202  
FXUS02 KWBC 060651  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
251 AM EDT FRI JUL 06 2018  
 
VALID 12Z MON JUL 09 2018 - 12Z FRI JUL 13 2018  
   
..OVERVIEW/GUIDANCE EVALUATION/PREFERENCES
 
 
A BROAD MID/UPPER-LEVEL RIDGE WILL REMAIN FIXED OVER A GOOD CHUNK  
OF THE NATION WITH GENERAL 2 TO 2.5 STANDARD DEVIATIONS ABOVE  
CLIMATOLOGY OBSERVED IN 500-MB HEIGHT FIELDS. THIS 594-DM  
ANTICYCLONE SHOULD PERIODICALLY BE DISTURBED BY INCOMING PACIFIC  
FEATURES AS WELL AS AMPLIFICATION WITHIN THE NORTHERN STREAM WHICH  
GENERALLY STRADDLES THE INTERNATIONAL BORDER WITH CANADA. WHILE  
SOLUTIONS AGREE ON TIMING OF THE PACIFIC SHORTWAVE CROSSING INTO  
THE PACIFIC NORTHWEST AND SOUTHERN BRITISH COLUMBIA ON TUESDAY  
MORNING, THEY CONTINUE TO STRUGGLE ACROSS OTHER AREAS OF  
DOWNSTREAM AMPLIFICATION. MODELS SEEM TO TAKE TURNS SHOWING LOCAL  
INVIGORATION OF THE FLOW WITH VARIOUS MODELS EXHIBITING SUCH  
BEHAVIORS. MOST RECENTLY, THE 00Z GFS SHIFTED BACK TOWARD A  
STRONGER UPPER TROUGH SWEEPING THROUGH SOUTHERN ONTARIO DOWN INTO  
THE UPPER GREAT LAKES ON MONDAY WHICH WAS SEEN IN THE 12Z CYCLE.  
ADDITIONALLY, THE 00Z GFS HAS STRUGGLED WITH A REMNANT UPPER LOW  
SPINNING OFF THE CAROLINAS SHOWING SLOW, BUT GENERAL STRENGTHENING  
WHILE LIFTING UP ALONG THE GULF STREAM. THE 00Z/12Z UKMET HAS  
DEPICTED A SIMILAR SCENARIO BUT WITH MORE EASTWARD DISPLACEMENT.  
OVERALL, THE EFFECTS OF THESE DISTURBANCES ON THE SYNOPTIC-SCALE  
PATTERN WILL BE TO REDUCE THE STRENGTH OF THE PERSISTENT 594-DM  
RIDGE ACROSS THE NATION. THE GUIDANCE OCCASIONALLY SHOW  
RE-ESTABLISHMENT AT THIS STRENGTH BUT VARY IN DETAILS. TO SUPPORT  
THE ABOVE ASSESSMENT, A MULTI-MODEL APPROACH WAS UTILIZED WITH  
REDUCED INFLUENCES OF OPERATIONAL SOLUTIONS BEYOND DAY  
5/WEDNESDAY. WHILE ENSEMBLE MEANS SUFFICIENTLY DAMPENED FORECAST  
DETAILS, MANY ASPECTS OF THE PATTERN REMAIN UNRESOLVABLE AS SUCH  
TIME RANGES.  
 
WEATHER THREATS/HIGHLIGHTS...  
 
THE UPPER RIDGE SHOULD KEEP NUMBERS ABOVE AVERAGE ACROSS A VAST  
MAJORITY OF THE COUNTRY. IN TERMS OF FORECAST DEPARTURES, THE  
PACIFIC NORTHWEST AND UPPER INTERMOUNTAIN WEST CAN EXPECT  
TEMPERATURES TO DIVERGE AROUND 10 TO 15 DEGREES FROM EARLY/MID  
JULY CLIMATOLOGY BY THE MIDDLE TO END OF NEXT WEEK. THIS WOULD  
ALLOW FOR UPPER 90S TO THRIVE OVER MUCH OF THIS REGION WITH 70S  
AND 80S MORE COMMONPLACE CLOSER TO THE COAST AND INTO SEATTLE, WA.  
MEANWHILE, SLIGHTLY BELOW AVERAGE READINGS ARE IN THE FORECAST  
FROM THE FOUR CORNERS EASTWARD ACROSS THE SOUTHERN PLAINS AND INTO  
THE GULF COAST. THIS WILL BE IN RESPONSE TO ENHANCED CLOUD COVER  
AND DAILY PRECIPITATION THREATS, PARTICULARLY WITHIN THE ACTIVE  
SOUTHWESTERN U.S. MONSOON. BESIDES THESE LOCATIONS, SHOWERS AND  
THUNDERSTORMS ARE EXPECTED ACROSS THE NORTH-CENTRAL U.S. DEPENDING  
ON HOW AMPLIFIED THE FLOW BECOMES. SOME RESIDUAL DOWNSTREAM  
PRECIPITATION THREATS WOULD BE LIKELY AS THE FRONTAL ZONE ADVANCES  
AND OCCASIONALLY MEANDERS. OVERALL, DIFFICULT TO SAY WHERE THE  
HEAVIEST RAINFALL WILL OCCUR DURING THE PERIOD ALTHOUGH MODEL  
NUMBERS ARE FAIRLY CONSERVATIVE IN A 24-HOUR SENSE.  
 
RUBIN-OSTER  
 
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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