433  
FXUS02 KWBC 252008  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
407 PM EDT THU AUG 25 2022  
 
VALID 12Z SUN AUG 28 2022 - 12Z THU SEP 01 2022  
   
..OVERVIEW
 
 
MOST GUIDANCE CONTINUES TO SUGGEST A TRANSITION FROM FAIRLY FLAT  
MEAN FLOW ALOFT ON SUNDAY TO AN AMPLIFIED REGIME CONSISTING OF AN  
EASTERN PACIFIC TROUGH, WESTERN NORTH AMERICAN RIDGE, AND EASTERN  
CANADA/NORTHEASTERN U.S. TROUGH BY NEXT TUESDAY-THURSDAY. THE  
DETAILS DURING THIS TRANSITION ARE A LITTLE LESS CLEAR, WITH A  
SHIFT TOWARDS A MORE PROGRESSIVE, IN PHASE SHORTWAVE TROUGH MOVING  
THROUGH THE WESTERN CONUS BEFORE THE NOTED FURTHER AMPLIFICATION  
TO THE EAST LATER IN THE PERIOD. THE PRIMARY AREAS OF FOCUS FOR  
RAINFALL DURING THE PERIOD WILL BE WITH A COLD FRONT THAT PUSHES  
FROM THE NORTHERN ROCKIES/PLAINS INTO THE EAST/SOUTH MONDAY INTO  
TUESDAY AS WELL AS WITH DIURNALLY FAVORED SHOWERS AND STORMS ALONG  
THE GULF. WARMEST TEMPERATURE ANOMALIES ARE FORECAST OVER THE  
NORTHWEST TUESDAY-THURSDAY AS THE RIDGE OVER THE WEST AMPLIFIES.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE FORECAST OF THE SHORTWAVE TROUGH REACHING THE NORTHWEST AT THE  
START OF THE PERIOD CONTINUES TO BE ONE OF LOWER  
CONFIDENCE/PREDICTABILITY. THE 00Z/06Z MODEL GUIDANCE WAS MUCH  
MORE PROGRESSIVE WITH A MORE COMPACT/IN PHASE SHORTWAVE TROUGH  
MOVING FROM THE NORTHWEST AND OVER THE NORTHERN PLAINS BY MONDAY  
COMPARED TO PREVIOUS FORECASTS. THE MEAN GUIDANCE WAS A BIT DEEPER  
AND FURTHER WEST OVER THE PACIFIC COAST THAN THE DETERMINISTIC  
MODELS, BUT ALL OF THE 00Z/06Z GUIDANCE WAS IN AGREEMENT WITH THE  
MORE PROGRESSIVE MOVEMENT. FORTUNATELY THE NEWER 12Z GUIDANCE  
MAINTAINED THIS FASTER TREND. A CLOSED CUTOFF LOW DEVELOPED IN THE  
00Z GEFS MEAN OVER NORTHERN CALIFORNIA COMPARED TO THE OTHER  
GUIDANCE, AND THUS THE INITIAL WPC FORECAST FOR SUNDAY/MONDAY  
FEATURED A GENERAL MODEL BLEND OF THE DETERMINISTIC GUIDANCE AND  
ECMWF MEAN.  
 
MOST OF THE FORECAST GUIDANCE SHOWS AN AMPLIFICATION OF THE  
PATTERN LATER INTO THE PERIOD, WITH A TROUGH DEEPENING OVER  
EASTERN CANADA/NORTHEASTERN U.S. AND A RIDGE AMPLIFYING OVER THE  
WEST. SMALL SCALE DIFFERENCES IN A POTENTIALLY DEEPER, EMBEDDED  
TROUGH AXIS OVER THE CENTRAL U.S. INDICATED MOST SIGNIFICANTLY IN  
THE DETERMINISTIC CMC LED TO A TREND AWAY FROM THE CMC AND FURTHER  
EMPHASIS ON THE ENSEMBLE MEANS LATER IN THE PERIOD. THE 06Z GFS  
WAS A NOTABLE OUTLIER DURING THE FORECAST PERIOD, WITH A CLOSED,  
CUTOFF LOW DEVELOPING OVER THE SOUTH CENTRAL U.S. TOWARDS THE END  
OF THE PERIOD, SO IT WAS NOT INCLUDED IN THE WPC FORECAST BLEND,  
FAVORING THE DETERMINISTIC 00Z GFS/ECMWF/CMC AND ECMWF MEAN/GEFS  
MEAN. HOWEVER, WHILE THE ECMWF CONTINUES TO SHOW MORE BROAD  
AMPLIFICATION OF THE RIDGE OVER THE WEST/CENTRAL U.S., THE NEWER  
12Z CMC AND GFS HAVE A SIMILAR SOLUTION TO THE 06Z GFS, AND THIS  
TREND WILL NEED TO BE MONITORED.  
 
FINALLY, THERE CONTINUED TO BE SOME INDICATION OF A SUBTLE  
SHORTWAVE MOVING THROUGH THE WEST AT THE END OF THE PERIOD  
INDICATED BY THE 00Z GFS/GEFS MEAN. GIVEN THE TREND AWAY FROM THIS  
SOLUTION FROM THE PRIOR 12Z GUIDANCE AND THE LACK OF A SHORTWAVE  
INDICATED BY THE ECMWF/CMC, OPTED TO STICK TOWARDS A SOLUTION  
WITHOUT THIS SCENARIO FOR NOW. A FLATTENING OF THE RIDGE WOULD  
HAVE AN IMPACT ON THE NOTABLE WARM TEMPERATURE ANOMALIES OVER THE  
NORTHWEST LATE IN THE PERIOD.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE BRIEF PERIOD OF MORE PROGRESSIVE FLOW ALOFT OVER THE WEST  
THROUGH THE WEEKEND WILL LEAD TO MUCH LIGHTER AND ISOLATED MONSOON  
SHOWERS OVER THE SOUTHWEST/FOUR CORNERS STATES INTO THE  
INTERMOUNTAIN WEST. SOME OF THE WESTERN U.S. DEEP MOISTURE THAT IS  
PUSHED EASTWARD MAY CONTRIBUTE TO THE AREA OF RAINFALL FORECAST TO  
SPREAD ACROSS PORTIONS OF THE CENTRAL/EASTERN U.S. AHEAD OF A HIGH  
PLAINS SURFACE TROUGH AND COLD FRONT PROGRESSING SOUTHEASTWARD  
FROM THE NORTHERN TIER. THERE MAY BE MULTIPLE AREAS OF LOCALLY  
MODERATE TO HEAVY RAINFALL WITHIN THE BROAD MOISTURE SHIELD BUT  
WITH LOWER THAN AVERAGE CONFIDENCE IN SPECIFICS. ONE POTENTIAL  
AREA OF FOCUS COULD BE OVER AND JUST EAST OF THE  
CENTRAL/SOUTH-CENTRAL PLAINS WHERE THE COLD FRONT COULD INTERACT  
WITH SOME GULF MOISTURE ON MONDAY. A SLIGHT RISK WAS CONSIDERED  
FOR THE EXPERIMENTAL DAY 5 ERO, BUT THERE WAS ENOUGH OF A SPATIAL  
DIFFERENCE BETWEEN THE HEAVIEST TOTALS AMONGST THE GUIDANCE TO  
HOLD OFF FOR NOW. FARTHER EAST, SHOWERS/THUNDERSTORMS WILL LIKELY  
CONTINUE OVER THE SOUTH AND FLORIDA PENINSULA THROUGH THE PERIOD  
BUT WITH ANY AREAS OF ENHANCED TOTALS LIKELY TO BE FAIRLY  
LOCALIZED AND UNCERTAIN ON A DAY-TO-DAY BASIS, INCLUDING SOME  
MODEL VARIABILITY WITH WHETHER THE BULK OF RAINFALL WILL BE  
OFFSHORE OR ONSHORE IN ANY GIVEN PERIOD.  
 
THE WARMEST TEMPERATURE ANOMALIES DURING THE PERIOD SHOULD BE OVER  
PARTS OF THE NORTHWEST DURING TUESDAY-THURSDAY AS MEAN RIDGING  
ALOFT BUILDS OVER THE WEST, WITH SOME LOCATIONS 10-15F ABOVE  
NORMAL, AND A SHIFT TOWARDS THE NORTHERN HIGH PLAINS BY THURSDAY.  
A FEW PLACES COULD CHALLENGE DAILY RECORDS FOR HIGHS/WARM LOWS.  
THERE IS STILL A LITTLE UNCERTAINTY DUE TO A POTENTIAL EMBEDDED  
SHORTWAVE/LOW BUT THE LATEST GUIDANCE HAS TRENDED AWAY FROM THIS  
SOLUTION. EXPECT HIGHS OF 5-10F ABOVE NORMAL FROM THE NORTHERN  
PLAINS INTO THE NORTHEAST EARLY IN THE WEEK FOLLOWED BY A COOLER  
TREND AFTER FRONTAL PASSAGE. CALIFORNIA MAY ALSO TREND A LITTLE  
ABOVE NORMAL BY MIDWEEK.  
 
PUTNAM/RAUSCH  
 
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE  
MISSISSIPPI VALLEY, THE LOWER  
MISSISSIPPI VALLEY, AND THE SOUTHERN PLAINS, MON-TUE, AUG 29-AUG  
30.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE LOWER  
MISSISSIPPI VALLEY AND THE SOUTHERN  
PLAINS.  
 
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL  
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE  
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/#PAGE=ERO  
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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