856  
FXUS02 KWBC 071555  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1155 AM EDT SAT JUL 07 2018  
 
VALID 12Z TUE JUL 10 2018 - 12Z SAT JUL 14 2018  
   
..PATTERN OVERVIEW/GUIDANCE EVALUATION/PREFERENCES
 
 
A MID/UPPER-LEVEL RIDGE WILL PERSIST ACROSS THE WESTERN/CENTRAL  
U.S. THROUGH THE PERIOD. WHILE 500-MB ANOMALIES SHOULD WEAKEN  
FROM THE EXPECTED 2 TO 2.5 SIGMA VALUES EARLY IN THE WEEK, THE  
ANTICYCLONE WILL MOST LIKELY SET UP ACROSS FOUR CORNERS/GREAT  
BASIN INTO SOUTH-CENTRAL PORTIONS OF THE PLAINS BY DAYS 6/7, JULY  
13/14. THE NORTHERN PERIPHERY OF THE MEAN RIDGE SHOULD FLATTEN  
WITH TIME DUE TO AN ACTIVE PATTERN INVOLVING A PAIR OF AMPLIFIED  
SYSTEMS TRACKING FROM THE PACIFIC NORTHWEST/SOUTHERN BRITISH  
COLUMBIA TOWARD HUDSON BAY. EACH WILL LIKELY BE FAIRLY IMPRESSIVE  
IN NATURE WITH ATTENDANT DEEP SURFACE CYCLONES TRACKING THROUGH  
CENTRAL CANADA. THEIR TRAILING FRONTS SHOULD EXTEND INTO THE  
NORTHERN TIER STATES. MEANWHILE THE NATIONAL HURRICANE CENTER IS  
ISSUING ADVISORIES FOR WHAT IS CURRENTLY TROPICAL DEPRESSION THREE  
OVER THE WESTERN ATLANTIC, WITH STRENGTHENING ANTICIPATED OVER THE  
COMING DAYS WHILE THE SYSTEM INITIALLY STALLS AND THEN TRACKS  
NORTHEASTWARD OFFSHORE THE EAST COAST. CONSULT NHC PRODUCTS FOR  
LATEST INFORMATION ON T.D. THREE. AN ELONGATED UPPER TROUGH THAT  
HELPS TO STEER THIS TROPICAL CYCLONE OUT TO SEA SHOULD LINGER OVER  
THE EASTERN U.S. INTO LATE WEEK BEFORE WEAKENING/MOVING OFFSHORE.  
 
EARLY IN THE PERIOD 00Z-06Z GFS RUNS AND THE 00Z ECMWF/CMC OFFERED  
GOOD AGREEMENT WITH SIGNIFICANT FEATURES (ASIDE FROM T.D. THREE)  
AND HAD GOOD SUPPORT FROM THE ENSEMBLE MEANS, SO THOSE SOLUTIONS  
PROVIDED THE BASIS OF THE FORECAST INTO DAY 5 THU. AT THAT TIME  
GUIDANCE BEGAN TO DIVERGE IN RESPONSE TO DIFFERENCES THAT DEVELOP  
WITH NORTH PACIFIC/ALASKAN FLOW. OF PARTICULAR NOTE THE 06Z GFS  
BECAME OUT OF SYNC RELATIVE TO THE 00Z GFS/ECMWF/CMC AND THEIR  
ENSEMBLE MEANS SO THE UPDATED BLEND REMOVED THAT RUN AFTER THU.  
MEANWHILE BY FRI-SAT CONSECUTIVE OPERATIONAL MODEL RUNS AND  
INDIVIDUAL ENSEMBLE MEMBERS SUGGEST DECREASING DETAIL CONFIDENCE  
WITHIN A PATTERN THAT AT LEAST SHOWS A GENERAL THEME OF BROADLY  
CYCLONIC FLOW OVER THE WESTERN HALF OF CANADA AND EXTENDING INTO  
THE NORTHERN TIER U.S. AS A RESULT THE FORECAST TRENDED MUCH MORE  
TOWARD THE 06Z GEFS/00Z ECMWF MEANS LATE IN THE PERIOD. LATEST  
GUIDANCE CONSENSUS SHOWS THE FRONT THAT DROPS INTO THE EASTERN  
U.S. TUE ONWARD PUSHING FARTHER SOUTH THAN PRIOR FORECAST AS WELL  
AS PERSISTING FOR A LONGER TIME BEFORE WEAKENING. THERE IS ALSO  
MORE OF A SIGNAL FOR SOME DEGREE OF WAVINESS (FRONTAL OR  
OTHERWISE) NEAR THE SOUTHERN MID ATLANTIC COAST DURING THE LATTER  
HALF OF THE PERIOD.  
   
..WEATHER THREATS/HIGHLIGHTS
 
 
A MAJORITY OF THE COUNTRY CAN EXPECT ABOVE AVERAGE TEMPERATURES  
NEXT WEEK, WITH THE PRIMARY EXCEPTION BEING BE THE DESERT  
SOUTHWEST EASTWARD INTO THE SOUTHERN PLAINS. AN ACTIVE MONSOONAL  
FLOW REGIME SHOULD MAINTAIN ENHANCED CLOUD COVER AND WIDESPREAD  
SHOWERS/THUNDERSTORMS ACROSS THE FOUR CORNERS, KEEPING HIGH  
TEMPERATURES SEVERAL DEGREES BELOW CLIMATOLOGY FOR MUCH OF THE  
PERIOD. THE EASTERN U.S. COLD FRONT AND TRAILING HIGH PRESSURE  
SHOULD BRING A COUPLE DAYS OF NEAR TO SLIGHTLY BELOW NORMAL  
TEMPERATURES TO THE NORTHEAST/MID ATLANTIC AROUND MIDWEEK. EXPECT  
THE INTERIOR WEST INTO NORTHERN PLAINS TO SEE WELL ABOVE NORMAL  
READINGS TUE-WED AHEAD OF THE FIRST FRONT PROGRESSING INTO/ACROSS  
THE NORTHERN TIER. THEN THE PACIFIC NORTHWEST WILL SEE A  
PRONOUNCED WARMING TREND BY WED-THU AHEAD OF THE NEXT FRONT. IN  
BOTH CASES SOME PLUS 10-20F ANOMALIES ARE POSSIBLE. IN TERMS OF  
PRECIPITATION, THE MOST ORGANIZED AND PERSISTENT AREA OF  
CONVECTION WILL BE VIA THE ACTIVE MONSOONAL FLOW OVER AND NEAR THE  
FOUR CORNERS STATES WHILE DIURNALLY FORCED ACTIVITY WILL OCCUR  
ACROSS THE SOUTHERN U.S. THE COLD FRONT PUSHING INTO AND  
EVENTUALLY STALLING OVER THE EASTERN U.S. MAY ADD SOME FOCUS FOR  
CONVECTION. TO THE NORTH, SOME LOCALLY HEAVY CONVECTION IS  
POSSIBLE WITH THE FRONT CROSSING THE NORTHERN PLAINS/UPPER MS  
VALLEY AROUND TUE-WED WITH AMOUNTS TENDING TO BE LIGHTER FARTHER  
SOUTH/EAST OF THIS REGION. THERE MAY BE ANOTHER PERIOD OF  
CONVECTION OVER THE NORTHERN TIER LATE IN THE PERIOD AS THE  
TRAILING PART OF THE FRONT RETURNS NORTHWARD AND THE SECOND FRONT  
FROM WESTERN CANADA APPROACHES.  
 
RAUSCH/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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