794  
FXUS02 KWBC 081550  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1150 AM EDT SUN JUL 08 2018  
 
VALID 12Z WED JUL 11 2018 - 12Z SUN JUL 15 2018  
   
..PATTERN OVERVIEW/GUIDANCE EVALUATION/PREFERENCES
 
 
LATEST MODELS AND ENSEMBLES CONTINUE TO SHOW A BROAD AREA OF MEAN  
RIDGING ACROSS THE CENTRAL AND WESTERN U.S., WITH THE POSSIBILITY  
OF AN EMBEDDED WEAKNESS FOR A TIME IN THE VICINITY OF THE CENTRAL  
ROCKIES/HIGH PLAINS. TO THE EAST OF THE RIDGE EXPECT AN UPPER  
TROUGH TO SUPPORT A FAIRLY FAR SOUTHWARD EXTENT OF A COLD FRONT  
THAT SHOULD EVENTUALLY STALL AND DISSIPATE, WHILE OVER THE  
ATLANTIC THE UPPER TROUGH SHOULD ENCOURAGE NORTHEASTWARD  
PROGRESSION OF TROPICAL STORM CHRIS. THERE HAS BEEN A STRAY  
SOLUTION OR TWO (SUCH AS THE 00Z UKMET) THAT SHOW GREATER EFFECTS  
ON THE EAST COAST BUT THUS FAR SUCH A SCENARIO HAS VERY LOW  
PROBABILITY. CONSULT NHC PRODUCTS FOR LATEST INFORMATION ON T.S.  
CHRIS. AS THE EASTERN UPPER TROUGH LIFTS AWAY, GUIDANCE IS  
HINTING THAT SOME WEAK ENERGY COULD BE LEFT BEHIND NEAR THE EAST  
COAST ALONG WITH A MODEST LINGERING SURFACE REFLECTION CONSISTING  
OF A TROUGH WITH ONE OR MORE EMBEDDED WAVES. MEANWHILE THE  
CONSENSUS FORECAST LED BY THE ENSEMBLE MEANS HAS MAINTAINED GOOD  
CONTINUITY IN PRINCIPLE FOR TWO VIGOROUS CANADIAN SYSTEMS WHOSE  
FRONTS WILL EXTEND INTO THE NORTHERN THIRD TO HALF OF THE  
CONTIGUOUS U.S. COMPARED TO YESTERDAY GUIDANCE CLUSTERING HAS  
IMPROVED FOR NORTH PACIFIC/ALASKA FLOW COMPARED TO YESTERDAY SO  
LATEST OPERATIONAL RUNS ARE GENERALLY CLOSER TO THE MEANS FROM THE  
NORTHEASTERN PACIFIC INTO WESTERN NORTH AMERICA IN THE LATE  
WEEK/WEEKEND TIME FRAME. BY DAY 7 SUN THE ONLY ITEMS OF NOTE ARE  
THAT THE 00Z GFS LEANS TOWARD THE AMPLIFIED SIDE OF THE ENVELOPE  
FOR NORTHERN U.S. TROUGHING ALOFT WHILE THE 00Z ECMWF/CMC BRING  
MORE SHORTWAVE ENERGY INTO THE WEST THAN MOST OTHER SOLUTIONS.  
 
GIVEN THE BETTER THAN AVERAGE AGREEMENT IN TODAY'S GUIDANCE, THE  
LATEST FORECAST BLEND UTILIZED A MAJORITY WEIGHT OF OPERATIONAL  
MODELS (00Z-06Z GFS AND 00Z ECMWF/CMC) VERSUS 00Z GEFS/ECMWF MEANS  
THROUGH DAY 5 FRI AND THEN TRENDED TOWARD AN EVEN MODEL/ENSEMBLE  
BLEND AMONG GFS/ECMWF RUNS AND THEIR MEANS. THE 00Z GEFS WAS  
SELECTED OVER THE 06Z RUN DUE TO BETTER DEFINITION OF THE SECOND  
CANADIAN SYSTEM BY DAY 7 SUN BUT OTHERWISE THE 06Z RUN PROVIDED A  
COMPARABLE FORECAST.  
 
   
..WEATHER THREATS/HIGHLIGHTS
 
 
EXPECT THREE GENERAL AREAS OF FOCUS FOR SIGNIFICANT RAINFALL  
DURING THE PERIOD. OVER AND JUST WEST OF THE FOUR CORNERS STATES  
AN ACTIVE MONSOONAL FLOW (WITH PRECIPITABLE WATER VALUES WELL  
ABOVE CLIMATOLOGICAL AVERAGES) WILL PROMOTE PERIODS OF SHOWERS AND  
THUNDERSTORMS WITH LOCALLY HEAVY AMOUNTS POSSIBLE. THE AREA  
EXTENDING FROM THE NORTHERN PLAINS INTO THE MIDWEST/AND UPPER  
GREAT LAKES WILL FIRST SEE EPISODES OF CONVECTION ALONG A LEADING  
COLD FRONT CROSSING THE NORTHERN TIER. THIS FRONT MAY CONTINUE TO  
SERVE AS A FOCUS FOR RAINFALL AS IT STALLS OVER THE NORTH-CENTRAL  
PLAINS/MS VALLEY, WITH MORE ACTIVITY TO FOLLOW AS THE FRONT LIFTS  
BACK TO THE NORTH AND A SECOND WAVE/COLD FRONT APPROACH BY NEXT  
WEEKEND. MEANWHILE LOCATIONS OVER THE SOUTH WILL SEE DIURNALLY  
ENHANCED CONVECTION WITH SOME ENHANCEMENT PROVIDED BY LOCALIZED  
BOUNDARIES AND THE EASTERN U.S. FRONT THAT SHOULD DISSIPATE BY THE  
LATTER HALF OF THE PERIOD.  
 
CLOUDS AND RAINFALL SHOULD KEEP HIGH TEMPERATURES BELOW NORMAL  
OVER THE SOUTHWEST/FOUR CORNERS REGION THROUGH THE PERIOD WHILE  
THE SECOND NORTHERN U.S. FRONT WILL BRING A PUSH OF COOL AIR INTO  
THE NORTHERN PLAINS BY SAT-SUN. OTHERWISE THE RIDGE ALOFT OVER  
THE CENTRAL/WESTERN U.S. WILL TEND TO KEEP READINGS ABOVE TO WELL  
ABOVE AVERAGE. THE INTERIOR PACIFIC NORTHWEST AND PARTS OF  
CALIFORNIA/NEVADA ARE LIKELY TO SEE HIGHEST ANOMALIES EXCEEDING  
PLUS 10F FOR MIN AND/OR MAX READINGS ON MULTIPLE DAYS. SURFACE  
HIGH PRESSURE BEHIND THE EASTERN U.S. FRONT WILL BRING A COUPLE  
DAYS OR SO OF NEAR OR SLIGHTLY BELOW NORMAL TEMPERATURES. EXPECT  
EASTERN U.S. TEMPERATURES TO TREND SOMEWHAT ABOVE NORMAL BY NEXT  
WEEKEND.  
 
RAUSCH  
 
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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