363  
FXUS02 KWBC 090525  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
124 AM EDT SAT JUN 09 2018  
 
VALID 12Z TUE JUN 12 2018 - 12Z SAT JUN 16 2018  
   
..PATTERN OVERVIEW
 
 
UPPER FLOW ACROSS NORTH AMERICA DURING THE MEDIUM RANGE IS  
EXPECTED TO SHOW A LARGE DEGREE OF BLOCKING, PARTICULARLY AT THE  
HIGHER LATITUDES. AN ANOMALOUS UPPER RIDGE IS EXPECTED TO BE IN  
PLACE ON DAY 3 (TUE) FROM THE UPPER GREAT LAKES NORTH ACROSS  
HUDSON BAY. AS SHORTWAVE ENERGY TRAVERSING THE WESTERLIES ACROSS  
NORTH AMERICA UNDERCUTS THIS RIDGE, THE MAIN ANOMALY CENTER SHOULD  
FOCUS NEAR/JUST NORTHWEST OF HUDSON BAY BY THE MIDDLE OF NEXT  
WEEK. AS WITH ANY HIGHLY ANOMALOUS BLOCKING PATTERN, A SIGNIFICANT  
QUESTION EXISTS AS TO HOW LONG THE SETUP WILL PERSIST, AND MODEL  
SOLUTIONS CONTINUE TO VARY IN THAT RESPECT. AS LONG AS THE BLOCK  
PERSISTS, A RELATIVELY ACTIVE FLOW REGIME WILL EXIST FROM THE  
PACIFIC NORTHWEST EASTWARD INTO THE MIDWEST, GREAT LAKES, AND  
NORTHEAST, SOUTH OF THE BLOCKING UPPER HIGH. A COUPLE SUCH  
SHORTWAVES ARE EXPECTED TO CROSS THE MIDWEST/GREAT LAKES/NORTHEAST  
TUE-FRI. ADDITIONALLY, MODELS SHOW CONSENSUS THAT AN UPPER WAVE  
SHOULD REACH THE PACIFIC NORTHWEST BY NEXT WED, WITH SOME DEGREE  
OF HEIGHT FALLS PRESSING INTO THE INTERIOR WESTERN U.S. THROUGH  
THE END OF NEXT WEEK. MEANWHILE, AN UPPER RIDGE IS ALSO EXPECTED  
TO REMAIN ANCHORED ACROSS THE SOUTH CENTRAL U.S., VARYING IN  
STRENGTH THROUGHOUT THE PERIOD.  
 
   
..MODEL GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE WPC FORECAST WAS INITIALLY BASED ON A HEAVILY DETERMINISTIC  
BLEND INCLUDING THE 12Z ECMWF/GFS DURING DAYS 3-4, WITH INCREASING  
WEIGHT PLACED TOWARD THE 12Z ECENS/NAEFS ENSEMBLE MEANS FROM DAY 5  
ONWARD.  
 
MODELS SHOWED SOME SIGNIFICANT DIFFERENCES AND RUN-TO-RUN  
VARIABILITY THROUGHOUT THE PERIOD. THE 18Z GFS WAS MUCH WEAKER  
WITH A SHORTWAVE INITIALLY ACROSS THE MID-ATLANTIC ON DAY 3, AND  
WAS REJECTED IN FAVOR OF THE 12Z RUN WHICH WAS MORE SIMILAR TO THE  
CONSENSUS INCLUDING THE ECMWF AND THE ENSEMBLE MEANS. WITH  
SHORTWAVE ENERGY CROSSING THE CONUS NORTHERN TIER DAYS 3-5,  
SOLUTIONS VARY WIDELY DUE TO COMPLEX INTERACTIONS WITH ARCTIC  
ENERGY ROUNDING THE EASTERN SIDE OF THE ANOMALOUS RIDGE. THE GFS  
HAS BEEN PERSISTENT IN AMPLIFYING A TROUGH ACROSS THE NORTHEAST BY  
DAYS 6-7, WHILE THE ECMWF SHOWS A SIMILAR SCENARIO BUT IS A BIT  
WEAKER AND QUICKER TO MOVE THE FEATURE EAST. THE 12Z GFS WAS  
PROBABLY THE MOST SIMILAR TO THE ECMWF IN THAT RESPECT. WITH THE  
UPPER ENERGY REACHING THE WEST ON DAY 4, THE ECMWF ALSO A BIT  
WEAKER AND QUICKER TO PUSH THE WAVE INTO THE INTERIOR WEST BY DAY  
6. THE GFS HAS BEEN RATHER VARIABLE WITH THE 18Z RUN EVEN KEEPING  
THE SYSTEM ALONG THE WEST COAST AS A RETROGRADING UPPER LOW INTO  
DAY 7, WHILE THE 12Z RUN SEEMED TO BE SOMEWHAT OF A REASONABLE  
MIDDLE GROUND SOLUTION (AND WAS RELATIVELY CLOSE TO THE ENSEMBLE  
MEAN BASED CONSENSUS). GIVEN THE UNSTABLE NATURE OF THIS FLOW  
PATTERN WITH A HIGH DEGREE OF BLOCKING, PREDICTABILITY IS LOW AND  
NO SCENARIO CAN REALLY BE RULED OUT, ESPECIALLY BY DAYS 6-7.  
FINALLY, THE GFS CONTINUES TO DEVELOP AN AREA OF LOW PRESSURE IN  
THE GULF OF MEXICO BY THE MIDDLE OF NEXT WEEK MORE SO THAN ANY  
OTHER DETERMINISTIC SOLUTIONS. THE ECMWF AND CMC BOTH CONTINUE TO  
SHOW A MUCH WEAKER AND BROAD AREA OF DISTURBED WEATHER DRIFTING  
WESTWARD ACROSS THE GULF. AT THIS TIME, THERE IS A LACK OF SUPPORT  
FOR A GFS-LIKE SOLUTION AMONG ECENS AND CMCE ENSEMBLE MEMBERS.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS ARE EXPECTED  
TUE-WED FROM THE MISSISSIPPI VALLEY EAST TO THE EASTERN SEABOARD  
ALONG A LINGERING SURFACE FRONTAL BOUNDARY AND AHEAD OF AN  
APPROACHING COLD FRONT MOVING FROM THE MIDWEST ON TUE TO THE  
NORTHEAST ON WED. AREAS OF HEAVY RAIN APPEAR POSSIBLE, BUT  
CONFIDENCE IN THE LOCATION OF ANY HEAVY RAIN IS LOW. AS THE COLD  
FRONT MOVES OFF THE EAST COAST BY THU, THE TRAILING FRONTAL  
BOUNDARY WILL LINGER ACROSS THE OHIO VALLEY AND CENTRAL PLAINS,  
WHERE IT WILL CONTINUE TO FOCUS AREAS OF CONVECTION THROUGH THE  
END OF NEXT WEEK. THE POTENTIAL SHORTWAVE CROSSING THE NORTHERN  
ROCKIES BY NEXT FRI-SAT MAY FURTHER ENHANCE THE  
SHOWER/THUNDERSTORMS POTENTIAL ACROSS THE NORTHERN PLAINS.  
 
TEMPERATURES ARE EXPECTED TO BE WELL ABOVE AVERAGE THROUGH THE  
MIDDLE OF NEXT WEEK FROM THE GREAT BASIN EAST ACROSS THE CENTRAL  
U.S., WHERE HIGH TEMPERATURES MAY RANGE FROM 5 TO 15 DEG F ABOVE  
AVERAGE. THE ARRIVAL OF LOWER HEIGHTS INTO THE WESTERN U.S. BY  
FRI-SAT WILL BRING TEMPERATURES DOWN CLOSER TO AVERAGE VALUES FOR  
MUCH OF THE WEST, BUT EXPECT HOT CONDITIONS TO CONTINUE FOR MUCH  
OF THE CENTRAL U.S. AS THE UPPER RIDGE PERSISTS.  
 
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