131  
FXUS02 KWBC 232043  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
442 PM EDT TUE AUG 23 2022  
 
VALID 12Z FRI AUG 26 2022 - 12Z TUE AUG 30 2022  
   
..OVERVIEW
 
 
EXPECT TROUGHING ACROSS EASTERN NORTH AMERICA FRIDAY TO LIFT AWAY  
FOR THE WEEKEND, WHILE A COUPLE OF SHORTWAVES ENHANCE MEAN  
TROUGHING IN THE CENTRAL U.S. THAT SHIFTS TOWARD THE MIDWEST/GREAT  
LAKES BY MONDAY-TUESDAY OF NEXT WEEK. RIDGING IS FORECAST TO BUILD  
ACROSS THE INTERIOR WEST BEHIND THAT TROUGH AND AHEAD OF  
AMPLIFYING TROUGHING IN THE EASTERN PACIFIC. THE BRIEF PERIOD OF  
MORE PACIFIC INFLUENCE ON MEAN FLOW ALOFT OVER THE WEST INTO THE  
WEEKEND SHOULD LEAD TO A SOMEWHAT DRIER TREND OVER THE FOUR  
CORNERS STATES WHILE POTENTIALLY ADDING SOME MOISTURE TO AN  
EXPANDING AREA OF PLAINS INTO MISSISSIPPI VALLEY/GREAT LAKES  
RAINFALL AHEAD OF THE DEVELOPING CENTRAL U.S. MEAN TROUGH AND  
LEADING SURFACE SYSTEM. SOME AREAS OF RAINFALL SHOULD PERSIST OVER  
THE SOUTH AND NEARBY AREAS DURING THE PERIOD BUT WITH ANY HEAVY  
TOTALS TENDING TO BE FAIRLY LOCALIZED. ABOVE NORMAL TEMPERATURES  
WILL TEND TO BE CONFINED TO THE NORTHWEST (FRIDAY AND  
MONDAY-TUESDAY) AND NORTHEASTERN U.S. (SUNDAY-TUESDAY) WHILE NEAR  
OR SLIGHTLY BELOW NORMAL HIGHS SHOULD PREVAIL OVER THE ROCKIES  
INTO THE PLAINS AND SOUTHEAST.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
MODEL GUIDANCE REMAINS STABLE WITH THE LARGER SCALE TROUGH EXITING  
OUT OF THE EAST AS WELL AS WITH THE INITIAL SHORTWAVE TRACKING  
ACROSS THE NORTHERN PLAINS LATE THIS WEEK. BUT MODELS SHOW MORE  
VARIABILITY WITH A SECOND NOTABLE SHORTWAVE THAT FEEDS INTO THE  
DEVELOPING MEAN TROUGH AND TO SOME DEGREE THE LARGER SCALE  
PACIFIC/WESTERN NORTH AMERICA PATTERN EARLY NEXT WEEK. WHILE ITS  
TRACK AND TIMING ENTERING THE PACIFIC NORTHWEST LIKELY SATURDAY  
HAVE SHOWN BETTER AGREEMENT IN THE PAST FEW MODEL CYCLES, THERE  
ARE CONSIDERABLE DIFFERENCES IN TIMING AFTER THAT, AS WELL AS WITH  
ITS AMPLITUDE. 00/06Z GFS RUNS REMAINED ON THE STRONGER SIDE OF  
THE SPREAD WITH A COMPACT CLOSED LOW MOVING THROUGH THE  
NORTHWESTERN U.S. AROUND SUNDAY, WHILE THE CMC IS ALSO STRONG BUT  
SLOWER THAN CONSENSUS AND THE ECMWF (FOR THE 00Z AND INCOMING 12Z  
RUN) IS WEAKER AND MORE PROGRESSIVE. THE 12Z GFS IS STILL STRONGER  
THAN THE ECMWF BUT WEAKER THAN ITS PREVIOUS RUNS. THOUGH SOME  
DIFFERENCES ARE ON THE SMALL SCALE INITIALLY, THEY HAVE  
IMPLICATIONS FOR THE LARGER SCALE PATTERN DOWNSTREAM INTO  
MONDAY-TUESDAY. PREFERRED THE ENSEMBLE MEANS RATHER THAN ANY  
PARTICULAR MODEL AT THAT POINT GIVEN AMPLE DIFFERENCES, WITH THE  
GFS RUNS PERHAPS CLOSEST TO THE EC/GEFS ENSEMBLE MEANS. THE NEWER  
12Z GUIDANCE APPEARS AT LEAST TO CONVERGE SOMEWHAT WITH THE LARGER  
SCALE FLOW BY THE END OF THE PERIOD WITH MORE AGREEABLE RIDGE AND  
TROUGH AXES COMPARED TO THE PREVIOUS 00/06Z CYCLE THAT WAS  
AVAILABLE FOR THIS MEDIUM RANGE FORECAST.  
 
THUS THE WPC FORECAST BEGAN WITH A BLEND OF MAINLY DETERMINISTIC  
00/06Z MODELS, BUT A SMALL ENSEMBLE COMPONENT GIVEN THE GREATER  
THAN USUAL DETAIL SPREAD. QUICKLY INCREASED THE PROPORTION OF THE  
GEFS/EC ENSEMBLE MEANS IN THE BLEND TO OVER HALF BY DAY 6-7 AS THE  
DETERMINISTIC DIFFERENCES BECAME LARGER SCALE, WHICH LED TO GOOD  
CONSISTENCY WITH THE PREVIOUS FORECAST.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE BRIEF TRANSITION TO MORE PROGRESSIVE FLOW ALOFT OVER THE WEST  
DURING THE WEEKEND SHOULD PROMOTE A LIGHTER AND MORE SCATTERED  
TREND FOR MONSOON RAINFALL OVER THE FOUR CORNERS STATES AFTER  
FRIDAY. SOME OF THE WESTERN U.S. DEEP MOISTURE THAT IS PUSHED  
EASTWARD MAY CONTRIBUTE TO THE EXPANDING AREA OF RAINFALL FORECAST  
TO SPREAD ACROSS THE PLAINS AND EVENTUALLY INTO THE MISSISSIPPI  
VALLEY/GREAT LAKES. A LEADING WARM FRONT FOLLOWED BY A SURFACE  
TROUGH AND COLD FRONT, AS WELL AS NORTHERN TIER UPPER DYNAMICS,  
WILL ALL PROVIDE VARYING DEGREES OF FOCUS FOR WHAT COULD BE  
MULTIPLE AREAS OF LOCALLY MODERATE TO HEAVY RAINFALL WITHIN THE  
BROAD MOISTURE SHIELD. CURRENT FORECASTS SHOW ONE AREA OF RAINFALL  
FOCUS AROUND KANSAS-MISSOURI WHERE THE FRONT COULD MOVE A LITTLE  
MORE SLOWLY THAN THE MORE PROGRESSIVE NORTH PART OF THE FRONT, BUT  
IT WILL TAKE ADDITIONAL TIME TO RESOLVE WHERE THE MOST FAVORED  
AREAS FOR HIGHEST TOTALS WILL BE.  
 
SHOWERS/THUNDERSTORMS WILL LIKELY CONTINUE OVER THE SOUTH AND  
FLORIDA PENINSULA THROUGH THE PERIOD BUT WITH ANY AREAS OF  
ENHANCED TOTALS LIKELY TO BE MORE 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. A WEAKENING FRONT REACHING THE GULF/SOUTHEAST COASTS MAY  
STILL PROVIDE SOME FOCUS LATE THIS WEEK INTO THE FIRST PART OF THE  
WEEKEND. A COLD FRONT DROPPING SOUTHWARD THROUGH THE EAST FROM  
FRIDAY THROUGH THE WEEKEND MAY PRODUCE AREAS OF RAINFALL WITH  
VARYING INTENSITY. WAVINESS ALONG THE FRONT COULD ENHANCE TOTALS  
OVER NORTHERN NEW ENGLAND ON FRIDAY.  
 
THE PRIMARY AREAS OF ABOVE NORMAL TEMPERATURES DURING THE PERIOD  
WILL BE OVER THE NORTHWEST AS WELL AS THE NORTHEAST AND VICINITY.  
THE NORTHWEST WILL BE MODESTLY ABOVE NORMAL FRIDAY, FOLLOWED BY A  
COOLER WEEKEND AND THEN REBOUND TO PLUS 5-10F OR SO ANOMALIES NEXT  
MONDAY-TUESDAY AS THE UPPER RIDGE DEVELOPS AND STRENGTHENS.  
MEANWHILE PARTS OF THE NORTHEAST/NORTHERN MID-ATLANTIC WILL SEE  
MODERATELY ABOVE NORMAL READINGS ON FRIDAY. THEN A LARGER AREA OF  
WARM TEMPERATURES SHOULD SPREAD ACROSS THE GREAT LAKES THROUGH  
NORTHEAST/NORTHERN MID-ATLANTIC SUNDAY-TUESDAY. HIGHS COULD  
LOCALLY REACH 10-15F ABOVE NORMAL EARLY NEXT WEEK. NEAR TO  
SOMEWHAT BELOW NORMAL HIGH TEMPERATURES (SINGLE-DIGIT ANOMALIES)  
WILL PREVAIL ACROSS MUCH OF THE SOUTHERN TIER AND NORTH THROUGH  
THE ROCKIES AND PLAINS.  
 
TATE/RAUSCH  
 
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  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL/SOUTHERN PLAINS, THE  
MIDDLE MISSISSIPPI VALLEY, AND THE  
LOWER MISSISSIPPI VALLEY, SUN, AUG 28.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHERN  
PLAINS.  
 
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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