716  
FXUS02 KWBC 291451  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1050 AM EDT FRI JUN 29 2018  
 
VALID 12Z MON JUL 02 2018 - 12Z FRI JUL 06 2018  
 
...EXTENDED PERIOD OF ABOVE AVERAGE TEMPERATURES EXPECTED FOR MUCH  
OF THE CENTRAL AND EASTERN U.S...  
   
..HEAVY RAIN THREAT FOR THE NORTHERN GULF COAST
 
 
   
..OVERVIEW
 
 
MODELS AND ENSEMBLES REMAIN IN GOOD AGREEMENT NEXT WEEK WITH THE  
UPPER PATTERN THAT WILL FEATURE AN EXPANDING UPPER HIGH THAT WILL  
LIKELY STRETCH FROM SOUTHERN CALIFORNIA NORTHEASTWARD TO THE  
APPALACHIANS. THIS WILL SUPPORT WELL ABOVE AVERAGE TEMPERATURES  
OVER THE EASTERN GREAT LAKES/NORTHEAST/MID-ATLANTIC WITH DAILY  
RECORD HIGHS LIKELY TO BE BROKEN. ONE UPPER LOW WILL LINGER OVER  
THE PACIFIC NORTHWEST AND ANOTHER OFF THE SOUTHEAST COAST WITH YET  
ANOTHER TO THE SOUTHWEST OF THE UPPER HIGH OVER THE GULF COAST. A  
SURFACE FRONTAL BOUNDARY WILL LIE ASTRIDE THE NORTH/NORTHWEST SIDE  
OF THE EXPANDING 594-597DM (MAYBE 600DM?) UPPER HIGH -- ROUGHLY  
FROM THE PACIFIC/INTERIOR WEST THROUGH THE NORTHERN PLAINS INTO  
THE GREAT LAKES.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
SIMILAR TO THE OVERNIGHT ISSUANCE, THE LATEST DETERMINISTIC MODELS  
FORMED A GOOD STARTING POINT FOR THE FORECAST THROUGH A MAJORITY  
OF THE PERIOD. THE FORECAST FOR DAYS 3-6 (MON-THU) WAS BASED ON A  
BLEND OF THE 00Z ECMWF/UKMET AND 06Z GFS. ENSEMBLE MEAN (00Z  
ECENS/NAEFS) WEIGHTING WAS GRADUALLY INCREASED FROM DAYS 5-7 TO  
ACCOUNT FOR SOME INCREASING SPREAD AMONG THE GUIDANCE. ALTHOUGH,  
SPREAD WITH RESPECT TO LARGE SCALE FEATURES WAS RELATIVELY LOW FOR  
THAT TIME PERIOD. A FEW POINTS OF CONTENTION EXISTED BY LATER IN  
THE FORECAST PERIOD. THE FIRST WAS THE TRACK/TIMING/STRENGTH  
DIFFERENCES WITH UPPER LOW OFF THE SOUTHEAST COAST, AND A  
COMPROMISE SOLUTION WAS FAVORED AT THIS TIME. ANOTHER WAS THE  
AMPLIFYING UPPER LOW OFF THE PACIFIC NORTHWEST BY WED-THU AS  
ENERGY SLIDES SOUTH ON THE EASTERN SIDE OF THE NORTH PACIFIC  
RIDGE. MODELS HAVE SHOWN A TREND TOWARD MORE AMPLIFICATION OF THIS  
FEATURE, WITH THE 06Z GFS LEADING THE WAY. GIVEN THE AMPLIFIED  
RIDGING ACROSS THE NORTH PACIFIC AND THE CENTRAL/EASTERN U.S.,  
THIS TREND MAKES SENSE CONCEPTUALLY, AND WAS INCLUDED IN THE  
LATEST FORECAST UPDATE. FINALLY, THE TIMING/AMPLITUDE OF SHORTWAVE  
ENERGY CROSSING CENTRAL CANADA NEXT THU-FRI HAS IMPLICATIONS FOR  
FRONTAL TIMING/POSITION ACROSS THE CONUS NORTHERN TIER. A TREND  
AMONG SOME OF THE GUIDANCE TOWARD SOMEWHAT GREATER AMPLIFICATION  
HERE RESULTED IN A FASTER FRONTAL TIMING ACROSS THE NORTHERN  
PLAINS/MIDWEST FOR DAYS 6-7 RELATIVE TO THE OVERNIGHT ISSUANCE.  
 
   
..WEATHER THREATS/HIGHLIGHTS
 
 
ASCENDANT UPPER HIGH WILL FORCE PRECIPITATION AROUND ITS  
CIRCULATION, FIRSTLY IN THE NORTHWEST IN CONJUNCTION WITH  
SOUTHWEST FLOW AHEAD OF THE UPPER LOW ATOP THE SURFACE BOUNDARY.  
THIS WILL EXTEND EASTWARD ACROSS MONTANA INTO THE PLAINS AND GREAT  
LAKES AS THE SURFACE LOW WANDERS THROUGH SOUTHERN CANADA. A LEAD  
FRONT INTO THE NORTHEAST NEXT MON/TUE WILL DO LITTLE BUT KNOCK  
TEMPERATURES A FEW DEGREES AND PERHAPS TOUCH OFF A SHOWER/STORM AS  
IT DISSIPATES BY WEDNESDAY. THE SOUTHEAST INTO FLORIDA MAY SEE AN  
INCREASE IN PRECIPITATION SHOULD THE ATLANTIC UPPER LOW WOBBLE  
WESTWARD TOWARD THE COAST LATER IN THE WEEK. FINALLY, THE MOST  
SIGNIFICANT PRECIPITATION MAY LIE ALONG THE GULF COAST FROM LA/MS  
WESTWARD TO THE UPPER TEXAS COAST AS A WEAKNESS DRIFTS WESTWARD.  
ECMWF/UKMET SEEMED A BIT AGGRESSIVE/WET BUT WITH PLENTY OF  
MOISTURE TO TAP (PW ANOMALIES ABOUT +2 TO +3 SIGMA) HEAVY RAINFALL  
IS CERTAINLY A POSSIBILITY.  
 
TEMPERATURES WILL BE NEAR/ABOVE RECORDS (15 TO 20 DEGREES ABOVE  
AVERAGE) IN THE NORTHEAST EARLY NEXT WEEK WITH A SLOW DOWNWARD  
TREND (BUT STILL ABOVE AVERAGE) BY LATE IN THE WEEK AS THE CORE OF  
THE UPPER HIGH MOVES SOUTHWESTWARD. HIGH TEMPERATURES ARE EXPECTED  
TO BE AT LEAST 5 DEGREES ABOVE AVERAGE FOR MOST OF THE CONTIGUOUS  
U.S. THROUGH MUCH OF NEXT WEEK, WITH WIDESPREAD 90S FOR MANY  
AREAS. MEANWHILE, COOLER THAN AVERAGE TEMPERATURES ARE EXPECTED  
FOR THE NORTHWEST AND ALSO ALONG THE GULF COAST (ESPECIALLY MAX  
TEMPS) GIVEN EXTENSIVE CLOUD COVER AND RAIN.  
 
FRACASSO/RYAN  
 
WPC MEDIUM RANGE FORECASTS OF 500 MB HEIGHTS, SURFACE SYSTEMS,  
WEATHER GRIDS, QUANTITATIVE PRECIPITATION, AND WINTER WEATHER  
OUTLOOK PROBABILITIES 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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page