979  
FOUS30 KWBC 130048  
QPFERD  
 
EXCESSIVE RAINFALL DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
848 PM EDT MON MAY 12 2025  
 
DAY 1  
VALID 01Z TUE MAY 13 2025 - 12Z TUE MAY 13 2025  
 
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE  
SOUTHEAST AND SOUTHEAST FLORIDA...  
   
..01Z UPDATE
 
 
IN COORDINATION WITH MFL/MIAMI, FL FORECAST OFFICE, THE MODERATE  
RISK WAS DOWNGRADED TO A SLIGHT FOR THE I-95 CORRIDOR FROM WEST  
PALM BEACH SOUTH. MUCH OF THE CONVECTION IN THE AREA HAS MOVED  
OFFSHORE, WITH ONLY ONE REMAINING TRAINING BAND SOUTH OF HOMESTEAD.  
HIRES MODELS CONTINUE TO SUGGEST OCCASIONAL STORMS FORMING ACROSS  
SOUTH FLORIDA OVERNIGHT, BUT AGREEMENT IS POOR ON THEIR COVERAGE.  
THUS, GIVEN THE EXPECTED ISOLATED OR WIDELY SCATTERED NATURE OF THE  
OVERNIGHT CONVECTION, FLASH FLOODING SHOULD BE ISOLATED FOR MOST  
AREAS.  
 
ELSEWHERE, THE SLIGHT ACROSS THE SOUTHEAST REMAINS LARGELY  
UNCHANGED, THOUGH COVERAGE OF HEAVY RAINFALL FROM STORMS IS QUITE  
LOW, SO MOST AREAS ARE IN A LOW-END SLIGHT. THAT SAID, A FEW LINES  
OF TRAINING STORMS ARE LOCALLY CAUSING FLASH FLOODING, SO THE  
POTENTIAL FOR ADDITIONAL LINE FORMATION AND TRAINING OVER OTHER  
AREAS JUSTIFIES THE CONTINUATION OF THE SLIGHT.  
 
THE MARGINAL WAS TRIMMED ON THE SOUTHERN END ACROSS THE SOUTHEAST  
BEHIND THE MOST PERSISTENT CONVECTION, WITH THE UPPER LOW AND ITS  
ASSOCIATED FORCING MOVING NORTH, RESULTING IN A SUB-MARGINAL THREAT  
FOR AREAS FURTHER SOUTH.  
 
WEGMAN  
 
DAY 2  
VALID 12Z TUE MAY 13 2025 - 12Z WED MAY 14 2025  
 
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF  
THE MID-ATLANTIC...  
 
NO SIGNIFICANT ADJUSTMENTS NEEDED TO THE DAY 2 UPDATE, OTHER THAN  
EXPANDING THE SLIGHT FURTHER ACROSS PORTIONS OF CENTRAL MD BASED ON  
THE LATEST QPF TRENDS.  
 
---PREVIOUS DISCUSSION---  
 
THE SLOW-MOVING UPPER LOW AND OCCLUDED SURFACE LOW WILL CONTINUE  
TO MOVE NORTH, AND SHOWERS AND STORMS WILL FOCUS ACROSS THE MID-  
ATLANTIC ON TUESDAY. DEEP MOISTURE AHEAD OF THE SYSTEM WILL PUSH  
PWAT VALUES ABOVE 1.5 INCHES, AND THERE WILL BE ENOUGH INSTABILITY  
(MUCAPE > 1500 J/KG) ACROSS PORTIONS OF NORTH CAROLINA AND VIRGINIA  
TO SUPPORT HIGH RAIN RATES (1-2 INCH PER HOUR), WHICH MAY RIVAL 1  
AND 3 HR FFGS. UPSLOPE FLOW ALONG THE APPALACHIANS FROM SOUTHERN  
PENNSYLVANIA THROUGH VIRGINIA WILL ALSO HELP TO ENHANCE RAINFALL,  
WITH GENERALLY 1.5-2.5 INCHES OF RAIN EXPECTED ACROSS THIS AREA  
WITH LOCALLY HIGHER AMOUNTS POSSIBLE. AFTER HEAVY RAIN ON MONDAY,  
THESE AREAS MAY BE MORE SENSITIVE TO FLOODING GIVEN HIGHER SOIL  
MOISTURE, AND ISOLATED TO SCATTERED FLASH FLOODING CONCERNS ARE  
EXPECTED. THIS WILL WARRANT A CONTINUATION OF THE SLIGHT RISK AREA  
FROM NORTHEASTERN NORTH CAROLINA THROUGH VIRGINIA AND PORTIONS OF  
WEST VIRGINIA, MARYLAND, AND SOUTHERN PENNSYLVANIA.  
 
ISOLATED FLASH FLOODING MAY ALSO BE POSSIBLE FOR PORTIONS OF THE  
OHIO VALLEY AND APPALACHIANS. MOISTURE WRAPPING AROUND THE NORTHERN  
SIDE OF THE LOW PRESSURE SYSTEM COMBINED WITH SUFFICIENT  
INSTABILITY NEAR THE SURFACE LOW WILL SUPPORT SCATTERED CONVECTION  
WITH RELATIVELY SLOW STORM MOTION. THEREFORE, A MARGINAL RISK IS IN  
PLACE FOR THESE REGIONS.  
 
DOLAN  
 
DAY 3  
VALID 12Z WED MAY 14 2025 - 12Z THU MAY 15 2025  
 
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF  
THE NORTHERN PLAINS AND MID-ATLANTIC...  
   
..NORTHERN PLAINS
 
 
A DEEP UPPER LEVEL TROUGH WILL PUSH ACROSS THE NORTHWEST TO THE  
PLAINS ON WEDNESDAY, RESULTING IN A STRENGTHENING LOW PRESSURE  
SYSTEM IN THE NORTHERN PLAINS. STRATIFORM RAIN WITH LIKELY SOME  
EMBEDDED CONVECTION ON THE NORTHERN AND WESTERN SIDE OF THE LOW ARE  
FORECAST TO PRODUCE 0.5-1 INCHES OF RAIN, WITH LOCALLY HIGHER  
AMOUNTS POSSIBLE, IN EASTERN MONTANA AND NORTHEASTERN WYOMING. THE  
MAIN THREAT WILL BE DUE TO THE PERSISTENT NATURE OF THE  
PRECIPITATION IN THIS AREA, STARTING UP TUESDAY NIGHT AND  
CONTINUING THROUGH WEDNESDAY INTO WEDNESDAY NIGHT. RAINFALL TOTALS  
WILL LIKELY COME CLOSE TO THE 6 HOUR FFGS IN EASTERN MONTANA.  
 
FOR THE DAKOTAS, CONVECTIVE PRECIPITATION IS FORECAST TO DEVELOP  
AHEAD OF THE LOW ALONG A STRENGTHENING FRONTAL BOUNDARY. MODELS ARE  
IN GOOD AGREEMENT ON THE AXIS OF HEAVIEST PRECIPITATION SETTING UP  
OVER CENTRAL NORTH DAKOTA AND EASTERN SOUTH DAKOTA. PWAT VALUES  
ARE EXPECTED TO BE AT LEAST 2 STANDARD DEVIATIONS ABOVE NORMAL  
(1-1.5 INCHES), AND THERE SHOULD BE ENOUGH INSTABILITY (MUCAPE >  
1500 J/KG) DURING THE DAY ON WEDNESDAY TO SUPPORT AT LEAST AN  
ISOLATED FLASH FLOOD THREAT.  
   
..MID-ATLANTIC
 
 
SOILS ARE EXPECTED TO BE THOROUGHLY SATURATED ACROSS THE MID-  
ATLANTIC AFTER HEAVY RAIN ON MONDAY AND TUESDAY, WHICH MAY CREATE A  
LOW END FLOOD THREAT WITH LINGERING SHOWERS ON WEDNESDAY. THE  
SLOW-MOVING SURFACE LOW IS FORECAST TO TRACK RIGHT OVER THE MID-  
ATLANTIC WITH SCATTERED PRECIPITATION, AND THERE SHOULD BE ENOUGH  
INSTABILITY NEAR THE LOW TO SUPPORT SOME CONVECTION CAPABLE OF  
PRODUCING LOCALLY HEAVY RAIN. THEREFORE, A MARGINAL RISK AREA WAS  
INTRODUCED FOR PORTIONS OF THE MID-ATLANTIC. THE NORTHERN EXTENT OF  
THE MARGINAL WAS NUDGED FURTHER UP INTO PORTIONS OF SOUTHEAST PA  
AND CENTRAL NJ BASED ON THE 12Z GUIDANCE.  
 
DOLAN/TAYLOR  
 
DAY 1 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/94EPOINTS.TXT  
DAY 2 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/98EPOINTS.TXT  
DAY 3 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/99EPOINTS.TXT  
 
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