773  
FXUS02 KWBC 171917  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
317 PM 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...  
 
   
..OVERVIEW  
 
A SLOW MOVING UPPER LOW OVER THE CENTRAL U.S. TUESDAY SHIFTS EAST  
AND STRENGTHENS OVER THE GREAT LAKES WEDNESDAY AND THE NORTHEAST ON  
FRIDAY BEFORE LINGERING OVER ATLANTIC CANADA NEXT WEEKEND.  
MEANWHILE, SUBTROPICAL RIDGING OVER THE SOUTHEAST BECOMES MORE  
SUPPRESSED FROM THE EASTERN LOW/TROUGHING BY MIDWEEK. FINALLY,  
GENERAL RIDGING OVER THE WEST WILL LEAD TO WARMER THAN AVERAGE  
CONDITIONS ACROSS CALIFORNIA AND THE GREAT BASIN/DESERT SOUTHWEST  
MIDWEEK, EXPANDING ACROSS THE FOUR CORNERS AND SOUTHERN HIGH  
PLAINS LATE IN THE WEEK.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT  
 
12Z GLOBAL GUIDANCE HAS IMPROVED AGREEMENT WITH THE UPPER LOW  
CLOSING OFF TUESDAY EVENING OVER THE CENTRAL PLAINS, A NEW AND  
DEEPER LOW DEVELOPMENT OVER THE GREAT LAKES ON WEDNESDAY, A MORE  
SOUTHERLY TRACK OF THE LOW OVER THE EASTERN GREAT LAKES THURSDAY  
AND THE DEPARTURE OF THE LOW FROM THE NORTHEAST FRIDAY INTO  
SATURDAY. THE GFS REMAINS THE MOST PROGRESSIVE SOLUTION AS IT OPENS  
THE LOW ON THURSDAY WHILE THE EC/CMC KEEP IT CLOSED. ONE OF THE  
MORE NOTABLE SHIFTS WITH 12Z GUIDANCE IS QPF ON WEDNESDAY FOCUSED  
FARTHER SOUTH OVER THE MID-ATLANTIC AND CENTRAL APPALACHIANS  
COMPARED TO PRIOR RUNS.  
 
UPSTREAM, CONSENSUS ON BROAD RIDGING OVER THE SOUTHWEST MIDWEEK  
THAT SHIFTS EAST TO THE SOUTHERN PLAINS BY FRIDAY. THE 00Z EC WAS  
THE LEAST WITH THE NEXT TROUGH INTO THE PACNW ON FRIDAY, BUT THE  
12Z CONSENSUS IS NOW FOR A TROUGH OR LOW TO REACH WASHINGTON ON  
FRIDAY.  
 
THE WPC FORECAST WAS BASED ON A BLEND OF MAINLY DETERMINISTIC  
MODELS FOR DAYS 3-5 WITH ECENS/GEFS ENSEMBLE MEAN INCLUSION FOR  
DAYS 6-7 AS SPREAD INCREASED.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS  
 
AMPLE MOISTURE AND INSTABILITY OVER THE MISS/OH VALLEYS TUESDAY  
AHEAD OF A DEEP LOW OVER THE EAST-CENTRAL PLAINS ALONG WITH STRONG  
DYNAMICAL LIFT ALOFT WILL LEAD TO WIDESPREAD RAIN AND  
THUNDERSTORMS AND MESOSCALE CONVECTIVE SYSTEMS INTO TUESDAY NIGHT.  
THIS COVERS A BROAD AREA INCLUDING MOST OF THE TN/OH VALLEYS AND  
BACK ACROSS THE MIDWEST THROUGH SOUTHERN MN WHERE A BROAD DAY 4  
SLIGHT RISK ERO REMAINS WITH ONLY MINOR EDITS TO THE SHAPE. THE SEVERE  
WEATHER THREAT AREA IS FOCUSED OVER THE SOUTHERN PORTIONS OF THIS  
PRECIP AREA IN THE WARM SECTOR OVER THE TN VALLEY PER THE STORM  
PREDICTION CENTER DAY 4 CONVECTIVE OUTLOOK.  
 
RAIN AND THUNDERSTORM POTENTIAL SHIFTS EAST OVER THE APPALACHIANS  
WEDNESDAY AS THE LOW TRACKS EAST. LOCALLY HEAVY RAINFALL IS  
POSSIBLE PARTICULARLY FOR THE MID- ATLANTIC REGION ON WEDNESDAY  
WHERE A DAY 5 MARGINAL ERO REMAINS. THERE IS BETTER AGREEMENT ON  
THE DAY 5 PRECIP AREA TODAY, BUT THE OVERALL MAGNITUDE SEEMS TO BE  
THE GREATEST REASON TO NOT UPGRADE TO A SLIGHT RISK AT TIME. 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.  
 
HEAT LINGERS OVER SOUTH TEXAS AND THE FLORIDA PANHANDLE THROUGH  
TUESDAY, BUT THE SUPPRESSED RIDGE SHOULD BRING SOME TEMPERATURE  
RELIEF BY WEDNESDAY. THE TROUGH/LOW ALOFT WILL PROMOTE BELOW  
NORMAL TEMPERATURES ACROSS THE NORTHERN TIER WITH 10 TO 15 DEGREE  
BELOW NORMAL TEMPERATURES WORKING EAST MID TO LATE WEEK.  
UPPER RIDGING OVER SOUTHWESTERN U.S. WILL RAISE TEMPERATURES TO  
ABOVE NORMAL THERE BY WEDNESDAY, EXPANDING EAST ACROSS THE FOUR  
CORNERS STATES BY THURSDAY AND INTO THE SOUTHERN PLAINS LATE IN THE  
WEEK. HIGHS WILL BE WELL INTO THE 100S IN THE DESERT SOUTHWEST WITH  
TEMPERATURES NEARING 100 AGAIN IN PARTS OF TEXAS EVENTUALLY.  
 
JACKSON  
 
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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