612  
FXUS02 KWBC 191859  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 PM EDT MON MAY 19 2025  
 
VALID 12Z THU MAY 22 2025 - 12Z MON MAY 26 2025  
 
   
..OVERVIEW  
 
OMEGA HIGH PATTERN LOOKS TO SET UP ACROSS NORTH AMERICA THURSDAY  
NIGHT AND THEN REBUILD EARLY NEXT WEEK, AS RIDGING FROM THE  
SOUTHWEST AMPLIFIES AS IT SHIFTS TO THE CENTRAL U.S. AND CONNECTS  
TO AN UPPER HIGH OVER HUDSON BAY, WHILE ROUNDS OF TROUGHING MOVE  
THROUGH THE NORTHWEST AND UPPER LOWS SPIN OVER THE GREAT  
LAKES/NORTHEAST. THE GREAT LAKES/NORTHEAST UPPER LOW THURSDAY/  
FRIDAY WILL PROMOTE COOLER THAN AVERAGE TEMPERATURES AND RAIN IN  
THE NORTHEAST, WHILE THE BUILDING RIDGE LEADS TO WARMER THAN  
AVERAGE TEMPERATURES OVER THE WEST. FRONTAL SYSTEMS EMERGING FROM  
THE WEST AND STALLING OVER THE PLAINS ALONG WITH GULF-SOURCED MOIST  
INFLOW AHEAD OF THEM WILL ALLOW FOR INCREASING RAIN AND  
THUNDERSTORM CHANCES IN THE CENTRAL U.S. FRIDAY THROUGH THE  
WEEKEND.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT  
 
MODEL AGREEMENT IMPROVES WITH UPPER LOW OVER THE GREAT LAKES AND  
ENERGY TRANSFERRING TOWARD A COASTAL SURFACE LOW MOVING ALONG THE  
NEW ENGLAND COAST THURSDAY/FRIDAY. THIS SLOW MOVING LOW, ALONG WITH  
GULF-STREAM SOURCED MOISTURE SETS UP A POTENTIALLY NOTABLE RAINFALL  
CASE FOR SOUTHERN/CENTRAL NEW ENGLAND AS NOTED BY CONSENSUS WITH  
THE 12Z GLOBAL SUITE.  
 
THE UPPER RIDGE BEHIND THIS TROUGHING ALSO SEEMS WELL PREDICTED BY  
THE MODELS, MOVING FROM THE SOUTHWESTERN TO SOUTH-CENTRAL U.S.  
THROUGH THE LATEWEEK. UNCERTAINTY REMAINS, HOWEVER, UPSTREAM WITH  
THE FLOW PATTERN IN THE NORTHEAST PACIFIC AND INTO THE WEST THROUGH  
THIS WEEKEND. THE 12Z GFS/EC ARE IN DECENT AGREEMENT WITH A  
THURSDAY NIGHT TROUGH INTO NORTHERN CA THAT CROSSES THE  
INTERMOUNTAIN WEST THROUGH THIS WEEKEND. THE CMC HAS BEEN MUCH  
MORE CLOSED/NORTH WITH THE LOW WHICH REMAINS IN THE 12Z VERSION  
TODAY. FURTHER RIDGING SPREADING FROM THE WEST COAST AFTER THIS  
TROUGH SETS UP ANOTHER OMEGA HIGH PATTERN OVER THE WESTERN  
U.S./CANADA EARLY NEXT WEEK.  
 
THE WPC FORECAST WAS BASED ON A BLEND OF THE DETERMINISTIC MODELS  
THAT INCREASINGLY DEPENDS ON ENSEMBLE MEANS BY DAY 5 GIVEN THE  
SPREAD IN THE WEST. THE TRANSIENT NATURE OF THE SHORTWAVES OUT WEST  
SHOULD CONTINUE TO LEAD TO UNCERTAINTY AS SEEN IN THE PROGRESS OF  
LOWS/TROUGHS OUT WEST IN 12Z GUIDANCE.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS  
 
INCREASED THREAT FOR FLASH FLOODING IN THE NORTHEAST THURSDAY WITH  
CONSENSUS IN THE 12Z GLOBAL SUITE FOR 2-3" IN SOUTHERN NEW ENGLAND.  
STILL, THERE ARE QUESTIONS FOR INSTABILITY, SO A DAY 4 MARGINAL  
RISK REMAINS IN PLACE FOR NOW, THOUGH AN UPGRADE IS POSSIBLE.  
LIGHTER RAIN LINGERS IN THE NORTHEAST FRIDAY AND SATURDAY UNDER THE  
SLOW MOVING UPPER LOW/TROUGH.  
 
A PROLONGED RAINFALL PATTERN OVER THE CENTRAL U.S. SETS UP AHEAD  
OF FRONTAL SYSTEMS ON FRIDAY WITH AMPLE GULF MOISTURE STREAMING  
NORTH ON RETURN FLOW FROM HIGH PRESSURE OVER THE SOUTHEAST. THIS  
CONVECTION, LIKELY INITIATING EAST OF A SOUTHERN HIGH PLAINS  
DRYLINE SHOULD BE ORGANIZED AT TIMES STARTING FRIDAY AFTERNOON  
OVER THE SOUTH- CENTRAL PLAINS TO THE OZARKS WITH POTENTIAL FOR  
HEAVY RAIN PERSISTING THROUGH THE WEEKEND AS FRONTAL BOUNDARIES  
LINGER. A MARGINAL RISK ERO WAS INTRODUCED FROM CENTRAL KS TO  
CENTRAL AR.  
 
PRECIPITATION, RAIN EXCEPT FOR SNOW THE HIGHEST PEAKS, IS POSSIBLE  
ACROSS THE NORTHWESTERN U.S. UNDERNEATH UPPER TROUGHING FRIDAY  
NIGHT/SATURDAY AND AS FRONTAL SYSTEMS MOVE THROUGH. THE DETAILS  
ARE UNCERTAIN BASED ON THE MODEL SPREAD WITH THE SUPPORTING  
ENERGIES.  
 
UPPER RIDGING WILL MAINTAIN THURSDAY MAX TEMPERATURES AROUND 10  
DEGREES ABOVE NORMAL OVER CALIFORNIA, THE CENTRAL GREAT BASIN, AND  
THE DESERT SOUTHWEST. A FEW ADDITIONAL DAILY MAX TEMPERATURE  
RECORDS ARE AT RISK IN THE LA METRO ON THURSDAY. THE WARMER THAN  
NORMAL TEMPERATURES WILL SHIFT INTO THE FOUR CORNERS STATES AND THE  
SOUTHERN PLAINS THIS WEEKEND, WITH GRADUAL MODERATING INTO EARLY  
NEXT WEEK WHILE THE GREAT BASIN RISES TO A FEW DEGREES ABOVE  
AVERAGE. MEANWHILE, COOLER THAN NORMAL TEMPERATURES WILL TAKE HOLD  
OVER THE NORTH-CENTRAL TO EASTERN U.S. LATE THIS WEEK AND INTO THE  
WEEKEND UNDERNEATH UPPER TROUGHING. HIGHS OF 10-20 DEGREES BELOW  
AVERAGE WILL BE COMMON IN THE APPALACHIANS TO NORTHEAST ON THURSDAY  
IN PARTICULAR BEFORE SLOWLY MODERATING AS THE UPPER LOW DRIFTS  
NORTHEAST.  
 
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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