008  
FXUS02 KWBC 161600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT SUN SEP 16 2018  
 
VALID 12Z WED SEP 19 2018 - 12Z SUN SEP 23 2018  
 
...GUIDANCE/PREDICTABILITY ASSESSMENT AND WEATHER  
HIGHLIGHTS/HAZARDS...  
 
THE WEATHER PREDICTION CENTER IS NOW ISSUING ADVISORIES ON CURRENT  
TROPICAL DEPRESSION FLORENCE THAT REMAINS AN ONGOING CATASTROPIC  
INLAND HEAVY RAINFALL AND FLASH FLOODING/FLOODING THREAT. BY  
WEDNESDAY MORNING AS PER COORDINATION WITH THE OCEAN PREDICTION  
CENTER, THE LATEST WPC 15 UTC ADVISORY DEPICTS FLORENCE AS AN  
EMERGING EXTRATROPICAL GALE OFF EASTERN NEW ENGLAND AND THE  
CANADIAN MARITIMES, WITH A SUBSEQUENT LATER WEEK TRACK OVER THE  
NORTHERN ATLANTIC AS A MARITIME HAZARD.  
 
MID-LEVEL HEIGHTS SHOULD GRADUALLY BUILD ACROSS THE EASTERN U.S.  
IN RESPONSE TO A PROGRESSIVE SHORTWAVE DIGGING THROUGH THE  
NORTH-CENTRAL U.S. THURSDAY. THIS IS EXPECTED TO ENHANCE A THREAT  
OF HEAVY RAINFALL TO SPREAD ACROSS THE NORTH-CENTRAL U.S.  
WIDESPREAD ACTIVITY WOULD BE FUELED BY AN INCREASINGLY DEEP RETURN  
FLOW OF MOISTURE FROM THE GULF OF MEXICO INTO THE FOCUSINGING  
BAROCLINIC ZONE AND LEAD LOW. THIS PATTERN SHOULD THEN DRIVE A  
DEVELOPING SURFACE CYCLONE ACROSS QUEBEC BY FRIDAY. THIS AND A  
DEVELOPING PATTERN WITH A SERIES OF U.S. NORTHERN TIER PROGRESSIVE  
SHORTWAVES FAVORS THE DRIVING OF A LEAD AND AMPLE COOLING/DRYING  
FRONT DOWN ACROSS MUCH OF THE WEST-CENTRAL TO EASTERN U.S. INTO  
NEXT WEEKEND. STRONG POST-FRONTAL HIGH PRESSURE SPILLING FROM  
CANADA WILL REINFORCE COLD AIR THAT SUPPORTS SOME NORTHERN ROCKIES  
SNOWS.  
 
BACK ACROSS THE EASTERN PACIFIC, A BROAD RIDGE EXTENDING UP INTO  
THE GULF OF ALASKA WILL HELP MAINTAIN LOWER HEIGHTS ALONG THE WEST  
COAST FOR MUCH OF THE PERIOD. AN INITIAL SHORTWAVE IS FORECAST TO  
SLIDE INTO THE PACIFIC NORTHWEST LATE THURSDAY BEFORE EVENTUAL  
ABSORPTION INTO THE ACTIVE CANADIAN NORTHERN STREAM. ON ITS HEELS  
SHOULD BE A MORE IMPRESSIVE AXIS OF HEIGHT FALLS WHICH FOCUSES A  
LONGWAVE TROUGH OVER THE FAR EASTERN PACIFIC NEXT WEEKEND. THE 00  
UTC ECMWF AND CANADIAN MODELS SHOW SUBSTANTIALLY MORE SHORTWAVE  
ENERGY DIGGING OVER ALASKA THEN NORTHEAST PACIIFC THAN THE 06 UTC  
GFS AND 06 UTC GEFS. 00 UTC NAEFS/ECMWF ENSEMBLE MEANS SUPPORT A  
SOLUTION TRENDING WPC CONTINUITY TOWARD THE MORE  
AMPLIFIED/OFFSHORE IDEA INTO NEXT WEEKEND.  
 
FINALLY, ACROSS THE DESERT SOUTHWEST, AN AREA OF DISTURBED WEATHER  
LIFTING OUT OF THE SUBTROPICAL PACIFIC SHOULD ENHANCE  
LOW/MID-LEVEL MOISTURE AND RAINFALL POTENTIAL ACROSS THE REGION.  
THE NATIONAL HURRICANE CENTER CURRENTLY SUGGESTS AN 80 PERCENT  
CHANCE FOR TROPICAL CYCLOGENESIS DURING THE NEXT 5 DAYS.  
 
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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