820  
FXUS02 KWBC 071610  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1209 PM EDT SUN OCT 07 2018  
 
VALID 12Z WED OCT 10 2018 - 12Z SUN OCT 14 2018  
 
...TROPICAL DEPRESSION FOURTEEN LIKELY TO AFFECT THE GULF COAST  
AND PORTIONS OF THE EAST...  
...MOISTURE FROM SERGIO SHOULD REACH INTO ARIZONA/SOUTHERN  
ROCKIES...  
 
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
TO COMMENCE THE FORECAST ON WEDNESDAY MORNING, WHAT IS CURRENTLY  
TROPICAL DEPRESSION FOURTEEN WILL LIKELY HAVE INTENSIFIED TO NEAR  
HURRICANE STRENGTH ON ITS APPROACH TOWARD THE WESTERN/CENTRAL  
FLORIDA PANHANDLE. THIS SYSTEM IS FORECAST TO WEAKEN UPON LANDFALL  
WITH A GENERAL NORTHEASTWARD TRACK ALONG THE COASTAL CAROLINAS  
BEFORE EXITING INTO THE ATLANTIC. ACROSS THE PACIFIC OCEANIC  
BASIN, HURRICANE SERGIO WILL BE IN THE PROCESS OF ACCELERATING  
TOWARD THE CENTRAL BAJA CALIFORNIA COAST WITH A LANDFALL SOMETIME  
EARLY FRIDAY MORNING. AS USUAL, THE CYCLONE SHOULD SHEAR APART  
ACROSS INTERIOR MEXICO AS IT ENCOUNTERS MOUNTAINOUS TERRAIN. ASIDE  
FROM THE TROPICAL SYSTEMS, THE LONGWAVE PATTERN WILL REMAIN QUITE  
AMPLIFIED IN NATURE WITH LEADING HEIGHT FALLS TRACKING TOWARD THE  
MISSISSIPPI RIVER ON 10/1200Z. THE COMPACT SHORTWAVE MIGRATING  
TOWARD THE UPPER GREAT LAKES WILL SUPPORT A LENGTHY PERIOD OF  
CYCLOGENESIS AS THE PARENT WAVE LIFTS INTO SOUTHERN ONTARIO. THE  
BAROCLINIC ZONE ATTENDANT TO THE CYCLONE IS FORECAST TO CONTINUE  
MARCHING EASTWARD WITH POSSIBLE TROPICAL INTERACTIONS ALONG THE  
EASTERN SEABOARD. SHIFTING FOCUS BACK TO THE WESTERN/CENTRAL NORTH  
AMERICA, BROAD RIDGING WILL EXTEND ACROSS THE EASTERN PACIFIC INTO  
THE IMMEDIATE WEST COAST FOR DAYS 5-7, OCTOBER 12-14. THIS WILL  
SUPPORT ANOTHER SHORTWAVE RACING FROM THE VICINITY OF  
ALBERTA/SASKATCHEWAN TOWARD THE GREAT LAKES ALTHOUGH A GREAT DEAL  
OF UNCERTAINTY IS NOTED. WELL TO THE SOUTH, AN UPPER LOW MAY CLOSE  
OFF ALONG THE CALIFORNIA/ARIZONA BORDER WITH GRADUAL MOTION  
DOWNSTREAM TO THE SOUTHERN ROCKIES BY NEXT SUNDAY.  
 
MODEL SPREAD REMAINS HIGH WITH THE PAIR OF TROPICAL SYSTEMS  
ALTHOUGH NOTABLE TRENDS ARE WORTH ACKNOWLEDGING. BEGINNING WITH  
TROPICAL DEPRESSION FOURTEEN, MODELS WHICH WERE CLOSER TO THE  
CENTRAL GULF COAST HAVE MOVED EASTWARD WITH MOST SOLUTIONS IN THE  
VICINITY OF THE FLORIDA PANHANDLE. IT IS MAINLY A TIMING ISSUE NOW  
WITH THE 06Z FV3-GFS WELL OUT AHEAD OF THE PACK WHILE THE 00Z  
ECMWF HOLDS THE SOLUTION BACK BY ABOUT A DAY FROM THE OFFICIAL  
FORECAST. THE 00Z GFS/UKMET BEST REPRESENT THIS TRACK THROUGH DAY  
6/FRIDAY ALTHOUGH THE LATTER IS MUCH DEEPER GIVEN LESS INTERACTION  
WITH LAND. BACK TO HURRICANE SERGIO, MODELS HAVE TRENDED SOUTH IN  
THE PAST DAY WITH THE 06Z/00Z GFS AHEAD OF THE SLOWER 00Z ECMWF.  
LIKE THE OTHER CYCLONE, THE NATIONAL HURRICANE CENTER FORECAST  
LEANS MORE IN THE GFS DIRECTION. ACROSS THE REMAINDER OF THE  
COUNTRY, TIMING ISSUES STILL LOOM WITH THE FRONTAL ZONE SWEEPING  
TOWARD THE EASTERN U.S. LATE IN THE WORK WEEK. THE 06Z/00Z GFS  
CONTINUE TO SIT AHEAD OF THE 00Z ECMWF WHILE THE 00Z UKMET IS  
MUDDLED IN THE MIDDLE. LARGER DIFFERENCES EXIST UPSTREAM WITH THE  
NEXT ROUND OF HEIGHT FALLS TRACKING ACROSS THE INTERNATIONAL  
BORDER WITH CANADA DOWN TO THE NORTH-CENTRAL U.S. WHILE ENSEMBLE  
SPAGHETTI PLOTS HAVE SHOWN A SLOW DECREASE IN SPREAD, THERE ARE  
STILL NOTABLE PHASE DIFFERENCES AMONG THE OPERATIONAL MODELS. AND  
FINALLY ACROSS THE DESERT SOUTHWEST, THERE HAS BEEN A WESTWARD  
TREND IN THE GUIDANCE WITH THE MIGRATORY CLOSED LOW. MANY ENSEMBLE  
MEMBERS ARE EVEN FURTHER WEST SUGGESTING FURTHER CHANGES MAY OCCUR.  
 
THE PREFERENCE WAS HEAVILY WEIGHTED TOWARD TROPICAL INFLUENCES  
WITH THE 00Z GFS/UKMET BEING THE CLOSEST FITS TO BOTH SYSTEMS.  
THUS, OVER 2/3 OF THE FORECAST BLEND WAS DEDICATED TO SUCH  
SOLUTIONS THROUGH DAY 5/FRIDAY WITH SMALLER CONTRIBUTIONS FROM THE  
00Z ECMWF AND 00Z GEFS/ECMWF ENSEMBLE MEANS. THEREAFTER, GIVEN THE  
GROWING SPREAD INTO NEXT WEEKEND, LEANED MORE TOWARD AN ENSEMBLE  
MEAN-BASED APPROACH.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE HEAVY RAINFALL WHICH HAD STAGNATED OVER THE CENTRAL U.S. WILL  
FINALLY BE MOVING TOWARD THE EASTERN THIRD OF THE COUNTRY AS THE  
FRONTAL ZONE EJECTS EASTWARD. HEAVY RAINFALL WILL BE LIKELY UP AND  
DOWN THE BOUNDARY AS TROPICAL MOISTURE FROM THE CYCLONE INTERCEPTS  
THIS FRONT. IN PARTICULAR, THE 06Z GFS SHOWS SOME FAIRLY HEFTY  
TOTALS ALONG THE APPALACHIAN CHAIN GIVEN TROPICAL UPSLOPE  
INFLUENCES. DOWN ALONG THE EASTERN GULF COAST, HEAVY RAINFALL  
ACCOMPANIED BY GUSTY WINDS AND ROUGH SURF ARE POSSIBLE IN RESPONSE  
TO THE ADVANCE OF THE TROPICAL CYCLONE. IF THE MORE PROGRESSIVE  
SOLUTIONS VERIFY, THEN THE PRECIPITATION IMPACTS SHOULD BE  
SHORTENED IN DURATION. HOWEVER, THE PAST SEVERAL RUNS OF THE ECMWF  
AND ITS ENSEMBLES CONTINUE TO BE SLOWER. BACK ACROSS THE  
SOUTHWESTERN U.S. AND FOUR CORNERS REGION, HEAVY RAINFALL MAY MOVE  
INTO THE REGION AS SERGIO SHEARS ACROSS MEXICO. WHILE THE  
CIRCULATION CENTER WILL SIGNIFICANTLY WEAKEN, ITS TROPICAL  
MOISTURE WILL LIKELY STREAM INTO THE MENTIONED REGIONS ACROSS THE  
U.S. UP TO THE CENTRAL U.S., SOME THREAT FOR PRECIPITATION IS  
POSSIBLE BUT TOO MUCH SPREAD EXISTS TO HONE IN ON ANY ONE SECTOR.  
 
WELL BELOW AVERAGE TEMPERATURES SHOULD CONTINUE TO OVERSPREAD  
LARGE SECTIONS OF THE WESTERN/CENTRAL STATES. THE MOST SIGNIFICANT  
ANOMALIES WILL LIKELY CENTER OVER THE NORTHERN/CENTRAL ROCKIES  
INTO THE ADJACENT GREAT PLAINS WITH NUMBERS AROUND 20 TO 30  
DEGREES BELOW CLIMATOLOGY. THIS WOULD SUPPORT HIGHS THAT WILL NOT  
GET OUT OF THE 30S THROUGH THURSDAY ACROSS THE NORTH-CENTRAL U.S.  
WHILE CHILLY CONDITIONS WILL PUSH EASTWARD WITH THE FRONTAL ZONE,  
THE AIR MASS WILL MODIFY IN TIME WITH ANOMALIES BACK INTO THE 10  
TO 15 DEGREE RANGE. IN ADVANCE OF THE COLD FRONT, IT WILL BE QUITE  
MILD WITH HIGHS AROUND 10 TO 15 DEGREES ABOVE CLIMATOLOGY OVER THE  
GREAT LAKES, OHIO VALLEY, AND NORTHEASTERN U.S. ALTHOUGH A COOL  
DOWN IS ANTICIPATED BEYOND THURSDAY GIVEN ABUNDANT PRECIPITATION  
AS WELL AS A FRONTAL PASSAGE. MOST IMPRESSIVELY, OVERNIGHT LOWS  
TEMPERATURES MAY SIT IN THE UPPER 60S TO LOWER 70S WITHIN THE VAST  
MOIST/WARM SECTOR ON WEDNESDAY/THURSDAY. CURRENT ANOMALIES ARE IN  
THE 20 TO 25 DEGREE RANGE WITH DOZENS OF DAILY RECORDS LIKELY  
BROKEN GIVEN THE LACK OF RADIATIONAL COOLING EFFECTS EACH NIGHT.  
 
RUBIN-OSTER  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND 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/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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