094  
FXUS02 KWBC 151546  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1146 AM EDT MON OCT 15 2018  
 
VALID 12Z THU OCT 18 2018 - 12Z MON OCT 22 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE LATEST RUNS OF OPERATIONAL MODELS/ENSEMBLES STILL SHOW GOOD  
AGREEMENT AND CONTINUITY FOR THE LONGWAVE PATTERN OVER THE LOWER  
48 THROUGH THE WEEKEND INTO EARLY NEXT WEEK. UPPER RIDGING WILL  
REBUILD OVER THE NORTHWEST U.S. AND WESTERN CANADA TO MAINTAIN AN  
EASTERN NORTH AMERICA MEAN TROUGH. SHORTWAVES EMBEDDED WITHIN THE  
TROUGH WILL SUPPORT PERIODIC FRONTAL PASSAGES OVER THE  
CENTRAL-EASTERN STATES. ACROSS SOUTHERN LATITUDES, A SHORT RANGE  
SOUTHWEST UPPER LOW IN THE PROCESS OF EJECTING FROM THE WEST AT  
THE START OF THE EXTENDED PERIOD WILL BE REPLACED BY ANOTHER UPPER  
LOW CONSISTING OF LEFTOVER ENERGY. MEANWHILE UPPER RIDGING THAT  
COVERS THE GULF COAST STATES WILL GRADUALLY BE SUPPRESSED AS  
EASTERN TROUGHING AMPLIFIES.  
 
AN OPERATIONAL MODEL CONSENSUS CONTINUES TO REPRESENT INDIVIDUAL  
FEATURES WELL FOR DAYS 3-5 THU-SAT. AFTER THAT TIME MODEL RUNS  
BEGIN TO SHOW GREATER SHORTWAVE DIFFERENCES AMONG EACH OTHER  
AND/OR IN CONSECUTIVE RUNS, FAVORING A TREND TOWARD 50 PERCENT  
TOTAL 06Z GEFS/00Z ECMWF ENSEMBLE MEAN INPUT FOR THE LATTER PART  
OF THE FORECAST. OF PARTICULAR NOTE THE 00Z GFS BRINGS LOW  
PRESSURE INTO THE UPPER GREAT LAKES LATE SUN-EARLY MON WHEREAS  
CONSENSUS KEEPS THE BEST-DEFINED SURFACE LOW WELL NORTH OVER  
CANADA. THE 06Z GFS DIFFERS FROM CONSENSUS FOR ITS SPECIFICS OF  
THE UPPER TROUGH APPROACHING THE WEST COAST TOWARD THE END OF THE  
PERIOD.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
BELOW AVERAGE TEMPERATURES WILL CONTINUE LATE THIS WEEK INTO NEXT  
MONDAY FOR THE SOUTHWEST THROUGH THE SOUTHERN PLAINS (ESPECIALLY  
TEXAS) NORTHEASTWARD THROUGH THE OHIO VALLEY INTO THE  
NORTHEAST/MID-ATLANTIC. THE MOST EXTREME ANOMALIES SHOULD BE OVER  
THE SOUTHERN HIGH PLAINS ON THU WITH SOME LOCATIONS 20-25F BELOW  
NORMAL. OTHERWISE EXPECT SOME LOCATIONS TO SEE AT LEAST 10-15F  
BELOW NORMAL HIGHS WITHIN THE BROAD AREA OF COOL TEMPERATURES. ON  
THE WARM SIDE OF THE SOUTHERN STATIONARY FRONT, FLORIDA WILL SEE  
WARM/HOT TEMPERATURES THAT MAY TIE OR BREAK RECORD HIGHS/WARM LOWS  
AT SOME LOCATIONS. UPPER RIDGING ACROSS THE PACIFIC NORTHWEST  
(WA/OR/ID INTO WESTERN MONTANA) WILL ALSO LEAD TO CONTINUED ABOVE  
AVERAGE TEMPERATURES FOR THAT REGION--GENERALLY PLUS 5-15F  
ANOMALIES FOR HIGHS.  
 
EXPECT HIGHEST 5-DAY RAINFALL TOTALS OVER PORTIONS OF TEXAS AND  
NEAR THE WESTERN GULF COAST, IN THE VICINITY OF AN INVERTED TROUGH  
AND TO THE NORTHWEST OF A STATIONARY BOUNDARY IN THE WESTERN GULF.  
SOME OF THIS SOUTHERN PLAINS MOISTURE MAY EXTEND NORTHEASTWARD  
ALONG A COLD FRONT CROSSING THE EAST DURING THE WEEKEND. THE  
LINGERING UPPER LOW IN THE SOUTHWEST WILL SUPPORT RAIN AND  
POSSIBLY HIGH ELEVATION SNOW SHOWERS MOSTLY FOCUSED ON/ALONG THE  
HIGHER TERRAIN WHILE A STATIONARY FRONT ACROSS FLORIDA WILL KEEP  
DAILY SHOWER/STORM CHANCES IN THE FORECAST. OVER THE GREAT  
LAKES/NORTHEAST LAKE EFFECT PRECIPITATION SHOULD BE TAPERING OFF  
THU. THEN THE LATE WEEK/WEEKEND FRONTAL SYSTEM WILL BRING A PERIOD  
OF MOSTLY LIGHT RAIN FOLLOWED BY ANOTHER EPISODE OF LAKE EFFECT  
RAIN/SNOW. THE NEXT SYSTEM IN THE SERIES MAY BRING AN AREA OF  
LIGHT PRECIPITATION TO THE GREAT LAKES AROUND THE START OF NEXT  
WEEK.  
 
RAUSCH/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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