815  
FXUS02 KWBC 170700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT SAT MAY 17 2025  
 
VALID 12Z TUE MAY 20 2025 - 12Z SAT MAY 24 2025  
 
...SEVERE WEATHER AND FLASH FLOODING FORECAST FOR PARTS OF THE  
MISSISSIPPI AND OHIO VALLEYS TUESDAY...  
 
...HAZARDOUS AND RECORD HEAT COULD CONTINUE ESPECIALLY ACROSS TEXAS  
AND FLORIDA INTO MID-NEXT WEEK...  
 
   
..OVERVIEW
 
 
AS THE MEDIUM RANGE PERIOD BEGINS TUESDAY, A SURFACE LOW PRESSURE  
SYSTEM OVER THE MID-MISSISSIPPI VALLEY SUPPORTED BY STRONG UPPER-  
LEVEL ENERGY WILL PROVIDE AMPLE LIFT AND INSTABILITY FOR RAIN AND  
THUNDERSTORMS IN THE MISSISSIPPI AND OHIO VALLEYS. THE LOW IS  
FORECAST TO TRACK EAST AND SPREAD RAIN AND THUNDERSTORM CHANCES TO  
THE MID-ATLANTIC IN PARTICULAR ON WEDNESDAY, AND SHIFTING INTO THE  
NORTHEAST LATER WEEK AS THE LOW PIVOTS NORTHWARD. ALOFT, THE  
SUBTROPICAL UPPER RIDGE PROVIDING POTENTIALLY HAZARDOUS AND RECORD  
SETTING HEAT TO PARTS OF TEXAS AND FLORIDA IN PARTICULAR THROUGH  
TUESDAY-WEDNESDAY SHOULD GIVE WAY TO COMBINING ENERGIES THAT SET UP  
TROUGHING OVER THE EAST FOR COOLER TEMPERATURES. MEANWHILE, RIDGING  
BEHIND THIS TROUGH WILL LEAD TO WARMER THAN AVERAGE CONDITIONS  
ACROSS CALIFORNIA AND THE GREAT BASIN/DESERT SOUTHWEST, EXPANDING  
ACROSS THE FOUR CORNERS AND SOUTHERN HIGH PLAINS INTO LATE WEEK.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODEL GUIDANCE IS AGREEABLE THAT CONSOLIDATED MID/UPPER LEVEL  
VORTICITY WILL BE ATOP THE CENTRAL PLAINS EARLY TUESDAY, THOUGH  
WITH SOME UNCERTAINTY REGARDING IF THE UPPER LOW WILL CLOSE OFF,  
AND ALSO WHEN THE ENERGY MAY TRANSFER FROM A SOUTHEAST EXTENSION OF  
A WESTERN CANADA TROUGH INTO A SOUTHWEST EXPANSION OF A GREAT  
LAKES/ONTARIO/QUEBEC UPPER LOW. THE DETAILS OF THE UPPER TROUGH/LOW  
AFFECT THE EXACT TIMING AND TRACK OF THE SURFACE LOW. THE GENERAL  
AGREEMENT OF THE SURFACE LOW OVER THE MIDDLE MISSISSIPPI VALLEY ON  
TUESDAY DIVERGES ESPECIALLY WITH THE TIMING BY WEDNESDAY. FOR THE  
12/18Z GUIDANCE, THE 12Z CMC WAS ON THE SLOW/WEST SIDE WHILE THE  
12Z GFS WAS ON THE FAST/EAST SIDE. SOME DIFFERENCES CONTINUE AS THE  
LOW MOVES NORTHEAST, AFFECTING PRECIPITATION TIMING. THE 00Z GFS  
ENDED UP BEING FASTER WITH THE LOW AND LIFTING THE PRECIPITATION  
SHIELD COMPARED TO OTHER GUIDANCE.  
 
UPSTREAM, MODELS INDICATE A SOUTHWEST UPPER RIDGE BUILDING AND  
SNEAKING GRADUALLY EAST INTO THE SOUTH-CENTRAL U.S. LATE WEEK.  
FARTHER NORTH THERE IS MORE UNCERTAINTY WITH WEAK SHORTWAVES IN THE  
MAIN FLOW OVER THE NORTHWEST FOR SOME FRONTAL SYSTEM TIMING  
DIFFERENCES. THE MAIN OUTLIER THERE WAS WITH THE 12Z AND 18Z GFS  
SHOWING A NOTABLE UPPER/SURFACE LOW SPINNING UP OVER SOUTH-CENTRAL  
CANADA BY LATE WEEK UNLIKE OTHER DYNAMICAL AND AI/ML MODELS. DID  
NOT FAVOR THESE GFS RUNS AND THE NEW 00Z GFS HAS BACKED OFF. THERE  
IS SOME SIGNAL FOR SLIGHTLY DEEPER TROUGHING TO MOVE FROM THE  
EASTERN PACIFIC INTO THE PACIFIC NORTHWEST BY FRIDAY OR SO, BUT  
ONCE AGAIN UNCERTAINTY WITH THE DETAILS ABOUNDS.  
 
THE WPC FORECAST WAS BASED ON A BLEND OF MAINLY DETERMINISTIC  
MODELS WITH MINOR ENSEMBLE MEAN INCLUSION EARLY IN THE FORECAST  
PERIOD, AND GRADUALLY INCREASED THE PROPORTION OF ENSEMBLE MEANS TO  
HALF DAY 5 AND MORE DAYS 6-7 AS SPREAD INCREASED.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE NOTABLE SURFACE LOW PRESSURE SYSTEM OVER THE MIDDLE  
MISSISSIPPI VALLEY TUESDAY WILL DRAW IN ABOVE AVERAGE MOISTURE  
(WITH PRECIPITABLE WATER VALUES NEARING THE 90TH PERCENTILE FOR  
THIS TIME OF YEAR) AND AMPLE INSTABILITY AHEAD OF ITS ASSOCIATED  
COLD FRONT. THE UPPER LOW SPINNING ALOFT WILL PROVIDE GOOD  
DYNAMICAL LIFT, AND THIS COMBINATION OF INGREDIENTS WILL LEAD TO  
WIDESPREAD RAIN AND THUNDERSTORMS AND MESOSCALE CONVECTIVE SYSTEMS,  
WITH BEST CHANCES SLOWLY PROGRESSING EAST FROM THE CENTRAL TO  
EAST-CENTRAL TO EASTERN U.S. AS NEXT WEEK PROGRESSES. THE GREATEST  
CHANCE FOR HEAVY RAIN CAUSING FLASH FLOODING SHOULD BE ACROSS THE  
MID-MISSISSIPPI AND OHIO VALLEYS INTO THE CENTRAL APPALACHIANS ON  
TUESDAY, AS MOISTURE AND INSTABILITY POOL NEAR A WARM FRONT  
STRETCHING WEST-EAST THAT COULD PROMOTE TRAINING STORMS. A  
RELATIVELY EXPANSIVE SLIGHT RISK IS IN PLACE IN THE DAY 4/TUESDAY  
ERO. SEVERE WEATHER IS ALSO POSSIBLE PER THE STORM PREDICTION  
CENTER, AS THEY SHOW A SEVERE AREA CENTERED OVER THE LOWER/MIDDLE  
MISSISSIPPI VALLEY ON TUESDAY. RAIN AND THUNDERSTORM POTENTIAL  
SHOULD PRESS TOWARD THE EASTERN SEABOARD BY MIDWEEK AS THE LOW  
TRACKS EAST. LOCALLY HEAVY RAINFALL IS POSSIBLE PARTICULARLY FOR  
THE MID-ATLANTIC REGION ON WEDNESDAY. THE DAY 5/WEDNESDAY ERO  
INDICATES A MARGINAL RISK FOR FLOODING POTENTIAL. A FUTURE SLIGHT  
RISK IS NOT OUT OF THE QUESTION, BUT PREFER TO WAIT ON BETTER MODEL  
AGREEMENT FOR THE LOW TRACK AND TIMING AND THUS THE PLACEMENT OF  
THE HIGHEST QPF. SOILS/STREAMFLOWS ARE CURRENTLY WET BUT SHOULD  
HAVE A FEW DAYS OF DRYING BEFORE MIDWEEK. RAIN CHANCES WILL MAKE  
THEIR WAY INTO THE NORTHEAST THURSDAY-FRIDAY AS THE SURFACE LOW  
PIVOTS NORTHWARD.  
 
ELSEWHERE, SOME WEAK TROUGHING ALOFT AND FRONTAL SYSTEMS TRACKING  
THROUGH THE NORTHWEST NEXT WEEK COULD PRODUCE ROUNDS OF MODEST  
PRECIPITATION THERE. MOST PRECIPITATION SHOULD BE RAIN ASIDE FROM  
THE HIGHEST PEAKS. SOME RAIN MAY EJECT INTO THE NORTHERN HIGH  
PLAINS BY THURSDAY, WITH POSSIBLY ANOTHER ROUND OF STORMS EMERGING  
IN THE CENTRAL U.S. BY FRIDAY, BUT WITH QUITE A BIT OF UNCERTAINTY.  
 
WARM TO HOT TEMPERATURES ARE LIKELY ACROSS THE SOUTHEASTERN U.S.  
AS THE SUBTROPICAL UPPER RIDGE REACHES THE REGION. SOUTHERN TEXAS  
IN PARTICULAR WILL REMAIN HOT INTO TUESDAY, WITH TEMPERATURES WELL  
INTO THE 100S LEADING TO MAJOR HEATRISK THROUGH TUESDAY. THE  
FLORIDA PENINSULA SHOULD SEE WARM TEMPERATURES IN THE MID 90S. BOTH  
AREAS COULD SEE RECORD OR NEAR RECORD WARM LOWS AND HIGHS.  
MEANWHILE THE TROUGH ALOFT WILL PROMOTE BELOW NORMAL TEMPERATURES  
ACROSS THE NORTHERN TIER, WITH HIGHS ONLY REACHING THE 50S IN THE  
NORTH-CENTRAL PLAINS ON TUESDAY. AS THE TROUGH TRACKS EAST AND ITS  
INFLUENCE DEEPENS, COOLER THAN AVERAGE TEMPERATURES ARE LIKELY IN  
THE EASTERN THIRD OF THE U.S. UNDER IT, AND THIS WILL ALSO MODERATE  
THE TEMPERATURES IN THE SOUTH. BUT UPPER RIDGING POKING INTO THE  
SOUTHWESTERN U.S. WILL RAISE TEMPERATURES TO ABOVE NORMAL THERE,  
EXPANDING EAST ACROSS THE FOUR CORNERS STATES BY THURSDAY AND INTO  
THE SOUTHERN PLAINS LATE NEXT WEEK. HIGHS WILL BE WELL INTO THE  
100S IN THE DESERT SOUTHWEST WITH TEMPERATURES NEARING 100 IN PARTS  
OF TEXAS EVENTUALLY.  
 
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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