087  
FXUS02 KWBC 261600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT FRI OCT 26 2018  
 
VALID 12Z MON OCT 29 2018 - 12Z FRI NOV 02 2018  
   
..PATTERN OVERVIEW
 
 
FROM THE LARGE SCALE PERSPECTIVE A MODERATELY PROGRESSIVE FLOW  
PATTERN ACROSS THE U.S. EARLY IN THE MEDIUM RANGE PERIOD WILL  
BECOME INCREASINGLY AMPLIFIED AND SLOWER BY THE MIDDLE OF NEXT  
WEEK. GUIDANCE AGREES THAT THE UPPER RIDGE WHICH HAS BEEN  
PREVALENT OFF THE WEST COAST WILL REBUILD WITH A BROAD AND  
AMPLIFIED MEAN TROUGH SETTING UP OVER THE CENTRAL U.S. THIS FLOW  
PATTERN WILL SET THE STAGE FOR TRANSPORT OF CHILLY AIR SOUTHWARD  
INTO THE CENTRAL U.S. WHILE WET CONDITIONS DEVELOP ON THE EASTERN  
SIDE OF THE EVOLVING TROUGH, ESPECIALLY FROM THE LOWER MISSISSIPPI  
VALLEY TO THE OHIO VALLEY.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
FOR ABOUT THE FIRST HALF OF THE PERIOD THERE IS REASONABLE  
CONSENSUS AMONG THE GUIDANCE REGARDING SIGNIFICANT FEATURES, WITH  
SOME TYPICAL DETAIL/TIMING DIFFERENCES THAT ARE BEST RESOLVED BY  
AN OPERATIONAL MODEL BLEND. GUIDANCE HAS NOT FULLY LOCKED IN  
THOUGH, AS THE LATEST CYCLE OF GUIDANCE SEEMS TO BE FURTHERING THE  
RECENT FASTER TREND FOR THE UPPER TROUGH CROSSING SOUTHERN CANADA  
AND NORTHERN U.S. EAST OF THE ROCKIES--ALONG WITH THE LEADING  
CANADIAN SURFACE LOW PRESSURE AND TRAILING FRONT CROSSING THE  
CENTRAL U.S. THIS TREND PROVIDES ADDED PUSH FOR THE INITIAL EAST  
COAST UPPER TROUGH AND NORTHEAST LOW PRESSURE TRACKING INTO THE  
CANADIAN MARITIMES.  
 
DURING THE MID-LATE WEEK TIME FRAME, THE EVOLUTION OF SHORTWAVE  
ENERGY REACHING THE VICINITY OF THE ROCKIES/PLAINS BY WED BECOMES  
A MAJOR UNCERTAINTY IN THE FORECAST. SPECIFICS OF THIS  
ENERGY--WHOSE SCALE LENDS ITSELF TO MODERATE TO LOWER  
PREDICTABILITY BY 6-7 DAYS OUT IN TIME--WILL DETERMINE THE  
TIMING/TRACK/STRENGTH OF A SURFACE WAVE THAT MAY LIFT  
NORTHEASTWARD FROM THE SOUTHERN PLAINS/MISSISSIPPI VALLEY. AS A  
WHOLE THE 00Z/06Z OPERATIONAL MODEL SOLUTIONS DISPLAY SOMEWHAT  
FASTER TIMING OF SUCH A WAVE THAN THE ENSEMBLE MEANS. RECENT  
FASTER TRENDS FOR SOME SYSTEMS PROVIDE SUPPORT FOR INCLUDING A  
COMPONENT OF THE OPERATIONAL MODEL IDEAS, BUT INDIVIDUAL ENSEMBLE  
MEMBERS FALL WITHIN A VERY BROAD ENVELOPE FOR POSSIBLE SURFACE  
WAVE LOCATION WITH MINIMAL CLUSTERING BY DAYS 6-7 THU-FRI. THUS IT  
IS ALSO PRUDENT TO INCORPORATE HALF OR MORE WEIGHT OF THE 06Z  
GEFS/00Z ECMWF MEANS THAT ARE SIMILAR TO EACH OTHER IN PRINCIPLE.  
 
AS THE AXIS OF THE UPSTREAM RIDGE ALOFT NEARS THE WEST COAST BY  
DAY 7 FRI THE OTHER SIGNIFICANT LATE-PERIOD UNCERTAINTY EMERGES,  
REGARDING THE CHARACTER OF APPROACHING NORTHERN PACIFIC SHORTWAVE  
ENERGY. ENSEMBLE SPAGHETTI PLOTS BECOME FAIRLY CHAOTIC BY THAT  
TIME AND INDIVIDUAL MODEL RUNS HAVE VARIED DEPICTIONS OF  
TIMING/AMPLITUDE OF THE SHORTWAVE ENERGY. AT THE VERY LEAST,  
STRENGTH OF THE RIDGE LEADING INTO FRI WOULD SEEM TO FAVOR LEANING  
AWAY FROM THE MORE AMPLIFIED SIDE OF THE ENVELOPE FOR THE  
SHORTWAVE. A BLEND OF THE ENSEMBLE MEANS AND MODEST WEIGHT OF ANY  
INDIVIDUAL MODEL RUN WOULD PROVIDE A GOOD STARTING POINT FOR  
MAINTAINING A FAIRLY STRONG RIDGE UNTIL THERE IS OVERWHELMING  
MODEL/ENSEMBLE AGREEMENT THAT ARGUES OTHERWISE.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE SYSTEM DEPARTING FROM NEW ENGLAND AFTER EARLY NEXT WEEK WILL  
BRING MOSTLY LIGHT PRECIPITATION TO PORTIONS OF THE NORTHEAST.  
THEN THE FOCUS WILL BE ON INCREASINGLY WET CONDITIONS EXPECTED TO  
DEVELOP OVER PORTIONS OF THE EASTERN HALF OF THE LOWER 48 MID-LATE  
WEEK AS MEAN TROUGHING ALOFT BECOMES ESTABLISHED OVER THE CENTRAL  
U.S. THIS PATTERN WILL FAVOR NORTHWARD TRANSPORT OF GULF OF MEXICO  
MOISTURE AND INSTABILITY WHERE IT WILL INTERACT WITH A SURFACE  
FRONTAL BOUNDARY AND ONE OR MORE EMBEDDED WAVES. OVERALL THE  
LATEST MODEL/ENSEMBLE GUIDANCE HIGHLIGHTS BEST POTENTIAL FOR  
HIGHEST RAINFALL TOTALS FROM THE LOWER HALF OF THE MISSISSIPPI  
VALLEY INTO THE OHIO VALLEY WITH MULTI-INCH RAINFALL TOTALS  
POSSIBLE OVER SOME AREAS. LOCATIONS FROM THE PACIFIC NORTHWEST  
THROUGH THE NORTHERN AND CENTRAL/SOUTH-CENTRAL ROCKIES WILL SEE  
MULTIPLE ROUNDS OF PRECIPITATION (RAIN AND HIGH ELEVATION SNOW) AS  
WEAKENING SHORTWAVES/FRONTAL SYSTEMS TRAVERSE THE NORTHERN  
PERIPHERY OF THE PACIFIC RIDGE. WITHIN THIS AREA THERE IS A FAIRLY  
GOOD GUIDANCE SIGNAL TOWARD HIGHEST AMOUNTS BEING OVER FAVORED  
TERRAIN FROM THE PACIFIC NORTHWEST INTO NORTHERN ROCKIES. SOME  
FOCUSED ACTIVITY IS LIKELY FARTHER SOUTHEAST BUT WITH SOMEWHAT  
LOWER 5-DAY TOTALS.  
 
PATTERN EVOLUTION ALOFT WILL LEAD TO AN AREA OF ABOVE AVERAGE  
TEMPERATURES PROGRESSING FROM THE WEST-CENTRAL U.S. EARLY IN THE  
WEEK TO THE EASTERN STATES BY MID-LATE WEEK. EASTERN U.S. WARMTH  
WILL BE CONFINED MORE TO MIN TEMPERATURES AS LOW LEVEL MOIST FLOW  
BECOMES ESTABLISHED. SOME ANOMALIES MAY REACH INTO THE PLUS 10-20F  
RANGE FOR MIN/MAX READINGS EARLY IN THE WEEK AND FOR MINS OVER THE  
EAST DURING THE LATTER HALF OF THE WEEK. THE WEST WILL SEE A  
PERIOD OF MODESTLY BELOW NORMAL READINGS BEFORE THE APPROACHING  
RIDGE ALOFT BRINGS A RETURN OF ABOVE NORMAL TEMPERATURES TO THE  
WEST COAST STATES. BELOW NORMAL TEMPERATURES WITH SOME MINUS  
10-15F ANOMALIES WILL EXTEND FROM THE CENTRAL-SOUTHERN HIGH PLAINS  
INTO EAST-CENTRAL U.S. MID-LATE WEEK.  
 
RAUSCH/RYAN  
 
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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