357  
FXUS02 KWBC 240659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 AM EDT SAT MAY 24 2025  
 
VALID 12Z TUE MAY 27 2025 - 12Z SAT MAY 31 2025  
 
 
...HEAVY RAIN/FLASH FLOODING THREATS FROM THE SOUTH THROUGH THE  
SOUTH-CENTRAL APPALACHIANS/MID-ATLANTIC EARLY-MID NEXT WEEK...  
 
   
..OVERVIEW
 
 
THIS UPCOMING MEDIUM RANGE PERIOD WILL FEATURE AN AMPLIFIED AND  
SLOW TO PROGRESS UPPER LEVEL PATTERN WITH A COUPLE CUTOFF LOWS  
THAT WILL DRIVE SURFACE FRONTAL SYSTEMS ACROSS THE LOWER 48. ONE  
LOW WILL WANDER ACROSS THE NORTH-CENTRAL U.S. AND MIDWEST WHILE  
THE OTHERS GRADUALLY APPROACH THE SOUTHWEST. THE EASTERN LOW  
SHOULD GAIN MOMENTUM LATE IN THE PERIOD AS IT TENDS TO SYNC WITH A  
BROAD UPPER LEVEL TROUGH, BUT SOUTHWEST LOWS WILL MOVE SLOWLY AS  
RIDGING BUILDS HEAT OVER THE WEST. THIS PATTERN WILL RESULT IN A  
LINGERING PERIOD WITH AREAS OF WET UNSETTLED WEATHER TO FOCUS FROM  
THE SOUTH UP THROUGH THE SOUTH-CENTRAL APPALACHIANS/MID-ATLANTIC.  
A SERIES OF PACIFIC FRONTAL APPROACHES TOWARD/NORTH OF THE PACIFIC  
NORTHWEST MAY OFFER SOME MODEST COASTAL RAINS CHANCES NEXT WEEK.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
GUIDANCE OFFERS A REASONABLY SIMILAR MID-LARGER SCALE PATTERN  
EVOLUTION FOR TUESDAY INTO THURSDAY DESPITE COMPLEX AND SLOW TO  
TRANSITION FLOW. BEST CLUSTERED GUIDANCE OF THE 18 UTC GFS AND 12  
UTC ECMWF/CANADIAN HAVE GOOD ENSEMBLE AND MACHINE LEARNING MODEL  
SUPPORT, AND A COMPOSITE BLEND SEEMS TO MITIGATE MUCH OF THE  
SMALLER SCALE SYSTEM AND WEATHER FOCUS DETAILS AS CONSISTENT WITH  
INDIVIDUAL PREDICTABILITY. FORECAST SPREAD CHARACTERISTICALLY  
INCREASES LATER NEXT WEEK, BUT A BLEND OF BEST CLUSTERED GUIDANCE  
OF THE 18 UTC GEFS MEAN AND 12 UTC ECMWF/CANADIAN ENSEMBLE MEANS  
BEST MAINTAINS CONTINUITY, WITH A SOLUTION IN LINE WITH LATEST 00  
UTC GUIDANCE COMPOSITE TRENDS THROUGH THESE LONGER TIME FRAMES.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
MAIN DEVELOPING LOWS ALONG A WAVY FRONTAL SYSTEM OVER THE SOUTH  
SHOULD ARE SLATED TO PROGRESS NORTHEASTWARD TUESDAY AND WEDNESDAY.  
THIS WILL EXPAND A THREAT OF LOCALIZED HEAVY RAIN UP THROUGH THE  
SOUTH-CENTRAL APPALACHIANS REGION/MID-ATLANTIC, WHILE THE MOISTURE  
POOLING TRAILING FRONT LINGERS BACK ACROSS THE SOUTH TO FOCUS  
LOCALLY HEAVY CONVECTIVE DOWNPOURS CHANCES THAT MAY EXTEND WELL  
INTO NEXT WEEK WITH ADVENT AND REINFORCEMENT FROM MIDWEST  
CYCLO/FRONTOGENESIS FROM NORTHERN STREAM ENERGIES. THE WPC  
DAY4/TUESDAY EXCESSIVE RAINFALL OUTLOOK (ERO) DEPICTS AN ELONGATED  
MARGINAL RISK THREAT AREA FROM TEXAS INTO THE SOUTH-CENTRAL  
APPALACHIANS REGION/MID-ATLANTIC GIVEN DEEP MOISTURE AND UPPER  
SUPPORT. A DAY 5/WEDNESDAY WPC ERO MARGINAL RISK SHOWS BEST FOCUS  
LINGERING OVER THE SOUTHEAST MID-ATLANTIC WITH LEAD LOW PASSAGE AND  
ALSO BACK OVER THE SOUTHERN PLAINS/LOWER MISSISSIPPI VALLEY WITH  
EJECTING SOUTHERN STREAM IMPULSE INDUCED RETURN FLOW.  
 
IN THE WEST, A BUILDING UPPER RIDGE WILL LEAD TO AN EXPANDING AREA  
OF HEAT FROM THE INTERMOUNTAIN WEST INTO THE WEST COAST STATES,  
WITH TEMPERATURES RISING UPWARDS TO 10 TO 15+ DEGREES ABOVE NORMAL  
DURING THE SECOND HALF OF NEXT WEEK THAT IN PARTICULAR MAY LEAD TO  
A HAZARDOUS HEAT FOCUS OVER THE CALIFORNIA CENTRAL VALLEY HEADING  
INTO AND THROUGH NEXT WEEKEND.  
 
SCHICHTEL  
 
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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