553  
FXUS02 KWBC 241948  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
348 PM EDT WED SEP 24 2025  
 
VALID 12Z SAT SEP 27 2025 - 12Z WED OCT 01 2025  
 
...HEAVY RAIN THREAT CONTINUES ACROSS THE SOUTHWEST THROUGH THE  
WEEKEND...  
   
..OVERVIEW
 
 
AN UPPER TROUGH/LOW OVER THE SOUTHEAST WILL BE SLOW TO DISLODGE  
THROUGH THE PERIOD DUE TO A LARGE BERMUDA HIGH ANCHORED OVER THE  
ATLANTIC. NORTHERN STREAM SHORTWAVES NEAR THE CANADIAN BORDER WILL  
BE MUCH MORE PROGRESSIVE. AN UPPER LOW OVER SOUTHERN CALIFORNIA  
WILL SHIFT SLOWLY THROUGH THE SOUTHWEST U.S. THIS WEEKEND AND  
WEAKEN AS IT LIFTS TOWARDS THE HIGH PLAINS. A RIDGE IN BETWEEN  
THESE TWO UPPER LOWS WILL STRENGTHEN EARLY NEXT WEEK WITH AN  
AMPLIFIED UPPER TROUGH APPROACHING THE WEST COAST. HEAVY RAINFALL  
THREATS THIS WEEKEND WILL FOCUS MOSTLY OVER THE SOUTHWEST AHEAD OF  
THE UPPER LOW, AS WELL AS THE CAROLINAS/APPALACHIANS NEAR A  
STATIONARY COASTAL FRONT. INCREASING AND MORE WIDESPREAD  
PRECIPITATION WILL SPREAD INTO MUCH OF THE WEST NEXT WEEK WITH SNOW  
POSSIBLE IN THE HIGHEST ELEVATIONS. TODAY'S GUIDANCE SHOWS MORE  
AGREEMENT ON STEERING A PAIR OF TROPICAL SYSTEMS OFF THE COAST OF  
THE SOUTHEAST U.S. HOWEVER, A HIGH DEGREE OF UNCERTAINTY REMAINS ON  
HOW THE TWO SYSTEMS MAY INTERACT WITH THE UPPER TROUGH/LOW OVER  
THE SOUTHEAST AND THE POTENTIAL IMPACTS THEY MAY BRING TO LAND.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE LATEST GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT ON THE LARGE  
SCALE SYNOPTIC SET UP THROUGH AT LEAST THE FIRST HALF OF THE  
PERIOD, BUT STILL WITH SOME UNCERTAINTY IN THE DETAILS. THE BIGGEST  
AND POTENTIALLY MOST IMPACTFUL AREA OF UNCERTAINTY REMAINS THE  
SOUTHEAST AND WESTERN ATLANTIC AS A PAIR OF POTENTIAL TROPICAL LOWS  
ROUND THE WEST SIDE OF THE BERMUDA HIGH AND PASS SOMEWHERE BETWEEN  
THE EAST COAST AND BERMUDA. THE SOUTHEAST UPPER TROUGH MAY TEND TO  
STEER THE TROPICAL SYSTEMS AWAY FROM THE COAST, BUT MORE COMPLEX  
INTERACTIONS BETWEEN THE SOUTHEAST UPPER-TROUGH/LOW AND THE  
TROPICAL SYSTEM(S) LEADING TO IMPACTS ALONG THE COAST OF THE  
SOUTHEASTERN U.S. CANNOT BE RULED. REFER TO THE TROPICAL WEATHER  
OUTLOOK FROM THE NATIONAL HURRICANE CENTER FOR THE LATEST ON THESE  
SYSTEMS OF CONCERN.  
 
OUT WEST, THE GUIDANCE SHOWS A SLIGHTLY FASTER EASTWARD EJECTION OF  
THE SOUTHWEST UPPER-LOW/TROUGH, WHICH LEADS TO A SLIGHTLY MORE  
EASTWARD PLACEMENT OF THE HEAVIEST QPFS ACROSS NEW MEXICO.  
MEANWHILE, AMPLIFIED TROUGHING LOOKS TO OVERTAKE THE WESTERN U.S.  
BY THE END OF THE PERIOD WITH UNCERTAINTIES ON THE TIMING OF  
INDIVIDUAL SHORTWAVES/ENERGY EMBEDDED WITHIN IT.  
 
THE WPC FORECASTS TODAY IS BASED ON THE CONSENSUS OF 40% FROM THE  
06Z GFS/GEFS, 40% FROM THE 00Z ECMWF/EC MEAN, AND 20% FROM THE 00Z  
CMC/CMC MEAN WITH A HIGHER PERCENTAGE FROM THE ENSEMBLE MEANS FOR  
THE LATTER HALF OF THE FORECAST PERIOD. THIS OVERALL MAINTAINS  
GOOD CONTINUITY WITH THE PREVIOUS SHIFT.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
A FRONTAL BOUNDARY LINGERING ALONG THE EAST COAST WILL SUPPORT  
DAILY SHOWERS AND STORMS ESPECIALLY FOR THE MID-ATLANTIC STATES  
INTO NEXT WEEK. ANOMALOUS MOISTURE WITH A POSSIBLE TROPICAL  
CONNECTION WILL MAINTAIN AT LEAST A LOCALIZED HEAVY RAINFALL THREAT  
FOR PARTICULARLY THE CAROLINAS AND SOUTHERN/CENTRAL APPALACHIANS.  
MARGINAL RISK AREAS ARE MAINTAINED ON THE DAYS 4 AND 5 (SATURDAY  
AND SUNDAY) EXCESSIVE RAINFALL OUTLOOKS FOR THIS REGION. THE THREAT  
MAY CONTINUE INTO NEXT WEEK WITH POTENTIAL FOR ADDITIONAL MOISTURE  
ASSOCIATED WITH POSSIBLE TROPICAL SYSTEMS TO MONITOR.  
 
MEANWHILE, PACIFIC MOISTURE AHEAD OF AN UPPER LOW OVER SOUTHERN  
CALIFORNIA WILL RESULT IN INCREASING RAINFALL CHANCES CONTINUING  
THIS WEEKEND ACROSS MUCH OF THE SOUTHWEST INTO CALIFORNIA. MOISTURE  
ANOMALIES 2 TO 3 STANDARD DEVIATIONS ABOVE NORMAL AND SUFFICIENT  
INSTABILITY WILL RESULT IN AT LEAST A LOCALIZED FLASH FLOOD THREAT,  
PARTICULARLY FOR VULNERABLE BURN SCAR AREAS. THIS REGION REMAINS  
HIGHLIGHTED WITH A MARGINAL RISK FOR BOTH FRIDAY AND SATURDAY EROS  
WITH A MORE TARGETED SLIGHT RISK ON DAY 4 ACROSS SOUTHEAST ARIZONA  
TO SOUTHWEST NEW MEXICO AND ON DAY 5 ACROSS CENTRAL NEW MEXICO  
WHERE QPF AMOUNTS ARE GREATEST. THE ACTIVITY WILL SHIFT SLOWLY  
EASTWARD WITH TIME AND SHOULD BEGIN TO TAPER OFF BY MONDAY.  
 
PRECIPITATION WILL INCREASE BY NEXT WEEK ACROSS THE NORTHWEST U.S.  
ASSOCIATED WITH AMPLIFIED TROUGHING OVER THE REGION. WIDESPREAD  
RAIN IS EXPECTED ACROSS THE PACIFIC NORTHWEST AND INTO THE NORTHERN  
GREAT BASIN/ROCKIES. THE HEAVIEST PRECIPITATION IS EXPECTED FROM  
WESTERN WASHINGTON TO NORTHERN CALIFORNIA AND THE SIERRA NEVADA.  
SOME SNOW MAY FALL IN THE HIGHEST ELEVATIONS OF THE WEST.  
 
WARMER THAN AVERAGE TEMPERATURES WILL SLOWLY SHIFT FROM THE  
NORTHWEST THIS WEEKEND INTO THE NORTHERN PLAINS AS UPPER RIDGING  
BUILDS OVER THE REGION NEXT WEEK. DAYTIME HIGHS COULD BE 10-15  
DEGREES ABOVE NORMAL FOR SOME LOCATIONS. BELOW NORMAL TEMPERATURES  
OVER THE SOUTHWEST WILL EXPAND NORTHWARD ALONG MUCH OF THE WEST  
COAST BY NEXT WEEK.  
 
KONG/SANTORELLI  
 
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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