENTILE AND  
AMPLE INSTABILITY WILL STREAM INTO THE FRONT, AND THE RIGHT  
ENTRANCE REGION OF THE JET PROVIDES DYNAMICAL SUPPORT. THIS WILL  
LEAD TO ADDITIONAL HEAVY RAIN, PERHAPS IN MULTIPLE ROUNDS, LIKELY  
CENTERED IN THE OZARKS AND VICINITY ON SUNDAY. THIS FOLLOWS HEAVY  
RAINFALL EXPECTED OVER ALMOST THE EXACT SAME REGION THE PRIOR TWO  
DAYS. A TARGETED MODERATE RISK ERO HAS BEEN INTRODUCED TO COVER THE  
THIRD DAY OF A POTENTIALLY SIGNIFICANT MULTI-DAY HEAVY RAIN AND  
FLASH FLOODING EVENT GIVEN INCREASINLY WET ANTECDENT CONDITIONS. A  
BROADER SLIGHT RISK IS IN PLACE FOR THE FROM THE SOUTH- CENTRAL  
PLAINS INTO PARTS OF THE LOWER AND MIDDLE MISSISSIPPI VALLEY. DUE  
TO MODELS CONVERGING BETTER ON TIMING AND PLACEMENT OF CONVECTION,  
THE SIZE OF A BROADER MARGINAL RISK HAS BEEN REDUCED COMPARED TO  
THE PREVIOUS COUPLE OF ISSUANCES.  
 
BY MEMORIAL DAY, THE TROUGH ALOFT SHOULD FINALLY PRESS THE FRONT  
GRADUALLY SOUTH TOWARD THE SOUTHERN TIER AND EAST TOWARD THE  
APPALACHIANS. MOISTURE AND INSTABILITY IN PLACE COULD STILL LEAD TO  
HEAVY RAIN RATES ACROSS THE SOUTH-CENTRAL U.S. INTO THE TENNESSEE  
VALLEY AND LOWER OHIO VALLEY, BUT AT LEAST THERE SHOULD BE  
RELATIVELY LESS POTENTIAL FOR TRAINING STORMS AS THE FRONT MOVES.  
FOR THE DAY 5/MONDAY ERO, SHOW A MARGINAL RISK DELINEATED ACROSS  
THESE AREAS AS A STARTING POINT. EMBEDDED SLIGHTS MAY BE NEEDED IN  
FUTURE ISSUANCES BUT THE DETAILS STILL NEED TO BE REFINED WITH  
TIME, AND MUCH OF THIS REGION WILL HAVE BEEN DRY IN THE PRIOR DAYS  
LEADING TO HIGH FFG VALUES. ON TUESDAY, THE EVENTUAL DOMINANT LOW  
ON THE FRONTAL SYSTEM SHOULD LIFT NORTHEAST AND BRING LOCALIZED  
HEAVY RAIN TO THE EASTERN SEABOARD, ESPECIALLY THE MID- ATLANTIC,  
WHILE THE TRAILING FRONT STILL LINGERS AND CAUSES SHOWERS AND  
STORMS ACROSS THE SOUTHERN TIER TUESDAY- WEDNESDAY.  
 
FARTHER NORTH, THE INITIAL TROUGH SHOULD PRODUCE SOME MODEST  
PRECIPITATION IN THE CENTRAL ROCKIES (EVEN SOME SNOW IN THE HIGHEST  
PEAKS) AND THE NORTHERN/CENTRAL PLAINS EARLY NEXT WEEK. THE  
FRONTAL BOUNDARY CURLING BACK INTO THE SOUTHERN/CENTRAL ROCKIES AND  
HIGH PLAINS COULD HELP PRODUCE SCATTERED CONVECTION THERE NEXT  
WEEK AS WELL. MEANWHILE, ROUNDS OF FRONTS COMING THROUGH THE  
NORTHWEST COULD ALLOW FOR LIGHT TO MODERATE PRECIPITATION.  
SUMMERTIME SCATTERED STORMS ARE ALSO LIKELY ACROSS THE FLORIDA  
PENINSULA.  
 
ONE MORE DAY OF HOT WEATHER IS LIKELY FOR TEXAS ACROSS THE  
SOUTHEAST ON SUNDAY. TEMPERATURES WELL INTO THE 90S TO AROUND 100  
WILL SUPPORT AREAS OF MAJOR HEATRISK IN SOUTHERN PARTS OF TEXAS AND  
LOUISIANA. MEANWHILE, COOLER THAN NORMAL TEMPERATURES BY 5 TO 15  
DEGREES WILL TAKE HOLD OVER THE NORTH-CENTRAL TO EASTERN U.S. INTO  
EARLY NEXT WEEK UNDERNEATH UPPER TROUGHING. THE TROUGH AND FRONT  
PRESSING SOUTH WILL ALLOW FOR TEMPERATURES TO COOL IN THE SOUTHERN  
TIER MONDAY AND TUESDAY. THE COOLER TEMPERATURES SHOULD GRADUALLY  
MODERATE CLOSER TO NORMAL AS NEXT WEEK PROGRESSES. BUT IN THE WEST,  
A BUILDING UPPER RIDGE WILL LEAD TO WARMER THAN AVERAGE  
TEMPERATURES BY 10 TO 15 DEGREES FOR SEVERAL DAYS OVER THE GREAT  
BASIN AND NORTHERN/CENTRAL ROCKIES.  
 
PUTNAM/TATE  
 
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  
 

 
 
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