897  
FXUS02 KWBC 141527  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1127 AM EDT SUN OCT 14 2018  
 
VALID 12Z WED OCT 17 2018 - 12Z SUN OCT 21 2018  
   
..PATTERN OVERVIEW
 
 
UPPER RIDGING OVER BRITISH COLUMBIA AND FLORIDA WILL FAVOR  
PROGRESSIVE TROUGHING THROUGH THE NORTHERN TIER EAST OF THE  
ROCKIES WITH A CLOSED LOW LINGERING ACROSS THE SOUTHWEST. A COUPLE  
CANADIAN FRONTS WITH LIMITED MOISTURE WILL SWING THROUGH THE GREAT  
LAKES/NORTHEAST LATER THIS WEEK INTO THE WEEKEND WITH A RENEWED  
PUSH OF COOLER AIR. FLORIDA WILL REMAIN WARM/HOT WITH SCATTERED  
SHOWERS/STORMS AND THE PACIFIC NORTHWEST SHOULD SEE ABOVE AVERAGE  
TEMPERATURES AND DRY CONDITIONS.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
A MULTI-MODEL DETERMINISTIC BLEND (GFS/ECMWF/UKMET) SUFFICED FOR  
THE DAY 3-5 (WED-FRI) PERIOD 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. BY THE WEEKEND, A COUPLE DIFFERENCES START TO EMERGE. THE  
FIRST BEING HOW MUCH EROSION/FLATTENING OF THE WESTERN NORTH  
AMERICAN RIDGE OCCURS AS SHORTWAVE ENERGY EXITS THE NORTHEASTERN  
PACIFIC. THE ECMWF, AND ITS ENSEMBLES, REMAIN A BIT MORE  
AGGRESSIVE WITH FLATTENING THE RIDGE, WHILE THE GFS/GEFS ARE  
CONSISTENT WITH MAINTAINING STRONG RIDGING, THOUGH THE ECMWF MAY  
BE STARTING TO TREND TOWARDS THE STRONGER GFS RIDGING. IN THE  
EAST, THE GFS/CANADIAN SOLUTIONS REMAIN MUCH STRONGER/SHARPER WITH  
AN UPPER TROUGH SWINGING THROUGH, WHILE THE ECMWF AND THE  
ECENS/GEFS ARE WEAKER. FOR BOTH SYSTEMS IN THE DAY 6-7 PERIOD, A  
MAJORITY ENSEMBLE MEAN BLEND (GEFS/ECENS) ALONG WITH SMALLER  
CONTRIBUTIONS FROM THE DETERMINISTIC GFS/ECMWF SEEMED TO PROVIDE A  
REASONABLE COMPROMISE AND FITS WELL WITH PREVIOUS SHIFT CONTINUITY.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
BELOW AVERAGE TEMPERATURES WILL CONTINUE LATE THIS WEEK INTO THE  
WEEKEND FOR THE SOUTHWEST THROUGH THE SOUTHERN PLAINS (ESPECIALLY  
TEXAS) NORTHEASTWARD THROUGH THE OHIO VALLEY INTO THE NORTHEAST.  
ON THE WARM SIDE OF THE STATIONARY FRONT, FLORIDA WILL SEE  
WARM/HOT TEMPERATURES THAT MAY TIE/BREAK RECORD HIGHS AT SOME  
LOCATIONS AND UPPER RIDGING ACROSS THE PACIFIC NORTHWEST WILL ALSO  
LEAD TO CONTINUED ABOVE NORMAL TEMPERATURES FOR THAT REGION.  
 
PRECIPITATION WISE, THE BEST CHANCE FOR HEAVY RAINFALL REMAINS  
ALONG THE SOUTHERN/CENTRAL TEXAS COAST ALONG AN INVERTED TROUGH  
AND JUST TO THE NORTHWEST OF A STATIONARY BOUNDARY IN THE WESTERN  
GULF. THIS SIGNAL HAS BEEN STEADY FOR SEVERAL MODEL/ENSEMBLE  
CYCLES NOW. A LINGERING UPPER LOW IN THE SOUTHWEST WILL SUPPORT  
RAIN/SNOW SHOWERS MOSTLY FOCUSED IN/ALONG THE HIGHER TERRAIN, AND  
A STATIONARY FRONT ACROSS FLORIDA WILL KEEP DAILY SHOWER/STORM  
CHANCES IN THE FORECAST FOR MUCH OF THE PERIOD. THE REST OF THE  
LOWER 48 LOOKS TO BE LARGELY DRY WITH SOME GENERALLY LIGHT  
RAIN/SNOW SHOWERS AROUND THE LAKES AND INTO THE NORTHEAST  
ALONG/AHEAD OF THE COLD FRONT NEXT WEEKEND. HOWEVER, IF A  
STRONGER/SHARPER UPPER TROUGH IN THE EAST WERE TO MATERIALIZE  
(LIKE THE GFS IS DEPICTING), THE CHANCES FOR HEAVIER PRECIP ALONG  
THE FRONT FROM GENERALLY THE CENTRAL GULF COAST TO THE  
MID-ATLANTIC WOULD INCREASE.  
 
SANTORELLI/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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