050  
FOUS30 KWBC 210719  
QPFERD  
 
EXCESSIVE RAINFALL DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
319 AM EDT THU AUG 21 2025  
 
DAY 1  
VALID 12Z THU AUG 21 2025 - 12Z FRI AUG 22 2025  
 
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF  
THE SOUTHEAST, SOUTH-CENTRAL TEXAS, SOUTHERN APPALACHIANS, EASTERN  
NORTH CAROLINA, UPPER MIDWEST, AND SOUTHWEST U.S...  
   
..SOUTHWEST  
 
ELEVATED MONSOONAL MOISTURE LINGERING UNDER THE WESTERN RIDGE WILL  
LEAD TO YET ANOTHER AFTERNOON OF SCATTERED CONVECTIVE DEVELOPMENT  
ACROSS MUCH OF THE DESERT SOUTHWEST AND ACCOMPANYING TERRAIN.  
PWATS RUNNING SLIGHTLY ABOVE NORMAL ACROSS THE REGION WILL PROVIDE  
JUST ENOUGH DEEP LAYER MOISTURE TO COUPLE WITH RELEVANT DIURNAL  
BUOYANCY TO ACCOUNT FOR PERIODS OF HEAVY RAINFALL IN SOME OF THE  
STRONGER CONVECTIVE CORES THAT MATERIALIZE THURSDAY AFTERNOON INTO  
THE EVENING. TOTALS GENERALLY WILL FALL <1" OVER THE SOUTHWEST WHEN  
LOOKING AT AREAL AVERAGES, HOWEVER SOME 1-2" TOTALS ARE CERTAINLY  
PLAUSIBLE IN THE SETUP WITH THE BEST THREAT FOR IMPACTS LIKELY IN  
THOSE SLOT CANYON AREAS, DRAINAGE ACROSS COMPLEX TERRAIN INTO  
ADJACENT VALLEYS, AND REMNANT BURN SCAR LOCATIONS. 00Z HREF  
NEIGHBORHOOD PROBS FOR >1" ARE RUNNING BETWEEN 30-45% ACROSS THE  
CENTRAL AND EASTERN MOGOLLON RIM, AND ACROSS THE SOUTHERN EXTENT OF  
THE SANGRE DE CRISTOS IN NM. THESE ARE THE AREAS WITH THE BEST  
FLASH FLOOD POTENTIAL GIVEN THE ANTICIPATED CONVECTIVE PATTERN AND  
TOPOGRAPHIC CHALLENGES THAT ACCOMPANY THESE LOCALES. THE PREVIOUS  
MRGL FORECAST WAS MAINTAINED WITH LITTLE TO NO ADJUSTMENTS.  
   
..TEXAS THROUGH THE SOUTHEAST AND SOUTHERN APPALACHIANS  
 
OUR SLOWLY PROGRESSING FRONT IS CURRENTLY ANALYZED ACROSS THE  
LOWER MISSISSIPPI VALLEY BACK INTO THE SOUTHERN OHIO VALLEY WITH A  
GENERAL SOUTH TO SOUTHEAST PROGRESSION OVER THE PAST 24 HRS. COLD  
FRONT WILL CONTINUE TO WANDER FURTHER SOUTH WITH YET ANOTHER DAY  
OF CONVECTIVE FIRING NEAR AND ALONG THE FRONT AS IT MIGRATES  
THROUGH SOUTH-CENTRAL TX AND TOWARDS THE GULF COAST WITH AN  
ELONGATED SURFACE TROUGH RUNNING PARALLEL TO THE IMMEDIATE GULF  
COAST FROM TX TO FL/GA. THE FRONT WILL ARC BACK INTO THE SOUTHERN  
APPALACHIANS WHERE SCATTERED THUNDERSTORM ACTIVITY IS LIKELY TO  
OCCUR FOR AT LEAST ONE MORE DAY IN THE TERRAIN WITH THE NORTHERN  
EXTENT EXTENDING UP INTO SOUTHERN WV AND SOUTHWEST VA. THE SIGNAL  
IS STILL SCATTERED IN TERMS OF CONVECTIVE COVERAGE AND FLASH FLOOD  
PROSPECTS LEANING TOWARDS ISOLATED TO PERHAPS SCATTERED WHEN  
ASSESSING THE HREF PROBS FOR HOURLY RATES AND FFG EXCEEDANCE PROBS  
IN THE 12-00Z WINDOW THU/FRI. THE STRONGEST SIGNATURE FOR HEAVY  
RAIN CONCERNS LIES WITHIN THE RIDGES AND EASTERN SLOPES OF THE  
SOUTHERN APPALACHIANS ACROSS WESTERN NC DOWN INTO THE FAR WESTERN  
SC ESCARPMENT. 3HR AND 6HR FFG EXCEEDANCE PROBABILITIES BETWEEN  
35-50% EXIST OVER THE ABOVE AREA WITH THE TIME FRAME OF INTEREST  
FALLING IN THAT AFTERNOON AND EARLY EVENING WINDOW WHERE DIURNAL  
INSTABILITY MAXIMUM AND CONVECTIVE TEMP BREACH OVERLAP.  
 
CONVECTION WILL LIKELY DISSIPATE SLOWLY AFTER SUNSET WITH THE LOSS  
OF DIURNAL HEATING AND SURFACE DECOUPLING PUTTING A CAP ON THE  
THREAT. TOTALS BETWEEN 3-5" ARE MOST COMMON AMONG SOME OF THE  
STRONGER CORES IN GUIDANCE, ALIGNING WELL WITH THE MODEST >3" PROBS  
AND LOW-END >5" PROBS WITHIN THE LATEST HREF ITERATION. DESPITE THE  
TOTALS IN QUESTION, THE FLASH FLOOD THREAT WILL LIKELY BE MORE  
COMPRISED OF 3 AND 6HR FFG EXCEEDANCE COMPARED TO LONE HOURLY  
RATES, HOWEVER SOME INSTANTANEOUS RATES UPWARDS OF 2-3"/HR IN THE  
TERRAIN COULD SPUR SOME FLASH FLOOD HAZARDS, ESPECIALLY AS STORM  
MOTIONS REMAIN ON THE WEAKER SIDE AND GENERALLY PARALLEL TO THE  
TOPOGRAPHY. THE PREVIOUS MRGL RISK WAS MAINTAINED GIVEN THE  
SIGNATURES ACROSS THE SOUTH AND APPALACHIAN FRONT. HIGHER FFG'S  
ACROSS THE ABOVE REGIONS WERE THE MAIN DETERRENT FOR A HIGHER  
RISK, BUT WILL BE MONITORING THE THREAT CLOSELY TO SEE IF A  
TARGETED UPGRADE IS NECESSARY.  
   
..NORTHERN PLAINS AND UPPER MIDWEST  
 
AN ENERGETIC UPPER-LEVEL SHORTWAVE IS FORECAST TO MOVE EAST ACROSS  
THE NORTHERN PLAINS AND UPPER MIDWEST LATER THIS AFTERNOON THROUGH  
THE OVERNIGHT. A STRONG COLD FRONT TRAILING A STRENGTHENING  
SURFACE LOW OVER SOUTHERN CANADA WILL AID IN SURFACE BASED FORCING  
TO COUPLE WITH THE IMPROVING MID AND UPPER DYNAMICS AS THE TROUGH  
MIGRATES ALONG THE CANADIAN BORDER. SUFFICIENT BUOYANCY AND  
MOISTURE ANOMALIES OF 1-2 DEVIATIONS ABOVE NORMAL WILL EXIST ALONG  
AND AHEAD OF THE FRONT COINCIDING WITH A STRONG, YET PROGRESSIVE  
LINE OF THUNDERSTORMS THAT WILL BE CAPABLE OF ISOLATED FLASH FLOOD  
PROSPECTS THANKS TO HOURLY RATES BETWEEN 1-2"/HR EXPECTED. TRENDS  
OF AN AREAL MAXIMUM ACROSS EASTERN SD HAVE GAINED TRACTION WITHIN  
THE LATEST CAMS AND MATCHES THE GLOBAL ENSEMBLE MEANS AND EC AIFS  
ENSEMBLE PROBS BEING HIGHEST IN-OF THAT REGION. THIS CORRELATES  
WITH THE STRONGER MID-LEVEL VORTICITY ADVECTION ENTERING THE AREA  
TO COUPLE WITH THE BEST LOW-LEVEL INSTABILITY AXIS ALONG THE  
SOUTHERN EDGE OF THE FRONT. THE PREVIOUS MRGL RISK WAS GENERALLY  
MAINTAINED WITH SOME MINOR TRIMMING ON THE EASTERN EDGE TO ACCOUNT  
FOR LOWER POTENTIAL DOWNSTREAM GIVEN TIMING OF CONVECTIVE  
ADVANCEMENT AMONG THE HI-RES.  
 
KLEEBAUER  
 
DAY 2  
VALID 12Z FRI AUG 22 2025 - 12Z SAT AUG 23 2025  
 
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF  
SOUTHEAST GEORGIA AND SOUTHERN SOUTH CAROLINA...  
   
..SOUTHEAST  
 
THE SLOW-MOVING FRONT THAT WILL PLAGUE THE SOUTH THROUGH THE WEEK  
WILL FINALLY HIT A ROAD BLOCK ONCE IT REACHES THE GULF COAST  
BECOMING A FOCAL QUASI-STATIONARY FRONT BY FRIDAY MORNING.  
HURRICANE ERIN WILL BE EXITING OFF INTO THE NORTHWEST ATLANTIC BY  
THIS POINT, BUT THE PROMINENT IN-FLOW TRAILING THE STORM WILL  
CONTINUE ACROSS THE WESTERN ATLANTIC LEADING TO POOLING MOISTURE  
SITUATED ALONG THE CONFINES OF THE BOUNDARY. PWATS WILL SURGE WITH  
AREAL AVERAGE 2.25-2.5" ENCOMPASSING A MAJORITY OF THE GULF COAST  
FROM LA OVER TOWARDS THE SOUTHEAST COASTAL PLAIN BETWEEN  
WILMINGTON, NC DOWN INTO NORTHERN FL. THE COMBINATION OF ELEVATED  
DEEP LAYER MOISTURE, INSTABILITY, AND ENHANCED SURFACE CONVERGENCE  
ALONG THE FRONT WILL YIELD SOME FAIRLY PROLIFIC RAINFALL MAKERS IN  
ANY CONVECTIVE SCHEME DURING THE PERIOD. THE BEST SIGNATURE FOR  
HEAVY RAIN IS MORE LIKELY TO OCCUR OVER THE SC/GA COAST WHERE  
THERE'S A STRONGER SFC-850MB CONVERGENCE SIGNATURE NEAR THE COAST  
LEADING TO AN AREAL AVERAGE OF ~2-3" OF PRECIP CURRENTLY FORECAST  
ACROSS SOUTHERN SC THROUGH MUCH OF SOUTHEASTERN GA.  
 
THE MOST ROBUST SIGNAL WAS WITHIN THE PROBABILITIES FOR FFG  
EXCEEDANCE JUST BASED OFF THE 12-00Z WINDOW ON FRI/SAT INDICATING  
>60% CHANCE OF BOTH 3HR AND 6HR FFG EXCEEDANCE PROBABILITIES  
CENTERED FROM CHARLESTON, SC DOWN THROUGH THE SC LOW COUNTRY INTO  
FAR SOUTHEAST GA. THIS INCLUDES THE SAVANNAH, GA AREA, A PLACE MORE  
PRONE TO FLASH FLOODING DUE TO ITS URBANIZATION FACTORS. THIS WILL  
BE A COMMON THEME IN THE FLASH FLOOD PROSPECTS WITH THIS SETUP AS  
HEAVY RAINFALL WILL DEVELOP FURTHER INLAND IN PROXIMITY TO THE  
FRONT LEADING TO EVEN INLAND AREAS OF GA SEEING A GREATER THREAT  
FOR LOCALIZED FLOODING THAN USUAL. RATES WILL BE PRETTY STOUT  
CONSIDERING THE ENVIRONMENTAL FACTORS IN PLACE WHEN YOU COUPLE  
1500-2500 J/KG SBCAPE WITH DEEP LAYER MOISTURE BEING FORECAST FROM  
THE SFC TO NEAR THE TROPOPAUSE. THIS IS A CLASSIC TROPICAL  
CONVECTIVE SCHEME THAT IS CAPABLE OF PRODUCING 2-3"/HR RATES MORE  
REGULARLY IN THE STRONGEST CELL CORES, EVEN SEEING 4-5"/HR  
INSTANTANEOUS RATES IF THE PWATS IN A GIVEN AREA GET UP TOWARDS  
THAT 2.5" MARKER. EVEN WITH THE HIGHER FFG'S IN PLACE, THE SIGNAL  
FOR ENHANCED CONVECTIVE RAINFALL OUTPUT AND FLASH FLOOD CONCERNS  
ARE WORTHY OF A HIGHER RISK COMPARED TO THE PREVIOUS FORECAST. IN  
COORDINATION WITH LOCAL WFOS ACROSS SC AND GA, A SLGT RISK UPGRADE  
IS NOW IN EFFECT FOR THE PERIOD BEGINNING FRIDAY AM, LIKELY  
CARRYING INTO EARLY SATURDAY AM.  
   
..TEXAS AND LOUISIANA GULF COAST  
 
POOLING MOISTURE ALONG A SHALLOW QUASI-STATIONARY FRONT ALONG THE  
GULF COAST WILL AMPLIFY ENVIRONMENTAL CONDITIONS TO FAVOR ISOLATED  
TO SCATTERED CONVECTIVE DEVELOPMENT CAPABLE OF LOCALIZED FLASH  
FLOODING THANKS TO DEEP LAYER MOISTURE BETWEEN 2-2.25" PWATS AND  
SLOWER MEAN CELL MOTIONS. THE SIGNAL IS NOT AS PROLIFIC AS AREAS  
DOWNSTREAM, BUT THE THREAT IS STILL BEING FORECAST BASED OFF THE  
LATEST CAMS WITH SOME LOCALIZED TOTALS OF 2-4" BEING FORECAST ALONG  
AND SOUTH OF I-10, ENOUGH TO MAINTAIN GENERAL MRGL RISK CONTINUITY  
FROM PREVIOUS FORECAST.  
   
..SOUTHWEST TO CENTRAL ROCKIES  
 
LITTLE CHANGE WAS NECESSARY GIVEN RUN TO RUN CONTINUITY ON THE  
NEXT WIDESPREAD CONVECTIVE PATTERN CENTERED OVER THE SOUTHWESTERN  
CONUS TO CENTRAL ROCKIES. WESTERN RIDGE WILL SHIFT TOWARDS THE  
GREAT BASIN/FOUR CORNERS BY THE END OF THE WEEK WITH THE MONSOONAL  
MOISTURE PATTERN ALSO MIGRATING WESTWARD TO INCLUDE MORE OF THE  
GREAT BASIN AND INTERIOR COLORADO RIVER BASIN. PWAT ANOMALIES ~ +1  
DEVIATION AND STRONG SURFACE DESTABILIZATION WILL YIELD A FAIRLY  
WIDESPREAD CONVECTIVE REGIME ACROSS THE SOUTHWESTERN PART OF THE  
CONUS WITH HEAVY RAIN SIGNATURES LITTERED AMONG THE ACTIVITY. RATES  
UP TO 1-1.5"/HR IN THE STRONGEST CORES WILL LIKELY PROMOTE FLASH  
FLOOD CONCERNS IN THOSE MORE PRONE DRY WASHES, SLOT CANYONS, AND  
BURN SCARS RESIDING OVER THE REGION. THE THREAT EXTENDS INTO THE  
CENTRAL ROCKIES AS SHORTWAVES ROUND THE EASTERN FLANK OF THE RIDGE  
AND AID IN CONVECTIVE INITIATION OVER THE TERRAIN OF CENTRAL CO.  
CONSISTENT SIGNAL IN THE MEANS AND MODEST PROBABILITIES WITHIN THE  
BEGINNING OF THE CONVECTIVE WINDOW ON THE END OF THE 00Z HREF WERE  
SATISFACTORY FOR MAINTAINING CONTINUITY IN THE CURRENT MRGL RISK  
OUTLINED. THUS, LITTLE CHANGE WAS NECESSITATED FROM THE PREVIOUS  
FORECAST.  
 
KLEEBAUER  
 
DAY 3  
VALID 12Z SAT AUG 23 2025 - 12Z SUN AUG 24 2025  
 
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF  
THE CENTRAL AND SOUTHERN APPALACHIANS, SOUTHEAST AND SOUTHWEST U.S...  
   
..SOUTHEAST INTO THE APPALACHIANS  
 
ELEVATED PWATS WILL LINGER ACROSS THE SOUTHEASTERN CONUS THROUGH  
THE FIRST HALF OF THE WEEKEND AS THE STALLED FRONTAL POSITIONING  
WILL LEAD TO SUSTAINED MOISTURE POOLING WITHIN THE CONFINES OF THE  
BOUNDARY. INCREASING MERIDIONAL COMPONENT UPSTREAM OVER THE  
MIDWEST/OHIO VALLEY WILL LEAD TO A MODEST SURGE IN MOISTURE ALONG  
THE APPALACHIAN FRONT FROM GA UP THROUGH WV ON SATURDAY AFTERNOON  
AND BEYOND ALLOWING FOR MORE SCATTERED CONVECTIVE SIGNATURES TO  
MATERIALIZE WITH THE AID OF DIURNAL DESTABILIZATION. TOTALS ACROSS  
THE SOUTHEAST AND APPALACHIANS ARE NOT AS ROBUST COMPARED TO  
PREVIOUS PERIODS TO WARRANT ANYTHING GREATER THAN A MRGL, HOWEVER  
ANTECEDENT SOIL CONDITIONS OVER PORTIONS OF THE CAROLINA'S AND  
GEORGIA MAY NECESSITATE A TARGETED UPGRADE IF THE CONDITIONS ARE  
TRULY COMPROMISED CONSIDERING THE PLETHORA OF RAIN FORECAST IN THE  
D2. THE TREND IS FOR AT LEAST SOME MODEST CONVECTIVE COVERAGE  
THROUGH THE MORNING AND AFTERNOON TIME FRAMES ON SATURDAY, SO  
THERE'S A NON-ZERO POSSIBILITY OF WARRANTING A GREATER RISK. FOR  
NOW, KEPT THE PREVIOUS FORECAST OVER THE SOUTHEAST WITH SOME TWEAKS  
ON THE NORTHERN EDGE OF THE MRGL IN THE APPALACHIAN FRONT.  
   
..WEST  
 
A RELATIVE REPEAT IN THE SETUP FROM D2 WILL YIELD WIDESPREAD  
CONVECTION ACROSS SOUTHERN AND EASTERN CA ACROSS THE INTERIOR WEST  
WITH THE EASTERN EXTENT LIKELY BACK OVER THE CENTRAL ROCKIES.  
RIDGING OVER THE WESTERN CONUS WILL REMAIN STATIONARY WITH A  
RECYCLED VORTICITY PATTERN ROTATING UNDER THE GUIDE OF THE RIDGE  
WITH ELEVATED MOISTURE PRETTY MUCH ENCOMPASSING THE SOUTHWESTERN  
U.S AND INTERIOR PORTIONS OF THE WEST LIKE NV/UT/CO. HEAVIEST QPF  
FOOTPRINT IS CURRENTLY SITUATED OVER THE SANGRE DE CRISTOS AND SAN  
JUAN MTNS. THANKS TO FORECASTED VORTICITY MAXIMA SLIDING DOWN THE  
EASTERN FLANK OF THE RIDGE AND PROVIDING FOCUSED ASCENT OVER THE  
AFOREMENTIONED TERRAIN. AREAS IN THE MORE PRONE SLOT CANYON, BURN  
SCAR REMNANTS, AND DRY WASHES WILL ONCE AGAIN BE THE TARGET OF  
INTEREST FOR FLASH FLOOD PROSPECTS ALLOWING FOR A BROAD MRGL RISK  
PLACEMENT TO ACCOUNT FOR THE THREAT. PENDING EVOLUTION OF GUIDANCE  
AND PERHAPS MORE FOCUSED AREAS OF CONCERN IN THE RANGE OF CAMS, AN  
UPGRADE COULD VERY WELL BE PLAUSIBLE IN FUTURE UPDATES.  
 
KLEEBAUER  
 
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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