021  
FXUS02 KWBC 040659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
159 AM EST MON NOV 4 2024  
 
VALID 12Z THU NOV 07 2024 - 12Z MON NOV 11 2024  
 
...WATCHING POTENTIAL TROPICAL CYCLONE EIGHTEEN AS IT TRACKS INTO  
THE GULF OF MEXICO TOWARD THE CENTRAL GULF COAST...  
 
...FOUR CORNERS UPPER LOW TO BRING SIGNIFICANT ROCKIES SNOW AND  
AREAS OF HEAVY RAIN TO THE PLAINS...  
   
..OVERVIEW  
 
MODELS AND ENSEMBLES AGREE FAIRLY WELL WITH THE LARGE SCALE PATTERN  
EVOLUTION, WITH NORTHEASTWARD EJECTION OF A FOUR CORNERS UPPER LOW  
WHILE UPPER RIDGING PREVAILS OVER PORTIONS OF THE WESTERN ATLANTIC,  
GULF OF MEXICO, AND EASTERN U.S. THE UPPER LEVEL REFLECTION OF  
POTENTIAL TROPICAL CYCLONE EIGHTEEN, FORECAST TO REACH THE GULF BY  
THE START OF THE PERIOD EARLY THURSDAY, SHOULD BECOME EMBEDDED  
WITHIN THE LARGER SCALE RIDGE. MEANWHILE THE WEST COAST WILL SEE  
STEADILY DECREASING HEIGHTS ALOFT AS A SEQUENCE OF SHORTWAVES  
DAMPEN INITIAL RIDGING, WITH THE STRONGEST ONE LIKELY TO REACH THE  
COAST AROUND NEXT MONDAY. THE FOUR CORNERS UPPER LOW WILL PRODUCE  
SIGNIFICANT SNOW OVER THE SOUTHERN HALF OF THE ROCKIES AND AREAS OF  
HEAVY RAIN OVER THE PLAINS, WHILE THE UNCERTAIN TRACK OF PTC  
EIGHTEEN KEEPS CONFIDENCE LOWER FOR HOW MUCH OF ITS MOISTURE MAY  
REACH INTO THE LOWER 48. TRENDS ALOFT NEAR THE WEST COAST WILL  
INCREASE PRECIPITATION COVERAGE AND INTENSITY OVER THE PACIFIC  
NORTHWEST INTO NORTHERN CALIFORNIA BY THE WEEKEND INTO EARLY NEXT  
WEEK. THE FOUR CORNERS STATES WILL SEE CHILLY TEMPERATURES LATE  
THIS WEEK WHILE MUCH OF THE EAST SHOULD SEE PERSISTENTLY ABOVE  
NORMAL TEMPERATURES THROUGH THE PERIOD.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT  
 
THE UPDATED FORECAST STARTED WITH A BLEND OF 12Z OPERATIONAL MODELS  
FOR THE FIRST HALF OF THE PERIOD WITH SOMEWHAT MORE ECMWF WEIGHT  
THAN OTHER MODELS, WITH SOME SUBSEQUENT EDITING TO ACCOMMODATE THE  
NATIONAL HURRICANE CENTER TRACK OF PTC EIGHTEEN. THEN THE BLEND  
INCORPORATED SOME OF THE 18Z GEFS/12Z ECENS MEANS WITH AN EVENTUAL  
SHIFT TO SLIGHTLY MORE 12Z/18Z GFS INPUT RELATIVE TO THE 12Z ECMWF  
BY DAY 7 MONDAY.  
 
DYNAMICAL AND MODEL GUIDANCE CONTINUES TO OFFER VERY DIVERSE TRACKS  
FOR PTC EIGHTEEN. ECMWF RUNS CONTINUE TO BE FAIRLY FAR ON THE  
EXTREME WESTERN SIDE OF THE ENVELOPE, TRACKING THE SURFACE  
REFLECTION INTO THE WESTERN GULF, WHILE THE NEW 00Z UKMET HAS  
TRENDED IN THAT DIRECTION AS WELL. REMAINING DYNAMICAL AND MACHINE  
LEARNING (ML) MODELS FAVOR A TRACK OVER THE CENTRAL OR EASTERN  
GULF INTO THE GULF COAST.  
 
WHILE SOME GFS RUNS HAVE LEADED A TAD ON THE FASTER SIDE OVER THE  
FOUR CORNERS/PLAINS, OVERALL THE LATEST DYNAMICAL MODEL RUNS OFFER  
FAIRLY GOOD CLUSTERING FOR THE UPPER LOW OF INTEREST AND THE ML  
MODELS SEEM TO AGREE SOMEWHAT BETTER WITH THE DYNAMICAL GUIDANCE  
TODAY AFTER RUNNING A LITTLE ON THE FAST SIDE IN RECENT DAYS. BY  
NEXT MONDAY MOST GUIDANCE SUGGESTS A LITTLE SLOWER TIMING OVER  
SOUTHEASTERN CANADA VERSUS THE 12Z ECMWF WITH A SURFACE PATTERN  
MORE SIMILAR TO GFS RUNS AND A NUMBER OF OTHER MODELS/ENSEMBLE  
MEANS.  
 
THERE IS A FAIR AMOUNT OF SPREAD FOR SPECIFICS OF SHORTWAVE ENERGY  
REACHING WESTERN NORTH AMERICA AROUND SATURDAY, WITH THE UKMET  
RUNNING ON THE FAST SIDE AND THE 18Z GFS LESS SO, WHILE MOST ML  
MODELS ARE STILL A LITTLE OFFSHORE EARLY IN THE DAY (WITH THE 00Z  
GFS NUDGING A LITTLE SLOWER THAN THE 18Z RUN). THE NEXT TROUGH  
LOOKS TO BE MORE VIGOROUS AND ML MODELS GENERALLY SUGGEST THAT THE  
12Z ECMWF AND ITS PRIOR RUNS MAY NOT BE AMPLIFIED ENOUGH. THE NEW  
00Z ECMWF HAS TRENDED A LITTLE DEEPER, SUPPORTING A CONSENSUS OF  
REMAINING GUIDANCE.  
   
..WEATHER/HAZARDS HIGHLIGHTS  
 
 
OVER THE SOUTHEAST/NORTHERN FLORIDA AS OF THURSDAY, GUIDANCE  
CONTINUES TO OFFER SOME SIGNAL OF LINGERING HEAVY RAINFALL  
POTENTIAL FROM ANOMALOUS MOISTURE AND SHORTWAVE ENERGY ROUNDING  
THE WESTERN ATLANTIC DEEP- LAYER RIDGE, TO THE NORTH OF POTENTIAL  
TROPICAL CYCLONE EIGHTEEN THAT SHOULD REACH THE SOUTHERN GULF OF  
MEXICO. CLUSTERING FOR SPECIFICS REMAINS FAIRLY POOR, FAVORING  
MAINTENANCE OF THE EXISTING MARGINAL RISK AREA IN THE DAY 4  
EXCESSIVE RAINFALL OUTLOOK. BY FRIDAY THE GUIDANCE SIGNAL BECOMES  
MORE DIFFUSE OVER THE SOUTHEAST, WHILE MOST RAINFALL DIRECTLY  
ASSOCIATED WITH PTC EIGHTEEN SHOULD STILL BE OVER THE GULF,  
FAVORING NO AREA IN THE DAY 5 OUTLOOK. AFTER EARLY SATURDAY EXPECT  
SOME INCREASED RAINFALL ALONG/INLAND FROM THE CENTRAL GULF COAST  
BASED ON THE 0300 UTC NHC ADVISORY TRACK FOR PTC EIGHTEEN, WITH  
SOME POTENTIAL INTERACTION WITH A FRONT APPROACHING FROM THE  
WEST/NORTH.  
 
THE UPPER LOW FORECAST TO TRACK ACROSS ARIZONA/NEW MEXICO AND THEN  
DEPART TO THE NORTHEAST WOULD BRING THE BEST POTENTIAL FOR  
SIGNIFICANT SNOWFALL TO PORTIONS OF THE COLORADO AND NEW MEXICO  
ROCKIES INTO LATE THIS WEEK, WITH SOME OF THIS SNOW LIKELY  
EXTENDING A LITTLE EASTWARD INTO THE HIGH PLAINS. JUST TO THE  
EAST, THIS SYSTEM SHOULD PRODUCE SOME AREAS OF LOCALLY HEAVY  
RAINFALL OVER THE SOUTHERN/CENTRAL PLAINS THURSDAY-FRIDAY. THE DAY  
4 ERO MADE ONLY MINOR ADJUSTMENTS TO THE EXISTING MARGINAL RISK  
AREA DEPICTED OVER THE SOUTHERN-CENTRAL PLAINS WHILE THE NEW DAY 5  
OUTLOOK EXPANDS THE MARGINAL RISK AREA. THE COMBINATION OF GUIDANCE  
TOTALS AND DAMP SOILS FROM OBSERVED/SHORT-TERM RAINFALL SUGGEST  
POTENTIAL FOR AN EMBEDDED SLIGHT RISK AREA, BUT WOULD LIKE TO SEE  
LESS SPREAD IN THE GUIDANCE TO HELP REFINE SUCH AN AREA. CONTINUED  
PROGRESSION OF THE UPPER LOW AND SURFACE SYSTEM/FRONTS WILL SPREAD  
RAINFALL OF VARYING INTENSITY INTO THE EAST BY THE WEEKEND.  
AFOREMENTIONED MOISTURE FROM PTC EIGHTEEN MAY PROVIDE SOME  
ENHANCEMENT DEPENDING ON THE SYSTEM'S TRACK.  
 
THE NORTHWEST WILL SEE A STEADILY WETTER PATTERN WITH HIGH  
ELEVATION SNOW FROM FRIDAY ONWARD DUE TO A SUCCESSION OF SYSTEMS,  
WITH THE ONE ARRIVING BY MONDAY LIKELY TO BRING THE HIGHEST TOTALS  
OF THE PERIOD ALONG WITH FARTHER SOUTHWARD EXTENT INTO NORTHERN  
CALIFORNIA.  
 
THE FOUR CORNERS STATES AND NEARBY AREAS WILL BE THE FOCUS FOR  
BELOW NORMAL TEMPERATURES LATE THIS WEEK AS THE UPPER LOW DRIFTS  
ACROSS THE REGION. SOME LOCATIONS MAY SEE HIGHS AT LEAST 20-25F  
BELOW NORMAL ON THURSDAY AND ONLY A FEW DEGREES WARMER ON FRIDAY.  
THE WEEKEND WILL BRING A NOTICEABLE MODERATING TREND AS THE UPPER  
LOW DEPARTS, THOUGH THE SOUTHERN ROCKIES MAY NOT QUITE RECOVER  
BACK TO NORMAL BY EARLY NEXT WEEK. THE REMAINDER OF THE WEST SHOULD  
TREND TO NEAR NORMAL READINGS BY THE WEEKEND INTO EARLY NEXT WEEK.  
EXCEPT FOR NORTHERN NEW ENGLAND LIKELY STAYING CLOSE TO NORMAL  
MOST DAYS, THE EASTERN U.S. SHOULD SEE ABOVE NORMAL TEMPERATURES  
THROUGH THE PERIOD DUE TO THE PERSISTENT MEAN RIDGE ALOFT OVER THE  
WESTERN ATLANTIC AND PARTS OF THE GULF, PLUS EXTENDING INTO THE  
EAST THROUGH EARLY SUNDAY. THURSDAY MORNING SHOULD BE PARTICULARLY  
WARM WITH LOWS 20-25F ABOVE AVERAGE FROM PARTS OF THE MID-ATLANTIC  
INTO THE SOUTHEAST. OTHERWISE, WITH DAY-TO-DAY VARIABILITY EXPECT  
SOME COVERAGE ON MOST DAYS OF PLUS 15-20F ANOMALIES FOR MORNING  
LOWS AND PLUS 10-15F ANOMALIES FOR DAYTIME HIGHS. ABOVE NORMAL  
TEMPERATURES SHOULD EXTEND ACROSS THE UPPER MIDWEST AND NORTHERN  
PLAINS AS WELL.  
 
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.PHPSCHICHTEL/HAMRICK  
 
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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