374  
FXUS02 KWBC 081600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT MON OCT 08 2018  
 
VALID 12Z THU OCT 11 2018 - 12Z MON OCT 15 2018  
 
...MICHAEL/HEAVY RAINFALL LIFT FROM THE SOUTHEAST TO OFF THE  
EASTERN SEABOARD THU/FRI...  
...SERGIO MOISTURE/RAINS TO REACH ARIZONA AND SOUTHERN  
ROCKIES/PLAINS INTO FRI/SAT...  
 
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
LATEST GUIDANCE MAINTAINS DECENT CONTINUITY FOR THE EVOLUTION OF  
THE LARGER SCALE MEAN PATTERN ALOFT, SHOWING A TRANSITION FROM A  
POSITIVELY TILTED SOUTHERN CANADA INTO WESTERN U.S. TROUGH DAY 3  
THU TOWARD STRONG RIDGE BUILDING NEAR THE WEST COAST AND  
DOWNSTREAM AMPLIFIED TROUGHING SETTLING FROM WEST-CENTRAL TO EAST  
-CENTRAL NORTH AMERICA OVER THIS PERIOD. MEANWHILE MOST SOLUTIONS  
SHOW SOME DEGREE OF SMALLER-SCALE TROUGHING LIKELY TO PERSIST OVER  
THE SOUTHWESTERN U.S. AND NORTHWESTERN MEXICO.  
 
OVER THE WEST, THE GREATEST UNCERTAINTY WILL BE WITH THE SPECIFICS  
OF INITIAL WESTERN ENERGY FOR WHICH MODELS/ENSEMBLES ARE SHOWING  
AN INCREASING SIGNAL OF CLOSING OFF FOR A TIME NEAR SOUTHERN  
CALIFORNIA--PLUS INTERACTION WITH SERGIO WHICH SHOULD BE TRACKING  
NORTHEASTWARD AHEAD OF THE AFOREMENTIONED ENERGY. THIS  
INTERACTION WILL BE VERY SENSITIVE TO THE EXACT TIMING OF SERGIO  
AND HOW THE WESTERN U.S. SHORTWAVE ENERGY IS EVOLVING AT A  
SPECIFIC POINT IN TIME (AND WHAT PROPORTION FEEDS SOUTHWESTWARD  
VERSUS CONTINUING ALONG IN THE WESTERLIES. THE OVERALL PATTERN  
APPEARS SUPPORTIVE FOR FASTER PROGRESSION THAN WHAT HAS BEEN  
DEPICTED IN ECMWF/ECMWF MEAN RUNS THUS FAR AND THE LATEST FORECAST  
FROM THE NHC SEEMS CLOSEST TO THE 00 UTC UKMET AND TO A LESSER  
EXTENT THE 00 UTC GFS. PLEASE CONSULT NATIONAL HURRICANE CENTER  
PRODUCTS FOR THE LATEST INFO ON MICHAEL.  
 
MEANWHILE THE FORECAST FOR MICHAEL, WHICH HAS REACHED HURRICANE  
STATUS AT THIS TIME AND SHOULD AFFECT THE SOUTHEAST AND EAST  
MID-LATER WEEK, IS ALSO UNCERTAIN IN LIGHT OF CONTINUED VERY BROAD  
MODEL/ENSEMBLE SPREAD FOR TRACK AND ESPECIALLY TIMING. AT THE VERY  
LEAST THE OVERALL PATTERN APPEARS SUPPORTIVE FOR FASTER  
PROGRESSION THAN WHAT HAS BEEN DEPICTED IN ECMWF/ECMWF MEAN RUNS  
THUS FAR AND THE LATEST FORECAST FROM THE NHC SEEMS CLOSEST TO THE  
00 UTC UKMET AND TO A LESSER EXTENT THE 00 UTC GFS. PLEASE CONSULT  
NATIONAL HURRICANE CENTER PRODUCTS FOR THE LATEST INFO ON MICHAEL.  
 
WPC SURFACE FRONTS/PRESSURES AND 500MB MASS FIELD PROGS WERE  
ACCORDINGLY PRIMARILY DERIVED FROM A SOLUTION CLOSEST TO THE 00  
UKMET DAYS 3-5 TO BEST MATCH THE NHCFORECASTS OF MICHAEL AND  
SERGIO. LATER, BLENDED THE 06 UTC GEFS MEAN AND THE 00 UTC ECMWF  
ENSEMBLE MEAN THAT DEVELOPS A BLENDED SOLUTION ALOFT OVER THE  
LOWER 48 ON THE MORE AMPLIFIED SIDE OF THE FULL ENVELOPE OF  
SOLUTIONS IN CONSIDERATION OF AMPLIFIED UPSTREAM RIDGE DEVELOPMENT  
OVER THE EASTERN PACIFIC IN MOST GUIDANCE.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
PARTS OF THE EASTERN U.S. WILL EXPERIENCE A PERIOD OF HEAVY  
RAINFALL WITH THE COMBINATION OF MICHAEL AND INTERACTION WITH AN  
APPROACHING COLD FRONT. GUIDANCE CONTINUES TO VARY WIDELY FOR  
TRACK AND TIMING OF MICHAEL SO CONFIDENCE IS FAIRLY LOW WITH  
RESPECT TO PRECISE LOCATION OF HEAVIEST RAINFALL AND  
TIMING-DEPENDENT DURATION OF THIS RAINFALL. WHILE MICHAEL BEGINS  
TO TRACK AWAY FROM THE EAST COAST, SERGIO MAY BRING MOISTURE INTO  
PORTIONS OF ARIZONA AND THE SOUTHERN ROCKIES/PLAINS. HIGHLY  
SENSITIVE DETAILS FOR EVOLUTION ALOFT LEAD TO LOW CONFIDENCE IN  
EXACT COVERAGE/INTENSITY OF RAINFALL HERE AS WELL--ESPECIALLY THE  
LATITUDE OF THE AXIS OF HEAVIER RAINFALL. THIS LACK OF CONFIDENCE  
EXTENDS TO HOW MUCH MOISTURE MAY INTERACT WITH A FRONT THAT DROPS  
INTO THE PLAINS DURING THE WEEKEND--WITH SOLUTIONS SPANNING THE  
WHOLE SPECTRUM FROM CONSIDERABLE TO MORE MODEST AMOUNTS.  
ELSEWHERE, THE INITIAL FRONT OVER THE EAST WILL LIKELY  
DECELERATE/STALL OVER THE FLORIDA PENINSULA LEADING TO PERIODS OF  
RAINFALL IN ITS VICINITY. THE CLIPPER SYSTEM BRUSHING THE EXTREME  
NORTHERN TIER WILL BE ACCOMPANIED BY AN AREA OF MOSTLY LIGHT RAIN  
AND TRAILING RAIN/SNOW FROM SAT ONWARD.  
 
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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