013  
FXUS02 KWBC 201600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1159 AM EDT SAT OCT 20 2018  
 
VALID 12Z TUE OCT 23 2018 - 12Z SAT OCT 27 2018  
 
...GUIDANCE/PREDICTABILITY ASSESSMENT AND WEATHER  
HIGHLIGHTS/THREATS...  
 
A FAVORED COMPOSITE OF LATEST MODELS AND ENSEMBLES THAT SEEM  
REASONABLY WELL CLUSTERED INTO DAY 5/6 AGREE THAT A SPLIT FLOW  
REGIME WILL FAVOR A WEAK SOUTHERN STREAM TROUGH TRACK FROM THE  
DESERT SOUTHWEST TOWARD THE MIDDLE OF THE COUNTRY NEXT WEEK. SOME  
PHASING WITH A NORTHERN BRANCH OF THE JET COULD LEAD TO  
CYCLOGENESIS ACROSS THE NORTHERN GULF OF MEXICO WITH THE FRONTAL  
WAVE TRACKING TOWARD THE SOUTHEASTERN U.S. THAT LIKELY OFFERS A  
THREAT OF HEAVY RAINFALL ALONG THE GULF COAST AND NORTHERN GULF OF  
MEXICO/FLORIDA. THERE IS A SUBSEQUENT THREAT FOR SIGNIFICANT  
LOW/STORM DEEPENING UP OFF THE EASTERN SEABOARD NEXT WEEKEND TO  
MONITOR THE WPC PRODUCT SUITE BY DAYS 6/7 WAS MORE IN LINE WITH A  
BLEND OF ENSEMBLES AND WPC CONTINUITY AMID GROWING FORECAST SPREAD  
AND UNCERTAINTY.  
 
ACROSS THE MORE NORTHERN LATITUDES, LOWER HEIGHTS SHOULD TEND TO  
WORK INTO NORTHEASTERN NORTH AMERICA AS AN UPPER LOW CONTINUES TO  
SPIN OVER NORTHERN NUNAVUT. AMPLIFYING FLOW SWINGING THROUGH THE  
GREAT LAKES WILL ULTIMATELY AID IN THE DEVELOPMENT OF A COASTAL  
WAVE IN THE VICINITY OF NOVA SCOTIA BY LATE TUESDAY/EARLY  
WEDNESDAY. NORTHERN MAINE COULD SEE SOME SNOWFALL ACCUMULATIONS AS  
THE COASTAL LOW TAKES SHAPE. BACK TO THE NORTHEASTERN PACIFIC,  
MULTIPLE DEEP CYCLONES ARE LIKELY TO APPROACH WESTERN BRITISH  
COLUMBIA DURING THE DAY 3-5, OCTOBER 23-25 TIMEFRAME. WHILE MOST  
OF THE ACTION SHOULD STAY NORTH OF THE INTERNATIONAL BORDER WITH  
CANADA, THE MEAN FLOW SHOULD TURN MORE ZONAL ACROSS THE EASTERN  
PACIFIC ALLOWING MORE OF AN ONSHORE FLOW REGIME INTO THE PACIFIC  
NORTHWEST. THE PERSISTENCE OF ONSHORE FLOW WILL KEEP A STEADY  
FOCUS FOR UPSLOPE DRIVEN RAINFALL ACROSS THE OLYMPICS AND  
WASHINGTON CASCADES. TOWARD NEXT WEEKEND, BROAD RIDGING IS  
FORECAST TO GRADUALLY ENCOMPASS THE EASTERN PACIFIC WITH LONGWAVE  
TROUGHING EXPECTED TO COVER THE MIDDLE OF THE COUNTRY. IT APPEARS  
THE BETTER ACTIVITY WILL HOLD OFF UNTIL LATER IN THE WEEK AS THE  
MEAN FLOW TURNS MORE ZONAL IN NATURE. GENERALLY SPEAKING, OUTSIDE  
OF THE MENTIONED AREAS OF CYCLOGENESIS, SYNOPTIC-SCALE GRADIENTS  
SHOULD REMAIN ON THE MORE WASHED OUT SPECTRUM ACROSS THE REMAINDER  
OF THE NATION.  
 
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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