751  
FXUS02 KWNH 080655  
PREEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
254 AM EDT THU MAY 8 2025  
 
VALID 12Z SUN MAY 11 2025 - 12Z THU MAY 15 2025  
 
   
..MULTI-DAY SOUTHEAST U.S. HEAVY RAINFALL/FLOODING THREAT
 
 
   
..OVERVIEW
 
 
A CLOSED LOW WILL MEANDER OVER THE LOWER MISSISSIPPI  
VALLEY/SOUTHEAST FOR SEVERAL DAYS BEFORE FINALLY LIFTING OUT OF THE  
REGION AROUND NEXT WEDNESDAY. THIS WILL SUPPORT DEEPLY POOLED  
MOISTURE TO FUEL DAILY HEAVY RAINFALL/CONVECTIVE THREATS INTO NEXT  
WEEK OVER THE SOUTHEAST INCLUDING FLORIDA, ALBEIT WITH AN EVENTUAL  
GRADUAL TRANSLATION UP THROUGH THE MID- ATLANTIC WITH SLOW SYSTEM  
EJECTION. AMPLIFIED UPPER TROUGHING OFF THE WEST COAST WILL MOVE  
INLAND BY SUNDAY, WITH WIDESPREAD PRECIPITATION EXTENDING ACROSS  
THE WEST INTO NEXT WEEK, INCLUDING ELEVATION SNOWS. THIS LOOKS TO  
EVENTUALLY SPIN UP A SURFACE LOW PRESSURE SYSTEM OVER THE NORTH-  
CENTRAL U.S. BY THE MIDDLE OF NEXT WEEK, WITH MODERATE TO HEAVY  
RAIN POTENTIAL ON THE BACKSIDE OF THE LOW ACROSS THE NORTHERN  
PLAINS.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODEL AND ENSEMBLE GUIDANCE CONTINUES TO BE REASONABLY WELL  
CLUSTERED THROUGH THE FIRST HALF OF THE PERIOD, DESPITE SOME  
DIFFERENCES STILL IN THE DETAILS AND SMALLER SCALE SENSIBLE WEATHER  
PARTICULARLY WITH THE STALLED UPPER LOW OVER THE SOUTHEAST. A  
GENERAL MODEL COMPROMISE WORKED WELL AS A STARTING POINT FOR THIS  
PERIOD. BY ABOUT TUESDAY, THERE ARE SOME GREATER DIFFERENCES WITH  
THE EVOLUTION OF ELONGATED/AMPLIFIED TROUGHING OVER THE WEST AND  
WHAT MAY BE EJECTION OF ENERGY AND EVENTUAL CLOSED LOW DEVELOPMENT  
OVER THE CENTRAL U.S. NEXT WEEK. THE GFS IS QUICKEST IN THIS, WHILE  
THE ECMWF WAS BY FAR THE WEAKEST (SHOWING A WEAKER SHORTWAVE VS  
DEEP CLOSED LOW) AND FARTHER NORTH THAN THE GFS. REGARDLESS, THERE  
IS AGREEMENT THAT SOME SORT OF DEVELOPED SURFACE SYSTEM WILL EMERGE  
INTO THE CENTRAL U.S. BY MID- NEXT WEEK. TO MITIGATE THE DETAIL  
DIFFERENCES AND TAKE A MORE MODEST APPROACH TO START, THE LATE  
PERIOD WPC FORECAST TRENDED MORE TOWARDS THE ENSEMBLE MEANS.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
A WAVY FRONTAL SYSTEM AND A CLOSED UPPER LOW MEANDERING INTO/OVER  
THE SOUTHEAST WILL CONTINUE TO SUPPORT A MULTI-DAY HEAVY  
RAINFALL/RUNOFF THREAT INTO NEXT WEEK AS FUELED BY THE POOLING OF  
HIGHLY ANOMALOUS MOISTURE. GIVEN THE INCREASED SIGNAL FOR HEAVY  
RAINS BY SUNDAY (AND SOME HEAVY RAINFALL POTENTIAL STARTING ON  
SATURDAY), WENT AHEAD AND INTRODUCED A SLIGHT RISK FOR NORTHERN  
FLORIDA AND SOUTHERN GEORGIA ON THE DAY 4 EXCESSIVE RAINFALL  
OUTLOOK (ERO). BY MONDAY, THIS POTENTIAL EXPANDS SOUTHWARD INTO THE  
FLORIDA PENINSULA AND NORTHWARD ACROSS MUCH OF THE SOUTHEAST AS  
STORMS MAY TRAIN ALONG A SLOW MOVING COLD FRONT LIFTING THROUGH THE  
REGION. AS SUCH, A SLIGHT RISK IS INCLUDED FOR MUCH OF THE  
SOUTHEAST ON THE DAY 5 ERO AS WELL. RAINFALL SHOULD GRADUALLY LIFT  
NORTHWARD WITH TIME INTO THE MID- ATLANTIC NEXT TUESDAY AND  
WEDNESDAY.  
 
OUT WEST, RAIN AND HIGHER ELEVATIONS SNOWS WILL BECOME MORE  
WIDESPREAD THROUGH THE WEEKEND AND INTO NEXT WEEK WITH MAIN  
AMPLIFIED SYSTEM COOLING AND SLOW PROGRESSION INLAND THROUGH EARLY  
AND MID NEXT WEEK. MODEST SNOWS ARE POSSIBLE IN THE HIGHER TERRAIN.  
AS THE SYSTEM PROGRESSES EAST, MODERATE TO HEAVY RAINFALL MAY  
DEVELOP ON THE NORTH AND WEST SIDE OF A SURFACE LOW OVER THE NORTH-  
CENTRAL PLAINS.  
 
GENERAL TROUGHING ACROSS THE SOUTH WILL KEEP TEMPERATURES NEAR OR  
BELOW NORMAL AT LEAST THROUGH MONDAY. UPPER RIDGING FROM THE  
SOUTHWEST TO THE PLAINS WILL SUPPORT MUCH ABOVE NORMAL TEMPERATURES  
ACROSS MUCH OF THE INTERMOUNTAIN WEST AND NORTHERN U.S., WITH  
DAYTIME HIGHS 20-30 DEGREES ABOVE NORMAL POSSIBLE IN THE NORTHERN  
PLAINS. PARTS OF THE SOUTHWEST SHOULD APPROACH OR EXCEED 100  
DEGREES WITH AT LEAST SOME LOCALIZED HEAT THREAT GIVEN EARLIER IN  
THE SEASON TIMING SUNDAY AND MONDAY. ABOVE NORMAL HEAT WITH  
MODERATE SOME AS IT PROGRESSES ACROSS THE REST OF THE PLAINS AND  
INTO THE MIDWEST AND EAST NEXT WEEK. UPPER TROUGHING OVER THE WEST  
WILL KEEP TEMPERATURES BELOW NORMAL FOR ESPECIALLY THE LATTER HALF  
OF THE PERIOD.  
 
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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