000  
FXUS02 KWBC 251601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT WED JUL 25 2018  
 
VALID 12Z SAT JUL 28 2018 - 12Z WED AUG 01 2018  
   
..HEAT WAVE LINGERS OVER THE WEST
 
 
...HEAVY RAINFALL THREAT TO SPREAD FROM THE CENTRAL PLAINS TO  
MID-SOUTH THEN THE SOUTHEAST/EASTERN U.S...  
 
   
..PATTERN OVERVIEW/GUIDANCE EVALUATION/PREFERENCES
 
 
SOME IMPRESSIVE MID-LEVEL HEIGHT ANOMALIES APPEAR ACROSS NORTH  
AMERICA AND THE SURROUNDING OCEANIC BASINS DURING THE PERIOD. ALL  
SUCH FEATURES REMAIN AROUND 1.5 TO 2 SIGMA ABOVE/BELOW AVERAGE,  
RESPECTIVELY. A PAIR OF 594-DM RIDGES WILL INHABIT THE  
SOUTHWESTERN U.S. AS WELL AS THE WESTERN ATLANTIC WITH THE LATTER  
RETROGRADING BACK TOWARD THE GULF STREAM. SANDWICHED IN BETWEEN  
THIS PAIR OF POSITIVE HEIGHT ANOMALIES WILL BE ANOTHER CUT-OFF LOW  
MEANDERING ABOUT THE MIDDLE MISSISSIPPI VALLEY INTO THE MID-SOUTH  
EARLY TO MID NEXT WEEK. INTO THE HIGHER LATITUDES, A RATHER DEEP  
UPPER LOW SINKING SOUTHWARD FROM NUNAVUT COULD BE PRIMED TO CARRY  
LOWERING HEIGHTS TO JUST SOUTH OF THE INTERNATIONAL BORDER WITH  
CANADA DEPENDING ON THE MODEL. OTHERWISE, A WEAK LONGWAVE TROUGH  
MAY POSITION ITSELF OFF THE PACIFIC NORTHWEST COAST EARLY MONDAY  
BEFORE GRADUALLY SLIDING INLAND THE SUBSEQUENT DAYS.  
 
GENERALLY SPEAKING, THE HEMISPHERIC PATTERN REMAINS RATHER INTACT  
WITH ENSEMBLE SPAGHETTI SPREAD ON THE LOWER END. OVER THE WEEKEND,  
MOST OF THE ISSUES LOOM UPSTREAM ACROSS THE NORTHEASTERN PACIFIC  
AS THE 00Z ECMWF ENSEMBLES FAVOR A MUCH FLATTER RIDGE. WHILE THE  
PAIR OF UPPER RIDGES INHABITING THE SOUTHWESTERN U.S. AND WESTERN  
ATLANTIC ARE WELL AGREED UPON, DIFFERENCES CONTINUE IN BETWEEN  
WITH SPATIAL/TEMPORAL UNCERTAINTIES SHOWN IN THE GUIDANCE.  
BEGINNING WITH THE UPPER TROUGH DRIFTING FROM THE NORTH-CENTRAL  
STATES TOWARD THE MID-SOUTH, A SLOW EVOLUTION IS SUPPORTED  
ALTHOUGH THE 00Z UKMET IS A WESTERN OUTLIER. EVENTUALLY FORWARD  
PROGRESSION IS STUNTED AS DOWNSTREAM RIDGING CONTINUES TO SHIFT  
TOWARD THE WEST. THE 06Z GFS DIVERGES FROM THE PACK AS WELL AS ITS  
OWN ENSEMBLE MEAN TRACKING LOWER HEIGHTS INTO THE LOWER GREAT  
LAKES BY DAY 7/AUGUST 1. FARTHER TO THE NORTH, LIKELY THE MOST  
CONTENTIOUS SECTOR OF THE CONTINENT AS DISCERNIBLE AMPLITUDE  
DIFFERENCES ARE NOTED BY AS EARLY AS DAY 5/JULY 30. WITH  
SUBSTANTIAL HEIGHT RISES DEPICTED ACROSS FAR EASTERN ALASKA INTO  
THE YUKON TERRITORY, A MORE AMPLIFIED FLOW REGIME IS TO BE  
EXPECTED DOWNSTREAM. IN SPITE OF SIMILAR RIDGE STRENGTHS ACROSS  
THIS REGION, THE 00Z GEFS/ECMWF ENSEMBLES DEPICT COMPLETELY  
DIFFERENT DOWNSTREAM PATTERNS. THE 00Z GEFS MEAN, AND TO SOME  
DEGREE THE 00Z NAEFS MEAN, FAVOR MORE SIGNIFICANT AMPLIFICATION  
WHILE OVER 90 PERCENT OF THE 00Z ECMWF ENSEMBLES STAY MUCH  
FLATTER. THIS WOULD HAVE AN IMPACT ON WHETHER A COLD FRONT WITH  
ASSOCIATED PRECIPITATION THREATS COULD CROSS INTO THE NORTHERN  
TIER BY THE MIDDLE OF NEXT WEEK.  
 
WEIGHTED THE FORECAST TOWARD OPERATIONAL GUIDANCE THROUGH DAY  
4/SUNDAY WITH MOST EMPHASIS ON THE 06Z GFS/00Z ECMWF. THEREAFTER,  
MOVED TOWARD A 50/50 APPROACH OF ENSEMBLES VS. OPERATIONAL  
SOLUTIONS WITH MODEL SPREAD RISING. GIVEN MENTIONED DIFFERENCES  
ACROSS THE HIGHER LATITUDES, LEANED A BIT MORE TOWARD THE 06Z  
GEFS/00Z NAEFS ENSEMBLE MEANS.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
WITH COLD ADVECTION CONTINUING ACROSS THE MIDDLE OF THE COUNTRY,  
WELL BELOW AVERAGE TEMPERATURES ARE ANTICIPATED FROM SATURDAY INTO  
MONDAY FROM THE NORTHERN ROCKIES EASTWARD INTO THE  
NORTHERN/CENTRAL PLAINS AS WELL AS THE MIDDLE MISSISSIPPI VALLEY.  
OVER THE WEEKEND, EXPECT HIGHS TO REMAIN IN THE 70S WHICH WOULD BE  
AROUND 10 TO POSSIBLY 15 DEGREES BELOW AVERAGE. GRADUALLY THIS  
COOL ANOMALY WILL MIGRATE EAST OF THE MISSISSIPPI RIVER BY NEXT  
WEEK ALTHOUGH NUMBERS SHOULD BE SLIGHTLY CLOSER TO CLIMATOLOGY. ON  
THE CONVERSE, FORECAST HIGHS SHOULD BE AROUND 5 TO 10 DEGREES  
ABOVE AVERAGE OVER THE PACIFIC NORTHWEST THROUGH MONDAY BEFORE THE  
LONGWAVE TROUGH APPROACHES FROM THE OFFSHORE WATERS. WHILE AN  
UPPER RIDGE WILL REMAIN FIXED OVER THE DESERT SOUTHWEST, READINGS  
IN THE LOWER 110S WOULD ONLY BE AROUND 5 DEGREES OR SO ABOVE LATE  
JULY CLIMATOLOGY.  
 
A BAND OF MODERATE TO HEAVY RAINFALL WILL ACCOMPANY THE SLOW  
MOVING UPPER TROUGH WITH THE MAIN AXIS INITIALLY OVER THE CENTRAL  
PLAINS INTO THE OZARKS. CONVECTION SHOULD GRADUALLY PUSH EASTWARD  
ALONG THE PRIMARY COLD FRONT WITH PLENTY OF WARM SECTOR  
THUNDERSTORMS FURTHER DOWNSTREAM. BY THE EARLY TO MIDDLE PART OF  
NEXT WEEK, THE SQUEEZE PLAY BETWEEN THE NEARLY STALLED UPPER LOW  
ACROSS THE MID-SOUTH AND THE BLOCKING DOWNSTREAM RIDGE COULD BRING  
MORE HEAVY RAINFALL ACROSS THE EASTERN THIRD OF THE U.S. 850-700  
MB MOISTURE FLUX ANOMALIES BEGIN TO EXCEED 3 SIGMA BY THE END OF  
THE PERIOD. FARTHER WEST, MONSOONAL ACTIVITY SHOULD NOT BE  
TERRIBLY WIDESPREAD WITH A MAJORITY OF THE ACTION FOCUSING OVER  
THE SOUTHERN ROCKIES PERHAPS BACK INTO ARIZONA DEPENDING ON THE  
MODEL.  
 
RUBIN-OSTER  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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