131  
FXUS02 KWBC 281439  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1039 AM EDT SUN MAY 28 2017  
 
VALID 12Z WED MAY 31 2017 - 12Z SUN JUN 04 2017  
 
   
..PATTERN OVERVIEW AND MODEL PREFERENCES
 
 
TROUGHING IS EXPECTED IN THE NORTHWEST AND NORTHEAST THIS PERIOD  
WITH RIDGING IN BETWEEN CENTERED ON THE NORTHERN PLAINS. SYSTEMS  
ORIGINATING IN THE SOUTHWEST MOVE ACROSS THE SOUTHERN ROCKIES AND  
PLAINS...EVENTUALLY REACHING THE LOWER-MID MS VALLEY NEXT WEEKEND.  
 
 
THE MODEL GUIDANCE DIFFERS ON THE TIMING/PHASING/AMPLITUDE OF THE  
DEEP CYCLONE IN SOUTHEAST CANADA AND A REINFORCING SECONDARY WAVE  
THAT FORMS NEAR HUDSON BAY OR JAMES BAY AND POTENTIALLY DEVELOPS  
INTO THE GREAT LAKES DAY 7 SUN 04 JUN. THE 00Z ECMWF COMPLETELY  
FLIPPED THE TREATMENT OF THE GREAT LAKES NEXT WEEKEND...CHANGING  
FROM A DEVELOPING RIDGE IN THE 12Z SAT RUN TO DEVELOPING CLOSED  
LOW ON THE 00Z SUN RUN. THIS PLACES LOW CONFIDENCE IN THE  
OPERATIONAL RUN. TELECONNECTIONS DO SUPPORT PERSISTENCE OF A  
NORTHEAST TROUGH AND THE GFS/CANADIAN DO SHOW A SECONDARY WAVE  
FORMING IN ONTARIO...JUST FURTHER NORTH AND WEAKER THAN THE 00Z  
ECMWF.  
 
THE MODELS SHOW DIFFERENCES IN THE TROUGH AMPLITUDE ACROSS THE  
PACIFIC NORTHWEST FRI-SUN AND EVOLUTION OF THE TROUGH. THE 00Z  
ECMWF CONTINUES TO HAVE A HIGHER AMPLITUDE TROUGH THAN MOST OF ITS  
ENSEMBLE MEMBERS...SO THE MEAN IS NOT AS AMPLIFIED.  
THE 06Z GFS ALSO TRIES TO TAKE A PIECE OF SHORTWAVE ENERGY AND  
MOVE IT EAST ACROSS THE NORTHERN ROCKIES AND PLAINS...MAINTAINING  
A SYSTEM THROUGH THE HEART OF THE DEEP LAYER RIDGE SHOWN IN THE  
MEAN AND TELECONNECTIONS THAT SUPPORT A CONTINUING MID LEVEL RIDGE  
IN THE NORTHERN PLAINS.  
 
TO ACCOUNT FOR UNCERTAINTY, THE PRESSURES/500 HPA HEIGHTS/WIND  
GRIDS STARTED OUT WITH AN EVEN SPLIT OF THE 00Z ECMWF/06Z GFS AND  
00Z ECMWF/06 GEFS ENSEMBLE MEANS...AND USED ONLY THE ECMWF/GEFS  
ENSEMBLE MEANS FOR DAYS 6 AND 7 GIVEN THE OPERATIONAL MODEL RUN TO  
RUN CHANGES AND DIFFERENCES WITH THEIR MEANS AND TELECONNECTIONS.  
 
   
..WEATHER HIGHLIGHTS
 
 
COOLER THAN NORMAL TEMPERATURES ARE EXPECTED TO CONTINUE INTO NEXT  
WEEK ACROSS THE GREAT LAKES AND NORTHEAST DUE TO LINGERING UPPER  
LEVEL TROUGHING. MEANWHILE, WARM CONDITIONS ARE EXPECTED ACROSS  
MUCH OF INTERMOUNTAIN WEST...WITH AN APPROACHING COLD FRONT  
BRINGING SOME ASSOCIATED LATE-SEASON PRECIPITATION.  
 
THE MOST WIDESPREAD RAINS THU AND FRI ARE FORECAST ACROSS THE  
CENTRAL AND SOUTHERN PLAINS WITH THE WAVE(S) MOVING EAST FROM THE  
SOUTHWEST US. LOCALLY HEAVY RAINS ARE POSSIBLE ACROSS PORTIONS OF  
THE SOUTHERN PLAINS AND MID-MISSISSIPPI VALLEY.  
 
WARM ADVECTION HELPS SHOWERS DEVELOP DOWNSTREAM INTO THE MID MS  
VALLEY. NEXT WEEKEND RAINS IN THE SOUTHERN PLAINS MOVE EAST INTO  
THE LOWER-MID MS VALLEY AND OH VALLEY TO THE NORTHEAST. RAINS IN  
THE NORTHERN PLAINS TO THE GREAT LAKES DEPEND ON THE STRENGTH OF  
UPPER TROUGH IN THESE REGIONS WITH SIGNIFICANT MODEL/ENSEMBLE  
VARIABILITY THAT HAS TO BE RESOLVED LATER.  
 
SHOWERS AND STORMS DEVELOP AND ACROSS FL AND SOUTHEAST COASTAL  
AREAS DUE TO LOW-LEVEL MOISTURE AVAILABILITY AND DAYTIME HEATING  
WITH LIFT INITIATED BY SEA BREEZES AND AN AGING STATIONARY FRONT.  
THE MODELS SHOW THEIR BEST AGREEMENT IN THESE AREAS FROM A QPF  
PERSPECTIVE.  
 
PETERSEN/ROTH  
 

 
 
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