769  
FXUS02 KWBC 230859  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
458 AM EDT FRI SEP 23 2022  
 
VALID 12Z MON SEP 26 2022 - 12Z FRI SEP 30 2022  
 
...TROPICAL DEPRESSION NINE OVER THE CARIBBEAN LIKELY TO INTENSIFY  
AND MAY AFFECT AT LEAST FLORIDA BY NEXT WEEK...  
 
   
..OVERVIEW
 
 
AN AMPLIFIED UPPER PATTERN FEATURING A WESTERN RIDGE AND EASTERN  
TROUGH EARLY NEXT WEEK SHOULD FLATTEN CONSIDERABLY AFTER WEDNESDAY  
AS AN EASTERN PACIFIC SHORTWAVE COMES ASHORE AND PROGRESSES  
INLAND. MEANWHILE THE 09Z NATIONAL HURRICANE CENTER ADVISORY FOR  
TROPICAL DEPRESSION NINE SHOWS THE SYSTEM STRENGTHENING TO A  
HURRICANE WITH A TRACK THAT WOULD HAVE IT APPROACHING THE FLORIDA  
PENINSULA BY THE END OF THE ADVISORY FORECAST NEXT TUESDAY NIGHT.  
SOME SPECIFICS OF THIS SYSTEM WILL BE SENSITIVE TO ITS SPEED AND  
LONGITUDE AS IT REACHES NEAR FLORIDA AND TIMING OF THE EXPECTED  
WEAKENING OF THE EASTERN U.S. UPPER TROUGH. EXPECT THE GREAT  
LAKES REGION TO SEE SOME RAINFALL WITH THE CHILLY CYCLONIC FLOW IN  
PLACE DURING THE FIRST HALF OF THE WEEK, WHILE THE NORTHWEST MAY  
SEE MOSTLY LIGHT RAINFALL AROUND MIDWEEK WITH THE FOUR CORNERS  
STATES ALSO SEEING SOME POTENTIAL FOR SCATTERED RAINFALL.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE UPDATED FORECAST (BASED ON DATA THROUGH THE 18Z CYCLE) STARTED  
WITH A BLEND OF THE 18Z GFS AND 00Z/22 ECMWF WITH LESSER INPUT  
FROM THE 12Z UKMET/CMC EARLY IN THE PERIOD AND THEN TRANSITIONED  
TO 60 PERCENT OF THOSE GFS/ECMWF RUNS AND 40 PERCENT 18Z GEFS/12Z  
ECMWF MEANS BY DAYS 6-7 THURSDAY-FRIDAY. THE MORE RECENT 12Z  
ECMWF WAS FAIRLY EXTREME RELATIVE TO OTHER GUIDANCE OVER THE EAST,  
BOTH FOR THE INITIAL SPEED OF ITS TROPICAL SYSTEM AS WELL AS THE  
AMPLITUDE/PERSISTENCE OF THE EASTERN TROUGH TO THE NORTH, WHICH  
ULTIMATELY LED TO AN EVEN FASTER TROPICAL SYSTEM PROGRESSION LATER  
IN THE PERIOD. EMPHASIS ON THE 18Z GFS AND 00Z/22 ECMWF (WITH A  
BIT OF A NUDGE SLOWER LATE) YIELDED A SOLUTION FAIRLY CLOSE TO  
YESTERDAY'S NHC/WPC COORDINATED TRACK FOR THE SYSTEM. THE NEW 00Z  
MODELS THROUGH MIDWEEK ARE BECOMING BETTER CLUSTERED, SOMEWHAT  
EAST OF PREVIOUS GFS RUNS AND WEST OF THE 12Z CMC. THE NEW 00Z  
ECMWF IS SLOWER THAN ITS PRIOR RUN INTO WEDNESDAY BUT STILL ON THE  
EAST SIDE OF THE SPREAD. A LATE REVISION TO THE MANUAL SURFACE  
FORECAST REFLECTS THE NEW 09Z NHC ADVISORY TRACK.  
 
OTHERWISE, THERE IS STILL MODERATE SPREAD WITH THE DETAILS OF THE  
EASTERN TROUGH BEYOND THOSE NOTED FROM THE 12Z ECMWF. DIFFERENCES  
FOR THE SYSTEM NEARING THE NORTHWEST AS OF DAY 5 WEDNESDAY ARE  
FAIRLY TYPICAL FOR A FORECAST THAT FAR OUT IN TIME, WITH SOME  
CONVERGENCE OF GFS/ECMWF OVER RECENT DAYS BUT STILL SOME  
RUN-TO-RUN VARIABILITY. THE NEW 00Z UKMET IS THE SOUTHWESTERN  
EXTREME AT THE MOMENT. UPSTREAM FLOW OVER THE EASTERN PACIFIC  
BECOMES MORE UNCERTAIN BY DAY 7 FRIDAY WITH MODELS/ENSEMBLE  
MEMBERS ULTIMATELY RANGING BETWEEN VARYING DEGREES OF TROUGHING OR  
RIDGING. THE BLEND NOTED ABOVE REFLECTS THE PREFERRED MODEL/MEAN  
APPROACH TO RESOLVE CURRENT DIFFERENCES.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE DOMINANT RAINFALL THREAT DURING THE PERIOD WILL BE WITH  
TROPICAL CYCLONE NINE THAT MAY AFFECT FLORIDA AND POTENTIALLY  
OTHER PARTS OF THE SOUTHEAST/EAST COAST. A FRONT EXPECTED TO  
STALL OVER FLORIDA BEFORE ARRIVAL OF THE SYSTEM COULD PROVIDE AN  
ADDED FOCUS FOR RAINFALL. NOTE THAT THERE IS STILL CONSIDERABLE  
UNCERTAINTY REGARDING THE ULTIMATE TRACK OF THIS SYSTEM BY THE  
LATTER HALF OF THE WEEK. HOWEVER INTO EARLY WEDNESDAY THERE IS  
SUFFICIENT POTENTIAL FOR HEAVY RAINFALL TO INTRODUCE A SLIGHT RISK  
AREA ON THE EXPERIMENTAL DAY 5 EXCESSIVE RAINFALL OUTLOOK OVER  
PARTS OF THE FLORIDA PENINSULA. CONTINUE TO MONITOR NATIONAL  
HURRICANE CENTER PRODUCTS FOR THE LATEST INFORMATION REGARDING  
THIS SYSTEM.  
 
EXPECT THE GREAT LAKES AND VICINITY TO SEE PERIODS OF RAIN THROUGH  
THE FIRST HALF OF THE WEEK WITH CHILLY AND BRISK CYCLONIC FLOW IN  
PLACE AT LOW LEVELS AND THE UPPER TROUGH OVERHEAD. A FEW FOCUSED  
BANDS TO THE LEE OF THE GREAT LAKES COULD PRODUCE SOME ENHANCED  
TOTALS. THE PACIFIC NORTHWEST SHOULD SEE A PERIOD OF LIGHT TO  
PERHAPS ISOLATED MODERATE RAINFALL AROUND MIDWEEK WITH THE FRONTAL  
SYSTEM FORECAST TO PUSH INTO THE REGION. SCATTERED RAIN OVER  
PORTIONS OF THE FOUR CORNERS STATES MAY GRADUALLY INCREASE IN  
COVERAGE OVER THE COURSE OF THE WEEK.  
 
THE EVOLUTION OF THE UPPER PATTERN WILL FAVOR CHILLY TEMPERATURES  
OVER A MAJORITY OF THE EASTERN U.S. WITH BEST POTENTIAL FOR HIGHS  
UP TO 10-15F BELOW NORMAL OVER AND NEAR THE GREAT LAKES/OHIO  
VALLEY, ESPECIALLY TUESDAY-THURSDAY. MEANWHILE THE WEST WILL BE  
ON THE WARM SIDE MONDAY-WEDNESDAY WITH SOME AREAS FROM THE  
NORTHWEST INTO NORTHERN ROCKIES LIKELY SEEING HIGHS UP TO 10-15F  
ABOVE NORMAL, FOLLOWED BY A COOLER TREND CLOSER TO NORMAL LATER IN  
THE WEEK AS THE WARM AIR REACHES THE HIGH PLAINS.  
 
RAUSCH  
 
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, EXPERIMENTAL EXCESSIVE RAINFALL  
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE  
AT:  
 
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  
 

 
 

 
 
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