166  
FXUS02 KWBC 160506  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
105 AM EDT MON JUL 16 2018  
 
VALID 12Z THU JUL 19 2018 - 12Z MON JUL 23 2018  
   
..OVERVIEW
 
 
CONFIDENCE IS NOW FAIRLY HIGH THAT THE FLOW PATTERN ACROSS THE  
CONTIGUOUS U.S. WILL BECOME MORE AMPLIFIED DURING THE MEDIUM  
RANGE, WITH AN UPPER-LEVEL RIDGE EXPANDING FROM THE GREAT BASIN TO  
THE SOUTHERN PLAINS, AND A SERIES OF UPPER WAVES GRADUALLY CARVING  
OUT A TROUGH ACROSS THE GREAT LAKES/OHIO VALLEY. A SHORTWAVE  
ORIGINATING IN THE GULF OF ALASKA WILL SKIRT THE PACIFIC NORTHWEST  
BY LATE IN THE WEEK, BRIEFLY LOWERING HEIGHTS ACROSS THAT REGION,  
BEFORE MOVING EAST TOWARD THE NORTHERN PLAINS/UPPER MIDWEST BY  
SUN-MON.  
 
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
 
 
MODEL SPREAD WAS SUFFICIENTLY LOW TO JUSTIFY USE OF A MAJORITY  
DETERMINISTIC MULTI-MODEL BLEND (INCLUDING THE  
ECMWF/GFS/CMC/UKMET) AS A BASIS FOR THE FORECAST STARTING ON DAY 3  
(THU) AND CONTINUING THROUGH DAY 5 (SAT). DURING DAYS 6-7  
(SUN-MON) WEIGHTING OF ENSEMBLE MEANS (ECENS/NAEFS) WAS GRADUALLY  
INCREASED TO ACCOUNT FOR AN INCREASE IN SPREAD DURING THAT TIME  
FRAME.  
 
MODELS CONTINUE TO SHOW SOME VARIABILITY WITH THE AMPLITUDE OF  
SHORTWAVE ENERGY CROSSING THE MIDWEST THU-SAT, ALTHOUGH THE TREND  
SEEN IN RECENT DAYS TOWARD MORE AMPLIFICATION OF THE FEATURE SEEMS  
TO HAVE SLOWED. IN GENERAL, CONTINUE TO FAVOR THE SOMEWHAT DEEPER  
ECMWF/CMC AS A CLOSED UPPER LOW DEVELOPS BY FRI-SAT, AND THIS IS  
REFLECTED IN THE FORECAST BLEND. AS THE FEATURE AMPLIFIES FURTHER  
ACROSS THE GREAT LAKES/OHIO VALLEY SUN-MON, THE ECMWF/CMC CONTINUE  
TO BE THE PREFERRED SOLUTIONS OVER THE LESS AMPLIFIED GFS. THE  
PAST COUPLE RUNS OF THE FV3 ALSO SHOWED A MORE AMPLIFIED LOW OVER  
THE OHIO VALLEY SIMILAR TO THE ECMWF/CMC, LENDING FURTHER CREDENCE  
TO THAT SCENARIO. FARTHER WEST, TIMING AND AMPLITUDE DIFFERENCES  
REMAIN WITH RESPECT TO SHORTWAVE ENERGY CROSSING BRITISH COLUMBIA  
AND SKIRTING THE U.S. NORTHWEST FRI-SAT. NO CLEAR OUTLIERS WERE  
EVIDENT, BUT IN GENERAL A SOLUTION WITH TIMING RESEMBLING THE  
ECENS MEAN WAS FAVORED, AND THE DESCRIBED MULTI-MODEL BLEND  
YIELDED SUCH A FORECAST. BY DAYS 6-7 AS THE SYSTEM CROSSES THE  
NORTHERN PLAINS, THE ECMWF WAS PERHAPS A BIT FAST WITH THE  
EASTWARD PROGRESSION OF THE SYSTEM (THE 12Z CMC MAY ACTUALLY BE  
THE CLOSEST SOLUTION TO CONSENSUS THROUGHOUT THE PROGRESSION OF  
THIS SYSTEM ACROSS THE NORTHERN TIER). THE HEAVIER ENSEMBLE MEAN  
WEIGHTING BY THAT TIME FRAME KEPT A FORECAST THAT IS IN LINE WITH  
THE CONSENSUS FOR THIS SYSTEM.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
A COLD FRONT EXPECTED TO BECOME STATIONARY FROM THE SOUTHEAST TO  
THE SOUTHERN/CENTRAL PLAINS WILL FOCUS SCATTERED TO NUMEROUS  
SHOWERS AND THUNDERSTORMS FROM LATE IN THE WEEK INTO NEXT WEEKEND,  
WITH AREAS OF HEAVY RAIN POSSIBLE. FARTHER NORTH, THE SHORTWAVE,  
AND A DEVELOPING ASSOCIATED SURFACE LOW PRESSURE SYSTEM CROSSING  
FROM THE NORTHERN PLAINS/MIDWEST TO THE OHIO VALLEY WILL GENERATE  
CONVECTION WITH LOCALLY HEAVY RAIN. THE AMPLIFYING UPPER TROUGH  
ACROSS THE GREAT LAKES/OHIO VALLEY BY NEXT WEEKEND COULD ALSO  
RESULT IN THE POTENTIAL FOR TRANSPORT OF DEEPER MOISTURE NORTHWARD  
ACROSS THE EASTERN U.S., WITH WIDESPREAD CONVECTION AND AREAS OF  
HEAVY RAIN POSSIBLE ACROSS PORTIONS OF THE MID-ATLANTIC AND  
NORTHEAST BY THE WEEKEND. FINALLY, MONSOONAL MOISTURE WILL 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.  
 
THE EXPANDING RIDGE FROM THE SOUTHWEST TO THE SOUTHERN PLAINS WILL  
RESULT IN RISING TEMPERATURES BY LATER IN THE WEEK. HIGH  
TEMPERATURES ACROSS THE SOUTHERN PLAINS ARE FORECAST TO BE 5 TO 15  
DEG F ABOVE AVERAGE FROM THU ONWARD, WITH TEMPERATURES EXPECTED TO  
SOAR PAST THE 100 DEGREE MARK FOR MANY AREAS. A NUMBER OF RECORD  
HIGH TEMPERATURES ACROSS THE SOUTHERN PLAINS COULD BE IN JEOPARDY.  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page