992  
FXUS02 KWBC 100525  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
125 AM EDT SUN JUN 10 2018  
 
VALID 12Z WED JUN 13 2018 - 12Z SUN JUN 17 2018  
   
..PATTERN OVERVIEW
 
 
MODELS/ENSEMBLE SHOW IMPROVED CONSENSUS THAT A BLOCKING UPPER HIGH  
INITIALLY IN PLACE NORTHWEST OF HUDSON BAY ON DAY 3 (WED) SHOULD  
BEGIN TO BREAK DOWN BY NEXT WEEKEND, ALLOWING SOMEWHAT MORE  
PROGRESSIVE FLOW TO TAKE HOLD ACROSS CANADA. AS THIS MORE  
PROGRESSIVE FLOW TAKES SHAPE, AMPLIFICATION OF UPPER TROUGHS  
ACROSS THE NORTHEASTERN U.S. AND THE NORTHERN GREAT BASIN/NORTHERN  
ROCKIES APPEARS PROBABLE BY NEXT WEEKEND. MEANWHILE, UPPER FLOW  
AFFECTING MUCH OF THE REMAINDER OF THE CONUS MAY BECOME LESS  
PROGRESSIVE, WITH THE POTENTIAL FOR A RE-INTENSIFICATION OF A  
BLOCKING UPPER HIGH ACROSS THE SOUTH CENTRAL U.S. BY NEXT WEEKEND,  
WITH ANOTHER SIMILAR FEATURE POSSIBLY DEVELOPING OFF THE PACIFIC  
NORTHWEST COAST.  
 
   
..MODEL GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
A MULTI-MODEL DETERMINISTIC BLEND INCLUDING THE 12Z ECMWF/UKMET  
AND 18Z GFS SERVED AS A BASIS FOR THE WPC FORECAST DURING DAYS 3-5  
(WED-FRI). THIS BLEND APPEARED TO FAVORABLY RESOLVE, AND REPRESENT  
A CONSENSUS SOLUTION FOR SHORTWAVE ENERGY CROSSING THE GREAT  
LAKES/NORTHEAST AND THE PACIFIC NORTHWEST/NORTHERN ROCKIES, AND  
THE ASSOCIATED SURFACE FRONTAL SYSTEMS, DURING THAT TIME PERIOD.  
THE GREATEST DIFFERENCES AMONG THE GUIDANCE FOR THE DAY 3-5 TIME  
FRAME WERE SURROUNDING THE TROUGH ACROSS THE NORTHWEST, WITH SOME  
QUESTION AS TO WHETHER THE WAVE WILL BE SLOWER WITH MORE  
AMPLIFICATION (AS SHOWN BY THE 18Z GFS/12Z UKMET) OR SLIGHTLY  
SLOWER TO AMPLIFY AND QUICKER TO MOVE INLAND (AS SHOWN BY THE 12Z  
ECMWF).  
 
FOR DAYS 6-7 (SAT-SUN), INCREASED WEIGHTING WAS PLACED ON THE 12Z  
ECENS/NAEFS ENSEMBLE MEANS. MODEL/ENSEMBLE SPREAD INCREASED DURING  
THIS TIME PERIOD AS THE UPPER FLOW ACROSS THE U.S. TRENDS TOWARD A  
BLOCKIER SETUP. WHAT IS CLEAR IS THAT AS UPPER RIDGING LIKELY  
STRENGTHENS ACROSS THE SOUTH CENTRAL U.S., AND ACROSS THE  
NORTHEAST PACIFIC, THE PATTERN SHOULD FAVOR SLOWER PROGRESSION AND  
AMPLIFICATION OF UPPER TROUGHS ACROSS THE WEST AND ALONG THE EAST  
COAST. IN THE WEST, SOME SOLUTIONS ARE MORE AGGRESSIVE AND QUICK  
TO CUT OFF AN UPPER LOW OVER THE GREAT BASIN, SOME EVEN  
RETROGRADING IT WESTWARD BENEATH THE UPPER RIDGE (18Z GFS/GEFS),  
WHILE OTHER SOLUTIONS KEEP A SLIGHTLY MORE PROGRESSIVE PATTERN  
WITH AN TROUGH THAT ATTEMPTS TO MOVE EASTWARD ACROSS THE ROCKIES,  
BUT STRUGGLES TO MAKE QUICK PROGRESS DUE TO THE EXPANDING RIDGE  
(12Z ECMWF/00Z GFS). AT THIS TIME, GIVEN THE OVERALL PATTERN, AND  
A TREND AMONG MANY ENSEMBLE MEMBERS TOWARD THE SLOWER/MORE  
AMPLIFIED SOLUTION, THE FORECAST WAS WEIGHTED AT LEAST SLIGHTLY  
MORE ON THE NAEFS DUE TO THE MORE AMPLIFIED GEFS/CMCE MEMBERS.  
 
FARTHER EAST, SIMILAR TIMING/AMPLITUDE DIFFERENCES EXIST WITH THE  
TROUGH DIGGING ACROSS THE GREAT LAKES/NORTHEAST/MID-ATLANTIC  
FRI-SAT. AN ENSEMBLE-HEAVY APPROACH WAS SUITABLE FOR THIS FEATURE  
AS WELL GIVEN LARGE MODEL-TO-MODEL AND RUN-TO-RUN VARIABILITY.  
WITH THE FLOW ACROSS THE NORTH ATLANTIC A BIT MORE PROGRESSIVE  
COMPARED TO THE NORTH PACIFIC AND CONUS, IT IS LESS CLEAR WHETHER  
A SLOWER/MORE AMPLIFIED OR FASTER/LESS AMPLIFIED SCENARIO IS  
PREFERRED. FINALLY, THE GFS CONTINUES TO DEVELOP A MORE  
WELL-DEFINED AREA OF LOW PRESSURE FROM A BROADER AREA OF DISTURBED  
WEATHER REACHING THE GULF OF MEXICO BY THU. GIVEN CONTINUED LACK  
OF SUPPORT FOR THIS SCENARIO AMONG ENSEMBLE MEMBERS (OTHER THAN  
THE GEFS), THE WPC FORECAST MAINTAINED A BROADER TROUGH/AREA OF  
DISTURBED WEATHER DRIFTING GENERALLY WESTWARD ACROSS THE GULF  
FRI-SUN.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS WITH LOCALLY HEAVY  
RAINS WILL BE POSSIBLE FROM THE CENTRAL PLAINS/MID-MISSISSIPPI  
VALLEY TO THE SOUTHEAST/MID-ATLANTIC THROUGH MUCH OF THE PERIOD AS  
A COLD FRONT PASSES AND THEN STALLS FROM THE PLAINS TO THE  
APPALACHIANS. CONVECTION WITH AREAS OF HEAVY RAIN MAY FLARE UP  
ACROSS THE NORTHERN PLAINS BY THU-FRI AS AN UPPER  
SHORTWAVE/SURFACE FRONTAL SYSTEM APPROACH, WITH THIS ACTIVITY  
LIKELY SPREADING EAST INTO THE MIDWEST AND SOUTH INTO THE CENTRAL  
PLAINS SAT-SUN IN ASSOCIATION WITH THE COLD FRONT. UNCERTAINTY  
REMAINS SURROUNDING THE EXPECTED BROAD AREA OF DISTURBED WEATHER  
CROSSING THE GULF OF MEXICO LATE IN THE WEEK, BUT BASED ON THE  
CURRENT FORECAST, POTENTIAL FOR MORE WIDESPREAD SHOWERS AND  
THUNDERSTORMS COULD BEGIN TO INCREASE BY NEXT WEEKEND ACROSS THE  
WESTERN GULF COAST STATES. ACROSS THE DESERT SOUTHWEST AND  
SOUTHERN GREAT BASIN, SHOWER AND THUNDERSTORM ACTIVITY MAY BE ON  
THE INCREASE BY LATE IN THE WEEK INTO NEXT WEEKEND AS PACIFIC  
MOISTURE ASSOCIATED WITH TROPICAL STORM BUD STREAMS NORTHWARD  
TOWARD THE REGION. CONFIDENCE IS LOW AT THIS TIME GIVEN THE TIME  
RANGE, BUT AREAS OF HEAVY RAIN ARE POSSIBLE.  
 
TEMPERATURES ARE EXPECTED TO BE ABOVE AVERAGE ACROSS MUCH OF THE  
U.S. THROUGH THE MEDIUM RANGE. THE GREATEST TEMPERATURE ANOMALIES  
SHOULD FOCUS ACROSS THE GREAT BASIN/CENTRAL ROCKIES WED-THU,  
SHIFTING EAST INTO THE CENTRAL PLAINS AND MID-MISSISSIPPI VALLEY  
BY FRI-SUN. HIGH TEMPERATURE ANOMALIES OF +5 TO +15 DEG F ARE  
POSSIBLE IN THESE AREAS. GIVEN THE TIME OF YEAR, HOWEVER, RECORD  
HIGH TEMPERATURES APPEAR UNLIKELY AT THIS TIME.  
 
RYAN  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page