143  
FXUS02 KWBC 220700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM 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 POSSIBLE IN THE OZARKS AND VICINITY, CONTINUING FROM  
THE SHORT RANGE PERIOD. 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  
 
MODEL GUIDANCE CONTINUES TO BE AGREEABLE ON THE BROAD SCALE (WITH  
TYPICAL DETAIL DIFFERENCES) AT THE START OF THE MEDIUM RANGE PERIOD  
SUNDAY, INDICATING AN UPPER TROUGH EXTENDING WESTWARD FROM AN  
ATLANTIC CANADA UPPER LOW ACROSS THE NORTHERN TIER AND ANOTHER  
TROUGH ATOP THE FOUR CORNERS TOWARD THE NORTHERN HIGH PLAINS. THESE  
TROUGHS ARE FORECAST TO COMBINE AND SUPPRESS THE INITIAL  
SUBTROPICAL RIDGE OVER THE SOUTHERN TIER. AT THE SURFACE THERE IS  
GENERAL CONSENSUS THAT THIS WILL PUSH THE MAIN FRONT SOUTH AND  
EAST, BUT THERE ARE SOME DIFFERENCES AS A SURFACE LOW EMERGES AS  
DOMINANT IN RESPONSE TO THE TROUGH. THE LOW SHOULD TRACK EASTWARD  
INTO THE LOWER OHIO VALLEY OR SO EARLY TUESDAY, BUT THE 18Z GFS WAS  
PARTICULARLY FAST TO TAKE THE LOW (AND SPREAD QPF TO) THE MID-  
ATLANTIC BY THEN. BUT THERE IS REASONABLE AGREEMENT THAT THE  
COMBINED TROUGH WILL SLOWLY MOVE EAST TUESDAY-THURSDAY OVER THE  
EASTERN HALF OF THE U.S., WITH NEWER 00Z MODELS INDICATING AN  
EMBEDDED UPPER LOW IN THE GREAT LAKES VICINITY AROUND MIDWEEK.  
 
FARTHER WEST, MODELS ARE AGREEABLE THAT AN UPPER RIDGE WILL  
DOMINATE ACROSS THE INTERIOR WEST THROUGH MUCH OF NEXT WEEK. BROAD  
TROUGHING WILL SET UP IN THE EASTERN PACIFIC WITH INITIAL AND THEN  
RELOADING NORTHEAST PACIFIC UPPER LOWS. THIS WILL SET UP AN OMEGA  
BLOCK PATTERN WITH THE PACIFIC TROUGH, WEST RIDGE, AND EAST TROUGH.  
BUT THE MORE UNCERTAIN PIECE IS WITH POTENTIAL FOR ENERGY TO BREAK  
OFF AND FORM SOUTHERN STREAM TROUGHING OR AN UPPER LOW OR TWO  
MOVING INTO THE WEST COAST. DYNAMICAL AND AI MODELS ALL SHOW A LOT  
OF SPREAD WITH THIS POTENTIAL. WITH THE 12/18Z MODEL CYCLE, THE CMC  
WAS PARTICULARLY AGGRESSIVE WITH A STRONGER UPPER LOW ATOP  
CALIFORNIA EARLY TUESDAY COMPARED TO OTHER GUIDANCE. THEN  
MIDLATITUDE PACIFIC ENERGY MAY ALSO REACH CALIFORNIA AROUND  
THURSDAY, THOUGH THE 12/18Z GFS AND 12Z ECMWF WERE OFFSHORE WITH  
THIS FEATURE. THE 00Z MODEL CYCLE FORTUNATELY SEEMS TO BE SHOWING  
MORE CONVERGENCE IN SOLUTIONS, AS THE 00Z CMC WEAKENED SOMEWHAT  
WHILE THE EC/GFS WERE A BIT STRONGER TUESDAY 12Z AND THUS ALIGN  
WELL. ADDITIONALLY, THE NEXT TROUGH/POSSIBLE LOW IS TRENDING A BIT  
FARTHER EAST AND REACHING CALIFORNIA BY THURSDAY.  
 
THE WPC FORECAST WAS ABLE TO USE A GENERAL MODEL BLEND EARLY IN  
THE PERIOD, WITH INCREASING PROPORTIONS OF THE ENSEMBLE MEANS TO A  
LITTLE MORE THAN HALF DAYS 6-7 GIVEN INCREASING SPREAD IN THE  
INDIVIDUAL MODELS.  
 
   
..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. A SLIGHT RISK IS IN  
PLACE FOR THE DAY 4/SUNDAY ERO FROM THE SOUTH-CENTRAL PLAINS INTO  
PARTS OF THE LOWER AND MIDDLE MISSISSIPPI VALLEY. OVER THE OZARKS,  
THIS IS CONSIDERED A HIGHER END SLIGHT RISK THAT MAY BECOME A  
MODERATE RISK EVENTUALLY, DEPENDING ON THE EXACT OVERLAP BETWEEN  
SUNDAY'S RAIN AND HEAVY RAIN DURING THE SHORT RANGE PERIOD. DUE TO  
MODELS CONVERGING BETTER ON TIMING AND PLACEMENT OF CONVECTION, WAS  
ABLE TO REDUCE THE SIZE OF THE BROADER MARGINAL A BIT ON THE  
SOUTHERN AND EASTERN SIDES, 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. 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.  
 
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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