658  
FXUS02 KWBC 061601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT SAT OCT 06 2018  
 
VALID 12Z TUE OCT 09 2018 - 12Z SAT OCT 13 2018  
   
..CENTRAL U.S. EXCESSIVE RAINFALL THREAT EXTENDS INTO MID-WEEK
 
 
...SEPARATE AREAS OF TROPICAL MOISTURE MAY REACH INTO THE GULF  
COAST-SOUTHEAST AND SOUTHWEST-SOUTHERN ROCKIES...  
...ACTIVE PATTERN CONTINUES OVER THE WEST THROUGH AT LEAST  
MID-WEEK...  
 
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
IT WILL PROVE TO BE A VERY ACTIVE PERIOD WITH MULTIPLE HAZARDS TO  
MONITOR NEXT WEEK. AMPLIFIED FLOW ACROSS THE COUNTRY WILL FEATURE  
IMPRESSIVE HEIGHT ANOMALIES AS SHOWN BY THE LATEST MODEL GUIDANCE.  
ON TUESDAY MORNING, A MID-LEVEL LOW CENTERED OVER THE SOUTHERN  
ROCKIES SHOULD BE COMPRISED OF ANOMALIES AROUND 3 TO 4 SIGMA BELOW  
CLIMATOLOGY WHILE A SPRAWLING 594-DM RIDGE AROUND 2 SIGMA ABOVE  
AVERAGE SITS OVER THE WESTERN ATLANTIC. THIS FORMER FEATURE IS  
EXPECTED TO LIFT UP THROUGH THE CENTRAL PLAINS LATE TUESDAY WHILE  
ATTAINING A NEGATIVE TILT. THE INDUCED AREA OF LOW PRESSURE IS  
FORECAST TO PRESS NORTH-NORTHEASTWARD WHILE DEEPING ON ITS  
APPROACH INTO THE UPPER GREAT LAKES ON WEDNESDAY. EVENTUALLY THE  
SOUTHERN EXTENSION OF THESE HEIGHT FALLS WILL FORCE THE WESTERN  
ATLANTIC RIDGE FARTHER DOWNSTREAM. SHIFTING FOCUS BACK TO THE  
WEST, A RENEWED AREA OF LOWER HEIGHTS WILL SINK DOWN FROM BRITISH  
COLUMBIA THUS RE-ESTABLISHING A TROUGH ACROSS THE WESTERN U.S. BY  
MID-WEEK. VARIOUS SCENARIOS ARE EVIDENT THEREAFTER BUT THE GENERAL  
IDEA IS FOR THIS SYSTEM TO DRAG EASTWARD TOWARD THE ROCKIES AND  
GREAT PLAINS BY EARLY NEXT WEEKEND.  
 
LOOKING DOWN IN THE TROPICS, A PAIR OF THREAT AREAS ARE WORTH  
NOTING. ACROSS THE BAJA CALIFORNIA PENINSULA INTO THE DESERT  
SOUTHWEST AND FOUR CORNERS REGION, ALL EYES ARE ON HURRICANE  
SERGIO. ALTHOUGH IT WILL BE IN THE PROCESS OF DECAYING AS IT  
CROSSES THE COOLER EASTERN PACIFIC WATERS, ITS MOISTURE IS  
EXPECTED TO MOVE INTO THE SOUTHWESTERN U.S. INTO THE SOUTHERN  
ROCKIES BY AS EARLY AS THURSDAY. FARTHER EAST, AN AREA OF  
DISTURBED WEATHER SITTING OVER THE WESTERN CARIBBEAN HAS BECOME  
BETTER ORGANIZED THE PAST 24 HOURS. THE NATIONAL HURRICANE CENTER  
CURRENTLY SUPPORTS AN 80 PERCENT CHANCE FOR TROPICAL CYCLOGENESIS  
THE NEXT 48 HOURS. WHAT EVOLVES SHOULD LIFT INTO THE MIDDLE OF THE  
GULF OF MEXICO WITH MANY SCENARIOS IN PLAY.  
 
REGARDING THE GUIDANCE, THERE HAS BEEN AN IMPROVED HANDLING OF THE  
INITIAL SHORTWAVE/ATTENDANT SURFACE LOW LIFTING THROUGH THE GREAT  
PLAINS AND GREAT LAKES ON TUESDAY/WEDNESDAY. THE PREVIOUSLY  
QUICKER GFS RUNS HAVE COME BACK TO THE REST OF THE PACK WITH  
ENSEMBLE LOW SCATTER PLOTS MUCH LOWER SPREAD THAN PREVIOUS CYCLES.  
THE 00Z ECMWF TRENDED QUITE A BIT DEEPER IN ITS LATEST RUN WHICH  
BRINGS IT CLOSER TO THE CONSENSUS WHICH IS AROUND 995-MB ON  
WEDNESDAY NIGHT. DOWNSTREAM RIDGING SHOULD FORCE THE SYSTEM UP  
TOWARD NORTHERN QUEBEC WHILE HIGH PRESSURE BUILDS OVER THE  
NORTH-CENTRAL U.S. LATE IN THE WEEK. MOVING WEST, THE NEXT ROUND  
OF HEIGHT FALLS DROPPING DOWN IN THE PACIFIC NORTHWEST HAS A FEW  
UNKNOWNS ATTACHED WITH IT. SOME OF THE LATEST ENSEMBLES IN THE  
SPAGHETTI PLOT HAVE SHOWN MORE AMPLIFICATION CARRYING SHORTWAVE  
ENERGY INTO THE DESERT SOUTHWEST. THE 00Z ECMWF ENSEMBLES ARE MOST  
EMPHATIC ABOUT THIS EVOLUTION WITH OTHER MODEL SUITES FARTHER  
DOWNSTREAM. THIS LEADS TO CONSIDERABLE TIMING DIFFERENCES AS THE  
LONGWAVE TROUGH TRACKS EASTWARD. THE 00Z GFS SITS WELL AHEAD OF  
THE 00Z ECMWF WHILE THE 00Z CMC POSITIONS ITSELF SOMEWHERE IN THE  
MIDDLE.  
 
BACK TO THE TROPICS, THE 06Z/00Z GFS ARE OUT AHEAD OF THE 00Z  
ECMWF WITH HURRICANE SERGIO BUT IT APPEARS THE LATEST NATIONAL  
HURRICANE CENTER FORECAST LEANS MORE TOWARD THE FORMER CAMP.  
EVENTUALLY THE SURFACE LOW WILL SHEAR WHILE ENCOUNTERING THE  
HIGHER TERRAIN OF MEXICO LATE IN THE WEEK. MOVING TO THE GULF OF  
MEXICO, THERE IS INCREASING CONFIDENCE OF A DEFINED AREA OF LOW  
PRESSURE PRIMED TO LIFT NORTHWARD TOWARD THE CENTRAL/EASTERN GULF  
COAST SOMETIME THE MIDDLE OF NEXT WEEK. SOLUTION SPREAD IS HIGH  
WITH POSITION AND TIMING WHICH REDUCES CONFIDENCE IN THE  
DETERMINITIC FORECAST. NOTABLY QUICK ARE THE 06Z GFS/00Z CMC WHILE  
THE 00Z ECMWF STILL ATTEMPTS TO STALL THE FEATURE ACROSS THE GULF  
COAST, ALBEIT IN A MORE WEAKENED STATE. ADDITIONALLY, THE  
GFS/UKMET RUNS SIT EAST OF THE ECMWF/CMC WHICH HAS BEEN A THEME  
THE PAST DAY OR TWO. OVERALL, UNCERTAINTY REMAINS BUT THE REGION  
BEARS WATCHING GIVEN THE TROPICAL IMPLICATIONS.  
 
THE MEDIUM RANGE PACKAGE WAS DRIVEN BY A COMBINATION OF THE  
OVERNIGHT CONTINUITY ALONG WITH SOME OF THE LATEST MODEL GUIDANCE.  
ATTEMPTED TO LEAN A BIT MORE TOWARD THE 00Z ECMWF/ECMWF ENSEMBLE  
MEAN ALTHOUGH INCORPORATED THE 00Z GFS/UKMET INTO THE MIX AS WELL.  
THE 00Z UKMET IS RATHER AGGRESSIVE WITH THE CYCLONE STRENGTH  
MOVING TOWARD THE FLORIDA PANHANDLE SO ATTEMPTED TO WEIGHT IT LESS  
IN THE BLEND. TOWARD THE END OF THE PERIOD, MOSTLY WENT TOWARD AN  
ENSEMBLE APPROACH LED BY THE 00Z ECMWF ENSEMBLE MEAN WITH SMALLER  
CONTRIBUTIONS FROM THE 00Z GEFS MEAN.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THREATS WILL BE NUMEROUS DURING THE PERIOD GIVEN THE AMOUNT OF  
AMPLIFICATION AND TROPICAL MOISTURE AFFECTING THE U.S. COLD  
TEMPERATURES WILL PREVAIL ACROSS THE WESTERN U.S. EXTENDING INTO  
THE NORTHERN/CENTRAL PLAINS AS WELL AS THE MIDDLE/UPPER  
MISSISSIPPI VALLEYS WITH 20 TO 30 DEGREE DEPARTURES FROM  
CLIMATOLOGY CENTERED OVER THE CENTRAL/NORTHERN ROCKIES INTO THE  
ADJACENT GREAT PLAINS. WHILE DAILY RECORDS ARE NOT ANTICIPATED, IT  
SHOULD PROVE TO BE RATHER CHILLY FOR SEVERAL DAYS AS HIGHS  
STRUGGLE TO ESCAPE THE 30S ALONG THE NORTHERN TIER WHILE OVERNIGHT  
LOWS PLUNGE INTO THE 20S FROM THE CENTRAL GREAT BASIN THROUGH THE  
INTERIOR WESTERN TERRAIN AND INTO THE NORTH-CENTRAL STATES.  
FARTHER DOWNSTREAM WITHIN THE VAST WARM/MOIST SECTOR, WELL ABOVE  
AVERAGE TEMPERATURES ARE LIKELY, PARTICULARLY WITH THE OVERNIGHT  
LOWS GIVEN LIMITED RADIATIONAL COOLING EFFECTS. ANOMALIES AROUND  
20 TO 25 DEGREES ABOVE CLIMATOLOGY ARE NOTED OVER THE OHIO VALLEY  
AND GREAT LAKES EXTENDING INTO THE NORTHEASTERN U.S. THE OVERNIGHT  
WARMTH WILL LIKELY LEAD TO SEVERAL DAILY RECORDS BEING BROKEN OVER  
A RATHER BROAD REGION.  
 
WITH TROPICAL MOISTURE PUMPING NORTHWARD AHEAD OF THE TROUGH  
ADVANCING INTO THE GREAT PLAINS, HEAVY RAINFALL WILL CONTINUE TO  
BE AN ISSUE ACROSS THE MIDDLE/UPPER MISSISSIPPI VALLEYS. THIS  
WOULD FALL ON TOP OF ANYTHING THAT OCCURS BEFORE THE MEDIUM RANGE  
WHICH SUGGESTS HYDROLOGIC ISSUES MAY BE POSSIBLE. ADDITIONALLY,  
COMMA-HEAD PRECIPITATION, MUCH IN THE FORM OF SNOW WILL BE LIKELY  
ON THE BACKSIDE OF THE SYSTEM. THIS WOULD PRIMARILY IMPACT THE  
DAKOTAS WITH ADDITIONAL ACTIVITY BACK INTO THE ROCKIES AS WELL.  
THE COLD FRONT WILL ADVANCE EASTWARD SPREADING A BROAD AXIS OF  
MODERATE TO LOCALLY HEAVY RAINFALL WITH IT. SHIFTING FOCUS TO  
AREAS OF TROPICAL IMPACTS, CONDITIONS SHOULD BECOME WET ACROSS  
SECTIONS OF ARIZONA/NEW MEXICO INTO THE SOUTHERN HIGH PLAINS AS  
THE TROPICAL MOISTURE FROM SERGIO SURGES INLAND.  
 
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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