470  
FXUS02 KWBC 051601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT FRI OCT 05 2018  
 
VALID 12Z MON OCT 08 2018 - 12Z FRI OCT 12 2018  
 
...CENTRAL U.S. EXCESSIVE RAINFALL THREAT/ACTIVE WESTERN U.S.  
PATTERN...  
...SEPARATE AREAS OF TROPICAL MOISTURE POSSIBLY ARRIVING INTO THE  
GULF COAST AND SOUTHWEST/SOUTHERN ROCKIES...  
 
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
TO COMMENCE THE PERIOD, HIGHLY AMPLIFIED FLOW WITH ANOMALOUS  
HEIGHT CENTERS WILL ENCOMPASS THE COUNTRY. RELATIVE TO  
EARLY/MID-OCTOBER CLIMATOLOGY, THE DEEP UPPER LOW OVER THE  
SOUTHWESTERN U.S. SHOULD FEATURE 500-MB HEIGHT DEPARTURES AROUND 3  
TO 3.5 SIGMA WHILE THE WESTERN ATLANTIC 594-DM RIDGE WILL FEATURE  
ANOMALIES AROUND 2 SIGMA. MODELS CONTINUE TO ADVERTISE THE  
SPRAWLING UPPER LOW SHOULD EJECT NORTHEASTWARD TOWARD THE CENTRAL  
PLAINS BY TUESDAY/WEDNESDAY INDUCING A MODEST AREA OF LOW  
PRESSURE. NOTABLE DEEPENING IS ANTICIPATED AS THE CYCLONE LIFTS  
TOWARD THE UPPER MIDWEST AND CROSSING THE INTERNATIONAL BORDER  
INTO ONTARIO. THE SOUTHERN EXTENSION OF HEIGHT FALLS SHOULD  
DISLODGE THE EASTERN U.S. RIDGE PLACING IT OUT INTO THE ATLANTIC.  
SHIFTING FOCUS BACK TO THE WESTERN U.S., REPLENISHMENT OF THE MEAN  
UPPER TROUGH IS EXPECTED AS LOWER HEIGHTS DESCEND FROM BRITISH  
COLUMBIA. UNLIKE THE PRECEDING UPPER LOW, THE NEXT SURGE OF  
SHORTWAVE ENERGY WILL DIG THROUGH THE CENTRAL GREAT BASIN BEFORE  
THE LONGWAVE TROUGH GRADUALLY DRIFTS EASTWARD IN TIME. IN ITS  
WAKE, ENSEMBLE MEANS SUGGEST AN UPPER RIDGE SETTLING OVER THE  
EASTERN PACIFIC ALTHOUGH OPERATIONAL MODEL RUNS SUPPORT SOME  
SHORTWAVE FEATURES INTRUDING ON THIS CONFIGURATION.  
 
CONSIDERING TROPICAL DEVELOPMENTS, WHAT IS CURRENTLY HURRICANE  
SERGIO WILL CONTINUE ITS WESTWARD PROGRESSION THROUGH THE WEEKEND  
BEFORE MAKING A QUICK NORTH AND THEN NORTHEAST TURN BACK TOWARD  
NORTH AMERICA. AT THIS POINT, THE REMAINS OF SERGIO AND ITS  
MOISTURE FLUXES WOULD REACH BAJA CALIFORNIA AND EVENTUALLY THE  
SOUTHWESTERN U.S. FARTHER EAST, AN AREA OF DISTURBED WEATHER  
CURRENTLY BEING MONITORED BY THE NATIONAL HURRICANE CENTER IS  
LIKELY TO LIFT INTO THE GULF OF MEXICO EARLY NEXT WEEK. DURING THE  
NEXT 5 DAYS, A 60 PERCENT CHANCE OF TROPICAL CYCLOGENESIS IS NOTED  
IN THE LATEST OUTLOOK.  
 
MODEL SPREAD IS A BIT HIGHER THAN USUAL DURING THE PERIOD WHICH  
SUGGESTED BELOW AVERAGE CONFIDENCE IN THE FORECAST FROM DAY  
5/WEDNESDAY ONWARD. BEGINNING WITH THE UPPER LOW EJECTING OUT OF  
THE FOUR CORNERS, PREVIOUS RUNS OF THE GFS CONTINUE TO BE QUICKER  
WITH THE TROUGH AND WAVE PROGRESSION. ITS SOLUTION APPEARS TO BE  
ON ITS OWN BUT ALL OF THE GUIDANCE SUGGEST CYCLOGENESIS UNFOLDING  
PERHAPS 12 TO 18 HOURS LATER. ENSEMBLE LOW PLOTS ARE SCATTERED  
ABOUT ALONG THE NORTH-CENTRAL U.S. WITH THE 00Z ECMWF BEING  
SIGNIFICANTLY DISPLACED TO THE WEST RELATIVE TO THE BETTER  
ENSEMBLE CLUSTERING, PARTICULARLY BY DAY 6/THURSDAY. CONSIDERING  
THE MEAN LONGWAVE TROUGH POSITION, THE PAST COUPLE OF GFS RUNS ARE  
DECIDEDLY QUICKER ALTHOUGH THE 06Z CYCLE DID SLOW DOWN A BIT. THE  
PAST FEW CYCLES OF THE ECMWF AND 00Z CMC ARE MORE ALIGNED FAVORING  
A FRONTAL PASSAGE ALONG THE I-95 CORRIDOR BY THE END OF THE  
PERIOD. MOVING DOWN TO THE TROPICS, WHILE THERE IS REASONABLE  
CLUSTERING WITH SERGIO'S MOVEMENT TOWARD BAJA CALIFORNIA, MODELS  
ARE STRUGGLING WITH THE GULF SYSTEM. THE 00Z UKMET IS QUICK AND  
DEEP TAKING A STRONG LOW INTO THE WESTERN FLORIDA PANHANDLE WHILE  
THE 00Z CMC HAS STRONGER OPERATIONAL MODEL SUPPORT BACK TOWARD THE  
CENTRAL GULF COAST. HOWEVER, AS USUAL, ITS SOLUTION IS DEEPER THAN  
MOST OTHERS AVAILABLE. THE ENSEMBLE LOW SPREAD IS RATHER HIGH WITH  
THE ENSEMBLE MEANS ACTUALLY SITTING OFF TO THE EAST NEAR THE  
FLORIDA PANHANDLE. EVENTUALLY MANY FORECASTS OUTSIDE OF THE GFS  
FAVOR STALLING THE CYCLONE GIVEN A SLOWER MID-LATITUDE TROUGH  
PROGRESSION.  
 
GIVEN THE UNCERTAINTY LOOMING THROUGHOUT MUCH OF THE PERIOD,  
DECIDED TO KEEP A LARGE CHUNK OF OVERNIGHT CONTINUITY IN THE MIX  
WHILE TAKING AN EVEN SPLIT OF OPERATIONAL AND ENSEMBLE GUIDANCE  
FOR THE REMAINDER OF THE BLEND. THIS INCLUDES THE 06Z GFS AND 00Z  
ECMWF/CMC WITH THE FOLLOWING ENSEMBLES: 06Z GEFS AND 00Z  
ECMWF/NAEFS MEANS.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
HEAVY RAINFALL ACROSS THE SOUTHERN/CENTRAL PLAINS SHOULD CONTINUE  
TO POSE AN ISSUE, PARTICULARLY GIVEN THE COMPROMISED STATE OF  
SOILS OVER THE REGION. THIS MULTI-DAY HEAVY RAINFALL EVENT WILL  
CONTINUE FROM THIS WEEKEND INTO THE FOLLOWING WEEK WHICH SUGGESTS  
FLASH FLOODING IS POSSIBLE OVER MANY LOCATIONS THE NEXT SEVERAL  
DAYS. HOWEVER, THE FRONTAL ZONE IS FORECAST TO BE ON THE MOVE  
SHIFTING THE FOCUS OF MODERATE TO LOCALLY HEAVY RAINFALL TO THE  
MISSISSIPPI RIVER VALLEY WITH A BETTER FOCUS NEAR THE SURFACE LOW  
MOVING INTO THE NORTH-CENTRAL U.S. WITH SUBSTANTIAL COLD AIR IN  
PLACE, WINTRY PRECIPITATION IS LIKELY OVER SECTIONS OF THE WESTERN  
DAKOTAS EXTENDING BACK INTO THE NORTHERN ROCKIES. IN ADDITION TO  
THE MID-LATITUDE SYSTEM THREATS, THE TROPICS WILL ALSO PROVIDE  
ADDITIONAL ISSUES. GIVEN THE CURRENT TRACK OF SERGIO, APPRECIABLE  
MOISTURE ADVANCING INTO THE DESERT SOUTHWEST AND SOUTHERN ROCKIES  
WILL RAISE THE PROBABILITIES FOR RAINFALL BY LATE NEXT WEEK. AND  
ACROSS THE CENTRAL TO EASTERN GULF COAST, SUBSTANTIAL MOISTURE  
COUPLED WITH ENERGETICS WITH THE LOW ITSELF COULD SPREAD HEAVY  
PRECIPITATION TO THE REGION BY MID/LATE NEXT WEEK.  
 
WITH THE AMPLIFIED FLOW IN PLACE, RATHER MARKED TEMPERATURE  
DIFFERENCES WILL BE LIKELY AS READINGS AROUND 20 TO 30 DEGREES  
BELOW CLIMATOLOGY ARE EXPECTED ACROSS THE CENTRAL/NORTHERN ROCKIES  
INTO THE ADJACENT GREAT PLAINS. OVER THE MOUNTAIN LOCATIONS,  
OVERNIGHT LOWS SHOULD PLUNGE INTO THE TEENS AND 20S FOR MULTIPLE  
NIGHTS. FARTHER EAST, GIVEN THE MILD AIR IN PLACE SOUTH AND EAST  
OF THE FRONTAL ZONE, TEMPERATURE ANOMALIES AROUND 10 TO 15 DEGREES  
FROM AVERAGE ARE ANTICIPATED WITH SLIGHTLY HIGHER DEPARTURES FOR  
THE OVERNIGHT MINIMA.  
 
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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