049  
FXUS02 KWBC 021600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1159 AM EDT TUE OCT 02 2018  
 
VALID 12Z FRI OCT 05 2018 - 12Z TUE OCT 09 2018  
 
...STORMY PATTERN FOR THE WEST/ROCKIES AND A CENTRAL U.S.  
EXCESSIVE RAINFALL THREAT...  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE INITIAL CONFIGURATION OF THE FLOW WILL FEATURE A SHORTWAVE  
SWEEPING ACROSS THE NORTH-CENTRAL U.S. WHILE BEING FORCED  
EAST-NORTHEASTWARD DUE TO THE PRESENCE OF A STRONG DOWNSTREAM  
RIDGE. BY THE WEEKEND, MODELS SHOW THE SYNOPTIC-SCALE PATTERN  
BECOMING MUCH MORE MERIDIONAL IN NATURE. STRONG HEIGHT FALLS  
DIVING THROUGH THE CENTRAL GREAT BASIN AND EVENTUALLY THE FOUR  
CORNERS REGION WILL HELP BOLSTER THE EASTERN U.S. POSITIVE HEIGHT  
ANOMALY. BY SUNDAY EVENING, THE 00Z GFS DEPICTS 500-MB HEIGHT  
ANOMALIES AROUND 3 TO 3.5 SIGMA BELOW CLIMATOLOGY OVER THE  
SOUTHWESTERN U.S. WITH OPPOSITE PHASED DEPARTURES AROUND 2 SIGMA  
OVER THE MID-ATLANTIC. THIS BECOMES A RATHER STAGNANT SET UP INTO  
NEXT WEEK AS THE UPPER TROUGH LIKELY RELOADS WITH ADDITIONAL  
SHORTWAVE ENERGY DIVING DOWN FROM WESTERN CANADA.  
 
FOR THE MOST PART, THE AVAILABLE GUIDANCE IS IN REASONABLE  
AGREEMENT TO START THE PERIOD. BY SATURDAY, THE 00Z CMC BECOMES A  
SLOW, DEEP OUTLIER WITH THE SURFACE CYCLONE TRAVELING TOWARD THE  
LOWER GREAT LAKES INTO ONTARIO/QUEBEC. TOWARD THE END OF THE  
WEEKEND, SOME VARIANCE EXISTS WITH THE PLACEMENT OF THE  
SOUTHWESTERN U.S. TROUGH. MOST NOTABLY, THE 00Z UKMET IS AHEAD OF  
THE PACK WHICH SITS EAST OF THE STRONGER ENSEMBLE CONSENSUS. THE  
BIGGEST DIFFERENCES EMERGE EARLY NEXT WEEK ACROSS THE PACIFIC  
NORTHWEST INTO BRITISH COLUMBIA/ALBERTA AS A SYSTEM FROM THE POLAR  
LATITUDES ATTEMPTS TO DROP SOUTHWARD TOWARD THE CONTINENTAL U.S.  
THE 00Z ECMWF GENERALLY KEEPS THIS DISTURBANCE CONFINED TO THE  
YUKON TERRITORY WHICH HAS IMPLICATIONS ON THE AMOUNT OF MODIFIED  
ARCTIC AIR WORKINGS ITS WAY TOWARD THE INTERNATIONAL BORDER WITH  
CANADA. A MAJORITY OF THE GUIDANCE FAVOR A TIGHT PRESSURE GRADIENT  
SETTING UP ACROSS THE PACIFIC NORTHWEST INTO THE INTERMOUNTAIN  
WEST. THE 00Z ECMWF BACKED OFF ON THIS SCENARIO WHICH REMAINS IN  
STARK CONTRAST FROM THE CONSENSUS. OTHERWISE, THE PATTERN OVER THE  
EASTERN U.S. SEEMS FAIRLY STRAIGHTFORWARD WITH A LARGE POSITIVE  
HEIGHT ANOMALY SITTING OVER THE EASTERN SEABOARD.  
 
THROUGH DAY 4/OCTOBER 6, UTILIZED A COMBINATION OF THE 06Z GFS/00Z  
GFS-PARALLEL IN CONJUNCTION WITH THE 00Z ECMWF/UKMET. THEREAFTER,  
TOOK AWAY THE 00Z UKMET GIVEN THE PROGRESSIVE NATURE OF THE  
SOUTHWESTERN U.S. TROUGH WITH A MORE BALANCED COMBINATION OF  
OPERATIONAL AND ENSEMBLE GUIDANCE. TOWARD THE DAY 6/7, OCTOBER 8/9  
TIMEFRAME, LEANED A BIT MORE TOWARD THE ENSEMBLE MEANS WITH A  
SLIGHT PREFERENCE TOWARD THE 06Z GEFS/00Z NAEFS ENSEMBLE MEANS.  
CONFIDENCE SITS ABOVE AVERAGE WITH THE SYNOPTIC-SCALE FLOW BUT THE  
UNCERTAINTY SITS MORE WITH THE HIGHER LATITUDE FLOW INTERACTIONS.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
GIVEN THE AMPLIFIED SET UP IN PLACE, THERE WILL BE A HEAVY  
RAINFALL THREAT ACROSS THE MIDDLE OF THE COUNTRY WHILE A  
DISCERNIBLE TEMPERATURE GRADIENT SEPARATES THE WESTERN AND EASTERN  
U.S. WITH MERIDIONAL FLOW EVOLVING, TREMENDOUS POLEWARD MOISTURE  
FLUXES ARE NOTED WITH 850-700 MB STANDARDIZED ANOMALIES AROUND 4  
TO 5 SIGMA AT TIMES DURING DAYS 5-7, OCTOBER 7-9. THE MULTI-DAY  
NATURE OF THE THREAT COULD PROVE TO CREATE FLASH FLOODING ISSUES  
IN SOME PORTIONS OF THE CENTRAL U.S. TOO DIFFICULT TO PINPOINT  
EXACT LOCATIONS BUT ANYWHERE FROM THE SOUTHERN/CENTRAL PLAINS UP  
INTO THE MIDDLE MISSISSIPPI VALLEY/UPPER MIDWEST WILL BE IN THE  
THREAT AREA. FARTHER WEST, COLDER TEMPERATURES ACROSS THE HIGHER  
TERRAIN SHOULD SPREAD AREAS OF SNOW OVER THE REGION, PARTICULARLY  
OVER THE NORTHERN/CENTRAL ROCKIES POTENTIALLY INTO THE ADJACENT  
HIGH PLAINS.  
 
REGARDING TEMPERATURES, WHILE A MAJORITY OF THE WESTERN U.S. CAN  
EXPECT BELOW AVERAGE TEMPERATURES, THE LARGEST DEPARTURES SHOULD  
SIT OVER THE NORTHERN/CENTRAL ROCKIES INTO THE NORTHERN PLAINS  
WITH NUMBERS IN THE 20 TO 30 DEGREE RANGE. BY EARLY NEXT WEEK,  
HIGHS COULD STRUGGLE TO GET ABOVE FREEZING OVER AREAS OF MONTANA  
AND WYOMING. MEANWHILE, FROM THE MISSISSIPPI RIVER EASTWARD, HIGH  
TEMPERATURES SHOULD BE AROUND 10 TO 15 DEGREES ABOVE CLIMATOLOGY  
WITH SOME CHANCE FOR DAILY RECORDS FOR WARM 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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