601  
FXUS02 KWBC 121558  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1058 AM EST MON NOV 12 2018  
 
VALID 12Z THU NOV 15 2018 - 12Z MON NOV 19 2018  
   
..OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
MODELS CONTINUE TO AGREE ON THE OVERALL PATTERN: THE UPPER RIDGE  
STRENGTHENING OVER THE WEST COAST WITH A DOWNSTREAM MEAN TROUGH  
SETTLING OVER THE EASTERN U.S. THE DETAILS IN BOTH OF THESE  
FEATURES DIVERGE WITH THE DIFFERENT SOLUTIONS.  
 
IN THE BEGINNING OF THE MEDIUM RANGE PERIOD, A CLOSED UPPER LOW  
OVER THE LOWER MISSISSIPPI VALLEY/TENNESSEE VALLEY WILL LIFT  
NORTHWARD TOWARD THE MID-ATLANTIC. IN THE EAST, THE 06Z GFS IS  
SLIGHTLY FASTER WITH THE PROGRESSION OF THIS CLOSED LOW AS  
COMPARED WITH THE 00Z ECMWF. MEANWHILE, THE 00Z CMC AGREES WITH  
THE SLOWER SOLUTION. THE 00Z UKMET WAS MUCH FASTER AND FARTHER  
NORTH WITH THIS LOW--THUS, IT WAS COMPLETELY DISCOUNTED. AT THE  
SURFACE, THE 06Z GFS WAS FASTER WITH THE FRONT AS A RESULT BUT  
BOTH THE GFS/ECMWF WERE STILL WITHIN A REASONABLE RANGE OF EACH  
OTHER. IN THE NORTHERN TIER STATES/GREAT LAKES, THE 06Z GFS/00Z  
ECMWF ARE IN AGREEMENT ON THE OVERALL TIMING WITH THE ENERGY  
SKIRTING ACROSS THE GREAT LAKES. BY THE WEEKEND, SHORTWAVE ENERGY  
WILL SLIDE DOWN THE UPPER RIDGE ON THE WEST COAST WHICH WILL LEAD  
TO A MORE ROUNDED EASTERN MEAN TROUGH. THE DETAILS BEGIN TO BECOME  
APPARENTLY DIFFERENT BY THE BEGINNING OF NEXT WEEK.  
 
OUT WEST, THE UPPER LEVEL RIDGE WILL BEGIN TO BUILD ACROSS THE  
WEST COAST. IN THE PACIFIC, A TROUGH WILL BEGIN TO DIG FARTHER  
SOUTH AND EVENTUALLY SPLIT TO BECOME A CLOSED LOW. THIS WILL LEAD  
TO THE RIDGE BREAKING DOWN BY THE END OF THE WEEKEND AND INTO  
EARLY NEXT WEEK. ONCE AGAIN, THE 06Z GFS AND THE 06Z GEFS MEAN  
WERE MORE PROGRESSIVE WITH THE LOW IN THE PACIFIC AND FASTER WITH  
PUSHING THE RIDGE INLAND WHILE BREAKING DOWN. THE 06Z GEFS MEAN  
ALSO CONTINUED TO SHOW MORE SEPARATION WITH THE CLOSED LOW THAN  
THE 00Z ECENS MEAN. THE OPERATIONAL MODELS AND THEIR MEANS ALL  
AGREE THAT THE RIDGE WEAKENS AS IT CENTERS OVER THE CENTRAL GREAT  
BASIN WHILE THE CLOSED LOW APPROACHES THE WEST COAST.  
 
WPC ENDED UP USING A BLEND OF THE 06Z GFS/00Z ECMWF THROUGHOUT THE  
MEDIUM RANGE FORECAST DUE TO THEIR OVERALL AGREEMENT WITH THE  
PATTERN. INCREASED THE USAGE OF THEIR RESPECTIVE MEANS BY THE  
WEEKEND AND INTO MONDAY TO HELP WITH THE DIFFERENCES IN DETAIL.  
   
..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.  
 
REINHART  
 
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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