473  
FXUS02 KWBC 271552  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1151 AM EDT THU JUL 27 2017  
 
VALID 12Z SUN JUL 30 2017 - 12Z THU AUG 03 2017  
   
..PATTERN OVERVIEW
 
 
FROM THE MULTI-DAY MEAN PERSPECTIVE GUIDANCE HAS BEEN CONSISTENT  
IN SHOWING A BUILDING WRN U.S. RIDGE LATE WEEK INTO THE WEEKEND  
WITH THIS RIDGE THEN PERSISTING THROUGH AT LEAST NEXT THU, PERHAPS  
EVEN BECOMING A BIT STRONGER BY THAT TIME. DOWNSTREAM TROUGHING  
HAS ALSO BEEN A CONSISTENT FEATURE BUT THE CHARACTER OF THIS  
TROUGH ON ANY PARTICULAR DAY HAS VARIED DEPENDING ON INDIVIDUAL  
FEATURES THAT HAVE TENDED TO DISPLAY RELATIVELY LOW  
PREDICTABILITY. THESE FEATURES INCLUDE AN INITIAL SMALL SCALE  
SHRTWV/UPR LOW SETTLING TOWARD THE EAST COAST DURING THE SHORT  
RANGE PERIOD AND THEN VARIOUS PIECES OF NERN PAC/GULF OF ALASKA  
ENERGY PROGRESSING ACROSS SRN CANADA.  
 
   
..GUIDANCE EVALUATION AND PREFERENCES
 
 
00Z/06Z GUIDANCE HAS MADE A PRONOUNCED ADJUSTMENT TOWARD A SLOWER  
TROUGH/UPR LOW REACHING THE MID ATLC BY THE START OF THE PERIOD  
SUN, ALONG WITH MUCH GREATER SEPARATION FROM A CLOSED LOW/TROUGH  
OVER ERN CANADA. AS A RESULT THE LATEST MAJORITY CLUSTER HOLDS  
ONTO SFC LOW PRESSURE OFF THE MID ATLC COAST FOR A CONSIDERABLY  
LONGER TIME THAN IN PRIOR RUNS. THE ORIGINATING FEATURE NOW NEAR  
THE U.S.-CANADIAN BORDER IS QUITE SMALL, WHICH MAKES IT DIFFICULT  
FOR GUIDANCE TO RESOLVE ITS EVOLUTION PROPERLY VERY FAR IN  
ADVANCE. ONCE THIS TROUGH LIFTS AWAY THERE IS RELATIVE AGREEMENT  
THAT TROUGHING SHOULD SETTLE INTO THE GREAT LAKES REGION BY NEXT  
WED-THU. DUE TO GUIDANCE CHANGING FOCUS ON WHICH BUNDLE OF SHRTWV  
ENERGY WILL LEAD TO THIS TROUGHING, THE LATE PERIOD NRN STREAM  
AMPLIFICATION IS ESSENTIALLY OCCURRING ABOUT TWO DAYS LATER THAN  
WAS FCST BY CONSENSUS TWO DAYS AGO. SEPARATE ENERGY ROUNDING THE  
WRN RIDGE AND REACHING THE PLAINS/MS VALLEY IN THE LATTER HALF OF  
THE PERIOD WILL RELOAD THE MORE DIFFUSE SRN PART OF THE OVERALL  
ERN TROUGH. HGTS OVER THE SERN U.S. SHOULD RISE WITH TIME AS A  
STRONG RIDGE OVER THE ATLC GRADUALLY BUILDS WWD.  
 
IN ORDER TO DEPICT THE LATEST CONSENSUS EVOLUTION TO A MORE  
REFINED EXTENT THAN THE MEANS WHILE DOWNPLAYING SPECIFICS OF ANY  
INDIVIDUAL MODEL RUN, THE SUN TO EARLY TUE PERIOD STARTED WITH AN  
OPERATIONAL MODEL BLEND CONSISTING OF THE 06Z GFS/00Z ECMWF AND TO  
A SLIGHTLY LESSER EXTENT 00Z UKMET/CMC. AFTER EARLY SUN MODEL  
DETAILS DIVERGED ENOUGH TO REQUIRE A FAIRLY RAPID TRANSITION  
TOWARD MOSTLY THE 06Z GEFS/00Z ECMWF MEANS AND CONTINUITY.  
 
   
..WEATHER HIGHLIGHTS
 
 
ABUNDANT MONSOONAL MOISTURE ALONG WITH MULTIPLE IMPULSES ALOFT  
TRACKING AROUND THE CORE OF THE STRONG WRN U.S. RIDGE WILL  
MAINTAIN THE POTENTIAL FOR AREAS OF HEAVY CONVECTION THAT SHOULD  
BE MOST LIKELY FROM THE SRN HALF OF THE ROCKIES EWD INTO THE  
PLAINS. ALBEIT WITH SOMEWHAT LOWER 5-DAY RAINFALL TOTALS EXPECT  
SOME OF THIS ACTIVITY TO EXTEND INTO THE SOUTHWEST AS WELL.  
CONFIDENCE IN SPECIFICS FOR TIMING/LOCATION OF HEAVIEST CONVECTION  
WITHIN THE FAVORED AREA WILL LIKELY BE LOW UNTIL WELL INTO THE  
SHORT RANGE TIME FRAME. WAVY FRONT EXTENDING OFF THE SERN/GULF  
COASTS SHOULD PROVIDE A FOCUS FOR PERIODS OF HEAVY RAIN ESPECIALLY  
OVER NRN-CNTRL FLORIDA WITH SOME CONVECTION ALSO POSSIBLE AT TIMES  
ALONG THE GULF/SERN COASTS AND SRN FL. ONE OR MORE FRONTAL  
BOUNDARIES AFFECTING THE NRN TIER MAY BRING SOME EPISODES OF  
CONVECTION OF VARYING INTENSITY BUT SO FAR WITH LESS OF A SIGNAL  
FOR HEAVY AMOUNTS COMPARED TO AREAS HIGHLIGHTED ABOVE.  
 
THE WRN RIDGE ALOFT WILL SUPPORT WELL ABOVE NORMAL TEMPS FROM  
INLAND PARTS OF NRN-CNTRL CA AND PAC NW INTO THE NRN ROCKIES, WITH  
MULTIPLE DAYS OF PLUS 5-15F ANOMALIES. ON THE OTHER HAND HIGHS  
WILL BE BELOW NORMAL, LOCALLY BY AT LEAST 10F ON ONE OR MORE DAYS,  
WHERE THERE IS SHWR/TSTM ACTIVITY OVER THE FOUR CORNERS STATES  
INTO THE CNTRL-SRN PLAINS. OVER THE EAST EXPECT MEAN TROUGHING  
ALOFT TO MAINTAIN NEAR TO BELOW NORMAL TEMPS FOR A MAJORITY OF THE  
PERIOD.  
 
RAUSCH  
 

 
 
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