771  
FXUS02 KWBC 021536  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1135 AM EDT MON JUL 02 2018  
 
VALID 12Z THU JUL 05 2018 - 12Z MON JUL 09 2018  
   
..OVERVIEW AND WEATHER THREATS/HIGHLIGHTS
 
 
A CLOSED UPPER HIGH WILL SETTLE INTO THE ROCKIES/FOUR CORNERS  
REGION BY LATE THIS WEEK AND WEEKEND AS UPPER TROUGHING OVER  
CANADA DIPS INTO NEW ENGLAND. THIS EVOLUTION WILL BRING A WARMING  
TREND TO A MAJORITY OF THE WEST INTO NORTHERN PLAINS (SOME  
READINGS 10F OR MORE ABOVE NORMAL) AND COOLER TEMPERATURES (BACK  
NEAR AVERAGE) TO THE EAST. EVEN WITH THE EPISODE OF UPPER  
TROUGHING OVER THE EASTERN U.S., EXPECT ABOVE AVERAGE HEIGHTS  
ALOFT OVER NEARLY THE ENTIRE LOWER 48. PRECIPITATION WILL  
GENERALLY FOCUS AROUND THE PERIPHERY OF THE UPPER HIGH. THE MOST  
AGREEABLE SIGNAL FOR HIGHEST 5-DAY RAINFALL TOTALS EXISTS NEAR THE  
CENTRAL GULF COAST WHERE A RETROGRADING UPPER LEVEL INVERTED  
TROUGH/LOW AND POSSIBLE WEAK SURFACE REFLECTION MAY ENHANCE  
ACTIVITY. CLOUDS/RAINFALL WILL TEND TO KEEP TEMPERATURES NEAR TO  
JUST BELOW AVERAGE OVER THE GULF COAST REGION. A FRONT  
PROGRESSING FROM THE GREAT LAKES-CENTRAL PLAINS INTO THE  
EAST/SOUTH WILL BRING A PERIOD OF SHOWERS/THUNDERSTORMS WITH SOME  
LOCALLY HEAVY RAINFALL. ANOTHER FRONTAL SYSTEM/UPPER SHORTWAVE  
PROGRESSING THROUGH THE NORTHWEST INTO THE NORTHERN PLAINS SHOULD  
BRING MOSTLY LIGHT/SCATTERED PRECIPITATION TO THE  
NORTHWEST/NORTHERN ROCKIES AND THEN SHOWERS/STORMS TO THE NORTHERN  
PLAINS-UPPER MS VALLEY.  
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
THE UPDATED FORECAST REFLECTED LITTLE MEANINGFUL CHANGE FROM  
PREVIOUS ISSUANCE. THERE IS STILL SUFFICIENT AGREEMENT FOR  
SIGNIFICANT FEATURES IN PRINCIPLE TO FAVOR AN OPERATIONAL MODEL  
BLEND DAYS 3-5 THU-SAT FOLLOWED BY A MODEL/ENSEMBLE MEAN BLEND TO  
ACCOUNT FOR TYPICAL INCREASE IN FORECAST UNCERTAINTY AT EXTENDED  
TIME FRAMES. DETAIL ISSUES OF NOTE: 00Z/06Z GFS RUNS BECOME  
FASTER AND MORE SHEARED THAN MOST OTHER GUIDANCE FOR THE UPPER  
FEATURE THAT RETROGRADES ALONG THE GULF COAST, WITH THE MODEL  
BLEND PROVIDING 70 PERCENT WEIGHT OF THE NON-GFS SCENARIO.  
INDIVIDUAL MODEL RUNS AND ENSEMBLE SPAGHETTI PLOTS SUGGEST  
INCREASING SHORTWAVE DETAIL UNCERTAINTY (WITHOUT WELL-DEFINED  
CLUSTERING AMONG ENSEMBLE SYSTEMS) OVER THE NORTHEASTERN  
PACIFIC/WESTERN NORTH AMERICA BY DAYS 6-7 SUN-MON. THIS SPREAD  
TEMPERS CONFIDENCE A BIT FOR DETAILS OF THE NORTHERN PLAINS FRONT  
LATE IN THE FORECAST.  
 
RAUSCH/FRACASSO  
 
WPC MEDIUM RANGE FORECASTS OF 500 MB HEIGHTS, SURFACE SYSTEMS,  
WEATHER GRIDS, QUANTITATIVE PRECIPITATION, AND WINTER WEATHER  
OUTLOOK PROBABILITIES 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  
 

 
 
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