106  
FXUS02 KWBC 131531  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1131 AM EDT SAT OCT 13 2018  
 
VALID 12Z TUE OCT 16 2018 - 12Z SAT OCT 20 2018  
 
...COOLER THAN AVERAGE TEMPERATURES FOR MUCH OF THE LOWER 48 NEXT  
WEEK...  
 
   
..PATTERN OVERVIEW
 
 
AN UPPER LOW NEAR BAFFIN ISLAND/DAVIS STRAIT WILL MEANDER IN PLACE  
AS UPPER RIDGING IN THE NORTHEAST PACIFIC PUSHES INTO WESTERN  
CANADA AND FLATTENS. THIS WILL FAVOR POSITIVELY TILTED TROUGHING  
FROM THE FOUR CORNERS REGION (WHERE AN UPPER LOW WILL WOBBLE  
AROUND) TO THE GREAT LAKES/NORTHEAST WHERE A COUPLE COLD FRONTS  
WILL SWING THROUGH. ACROSS FLORIDA, SUBTROPICAL RIDGING WILL HOLD  
IN PLACE, MAINTAINING WARM WEATHER BUT WITH A DAILY CHANCE OF  
RAIN/STORMS AS A FRONT STALLS OVER THE PENINSULA.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
BEGAN THE MEDIUM RANGE FORECAST WITH A MULTI-MODEL DETERMINISTIC  
BLEND (ECMWF/GFS/UKMET) DURING DAYS 3-5 (TUE-THU), AS MODELS  
SHOWED GENERALLY GOOD CONSENSUS WITH RESPECT TO THE UPPER LOW  
LINGERING ACROSS THE SOUTHWEST AND WITH AMPLIFYING SHORTWAVE  
ENERGY CROSSING THE GREAT LAKES, PUSHING A SURFACE FRONT TOWARD  
THE EAST COAST DURING THE TIME PERIOD. DURING DAYS 6-7, THE MAIN  
POINT OF CONTENTION AMONG THE GUIDANCE BECOMES HOW MUCH  
EROSION/FLATTENING OF THE WESTERN NORTH AMERICAN RIDGE OCCURS AS  
SHORTWAVE ENERGY TRAVERSES THE NORTHERN PERIPHERY OF THE RIDGE.  
THE 00Z ECMWF WAS THE MOST AGGRESSIVE DETERMINISTIC SOLUTION WITH  
FLATTENING THE RIDGE, RESULTING IN AN OVERALL DEAMPLIFICATION OF  
THE UPPER FLOW ACROSS NORTH AMERICA RELATIVE TO THE GFS/CMC. AT  
THIS POINT, PREFERRED TO COMPROMISE, BUT LEANED SLIGHTLY TOWARD  
THE MORE AMPLIFIED SOLUTIONS GIVEN THE PERSISTENT AMPLIFIED FLOW  
REGIME ACROSS MUCH OF THE NORTHERN HEMISPHERE. THE DAY 6-7  
(FRI-SAT) FORECAST WAS BASED ON INCREASED ECENS/GEFS MEAN  
WEIGHTING ALONG WITH CONTINUED MINORITY COMPONENTS OF THE  
ECMWF/GFS.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
WELL BELOW AVERAGE TEMPERATURES ON TUESDAY (LIKELY BREAKING RECORD  
LOW MINIMA AND MAXIMA OVER MANY STATIONS FROM KS/CO SOUTHWARD TO  
TX/LA) WILL START TO RELENT BUT STILL CONTINUE INTO WEDNESDAY  
ACROSS MUCH OF TEXAS WHERE HIGHS WILL STRUGGLE TO REACH THE 60S  
AWAY FROM THE COAST. ON THE WARM SIDE, PARTS OF FLORIDA MAY  
TIE/BREAK RECORD HIGHS SOUTH OF THE FRONT WHERE UPPER RIDGING WILL  
BE CENTERED.  
 
PRECIPITATION MAY BE HEAVY ON TUESDAY OVER NORTHERN TEXAS ON THE  
COOL SIDE OF THE FRONT BUT BETWEEN THE UPPER LOW TO THE WEST AND  
THE UPPER RIDGE TO THE EAST. THE RAIN AXIS WILL EXTEND  
NORTHEASTWARD TO THE MID-ATLANTIC BUT IN LESSENED AMOUNTS. THE  
REST OF THE LOWER 48 BEHIND THE FRONT WILL BE LARGELY DRY WITH  
SOME RAIN/SNOW SHOWERS AROUND THE LAKES.  
 
RYAN/FRACASSO  
 
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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