190  
FXUS02 KWBC 121608  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1108 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 ON THURSDAY AND INTO FRIDAY. 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 WEEKEND.  
 
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
 
 
AS THE OCCLUDED SYSTEM BEGINS TO LIFT OUT OF THE SOUTHEAST AND  
MOVE INTO THE MID-ATLANTIC, PRECIPITATION OF VARIOUS TYPES WILL BE  
IMPACTING THESE REGIONS. IN THE SOUTHEAST AND MID-ATLANTIC, HEAVY  
RAINFALL COULD BE A CONCERN ON THURSDAY AND FRIDAY--WITH WINTRY  
PRECIPITATION IN THE HIGHER ELEVATIONS OF THE CENTRAL APPALACHIANS  
AND THE INTERIOR OF NEW ENGLAND. WITH THE SYSTEM MOVING INTO THE  
GREAT LAKES LATE THIS WEEK, LIGHT PRECIPITATION CAN BE EXPECTED.  
HOWEVER, WITH CYCLONIC LOW LEVEL FLOW DUE TO THE MEAN TROUGH  
SETTING UP OVER THE EASTERN U.S., SOME LAKE EFFECT SNOW CAN BE  
EXPECTED. AS THE SHORTWAVE DROPS INTO THE NORTHERN TIER STATES  
EARLY INTO THE WEEKEND, THERE IS A POSSIBILITY OF SNOW ACROSS THE  
NORTHERN ROCKIES/HIGH PLAINS ON FRIDAY AND INTO SATURDAY. THERE  
COULD BE LIGHT PRECIPITATION ON THURSDAY AND INTO FRIDAY FOR THE  
PACIFIC NORTHWEST, HOWEVER THE WEST COAST WILL STAY DRY FOR THE  
REST OF THE MEDIUM RANGE PERIOD.  
 
TEMPERATURES WILL BE QUITE COOL FOR THE CENTRAL AND EASTERN U.S.  
BY THE WEEKEND AND THROUGH MONDAY. HIGH TEMPERATURE ANOMALIES  
WILL BE 12-16 DEGREES BELOW NORMAL. THE WESTERN U.S. CAN EXPECT  
HIGH TEMPERATURES TO BE 5 TO 15 DEGREES ABOVE NORMAL.  
 
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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