685  
FXUS02 KWBC 240701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT WED OCT 24 2018  
 
VALID 12Z SAT OCT 27 2018 - 12Z WED OCT 31 2018  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
TO COMMENCE THE PERIOD ON SATURDAY MORNING, LOWER HEIGHTS TRACKING  
TOWARD THE SOUTHERN APPALACHIANS WILL LIFT AN ONGOING SURFACE WAVE  
UP TOWARD THE DELMARVA PENINSULA. ITS INTENSITY SHOULD HAVE  
ALREADY CAPPED OUT BY 27/1200Z WITH THE SYSTEM FILLING UPON  
APPROACH TOWARD THE SOUTHERN NEW ENGLAND COAST. ADDITIONAL  
SHORTWAVE ENERGY ROUNDING THE BASE OF THE MEAN TROUGH SHOULD SWEEP  
ACROSS THE MISSOURI VALLEY MIDDAY SUNDAY WHILE POTENTIALLY  
INDUCING ADDITIONAL AREAS OF LOW PRESSURE OVER THE EASTERN U.S. ON  
MONDAY/TUESDAY. EVENTUALLY THE CORE OF THE UPPER LOW SHOULD  
SITUATE OVER THE CANADIAN MARITIMES BY THE MIDDLE OF NEXT WEEK AS  
SUGGESTED BY MOST OF THE GUIDANCE. SHIFTING FOCUS TOWARD THE WEST,  
A SPRAWLING UPPER RIDGE WILL SITUATE ITSELF ACROSS THE WESTERN  
U.S. THROUGH THE WEEKEND WHILE WELL ESTABLISHED HEIGHT FALLS LOOM  
OFF THE COAST. THIS LONGWAVE TROUGH IS FORECAST TO MAKE ITS WAY  
DOWNSTREAM WITH THE CORE OF THE ENERGETICS FOCUSING OVER THE  
PACIFIC NORTHWEST/SOUTHWESTERN BRITISH COLUMBIA LATE SUNDAY/EARLY  
MONDAY. A FULL-LATITUDE TROUGH SHOULD PROGRESS EASTWARD WITH A  
POSITION IN THE VICINITY OF THE ROCKIES BY DAY 7/OCTOBER 31 WHILE  
AN EXPANSIVE RIDGE CENTERS ITSELF ALONG THE 140W LONGITUDE.  
 
AFTER DAYS OF STRUGGLING WITH THE INITIAL COASTAL LOW ACROSS THE  
NORTHEASTERN U.S., THE GUIDANCE HAVE COME INTO MUCH BETTER  
AGREEMENT, ALBEIT WITH A QUICKER TREND NOTED. OVERALL, THE ENTIRE  
SYNOPTIC-SCALE PATTERN HAS SHIFTED TOWARD MORE PROGRESSION  
CONSIDERING MULTI-DAY ENSEMBLE SPAGHETTI PLOT COMPARISONS. WHILE  
THE INITIAL WAVE DECAYS A BIT ACROSS NEW ENGLAND, ADDITIONAL  
HEIGHT FALLS ACCOMPANYING A CLIPPER-LIKE SYSTEM WILL TRAVERSE THE  
MISSOURI VALLEY AND EVENTUALLY THE OHIO/TENNESSEE VALLEYS BY LATE  
SUNDAY. GIVEN THE LEVEL OF AMPLIFICATION SUGGESTED, A SECONDARY  
COASTAL LOW MAY EMERGE OFF THE DELMARVA PENINSULA EARLY TUESDAY  
WITH THE 18Z GFS BEING THE MOST AGGRESSIVE. THIS DEFINITELY NEEDS  
TO BE MONITORED GIVEN THE MAGNITUDE OF COLDER THICKNESSES SWEEPING  
THROUGH. ACROSS THE WESTERN/CENTRAL U.S., MODELS AGREE ON SHIFTING  
A FULL-LATITUDE TROUGH EASTWARD WITH SOME SUGGESTIONS OF AN UPPER  
LOW PINCHING OVER THE SOUTHWESTERN U.S. AS SHOWN BY THE 18Z GFS AS  
WELL AS MANY 00Z MODELS (GFS/ECMWF/CMC). ONE THING THAT APPEARS  
CERTAIN IS THE ESTABLISHMENT OF AN UPPER RIDGE WELL OFFSHORE OVER  
THE PACIFIC.  
 
OVERALL PREFERENCES WERE HEAVILY WEIGHTED ON THE GFS/ECMWF  
MODELING SYSTEMS WITH INITIAL FOCUS ON THE 18Z/12Z GFS AND 12Z  
ECMWF. DAILY REDUCTIONS IN THE OPERATIONAL COMPONENTS OF THE BLEND  
WERE MADE WHICH LED TO HEAVIER ENSEMBLE USE INTO NEXT WEEK. THE  
LOWEST CONFIDENCE PORTION OF THE FORECAST IS WITH THE SECONDARY  
HEIGHT FALLS SWEEPING THROUGH THE TENNESSEE VALLEY AND THE  
POTENTIAL DEVELOPMENT OF COASTAL LOW PRESSURE.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
WET WEATHER IS IN STORE FOR THE NORTHEASTERN SECTOR OF THE COUNTRY  
GIVEN THE SLOW-MOVING WAVE OF LOW PRESSURE INHABITING THE REGION.  
WHILE RAINFALL WILL BE THE PRIMARY THREAT ALONG I-95 AND POINTS  
EASTWARD, WINTRY PRECIPITATION IS POSSIBLE BACK TOWARD THE HIGHER  
TERRAIN, PARTICULARLY OVER INTERIOR NEW ENGLAND THIS WEEKEND. SOME  
ADDITIONAL PRECIPITATION THREATS WILL ACCOMPANY THE NEXT SHOT OF  
ARCTIC AIR ALTHOUGH MOISTURE MAY BE LACKING WITH THIS SYSTEM. BACK  
ACROSS THE PACIFIC NORTHWEST, THE STEADY PERIOD OF ONSHORE FLOW  
AND PERTURBATIONS ALOFT WILL KEEP PRECIPITATION IN THE FORECAST  
OVER THE OLYMPICS AND CASCADES INTO NEXT WEEK. AN ADDITIONAL  
MAXIMA IS LIKELY FARTHER DOWNSTREAM INTO THE UPPER INTERMOUNTAIN  
WEST GIVEN FAVORABLE UPSLOPE FLOW. REGARDING TEMPERATURES, THE  
COOLEST CONDITIONS DURING THE PERIOD WILL CONGREGATE OVER THE  
EASTERN THIRD OF THE COUNTRY GIVEN LOWER HEIGHTS ACCOMPANIED BY  
CLOUD COVER AND PRECIPITATION. DEPARTURES FROM CLIMATOLOGY MAY  
REACH THE 10 TO 15 DEGREE RANGE IN PLACES AS HIGHS STRUGGLE TO GET  
OUT OF THE 50S WITH EVEN SOME 40S UP INTO NEW ENGLAND. MEANWHILE,  
WARM WEATHER IS TO PREVAIL OVER THE WESTERN U.S., PARTICULARLY  
OVER THE SOUTHWESTERN U.S. AND INTO THE CENTRAL GREAT BASIN. UPPER  
RIDGING WILL RAISE THE MERCURY INTO THE 80S OVER MANY LOCATIONS OF  
CALIFORNIA WITH EVEN SOME LOW 90S POSSIBLE ACROSS THE DESERT  
LOCALES.  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page