779  
FXUS02 KWBC 111357  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
955 AM EDT WED JUL 11 2018  
 
VALID 12Z SAT JUL 14 2018 - 12Z WED JUL 18 2018  
   
..OVERVIEW
 
 
AMPLIFIED FLOW SHOULD REMAIN CONFINED TO THE INTERNATIONAL BORDER  
WITH CANADA THROUGHOUT THE PERIOD. BROAD LONG WAVE TROUGHING WILL  
TRACK FROM ALBERTA TO THE VICINITY OF HUDSON BAY BY TUESDAY WITH  
THE SOUTHERN EXTENSION OF HEIGHT FALLS SLIPPING ACROSS THE GREAT  
LAKES AND OHIO RIVER VALLEY. IN ITS WAKE, RENEWED AMPLIFICATION IS  
LIKELY ACROSS WESTERN CANADA INTO THE PACIFIC NORTHWEST BY DAY  
6/7, JULY 17/18. ELSEWHERE, WHILE AN ELONGATED UPPER TROUGH  
LINGERS OVER THE WESTERN ATLANTIC, AN EXPANSIVE 5940 METER 500 HPA  
RIDGE IS LIKELY TO UNFOLD OVER THE DESERT SOUTHWEST WHILE A WEAKER  
ANTICYCLONE IS EXPECTED ACROSS THE SOUTHEASTERN U.S.  
 
   
..GUIDANCE EVALUATION AND PREFERENCES
 
 
THE GUIDANCE SHOWS SOME ISSUES WITH LESS PREDICTABLE SHORTWAVE  
DETAILS, BUT IS OTHERWISE IN GOOD AGREEMENT. FOR PRESSURES, 500  
HPA HEIGHTS, AND WINDS, A COMPROMISE OF THE 00Z CANADIAN, 00Z  
UKMET, 00Z ECMWF, AND 06Z GFS WAS USED FROM SATURDAY INTO MONDAY,  
BEFORE INCREASING AMOUNTS OF THE 00Z ECMWF ENSEMBLE MEAN AND 00Z  
NAEFS MEAN IS USED TO REPLACE THE UKMET IN THE BLEND. THE  
REMAINDER OF THE GRIDS ARE AN EVEN BLEND OF DETERMINISTIC AND  
ENSEMBLE MEAN GUIDANCE TO ACCOUNT FOR UNCERTAINTY. A COMPROMISE  
OF THE 12Z NATIONAL BLEND OF MODELS, 00Z CANADIAN, 06Z GFS, AND  
00Z ECMWF IS PLANNED FOR THE DAYS 4-7 QPF. IF THE 12Z GFS PROVES  
USEFUL, IT COULD BE INCLUDED INTO THE QPF MIX.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
WHILE MANY LOCATIONS ACROSS THE NATION CAN EXPECT TEMPERATURES  
NEAR TO ABOVE CLIMATOLOGY, THERE ARE A FEW AREAS WHICH WILL BE ON  
THE COOLER SIDE. AN ACTIVE SOUTHWESTERN U.S. MONSOONAL CIRCULATION  
SHOULD KEEP THESE LOCATIONS WET GIVEN DAILY THUNDERSTORM CHANCES  
WITH ACCOMPANYING ENHANCED CLOUD COVER. IN A GENERAL SENSE,  
EXPECTED HIGHS SHOULD BE AROUND 5 DEGREES BELOW CLIMATOLOGY.  
MEANWHILE, SUNDAY SHOULD PROVE TO BE A RATHER COOL DAY FOR JULY  
STANDARDS OVER THE NORTHERN ROCKIES INTO THE ADJACENT NORTHERN  
PLAINS AS WELL AS PORTIONS OF NEBRASKA. 10 TO 15 DEGREE DEPARTURES  
WILL KEEP HIGHS IN THE 70S GIVEN COLD ADVECTION IN THE WAKE OF THE  
TROUGH PASSAGE.  
 
REGARDING RAINFALL THREATS, AS MENTIONED, THE FOUR CORNERS REGION  
WILL REMAIN WET DUE TO MONSOON CONSIDERATIONS WITH ACTIVITY  
GRADUALLY REACHING THE CENTRAL GREAT BASIN AND CIRCULATING INTO  
THE CENTRAL ROCKIES. FARTHER EAST, WIDESPREAD CONVECTION IS  
ANTICIPATED ALONG THE SLOW MOVING FRONT WHICH WILL MIGRATE FROM  
THE MIDDLE OF THE NATION TOWARD THE EASTERN SEABOARD FROM DAY 4-7,  
JULY 15-18. THERE IS ALSO A SIGNAL FOR ENHANCED THUNDERSTORM  
CHANCES ACROSS THE SOUTHEASTERN U.S. AS HIGH PRECIPITABLE WATER  
AIR POOLS ACROSS THE REGION.  
 
ROTH/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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