616  
FXUS02 KWBC 120657  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
157 AM EST MON NOV 12 2018  
 
VALID 12Z THU NOV 15 2018 - 12Z MON NOV 19 2018  
   
..OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
THE ONE POINT OF AGREEMENT/CONSISTENCY IN THE FORECAST IS THE  
BUILDING OF AN UPPER RIDGE TOWARD THE WEST COAST WITH A DOWNSTREAM  
MEAN TROUGH PREVAILING OVER THE EASTERN HALF OF NORTH AMERICA.  
OTHERWISE SOLUTIONS HAVE BEEN SHOWING MEANINGFUL  
ADJUSTMENTS/TRENDING FOR ASPECTS OF THE RIDGE AND DOWNSTREAM  
TROUGH AS WELL AS FOR EASTERN PACIFIC ENERGY TRYING TO PUSH INTO  
THE RIDGE. OVER THE EAST, GUIDANCE IS STABILIZING FOR THE GENERAL  
IDEA OF SHORT RANGE ENERGY CLOSING OFF AN UPPER LOW OVER THE  
SOUTHERN PLAINS WITH THE FEATURE PROGRESSING NORTHEASTWARD DURING  
THE FIRST HALF OF THE MEDIUM RANGE PERIOD--BUT THERE IS STILL A  
LOT OF SPREAD AND VARIABILITY FOR TIMING AND SURFACE DETAILS.  
 
FOR THE LATE WEEK SYSTEM AFFECTING THE EAST THE 12Z ENSEMBLE  
GUIDANCE DEPICTED A VERY WIDE TIMING SPREAD, SUFFICIENTLY WIDE TO  
INCLUDE THE 12Z UKMET THAT WAS ON THE SLOW SIDE AND THE NEW 00Z  
RUN THAT HAS SWITCHED TO ONE OF THE FASTEST SOLUTIONS. THE 12Z  
CMC WAS SOMEWHAT SLOWER THAN THE 12Z ECMWF AND RECENT GFS RUNS.  
AT THE SURFACE THERE IS SOME SEMBLANCE OF CLUSTERING NEAR THE  
MID-ATLANTIC/NEW ENGLAND COAST FOR THE CORRESPONDING LOW TRACK BUT  
STILL A MEANINGFUL NUMBER OF SOLUTIONS STILL OFFSHORE. OVERALL  
THE 18Z GFS/12Z ECMWF PROVIDED THE BEST MAJORITY INPUT FOR  
YIELDING AN INTERMEDIATE TIMING ALONG WITH A NEAR-COAST SURFACE  
LOW TRACK THAT ACCOUNTS FOR WESTWARD TRENDS OVER THE PAST 1-2 DAYS.  
 
MODELS/ENSEMBLES HAVE BEEN SHOWING SOME DETAIL UNCERTAINTIES FOR  
EVOLUTION OF SURFACE LOW PRESSURE OVER AND NORTHEAST OF THE UPPER  
GREAT LAKES LATE IN THE WEEK BUT THE MAJORITY CLUSTERING FROM DAY  
TO DAY HAS HELD FAIRLY STEADY. GFS RUNS FROM THE PAST COUPLE DAYS  
HAVE TENDED TO BE ON THE NORTHERN SIDE OF THE SPREAD BUT THE 00Z  
VERSION HAS ADJUSTED TO THE CONSENSUS OVER LAKE SUPERIOR AS OF 12Z  
FRI.  
 
FARTHER WESTWARD, OVER THE PAST DAY THE GUIDANCE HAS TRENDED  
SLOWER/SHARPER WITH THE UPPER RIDGE BUILDING TOWARD THE WEST  
COAST. THE DOWNSTREAM EFFECTS ARE MORE WESTERN CANADA SHORTWAVE  
ENERGY DROPPING INTO THE WEST-CENTRAL U.S. (SPECIFICS VARYING  
CONSIDERABLY IN THE MODELS/ENSEMBLES) WHICH ULTIMATELY LEADS TO A  
MORE ROUNDED EASTERN MEAN TROUGH, A REVERSAL OF YESTERDAY'S TREND  
TOWARD A MORE AMPLIFIED EASTERN TROUGH. MEANWHILE GUIDANCE IS  
CONTINUING TO SUGGEST THAT APPROACHING EASTERN PACIFIC TROUGH  
ENERGY WILL SPLIT AS IT NEARS THE WEST COAST. THE 18Z GFS/12Z  
ECMWF PROVIDED THE BEST REFLECTION OF THIS IDEA WITHIN THE  
FRAMEWORK OF THE MEANS WHICH HAVE BEEN SHOWING LESS FLOW  
SEPARATION DUE TO THEIR AVERAGING OF MANY VARIED MEMBER SOLUTIONS.  
THE NEW 00Z GEFS MEAN HAS MORE OF A SEPARATION SIGNAL THAN SEEN  
IN PREVIOUS GEFS OR OTHER ENSEMBLE MEAN RUNS, WHILE THE NEW 00Z  
GFS AND RECENT CMC RUNS OFFER POTENTIAL FOR A FARTHER SOUTH TRACK  
OF SOUTHERN ENERGY.  
 
BASED ON FORECAST CONSIDERATIONS THROUGH THE PERIOD THE 18Z  
GFS/12Z ECMWF SERVED AS THE PRIMARY OPERATIONAL MODEL INPUT FOR  
THE FORECAST, THOUGH DURING THE FIRST HALF OF THE PERIOD THE 12Z  
CMC PROVIDED SOME MODEST ACCOUNT FOR REMAINING DETAIL DIFFERENCES  
WHILE STAYING WITHIN THE CONSENSUS MEAN PATTERN. THE FORECAST  
INCORPORATED 18Z GEFS/12Z ECMWF ENSEMBLE MEANS MID-LATE PERIOD,  
BUT KEPT THEIR TOTAL WEIGHT TO 50 PERCENT OR LESS GIVEN THE DESIRE  
TO REFLECT SOME SPLIT IN THE FLOW NEAR THE WEST COAST.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE SYSTEM AFFECTING THE EAST WILL SPREAD PRECIPITATION OF VARIOUS  
TYPES NORTHEASTWARD DURING THU-FRI. BEST POTENTIAL FOR AT LEAST  
SOME WINTRY WEATHER WILL BE OVER INLAND/HIGHER ELEVATION  
LOCATIONS. GUIDANCE SPREAD FOR VARIOUS ASPECTS OF THIS SYSTEM  
KEEPS CONFIDENCE LOWER THAN DESIRED FOR TIMING AS WELL AS  
COVERAGE/DURATION OF THE VARIOUS PRECIPITATION TYPES. LOW  
PRESSURE TRACKING OVER OR NEAR THE UPPER GREAT LAKES LATE THIS  
WEEK WILL BRING AN AREA OF MOSTLY LIGHT PRECIPITATION TO THE  
REGION. BEHIND THIS SYSTEM EXPECT COLD CYCLONIC LOW LEVEL FLOW TO  
GENERATE AN EPISODE OF LAKE EFFECT SNOW. MEANWHILE THE  
COMBINATION OF SHORTWAVE ENERGY DROPPING OUT OF CANADA AND LOW  
LEVEL UPSLOPE FLOW SUPPORTED BY HIGH PRESSURE BUILDING INTO THE  
NORTHERN PLAINS MAY PRODUCE AREAS OF SNOW OVER PARTS OF THE  
NORTHERN ROCKIES/HIGH PLAINS AROUND FRI-SAT. TRENDS CONTINUE TO  
BE TOWARD LESS MOISTURE REACHING THE PACIFIC NORTHWEST WITH EITHER  
LIGHT OR NO PRECIPITATION BEING MOST LIKELY. DEPENDING ON THE  
CHARACTER OF UPPER TROUGH ENERGY THAT MAY SPLIT OFFSHORE THE WEST  
COAST, SOME LIGHT PRECIPITATION COULD REACH CALIFORNIA VERY LATE  
IN THE PERIOD BUT WITH BELOW AVERAGE CONFIDENCE AT THIS TIME.  
 
LOCATIONS FROM THE WEST COAST TO INTERMOUNTAIN WEST SHOULD SEE THE  
MOST PERSISTENT WARMTH DURING THE PERIOD WITH HIGHS GENERALLY  
5-15F ABOVE NORMAL. THE NORTHERN HIGH PLAINS AND VICINITY SHOULD  
SEE A WARM START TO THE PERIOD FOLLOWED BY A COOLING TREND INTO  
THE WEEKEND AND THEN A WARMER TREND EARLY NEXT WEEK. THE SOUTH  
AND EAST WILL TEND TO SEE BELOW NORMAL TEMPERATURES THROUGH THE  
PERIOD. BEST POTENTIAL FOR MINUS 10-20F ANOMALIES WILL EXTEND  
FROM THE SOUTHERN PLAINS THROUGH MUCH OF THE EAST ON THU AND THEN  
WITH A REINFORCING PUSH OF COLD AIR PROGRESSING FROM THE NORTHERN  
PLAINS INTO THE EAST SAT-MON.  
 
RAUSCH  
 
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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