648  
FXUS02 KWBC 091457  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1057 AM EDT TUE OCT 09 2018  
 
VALID 12Z FRI OCT 12 2018 - 12Z TUE OCT 16 2018  
 
...MICHAEL AND ASSOCIATED HEAVY RAINFALL MOVE AWAY FROM THE EAST  
COAST FRI...  
...SERGIO MOISTURE/RAINS TO REACH ARIZONA-SOUTHERN ROCKIES AND  
EXTEND NORTHEASTWARD TO THE SOUTHERN PLAINS...  
 
   
..15 UTC UPDATE
 
 
NO MAJOR CHANGES WERE MADE TO THE INHERITED FORECAST FROM  
OVERNIGHT. A BLEND OF THE GFS AND UKMET WAS CLOSEST TO THE  
OFFICIAL NHC FORECAST TRACKS FOR BOTH HURRICANE MICHAEL AND  
HURRICANE SERGIO. PLEASE REFER TO PRODUCTS ISSUED BY THE NHC FOR  
THE LATEST INFORMATION ON THESE TROPICAL SYSTEMS. ELSEWHERE, A  
MULTI-MODEL BLEND SERVED A GOOD STARTING POINT DURING DAYS 3-5  
(FRI-SUN) FOR THIS FORECAST UPDATE (INCLUDING THE  
GFS/UKMET/ECMWF), WITH A TREND TOWARD HEAVIER WEIGHTING OF  
ENSEMBLE MEANS (ECENS/GEFS) DURING DAYS 6-7 (MON-TUE). THE  
FORECAST CONTINUES TO SHOW A FRONTAL WAVE CROSSING THE  
MID/UPPER-MISSISSIPPI VALLEY AND GREAT LAKES SUN-MON. THE LATEST  
MODEL GUIDANCE SHOWED A SLIGHTLY SLOWER TREND WITH RESPECT TO THIS  
FEATURE, AND THIS IS REFLECTED IN THE UPDATED WPC FORECAST. AS  
UPPER TROUGH AMPLIFICATION OCCURS ACROSS THE CENTRAL U.S. EARLY  
NEXT WEEK, A FAST-MOVING CLIPPER-LIKE SYSTEM SHOULD CROSS THE  
NORTHERN PLAINS AND MIDWEST. FORECAST CONFIDENCE IS ACTUALLY  
SLIGHTLY LOWER WITH RESPECT TO THE SUN-MON LOW PRESSURE WAVE  
(COMPARED TO THE CLIPPER) DUE TO THE POTENTIAL INCORPORATION OF  
MID/UPPER-LEVEL ENERGY FROM SERGIO, INTRODUCING A BIT OF INCREASED  
SPREAD WITH RESPECT TO BOTH THE LOCATION AND INTENSITY OF THIS  
FEATURE.  
 
RYAN  
 
PREVIOUS DISCUSSION (ISSUED AT 0647 UTC)  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
TODAY'S GUIDANCE CONTINUES TO SHOW A LARGE SCALE EVOLUTION TOWARD  
A SLOW/AMPLIFIED EASTERN PACIFIC TO WEST COAST RIDGE AND  
CORRESPONDING DOWNSTREAM TROUGH, BUT WITH SOME IMPORTANT TRENDS.  
AT THE VERY START OF THE FORECAST EARLY DAY 3 FRI CONSENSUS IS  
STRONGER WITH SHORTWAVE ENERGY REACHING WESTERN CANADA AND  
THEREAFTER THE UPSTREAM AMPLIFYING RIDGE IS SOMEWHAT  
STRONGER/SLOWER THAN CONTINUITY FROM 24 HOURS AGO. AS A RESULT BY  
THE WEEKEND THE CENTRAL/WESTERN U.S. TROUGH ALOFT SHOWS  
CONSIDERABLY MORE SOUTHWESTWARD ELONGATION. TELECONNECTIONS  
RELATIVE TO THE CORE OF POSITIVE HEIGHT ANOMALIES OFF THE ALASKA  
PANHANDLE IN D+5 MULTI-DAY MEAN CHARTS SUPPORT THE IDEA OF SOME  
TROUGH ELONGATION OVER THE WEST. THE CHANGES FOR HANDLING OF THE  
UPPER TROUGHING LEAD TO A MORE DIFFUSE APPEARANCE OF THE CLIPPER  
SYSTEM BY THE TIME IT REACHES NEAR THE UPPER GREAT LAKES DURING  
THE WEEKEND. MEANWHILE THERE IS STILL THE TENDENCY FOR ENERGY TO  
COLLECT/PERSIST OVER OR NEAR THE SOUTHWEST DURING THE  
PERIOD--CONSISTING OF ENERGY OVER OR OFFSHORE SOUTHERN CALIFORNIA  
AND THEN POSSIBLY ADDITIONAL ENERGY FROM AMPLIFYING NORTHERN  
STREAM ENERGY OVER THE WEST.  
 
CONSULT LATEST NATIONAL HURRICANE CENTER PRODUCTS FOR THE LATEST  
INFORMATION REGARDING MICHAEL AND SERGIO. CURRENTLY EXPECT  
MICHAEL TO REACH A POSITION JUST OFF THE EAST COAST BY EARLY FRI  
AND THEN CONTINUE TRACKING NORTHEASTWARD. TIMING DIFFERENCES ARE  
STILL SIGNIFICANT BUT LESS EXTREME THAN IN PREVIOUS DAYS. SERGIO  
HAS GENERALLY BEEN BETTER BEHAVED IN TERMS OF GUIDANCE CONSENSUS  
FOR THE SURFACE REFLECTION, LIKELY TRACKING FROM BAJA CALIFORNIA  
INTO THE EXTREME SOUTHERN ROCKIES/HIGH PLAINS FROM EARLY FRI INTO  
EARLY SAT. HOWEVER THERE HAD BEEN CONSIDERABLE UNCERTAINTY OVER  
HOW SERGIO'S ENERGY ALOFT WOULD INTERACT WITH ENERGY TO THE WEST  
AS WELL AS NORTHERN STREAM FLOW. THIS ASPECT OF THE FORECAST HAS  
COME INTO MUCH BETTER AGREEMENT. MAJORITY CLUSTERING NOW SHOWS  
SERGIO'S ENERGY/MOISTURE PROGRESSING STEADILY NORTHEASTWARD ACROSS  
SOUTHEAST AZ, NM, AND CENTRAL PLAINS/MID MS VALLEY.  
 
EARLY IN THE PERIOD A BLEND OF PRIMARILY OPERATIONAL MODELS  
PROVIDED A GOOD REPRESENTATION OF CONSENSUS TRENDS WHILE RESOLVING  
DIFFERENCES OVER SOME AREAS. THE 12Z RUN WAS PREFERRED FOR THE  
GFS COMPONENT AS THE 18Z VERSION PULLED THE INITIAL CA UPPER LOW  
FARTHER WEST THAN MOST SOLUTIONS. HOWEVER NOTE THAT NEW 00Z MODEL  
RUNS SEEM TO BE FOLLOWING THE LEAD OF THE 18Z GFS. SOME 12Z  
ECMWF/CMC INPUT WAS REASONABLE SINCE THEIR MORE AMPLIFIED WESTERN  
TROUGH REFLECTS RECENT TRENDS. THE 18Z GEFS/12Z ECMWF MEANS HAD  
GREATER WEIGHT IN THE FORECAST LATER IN THE PERIOD GIVEN LOWER  
PREDICTABILITY DIFFERENCES AMONG OPERATIONAL SOLUTIONS AT THAT  
TIME.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
EAST COAST RAINFALL ASSOCIATED WITH MICHAEL SHOULD BE TAPERING OFF  
ON FRI. MEANWHILE SERGIO'S MOISTURE IS MOST LIKELY TO STREAM  
ACROSS SOUTHEAST AZ AND THEN CONTINUE NORTHEASTWARD ACROSS THE  
EXTREME SOUTHERN ROCKIES, CENTRAL/SOUTH-CENTRAL PLAINS, MIDDLE MS  
VALLEY AND TO A LESSER EXTENT (AND WITH GREATER UNCERTAINTY OF  
SPECIFICS) OHIO VALLEY/GREAT LAKES. BEST POTENTIAL FOR LOCALLY  
MODERATE-HEAVY RAINFALL SHOULD BE OVER THE PLAINS PORTION OF THE  
PRECIP SHIELD GIVEN POTENTIAL INTERACTION WITH A SURFACE TROUGH  
AND AN APPROACHING FRONT. SOME ASPECTS OF THE PATTERN ARE STILL  
TRENDING IN THE GUIDANCE BUT GENERAL FORECAST CONFIDENCE IS  
DEFINITELY HIGHER THAN IT WAS YESTERDAY. THE UPPER TROUGH  
DROPPING INTO THE WEST WILL SPREAD AN AREA OF PRECIPITATION--A  
DECENT PERCENTAGE IN THE FORM OF SNOW--SOUTHEASTWARD ALONG THE  
ROCKIES FROM ABOUT FRI NIGHT ONWARD. BY THE LATTER HALF OF THE  
PERIOD LOW LEVEL UPSLOPE FLOW SOUTH OF STRONG HIGH PRESSURE  
BUILDING SOUTHWARD OVER THE ROCKIES MAY SERVE TO ENHANCE RAINFALL  
OF VARYING INTENSITY OVER PARTS OF THE SOUTHERN PLAINS. NORTHERN  
TIER/GREAT LAKES LOCATIONS WILL SEE SOME PRECIPITATION WITH THE  
LOW PRESSURE/FRONTAL SYSTEM AFFECTION THE REGION EARLY-MID PERIOD.  
LIGHT PRECIPITATION MAY ACCOMPANY ANOTHER CLIPPER SYSTEM AROUND  
NEXT TUE. THE FLORIDA PENINSULA SHOULD SEE PERIODS OF RAIN AS A  
FRONT STALLS OVER THE AREA.  
 
RECENT TRENDS ALOFT HAVE LED TO A COLDER FORECAST TEMPERATURES  
OVER THE WEST-CENTRAL U.S./PLAINS, WITH STRONG HIGH PRESSURE  
BUILDING DOWN FROM WESTERN CANADA SUPPORTING ONE OR MORE DAYS WITH  
HIGHS AT LEAST 20F BELOW NORMAL FROM THE WEEKEND INTO EARLY NEXT  
WEEK. THE NORTHERN HALF OF THE EAST WILL TEND TO SEE BELOW NORMAL  
HIGH TEMPERATURES WITH MON LIKELY BEING CLOSEST TO NORMAL, WHILE A  
MAJORITY OF THE EASTERN STATES WILL SEE NEAR TO ABOVE NORMAL MINS.  
LOCATIONS NEAR THE WEST COAST SHOULD SEE MODESTLY ABOVE NORMAL  
READINGS.  
 
RAUSCH  
 
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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