520  
FXUS02 KWBC 030501  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
101 AM EDT WED OCT 03 2018  
 
VALID 12Z SAT OCT 06 2018 - 12Z WED OCT 10 2018  
 
...STORMY PATTERN FOR THE WEST/ROCKIES AND A CENTRAL U.S.  
EXCESSIVE RAINFALL THREAT...  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODELS AND ENSEMBLES ARE REASONABLY WELL CLUSTERED WITH LARGER  
SCALE DEVELOPMENT OF A HIGHLY AMPLIFIED WEATHER PATTERN FOR THE  
NATION THIS WEEKEND INTO NEXT WEEK. THIS PATTERN OFFERS HEIGHT  
ANOMALIES OF 2+ STANDARD DEVIATIONS ABOVE/BELOW NORMAL WITH A  
DIGGING WESTERN U.S. LONGWAVE TROUGH SANDWICHED BETWEEN RIDGES  
OVER THE EASTERN PACIFIC AND THE EAST COAST/ATLANTIC OCEAN. A  
DEEPENING/CLOSED LOW SETS UP OVER THE GREAT BASIN REGION AND  
MULTIPLE WAVES LIFT FROM THE GREAT BASIN/SOUTHERN AND CENTRAL  
ROCKIES INTO THE PLAINS WHERE A DEEP LAYERED SOUTHERLY FUNNEL OF  
GULF OF MEXICO MOISTURE POOLS TO 2+ STANDARD DEVIATIONS FROM  
NORMAL INTO/OVER A SLOW MOVING BAROCLINIC ZONE. HOWEVER, RECENT  
MODELS ARE SHOWING INCREASED RUN TO RUN VARIANCE WITH THE TIMING  
AND EMPHASIS OF SMALLER SCALE EMBEDDED SYSTEMS EMBEDDED WITHIN THE  
SYNOPTIC SCALE FLOW, ESPECIALLY THE 00 UTC GFS. ACCORDINGLY, THE  
WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED BY BLENDING  
THE 18 UTC GEFS MEAN AND 12 UTC ECMWF ENSEMBLE MEAN THAT AGREE TO  
SHOW A STRONG PATTERN SIGNAL. APPLIED STRONGER WEIGHTING TO THE  
ECMWF ENSEMBLES THAT MAINTAIN CLOSER WPC CONTINUITY.  
   
..WEATHER HIGHLIGHTS/THREATS
 
 
COLDER THAN NORMAL TEMPERATURES AND HIGHLY UNSETTLED/WET WEATHER  
WILL DEVELOP AS A PERSISTENT AND HIGHLY AMPLIFIED TROUGH ALOFT  
SETS UP AND IS REINFORCED OVER THE WEST, CENTERED FROM THE GREAT  
BASIN/SOUTHWEST TO THE ROCKIES. TERRAIN AND UPSLOPE FED SNOWS  
SPREAD DOWN TO FOCUS OVER THE NORTHERN ROCKIES/HIGH PLAINS,  
ENHANCED BY A POST-FRONTAL COLD HIGH PRESSURE SURGE INTO EARLY  
NEXT WEEK. WITH SUCH A STRONG WARMING/BLOCKING RIDGE OVER THE  
EAST, WAVES ALONG/OVER CENTRAL U.S. FRONTS WILL SHOW LITTLE  
EASTWARD PROGRESSION. THIS WILL SET THE STAGE FOR A PROLONGER  
PERIOD FAVORING MULTIPLE ROUNDS OF HEAVY RAIN/CONVECTION WITH SOME  
FAR NORTHERN TIER FRINGE SNOW. TRAINING IN A PRONOUNCED AXIS  
OFFERS AN EXTENDED THREAT OF EXCESSIVE RAINFALL. WARM SECTOR  
TEMPERATURES SOUTH OF THE FRONT WILL BE SUMMER-LIKE, SO A MAIN  
FRONTAL ZONE WILL REMAIN QUITE DEFINED.  
 
ELSEWHERE, A DEEP LAYERED EASTERLY FETCH OFF THE ATLANTIC  
FORTIFIES AND PERSISTS INTO NEXT WEEK INTO THE SOUTHEAST,  
SPREADING SHOWERS ACROSS FLORIDA AND THE GULF COAST/NORTHERN GULF  
OF MEXICO UNDERNEATH A NORTHWARD SHIFTING EASTERN U.S. CLOSED  
RIDGE ALOFT.  
THIS LEAVE ROOM FOR ATLANTIC ENERGIES AND/OR A CARRIBEAN BASED  
TROPICAL DISTURBANCE TO WORK INTO FLORIDA AND/OR THE GULF OF  
MEXICO NEXT WEEK TO ENHANCE LIFT/MOISTURE POOLING. MODELS SHOW A  
WIDE ENVELOPE OF POTENTIAL DEVELOPMENTS THAT IS BEING MONITORED BY  
WPC/NHC.  
 
SCHICHTEL  
 
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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