681  
FXUS02 KWBC 110654  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
254 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 LONGWAVE 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 594-DM RIDGE IS  
LIKELY TO UNFOLD OVER THE DESERT SOUTHWEST WHILE A WEAKER  
ANTICYCLONE IS EXPECTED ACROSS THE SOUTHEASTERN U.S.  
 
   
..GUIDANCE EVALUATION AND PREFERENCES
 
 
STARTING WITH THE UPPER TROUGH SITTING OVER THE WESTERN ATLANTIC,  
THE NATIONAL HURRICANE CENTER HAS THE REGION IN A 50 PERCENT  
THREAT FOR TROPICAL CYCLONE DEVELOPMENT DURING THE NEXT 5 DAYS.  
THE 18Z GFS WAS MOST AGGRESSIVE WITH THIS SCENARIO DEPICTING A  
COUPLE OF CLOSED ISOBARS SURROUNDING THE CIRCULATION. EVENTUALLY  
THIS ELONGATED NEGATIVE HEIGHT ANOMALY LIFTS NORTHEASTWARD AS  
HEIGHTS BUILD ALONG THE EAST COAST.  
 
LOOKING TO THE ACTIVE PATTERN ALONG THE CANADIAN BORDER, MODELS  
ARE INITIALLY IN DECENT AGREEMENT EJECTING LOWER HEIGHTS ACROSS  
THE PROVINCE OF ALBERTA ON SATURDAY. ISSUES WITH TIMING AND  
OVERALL PLACEMENT BECOME MORE NUMEROUS AS THE TROUGH CLOSES OFF  
AND ATTAINS A RATHER FORMIDABLE APPEARANCE. THE 12Z ECMWF, AND NOW  
THE 00Z UKMET ARE WELL NORTHEAST OF THE RECENT GFS/CMC SOLUTIONS.  
MULTI-CYCLE COMPARISONS HAVE SHOWN FORECASTS BOUNCING AROUND A BIT  
SO CONFIDENCE BEGINS TO DIMINISH FROM DAY 5/MONDAY ONWARD. IN  
SPITE OF THE MODEL SPREAD, IT APPEARS REASONABLE TO BELIEVE A  
SLOW-MOVING BAROCLINIC ZONE SHOULD BE CROSSING THE I-95 CORRIDOR  
BY LATE TUESDAY/EARLY WEDNESDAY NEXT WEEK.  
 
WHERE MUCH OF THE FORECAST SPREAD LOOMS IS WITH THE NEXT TROUGH  
APPROACHING WESTERN NORTH AMERICA BEGINNING EARLY TUESDAY. MOST  
NOTABLY, THE 12Z ECMWF AND A FAIR SHARE OF ITS ENSEMBLE MEMBERS  
TRENDING SIGNIFICANTLY QUICKER WITH THIS FEATURE. WHILE PERHAPS A  
TREND, IT ALSO HAS NO SUPPORT FROM ALL OF THE AVAILABLE 00Z  
GUIDANCE. ITS DOWNSTREAM EFFECTS WOULD FAVOR A SHORTWAVE ACROSS  
WESTERN CANADA WHERE OTHER MODELS BUILD HEIGHTS. THIS APPEARS TO  
BE A CONTENTIOUS REGION OF THE MAP SO WILL CONTINUE TO STAY AWAY  
FROM THIS OUTLYING 12Z ECMWF SUITE IN FAVOR OF ITS PRECEDING CYCLE.  
 
THERE IS A FAIRLY UNANIMOUS SIGNAL IN THE GUIDANCE FAVORING A  
MARKED UPTICK IN MID-LEVEL HEIGHTS LATE IN THE WEEKEND INTO NEXT  
WEEK. 594-DM HEIGHTS ARE SUPPORTED FROM THE DESERT SOUTHWEST INTO  
THE FOUR CORNERS REGION WITH THE GFS RUNS BEING THE MOST  
AGGRESSIVE.  
 
THE MEDIUM RANGE PREFERENCE INITIALLY FAVORED A COMBINATION OF THE  
18Z/12Z GFS AND PREVIOUS 00Z ECMWF (10/0000Z) THROUGH DAY 4/SUNDAY  
BEFORE GRADUALLY INCREASING ENSEMBLE INFLUENCES INTO THE PICTURE.  
BY THE MIDDLE OF NEXT WEEK, HAD LITTLE CONFIDENCE IN ANY ONE  
SOLUTION SO TOOK A MULTI-ENSEMBLE BLEND APPROACH UTILIZING THE 18Z  
GEFS/12Z NAEFS/00Z ECMWF ENSEMBLE MEANS.  
 
   
..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.  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page