174  
FXUS02 KWBC 201857  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
257 PM EDT FRI SEP 20 2024  
 
VALID 12Z MON SEP 23 2024 - 12Z FRI SEP 27 2024  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
AS EARLY AS DAY 4, THERE IS INCREASING UNCERTAINTY IN THE OVERALL  
UPPER LEVEL FLOW PATTERN OVER THE CONUS. 00Z RUNS OF THE UKMET AND  
CMC, ALONG WITH THE 06Z GFS, HAD TRENDED TOWARDS LESS SEPARATION OF  
ENERGY FROM A SHORTWAVE DIVING SOUTH OUT OF THE NORTHERN ROCKIES  
EARLY IN THE WEEK. ECMWF AND SOME ENSEMBLE MEMBERS (AND NOW THE NEW  
12Z CMC) HOWEVER CONTINUE TO SHOW ENERGY BREAKING OFF MOVING BACK  
TOWARDS THE SOUTHWEST AS THE PARENT TROUGH CONTINUES EAST INTO THE  
MIDWEST. AFTER THIS THOUGH, THERE IS SOME NOTABLE AGREEMENT THAT  
ADDITIONAL ENERGY WILL BREAK OFF INTO A CUTOFF LOW OVER THE MIDWEST  
OR THE NORTHEAST LATE PERIOD, BUT UNCERTAINTY IN THE TIMING OF  
THIS. REGARDLESS, STEERING FLOW AND EVOLUTION OF POSSIBLE TROPICAL  
SYSTEM DEVELOPMENT INTO THE GULF OF MEXICO LATE NEXT WEEK IS  
ENTIRELY DEPENDENT ON THE OVERALL FLOW PATTERN OVER THE CONUS. THE  
GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT ON THE DEVELOPMENT OF  
SOME SORT OF SYSTEM IN THE SOUTHERN OR WESTERN GULF, BUT WHERE IT  
TRACKS AND WHAT IMPACTS IT HAS ON THE GULF COAST REGION OF THE US  
IS HIGHLY UNCERTAIN.  
 
THE WPC BLEND TODAY LEANED CLOSELY TOWARDS THE GFS, THE ENSEMBLE  
MEANS, AND WPC CONTINUITY AMIDST GROWING UNCERTAINTY IN THE  
GUIDANCE. THIS WAS ALSO CONSISTENT WITH NHC PREFERENCES FOR GULF OF  
MEXICO TROPICAL ACTIVITY.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
IF ENERGY OVER THE WEST SPLITS SOUTHWARD OVER THE ROCKIES, THEN  
SOUTHWESTWARD TOWARD THE SOUTHWEST THROUGH EARLY-MID NEXT WEEK.  
THIS WOULD PROVIDE A PERIOD FAVORABLE FOR ENHANCED RAINFALL OVER  
THE SOUTHERN HIGH PLAINS AND SOUTHERN ROCKIES TUESDAY INTO  
WEDNESDAY IN UPPER DIFFLUENT FLOW AND WITH FRONTAL PROXIMITY. A WPC  
MARGINAL RISK AREA CONTINUES IN THE DAY 5/TUESDAY ERO PERIOD.  
 
MEANWHILE FARTHER NORTH, UPPER TROUGH ENERGY AND WAVY FRONTAL  
SYSTEMS WILL BE KICKED FROM THE PLAINS TO THE MIDWEST/EAST EARLY  
NEXT WEEK ALONG WITH AN ASSOCIATED THREAT OF SHOWERS/THUNDERSTORMS  
WITH SOME LOCAL RUNOFF ISSUES. WPC EXCESSIVE RAINFALL OUTLOOK (ERO)  
MARGINAL RISK AREAS ARE DEPICTED TO SHIFT EASTWARD DAY4/MONDAY AND  
DAY/5 TUESDAY ACROSS THE GREAT LAKES/OHIO VALLEY TO THE NORTHERN  
MID-ATLANTIC. UPPER TROUGH REINFORCEMENT MAY SUPPORT ADDITIONAL  
HEAVY RAINFALL POTENTIAL TO MONITOR OVER THE EAST MID-LATER NEXT  
WEEK IN AMPLIFYING FLOW. THIS OCCURS AS FAR UPSTREAM DEVELOPMENT OF  
A POTENT AND SLOWLY PROGRESSIVE UPPER TROUGH FROM THE NORTHEAST  
PACIFIC EARLY NEXT WEEK PROVOKES DOWNSTREAM UPPER RIDGE  
AMPLIFICATION AND WARMING, WITH AN EASTWARD SHIFT FROM THE NOAM  
WEST COAST TO MID-CONTINENT NEXT WEEK.  
 
MEANWHILE NHC AND WPC WILL CONTINUE TO MONITOR POSSIBLE TROPICAL  
DEVELOPMENT IN THE CARIBBEAN THAT MAY SLOWLY MOVE NORTHWARD NEXT  
WEEK. THE ULTIMATE POSITION AND SOUTHWARD BREATH OF THE UPPER  
TROUGH OVER THE LOWER 48 WILL DETERMINE EXTENT OF NORTHWARD  
LIFTING. GIVEN SOME OF THE LATEST GUIDANCE TRENDS, THERE IS  
POTENTIAL THAT HEAVY RAINFALL MAY BEGIN IMPACTING PARTS OF THE GULF  
COAST BY LATE NEXT WEEK. THE TIMING AND EXACT LOCATION OF IMPACTS  
IS HIGHLY UNCERTAIN STILL AT THIS TIME.  
 
FARTHER WEST, MOST AREAS SHOULD STAY DRY UNDER MEAN RIDGING. THE  
WASHINGTON COASTAL RANGES/CASCADES COULD BE AN EXCEPTION AND OFFER  
GROWING POTENTIAL OVER TIME WITH SUBSEQUENT AMPLE PACIFIC ENERGY  
APPROACH. THEN IN SOUTH FLORIDA, SHOWERS AND STORMS MAY FOCUS NEAR  
A FRONTAL BOUNDARY LINGERING IN A MOIST ENVIRONMENT. THESE DO NOT  
LOOK TO BE TOO HEAVY NEXT WEEK UNTIL AROUND LATE WEEK, WHEN THERE  
MAY BE SOME SURGE OF TROPICAL MOISTURE NORTHWARD AHEAD OF ANY  
POTENTIAL TROPICAL DEVELOPMENT.  
 
SANTORELLI/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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