429  
FXUS02 KWBC 161557  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1156 AM EDT TUE OCT 16 2018  
 
VALID 12Z FRI OCT 19 2018 - 12Z TUE OCT 23 2018  
   
..PATTERN OVERVIEW
 
 
A MEAN TROUGH ALOFT WILL PERSIST OVER EASTERN NORTH AMERICA  
DOWNSTREAM FROM A PACIFIC NORTHWEST/WESTERN CANADA RIDGE. THE  
GRADUAL APPROACH OF A NORTHEASTERN PACIFIC UPPER TROUGH WILL BEGIN  
TO PUSH THE RIDGE AXIS A LITTLE EASTWARD BY THE FIRST PART OF NEXT  
WEEK. UNDER THE EASTERN UPPER TROUGH A SERIES OF CANADIAN FRONTS  
WILL SWING THROUGH THE CENTRAL-EASTERN STATES TO MAINTAIN BELOW  
AVERAGE TEMPERATURES AND SPARK OFF SOME RAIN/SNOW SHOWERS  
ESPECIALLY IN FAVORED LAKE-EFFECT AREAS. THE STRONG UPPER RIDGE  
OVER FLORIDA WILL SLOWLY WEAKEN BY NEXT WEEK AND GET SQUASHED INTO  
CUBA. ON ITS WEST SIDE WILL BE A STALLED FRONT OFF THE TEXAS COAST  
AND NEARBY SURFACE TROUGH WHICH WILL KEEP A DAILY CHANCE OF  
RAINFALL IN THE FORECAST, OVER SOUTHERN TEXAS IN PARTICULAR.  
FINALLY TO THE SOUTH OF THE NORTHWEST RIDGE, A WEAK UPPER LOW NEAR  
SOUTHERN CALIFORNIA WILL LIKELY EJECT INTO THE GREAT BASIN EARLY  
NEXT WEEK WITH THE APPROACH OF MORE PROGRESSIVE PACIFIC FLOW,  
HELPING TO WRING OUT SOME LIGHT SHOWERS.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
NOTE THAT 00Z CMC/CMC ENSEMBLE RUNS WERE NOT AVAILABLE FOR THE  
FORECAST. REMAINING GUIDANCE IN THE 00Z-06Z CYCLES OFFER BETTER  
THAN AVERAGE AGREEMENT, AND EVEN BY DAY 7 TUE OPERATIONAL RUN  
DIFFERENCES FALL WITHIN TYPICAL ERROR RANGE. BY LATE DAY 7 THE  
06Z GFS/00Z ECMWF TREND A BIT TOWARD THE DEEPER/SHARPER SIDE OF  
THE SPECTRUM WITH THE SHORTWAVE NEARING THE EAST COAST BUT STILL  
COMPARE ACCEPTABLY TO THE OVERALL PATTERN THUS MERITING INCLUSION  
FOR THE FORECAST. ECMWF ENSEMBLES AS A WHOLE ARE STILL A LITTLE  
MORE EAGER TO LOWER HEIGHTS ALONG WEST COAST LATE IN THE PERIOD  
BUT THE OPERATIONAL 00Z ECMWF HAS MADE A FAVORABLE ADJUSTMENT,  
TOWARD SLOWER ARRIVAL OF SHORTWAVE ENERGY THAN THE 12Z/15 RUN.  
 
DUE TO AN INITIAL PIECE OF FOUR CORNERS ENERGY THAT THE 00Z ECMWF  
PULLS INTO THE NORTHWEST FRI-MON IN A STRONG LOW-CONFIDENCE  
FASHION (SOMEWHAT MORE SHEARED IN THE 00Z UKMET), THE PREFERRED  
DAYS 3-5 FRI-SUN MODEL BLEND INCLUDED THE PAST TWO ECMWF RUNS  
ALONG WITH THE 00Z/06Z GFS AND 00Z UKMET. DAYS 6-7 MON-TUE  
INCORPORATED 40-50 PERCENT TOTAL WEIGHT OF THE 06Z GEFS/00Z ECMWF  
MEAN TO TEMPER TIMING DIFFERENCES THAT ARISE AMONG THE GFS/ECMWF.  
DUE TO THE AFOREMENTIONED ISSUE WITH THE OLD 12Z ECMWF NEAR THE  
WEST COAST, THAT RUN WAS REMOVED FROM THE BLEND AFTER DAY 5. THE  
RESULTING FORECAST YIELDED MODEST AND TYPICAL RUN-TO-RUN  
DETAIL/TIMING ADJUSTMENTS FOR INDIVIDUAL FEATURES BUT GOOD  
CONTINUITY OVERALL.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
EXPECT ABOVE AVERAGE TEMPERATURES OVER MUCH OF THE WESTERN U.S.  
AWAY FROM THE INFLUENCE OF THE SOUTHERN UPPER LOW, GENERALLY 5-10F  
ABOVE AVERAGE BUT WITH SOME LOCALLY HIGHER ANOMALIES OVER PARTS OF  
THE NORTHWEST/EXTREME NORTHERN ROCKIES. UPPER TROUGHING FARTHER  
EAST AND CLOUD COVER OVER TEXAS WILL KEEP TEMPERATURES BELOW  
AVERAGE OVER A BROAD AREA FROM THE SOUTHERN PLAINS INTO THE  
NORTHEAST. THOSE TWO AREAS SHOULD SEE THE GREATEST NEGATIVE  
DEPARTURES FROM NORMAL ON ONE OR MORE DAYS. FRONTAL PASSAGES WILL  
PROVIDE SOME DAILY VARIATION IN TEMPERATURES. A FEW LOCATIONS  
COULD SEE READINGS NEAR RECORD VALUES FOR WARMTH OVER WA/OR AND FL  
WHILE A FEW DAILY RECORDS FOR COOL HIGHS MAY BE POSSIBLE OVER THE  
GREAT LAKES/EAST COAST REGIONS.  
 
HIGHEST 5-DAY RAINFALL TOTALS WILL BE 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, THOUGH  
WITH SOME LINGERING UNCERTAINTY OVER PRECISE RAINFALL AMOUNTS. THE  
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 WILL START ANEW THIS  
WEEKEND BEHIND A COLD FRONT AND THEN AGAIN LATE IN THE FORECAST  
WITH THE PASSAGE OF A WEAK SYSTEM. COASTAL WA/OR WILL SEE  
LIGHT-MODERATE RAIN DEVELOP AND EXPAND INLAND EARLY NEXT WEEK AS  
UPPER TROUGHING APPROACHES.  
 
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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