151  
FXUS02 KWBC 161559  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1159 AM EDT MON JUL 16 2018  
 
VALID 12Z THU JUL 19 2018 - 12Z MON JUL 23 2018  
   
..OVERVIEW
 
 
LATEST GUIDANCE CONTINUES TO PROVIDE ABOVE AVERAGE CONFIDENCE THAT  
THE LARGE SCALE FLOW PATTERN ALOFT WILL BECOME MORE AMPLIFIED  
DURING THE PERIOD. A RIDGE POSITIONED OVER THE GREAT BASIN/FOUR  
CORNERS AS OF EARLY THU WILL EXPAND AND SETTLE OVER THE SOUTHERN  
ROCKIES/PLAINS BY SAT-MON. MEANWHILE MULTIPLE PIECES OF ENERGY  
WILL CARVE OUT A TROUGH OVER THE EASTERN HALF OF THE COUNTRY WITH  
A POSSIBLE EMBEDDED LOW CENTER MOST LIKELY TO TRACK INTO THE GREAT  
LAKES. FARTHER UPSTREAM A SHORTWAVE ORIGINATING FROM THE GULF OF  
ALASKA WILL SKIRT THE PACIFIC NORTHWEST BY LATE IN THE WEEK,  
BRIEFLY LOWERING HEIGHTS ACROSS THAT REGION BEFORE CONTINUING  
EASTWARD ACROSS THE NORTHERN TIER SUN ONWARD.  
 
A LOOK AT HEMISPHERIC TELECONNECTIONS SHOWS SUPPORT FOR THIS  
PATTERN EVOLUTION ACROSS NORTH AMERICA, FURTHER INCREASING  
CONFIDENCE IN THE IMPENDING PATTERN CHANGE. AN ANOMALOUS AND  
PERSISTENT REX BLOCK ACROSS EASTERN ASIA FAVORS UPPER RIDGING  
ACROSS THE SOUTHWESTERN AND SOUTH CENTRAL U.S., WITH A RELATIVELY  
STRONG VORTEX ACROSS THE ARCTIC, AND AN EQUATORWARD EXTENSION IN  
THE FORM OF FAVORED TROUGHING ACROSS HUDSON BAY AND THE GREAT  
LAKES. GIVEN THE PERSISTENT NATURE OF THE AFOREMENTIONED REX  
BLOCK, WOULD EXPECT THAT THE UPCOMING PATTERN SHIFT ACROSS NORTH  
AMERICA WILL NOT BE A TRANSIENT ONE.  
 
   
..GUIDANCE EVALUATION AND PREFERENCES
 
 
DURING THE EARLY/MIDDLE PART OF THE FORECAST PERIOD A BLEND OF  
MOSTLY OPERATIONAL GUIDANCE REPRESENTED CONSENSUS WELL AND IN MOST  
CASES PROVIDED GOOD CONTINUITY. THE ONE NOTABLE CHANGE IS THAT  
THE MAJORITY OF GUIDANCE IS SHOWING SOMEWHAT MORE OF A SIGNAL FOR  
A DEFINED WAVE ALONG THE EAST COAST BOUNDARY THAT STARTS LIFTING  
UP AS A WARM FRONT BY LATE FRI-SAT--AND WITH A SLOWER NORTHWARD  
PROGRESSION. ALSO OF NOTE, OPERATIONAL 00Z-06Z GFS RUNS WERE  
WEIGHTED LESS FROM THE START OF THE PERIOD THAN WOULD TYPICALLY BE  
THE CASE WITH SOME INCLUSION OF THE 06Z GEFS PREFERRED AS A  
SUBSTITUTE. GFS RUNS WERE FASTER THAN CONSENSUS (INCLUDING THE  
GEFS MEAN) WITH TIMING OF THE WAVY EASTERN FRONT AND ALSO DIFFERED  
FROM OTHER SOLUTIONS FOR SOME FLOW DETAILS ALOFT BETWEEN HUDSON  
BAY AND THE UPPER GREAT LAKES. IN ADDITION GUIDANCE TRENDS HAVE  
BEEN GRAVITATING MUCH CLOSER TO WHAT ECMWF/CMC-BASED GUIDANCE HAD  
ADVERTISED A COUPLE DAYS AGO. IT REMAINS TO BE SEEN WHETHER THE  
UPPER LOW WITHIN THE TROUGH WILL TRACK AS FAR SOUTH AS DEPICTED IN  
RECENT PARALLEL FV3 GFS RUNS THOUGH. ELSEWHERE, THE 00Z ECMWF  
LEANED TOWARD THE EXTREME SIDE OF THE SOLUTION ENVELOPE FOR  
TROUGHING OVER THE NORTHWEST BY FRI-SAT BUT WAS STILL WITHIN THE  
TYPICAL RANGE OF ERROR AT THAT TIME FRAME.  
 
INCREASING DETAIL SPREAD/VARIABILITY AMONG OPERATIONAL RUNS AND  
AGREEABLE SOLUTIONS AMONG THE GEFS/ECMWF ENSEMBLE MEANS  
RECOMMENDED TRENDING TOWARD A FAIRLY EVEN MODEL/ENSEMBLE MEAN  
BLEND BY LATE IN THE FORECAST. TIMING/DETAILS OF ENERGY CROSSING  
SOUTHERN CANADA AND THE NORTHERN U.S. WILL LIKELY PROVIDE ONGOING  
UNCERTAINTY--WITH SOME SLOWER TRENDS EVIDENT OVER THE PAST COUPLE  
DAYS. THE SAME WILL BE CASE FOR SPECIFICS OF THE EASTERN U.S.  
TROUGH INCLUDING THE DEGREE OF INFLUENCE FROM UPSTREAM FLOW.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE EVOLVING PATTERN WILL BRING THE POTENTIAL FOR ONE OR MORE  
PERIODS OF SIGNIFICANT RAINFALL TO LOCATIONS FROM THE NORTHERN  
PLAINS/MS VALLEY THROUGH MUCH OF THE EAST. THIS ACTIVITY WILL BE  
BENEFICIAL FOR SOME AREAS THAT HAVE RECEIVED VERY LITTLE RAIN OVER  
RECENT WEEKS (PENDING ACTIVITY THAT IS POSSIBLE IN THE SHORT RANGE  
TIME FRAME) WHILE IT MAY BE MORE PROBLEMATIC OVER OTHER AREAS. A  
COLD FRONT LIKELY BECOMING STATIONARY FROM THE SOUTHEAST TO THE  
SOUTHERN/CENTRAL PLAINS AS OF THE START OF THE PERIOD WILL PROVIDE  
ONE FOCUS FOR SCATTERED TO NUMEROUS SHOWERS AND  
THUNDERSTORMS--SOME WITH HEAVY RAINFALL--FROM LATE IN THE WEEK  
ONWARD. THIS BOUNDARY WILL EVENTUALLY LIFT NORTHWARD AS A WARM  
FRONT. FARTHER NORTH EVOLVING TROUGH ENERGY ALOFT AND THE  
ASSOCIATED SURFACE LOW PRESSURE SYSTEM DRIFTING FROM THE NORTHERN  
PLAINS INTO THE GREAT LAKES WILL GENERATE CONVECTION WITH LOCALLY  
HEAVY RAIN. THE AMPLIFYING UPPER TROUGH OVER THE EAST MAY ALSO  
PROMOTE TRANSPORT OF DEEPER MOISTURE NORTHWARD ACROSS THE EASTERN  
U.S., WITH WIDESPREAD CONVECTION/AREAS OF HEAVY RAIN POSSIBLY  
REACHING PORTIONS OF THE MID-ATLANTIC AND NORTHEAST BY THE  
WEEKEND. FINALLY, EXPECT MONSOONAL MOISTURE TO RESULT IN  
SCATTERED AFTERNOON/EVENING CONVECTION FROM THE SOUTHERN GREAT  
BASIN TO THE SOUTHERN/CENTRAL ROCKIES THROUGH MUCH OF THE WEEK AND  
INTO THE WEEKEND. SOME LOCALLY ENHANCED AMOUNTS ARE POSSIBLE BUT  
ACTIVITY SHOULD GENERALLY BE LIGHTER AND/OR LESS ORGANIZED THAN IN  
SOME RECENT EPISODES.  
 
THE EXPANDING RIDGE ALOFT FROM THE SOUTHWEST INTO SOUTHERN PLAINS  
WILL BE ACCOMPANIED BY MULTIPLE DAYS OF HOT CONDITIONS FROM LATE  
WEEK ONWARD. THE FOCUS FOR HIGHEST MAX TEMPERATURE ANOMALIES WILL  
LIKELY BE OVER TEXAS AND VICINITY WITH MANY 100+F HIGHS AND SOME  
LOCATIONS REACHING 10-15F ABOVE NORMAL. READINGS MAY REACH OR  
EXCEED RECORD HIGH/WARM LOW VALUES AT A NUMBER OF LOCATIONS. THE  
SOUTHERN 2/3 OF THE WEST SHOULD SEE RATHER WARM MIN TEMPERATURES  
MOST DAYS BUT HIGHS SHOULD BE LESS EXTREME RELATIVE TO NORMAL.  
EXPECT SOME BELOW NORMAL READINGS OVER THE EAST AT THE START OF  
THE PERIOD (ESPECIALLY MORNING LOWS THU), AND BELOW NORMAL HIGHS  
OVER AREAS THAT SEE CLOUDS/RAINFALL FROM THE MIDWEST INTO THE EAST  
DURING THE PERIOD AS WELL AS THE NORTHERN ROCKIES/PLAINS BY EARLY  
NEXT WEEK.  
 
RAUSCH/RYAN  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND AT:  
 
HTTP://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTP://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTP://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTP://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTP://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTP://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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