556  
FXUS02 KWBC 120616  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
215 AM EDT FRI OCT 12 2018  
 
VALID 12Z MON OCT 15 2018 - 12Z FRI OCT 19 2018  
 
...IMPRESSIVE RECORD COLD FOR THE CENTRAL/SOUTHERN PLAINS EARLY  
NEXT WEEK...  
 
   
..PATTERN OVERVIEW
 
 
AN UPPER LOW NEAR BAFFIN ISLAND/DAVIS STRAIT WILL SLOWLY TRANSLATE  
SOUTHEASTWARD AS UPPER RIDGING IN THE NORTHEAST PACIFIC BREAKS  
DOWN. THIS WILL ALLOW TROUGHING INITIALLY OVER THE GREAT LAKES TO  
SPLIT BETWEEN A NORTHERN AND SOUTHERN PORTION WITH THE FORMER  
EXITING MUCH QUICKER THAN THE LATTER. ACROSS FLORIDA, SUBTROPICAL  
RIDGING WILL HOLD IN PLACE, PREVENTING A COLD FRONT FROM SLIPPING  
SOUTHWARD TO LAKE OKEECHOBEE.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MULTI-MODEL/ENSEMBLE BLEND SUFFICED FOR A STARTING POINT FOR MUCH  
OF THE PERIOD OVER MUCH OF THE CONUS, EXCEPT FOR A COUPLE AREAS.  
FIRSTLY, EXITING COMPACT UPPER LOW THROUGH THE GREAT LAKES HAS  
BEEN TRENDING SLOWER THOUGH THE GFS RUNS REMAINED QUICKER  
(PARALLEL FV3-GFS WAS A LITTLE SLOWER THAN THE OPERATIONAL RUN).  
RELIED ON THE ECMWF/CANADIAN/UKMET THERE. SECONDLY, THE EMBEDDED  
VORTICITY ROUNDING THE BASE OF THE TROUGH THROUGH THE LAKES ON  
WEDNESDAY HAS MOSTLY TRENDED SLOWER AS WELL AND THE 18Z GFS  
REGAINED ITS CLUSTERING WITH THE OTHERS EXCEPT FOR THE UKMET WHICH  
APPEARED MUCH TOO AGGRESSIVE THE BREAK DOWN THE UPPER RIDGE OFF  
THE WEST COAST. BY THE END OF NEXT WEEK, BLEND OF THE  
DETERMINISTIC AND ENSEMBLE GUIDANCE SMOOTHED OUT SOME UNCERTAIN  
FEATURES IN THE NORTHERN STREAM AROUND THE UPPER LOW IN  
NORTHEASTERN CANADA BUT MAINTAINED THE UPPER LOW IN THE SOUTHWEST  
THAT SHOULD SLOWLY LIFT NORTHEASTWARD THROUGH THE WEEK.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
WELL BELOW AVERAGE TEMPERATURES (LIKELY BREAKING RECORD LOW MINIMA  
AND MAXIMA OVER MANY STATIONS AND STATES) WILL SINK SOUTHWARD  
BEHIND A STRONG COLD FRONT LATE THIS WEEKEND INTO NEXT MONDAY.  
HIGHS IN THE 40S ARE FORECAST FOR MOST OF THE CENTRAL PLAINS INTO  
TEXAS EVEN TO THE BIG BEND WHICH WILL BE ABOUT 25-35 DEGREES BELOW  
AVERAGE. SOME LOCATIONS MAY BREAK THEIR RECORD LOW DAYTIME HIGH  
TEMPERATURE BY 5-10 DEGREES EVEN WHERE RECORDS GO BACK OVER 100  
YEARS. THE COLD WILL START TO RELENT AFTER MONDAY AS IT SETTLES TO  
THE GULF COAST AND LOWER MISSISSIPPI RIVER VALLEY. THE COLD FRONT  
WILL HAVE LESS BITE FARTHER EAST FROM THE GREAT LAKES TO THE  
NORTHEAST/MID-ATLANTIC WHERE TEMPERATURES WILL ONLY BE A FEW  
DEGREES BELOW AVERAGE. TO THE SOUTH, FLORIDA WILL MAINTAIN ABOVE  
AVERAGE TEMPERATURES THANKS TO UPPER RIDGING.  
 
PRECIPITATION MAY BE LOCALLY HEAVY ACROSS TEXAS NORTHEASTWARD AS  
THE UPPER LOW BEHIND FUTURE EX-SERGIO MEANDERS EASTWARD THROUGH  
THE FOUR CORNERS REGION AND MOISTURE FROM THE WESTERN GULF FLOWS  
NORTHWARD ATOP THE FRONT. THE RAIN AXIS WILL EXTEND TO THE  
MID-ATLANTIC BUT IN LESSENED AMOUNTS. THE REST OF THE LOWER 48  
BEHIND THE FRONT WILL BE LARGELY DRY WITH SOME SHOWERS AROUND THE  
LAKES (SOME SNOW, SOME RAIN). WIDESPREAD SNOW (SOME LOWER  
ELEVATION RAIN) WILL EXIT THE SOUTHERN ROCKIES ON MONDAY WITH SOME  
SNOW ACCUMULATION THEREAFTER AS THE UPPER LOW SWINGS THROUGH.  
 
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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