129  
FXUS02 KWBC 101600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1159 AM EDT SUN JUN 10 2018  
 
VALID 12Z WED JUN 13 2018 - 12Z SUN JUN 17 2018  
   
..PATTERN OVERVIEW
 
 
LATEST GUIDANCE CONTINUES TO REFINE IDEAS FOR FLOW EVOLUTION OVER  
CANADA AND CONTIGUOUS U.S. THE GENERAL CONSENSUS IS FOR THE  
STRONG UPPER HIGH FORECAST TO BE NORTHWEST OF HUDSON BAY AS OF  
EARLY WED TO COLLAPSE/MERGE WITH A RIDGE THAT DEVELOPS AND THEN  
PROGRESSES AHEAD OF ENERGY EJECTING FROM THE UPPER TROUGH MOVING  
INTO WESTERN NORTH AMERICA. TROUGHING SHOULD PERSIST OVER THE  
WEST THROUGH THE END OF THE PERIOD GIVEN THE STRENGTH/SHARPNESS OF  
THE RIDGE OVER THE EASTERN PACIFIC. AT THE SAME TIME AN EASTERN  
U.S./CANADA TROUGH SHOULD AMPLIFY DURING THE LATTER HALF OF THE  
WEEK AND THEN PROCEED INTO THE WESTERN ATLANTIC DURING THE  
WEEKEND. MULTI-DAY TRENDS SEEM TO SUGGEST SOME WEAKENING AND/OR  
EASTWARD ADJUSTMENT OF MEAN RIDGE OVER THE SOUTHERN PLAINS. THE  
OVERALL PATTERN EVOLUTION MAY PROMOTE A FLOW OF TROPICAL EASTERN  
PACIFIC MOISTURE INTO PARTS OF THE SOUTHWESTERN U.S./ROCKIES AND  
EVENTUALLY A SEPARATE AREA OF MOISTURE INTO THE WESTERN HALF OF  
THE GULF OF MEXICO.  
 
   
..MODEL GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
AS HAS BEEN THE CASE IN RECENT DAYS, AN OPERATIONAL MODEL BLEND  
(MORE 06Z GFS/00Z ECMWF THAN 00Z UKMET/CMC) REPRESENTED THE MOST  
COMMON THEMES OF GUIDANCE WELL IN THE 3-5 DAY TIME FRAME. THEN  
THE ENSEMBLE MEANS (00Z ECMWFENS/NAEFS AND 06Z GEFS) BECAME MORE  
USEFUL FOR THEIR STABILITY AND TELECONNECTION SUPPORT, THOUGH SOME  
OPERATIONAL GUIDANCE MATCHED UP BETTER IN PRINCIPLE THAN IN SOME  
PREVIOUS CYCLES.  
 
ONE EMERGING TREND IN THE GUIDANCE, REINFORCED IN THIS CYCLE, IS  
FOR A FAIRLY PROGRESSIVE EJECTION OF INITIAL UPPER LOW ENERGY  
INITIALLY NEAR VANCOUVER ISLAND AND REACHING INLAND BY THU. THIS  
TREND, AND POSSIBLE INCORPORATION OF SOME UPPER LOW/TROUGH ENERGY  
TO THE NORTH, IS STEADILY INCREASING SUPPORT FOR A FAIRLY STRONG  
LOW PRESSURE SYSTEM TRACKING INTO SOUTH-CENTRAL CANADA. THE  
EJECTION OF LEADING ENERGY IS ENCOURAGED IN PART BY AN UPSTREAM  
SHORTWAVE/POSSIBLE COMPACT LOW THAT MAY REACH THE NORTHWEST BY  
AROUND SAT AND IS MUCH MORE DEFINED THAN IT WAS 24 HOURS AGO.  
THIS SECOND BUNDLE OF ENERGY MOST LIKELY DRIFTS INTO THE NORTHERN  
INTERMOUNTAIN WEST/ROCKIES BY SUN WITH SOME TROUGHING EXTENDING  
SOUTHWESTWARD. THIS EVOLUTION COMPARES WELL WITH TELECONNECTION  
IDEAS RELATIVE TO THE UPSTREAM RIDGE'S POSITIVE HEIGHT ANOMALY  
CENTER--SOME BROADNESS TO THE NORTHERN PART OF THE MEAN TROUGH AND  
ONLY WEAK TROUGHING EXTENDING OVER/THROUGH CALIFORNIA. GFS/ECMWF  
RUNS ARE NOW FAIRLY CLOSE TO THIS IDEA AS WELL, AFTER THE GFS  
TRENDED AWAY FROM A DEEPER CA UPPER LOW (NOW IN THE 00Z CMC) AND  
ECMWF PULLED THE SOUTHERN PART OF THE TROUGH WESTWARD.  
 
EXACT DETAILS OF THE WESTERN TROUGH WILL BE CRITICAL FOR  
DETERMINING TIMING/AXIS OF A POTENTIAL SURGE OF DEEP LAYER  
MOISTURE FROM EASTERN PACIFIC T.S. BUD INTO PARTS OF THE  
SOUTHWESTERN U.S. THE MOST AGREEABLE FOCUS IN THE GEFS/ECMWF  
ENSEMBLES IS OVER SOUTHERN ARIZONA LATE THIS WEEK/EARLY WEEKEND  
WITH PRECIPITABLE WATER VALUES POTENTIALLY REACHING 4-6 STANDARD  
DEVIATIONS ABOVE NORMAL AND THE 95TH OR GREATER CLIMATOLOGICAL  
PERCENTILES. SOMEWHAT WESTWARD AXIS IN THE ECMWF SCENARIO WOULD  
LEAD TO SUCH ANOMALIES EXTENDING INTO SOUTHERN CALIFORNIA. SOME  
MOISTURE MAY EVENTUALLY CONTINUE NORTHEASTWARD ALONG THE SURFACE  
FRONT INTO THE ROCKIES/PLAINS.  
 
OVER/NEAR THE GULF OF MEXICO, SURFACE SOLUTIONS STILL VARY WIDELY  
THOUGH A MORE AGREEABLE SIGNAL IS DEVELOPING TOWARD AT LEAST SOME  
SHORTWAVE ENERGY/MOISTURE REACHING THE WESTERN HALF OF THE GULF BY  
THE LATTER HALF OF THE PERIOD. THE ECMWF DOES NOT YET HAVE A  
MEANINGFUL SURFACE REFLECTION BUT THE PAST COUPLE RUNS HAVE  
NOTICEABLY INCREASED THE AMOUNT OF SHORTWAVE ENERGY OVER THE  
WESTERN GULF. THUS THE DEPICTION OF A SURFACE TROUGH HEADING INTO  
THE WESTERN GULF CONTINUES TO PROVIDE THE MOST REASONABLE WAY TO  
DEPICT POTENTIAL FOR SOME SENSIBLE WEATHER EFFECTS LATER IN THE  
FORECAST.  
 
CONFIDENCE IS FAIRLY LOW WITH EASTERN U.S. TROUGH DETAILS BY THE  
LATTER HALF OF THE PERIOD. ENSEMBLE MEAN TRENDS HAVE BEEN TOWARD  
MORE PROGRESSION, LIKELY DUE IN PART TO TRENDS UPSTREAM, THOUGH  
THE CMC AND SOME RECENT ECMWF RUNS SUGGEST ENERGY COULD CLOSE OFF  
JUST BEYOND THE EAST COAST.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THERE WILL BE MULTIPLE AREAS OF FOCUS FOR ENHANCED RAINFALL  
POTENTIAL DURING THE PERIOD. ONE WILL BE ALONG AN INITIALLY  
STALLED FRONTAL BOUNDARY OVER AND EAST OF THE CENTRAL PLAINS, WITH  
EMERGING WESTERN U.S. LOW PRESSURE PUSHING IT NORTH AS A WARM  
FRONT. WHILE THE NORTHWEST WILL LIKELY SEE JUST LIGHT-MODERATE  
ACTIVITY WITH THE STRONG UPPER TROUGH MOVING INTO THE REGION,  
EXPECT PRECIPITATION TO BECOME HEAVIER AND MORE WIDESPREAD LATE  
WEEK/WEEKEND FROM THE SOUTHWEST INTO PARTS OF THE ROCKIES AS THE  
FLOW ALOFT MAY BRING SOME MOISTURE FROM T.S. BUD ACROSS THE  
REGION. CONFIDENCE IS NOT ESPECIALLY HIGH WITH TIMING/AXIS  
SPECIFICS BUT COMPARED TO YESTERDAY THERE IS A STRENGTHENING  
SIGNAL TOWARD SOME RAINFALL ENHANCEMENT FROM THE EASTERN PACIFIC  
TROPICAL MOISTURE. BY LATE IN THE PERIOD SOME OF THIS MOISTURE  
COULD INTERACT WITH THE WESTERN FRONT EXTENDING INTO THE PLAINS  
AND SLOWER FRONTAL MOTION COULD PROMOTE REPEAT ACTIVITY/TRAINING  
AT SOME LOCATIONS. ALSO BY THE WEEKEND THERE IS INCREASING  
POTENTIAL FOR SOME AREAS ALONG THE WESTERN HALF OF THE GULF COAST  
TO SEE INCREASING INTENSITY OF RAINFALL WITH LOW LEVEL GULF INFLOW  
AND UPPER LEVEL SHORTWAVE ENERGY, EVEN THERE IS NOT A PRONOUNCED  
SURFACE REFLECTION. FARTHER EAST, THE SOUTHEAST AND MID ATLANTIC  
WILL LIKELY SEE SHOWERS AND THUNDERSTORMS WITH A FRONT PROVIDING  
ADDED FOCUS WHILE A SYSTEM SOUTHERN CANADA/MAINE WILL LIKELY  
PRODUCE AN AXIS OF ENHANCED RAINFALL OVER EXTREME NORTHERN NEW  
ENGLAND DURING THE LATTER HALF OF THE WEEK.  
 
WELL ABOVE AVERAGE TEMPERATURES WILL PROGRESS FROM MUCH OF THE  
WEST ON WED INTO THE PLAINS AND THEN MS VALLEY. EACH DAY SHOULD  
FEATURE AN AREA OF PLUS 10-20F ANOMALIES. UPPER TROUGH MOVING  
INTO THE WEST WILL BRING A PRONOUNCED COOLING TREND, WITH CLOUDS  
AND RAINFALL POSSIBLY LEADING TO MUCH BELOW NORMAL MAX  
TEMPERATURES OVER PARTS OF THE SOUTHWEST/GREAT BASIN/ROCKIES BY  
THE LATTER HALF OF THE PERIOD.  
 
RAUSCH  
 
WPC MEDIUM RANGE FORECASTS OF 500 MB HEIGHTS, SURFACE SYSTEMS,  
WEATHER GRIDS, QUANTITATIVE PRECIPITATION, AND WINTER WEATHER  
OUTLOOK PROBABILITIES CAN BE 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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