436  
FXUS02 KWBC 191905  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
305 PM EDT FRI AUG 19 2022  
 
VALID 12Z MON AUG 22 2022 - 12Z FRI AUG 26 2022  
 
...SIGNIFICANT EXCESSIVE RAINFALL/FLASH FLOODING THREAT LIKELY TO  
SETTLE OVER THE SOUTHERN PLAINS/LOWER MISSISSIPPI VALLEY NEXT WEEK  
WHILE SOUTHWEST AND SOUTH-CENTRAL GREAT BASIN/ROCKIES MONSOONAL  
RAINFALL TRENDS LIGHTER...  
 
19Z UPDATE: THE 12Z DETERMINISTIC GUIDANCE HAS GOOD OVERALL  
AGREEMENT ON MASS FIELDS ACROSS THE CONTINENTAL U.S. FOR THE  
BEGINNING OF NEXT WEEK, WITH MESOSCALE DIFFERENCES WITH INDIVIDUAL  
SHORTWAVES BECOMING APPARENT AS EARLY AS TUESDAY. THE UKMET IS  
CONSIDERABLY MORE PROGRESSIVE WITH THE DISTURBANCE ACROSS THE  
SOUTH-CENTRAL U.S. AND THEREFORE ITS QPF IS WELL EAST OF THE MODEL  
CONSENSUS, WHICH IS MAINLY ACROSS CENTRAL TEXAS WHERE THE SLIGHT  
RISK FOR EXCESSIVE RAINFALL IS MAINTAINED FOR THE DAY 4 AND 5 TIME  
PERIODS. THE POTENTIAL FOR 4 TO 8 INCH TOTALS FROM THE ARKLATEX  
TO THE GREATER AUSTIN-SAN ANTONIO AREA ARE STILL EXPECTED THROUGH  
TUESDAY. THE ANTECEDENT DRY CONDITIONS MITIGATES THE POTENTIAL  
FOR FLOODING SOME, SO NO MODERATE RISK AREAS ARE WARRANTED AT THIS  
TIME. BY THE END OF THE FORECAST PERIOD, THE ECMWF BECOMES MORE  
PROGRESSIVE WITH THE TROUGH CROSSING THE NORTHERN ROCKIES AND  
NORTHERN PLAINS. THE WPC FORECAST WAS PRIMARILY DERIVED FROM A  
GFS/ECMWF/CMC CONSENSUS WITH A LITTLE OF THE UKMET (AWAY FROM  
TEXAS AND THE GULF COAST) AND PREVIOUS WPC CONTINUITY THROUGH  
TUESDAY NIGHT, AND THEN GRADUALLY INCREASING USE OF THE GEFS AND  
ECENS FOR THE END OF THE WEEK. THE PREVIOUS DISCUSSION FOLLOWS  
BELOW FOR REFERENCE. /HAMRICK  
 
   
..OVERVIEW
 
 
EXPECT MEAN TROUGHING OVER THE EAST TO TREND A BIT WEAKER BY THE  
LATTER HALF OF NEXT WEEK AS INITIAL ENERGY IN ITS CORE LIFTS  
NORTHEASTWARD, WHILE DEEPER TROUGHING PREVAILS OVER THE EASTERN  
HALF OF CANADA. OVER THE WEST, SOUTHERN AREAS SHOULD SEE MEAN  
RIDGING ALOFT FOR MOST OF THE PERIOD AS A TROUGH WITH EMBEDDED  
UPPER LOW TRACKS OVER THE NORTHWEST. THE HEAVIEST RAINFALL DURING  
THE PERIOD SHOULD BE OVER THE SOUTHERN PLAINS AND VICINITY AS  
ROCKIES/SOUTHERN TIER SHORTWAVE ENERGY INTERACTS WITH A STATIONARY  
FRONT. ONE OR MORE FRONTS ON THE LEADING SIDE OF THE EASTERN  
UPPER TROUGH WILL FOCUS SHOWERS/THUNDERSTORMS AT TIMES, AND THE  
COMBINATION OF UPPER TROUGH/LOW CROSSING THE NORTHWEST AND A FRONT  
SETTING UP OVER THE NORTHERN TIER MAY PRODUCE AREAS OF RAINFALL  
FROM THE NORTHERN ROCKIES EASTWARD. PERSISTENT CLOUDS AND  
RAINFALL WILL KEEP SOUTHERN TIER HIGH TEMPERATURES WELL BELOW  
NORMAL FOR MOST OF THE WEEK WHILE THE MAIN AREA OF ABOVE NORMAL  
HIGHS SHOULD BE OVER THE NORTHWEST MID-LATE WEEK.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
BASED ON GUIDANCE FROM THE 12Z/18Z CYCLES, A COMPOSITE OF  
OPERATIONAL MODEL RUNS PROVIDED A REASONABLE DEPICTION OF THE  
PATTERN EVOLUTION DURING THE FIRST HALF OF THE PERIOD AND ADDING  
IN SOME 18Z GEFS/12Z ECMWF MEANS WITH THE MODELS ACCOUNTED FOR  
DECREASING CONFIDENCE IN DETAIL SPECIFICS LATER IN THE PERIOD.  
THE RESULTING FORECAST OFFERED GOOD CONTINUITY, ESPECIALLY ALOFT.  
SHORTWAVE DETAILS FROM THE ROCKIES INTO THE SOUTHERN TIER HAVE  
LOWER THAN DESIRED PREDICTABILITY GIVEN THEIR MEDIUM TO SMALLER  
SCALE, BUT WILL BE VERY IMPORTANT FOR RESOLVING SPECIFICS OF THE  
POTENTIAL HEAVY RAINFALL OVER THE REGION. SOME DETAILS OF THE  
SHORTWAVE ENERGY CROSSING THE NORTHEAST BECOME SOMEWHAT MURKY  
AFTER EARLY TUESDAY. THERE HAS BEEN ONGOING TIMING SPREAD FOR THE  
NORTHWEST TROUGH/UPPER LOW, WITH THE GFS LEANING A BIT ON THE  
FASTER SIDE OF THE ENVELOPE. THE ECMWF HAS TRENDED MODERATELY  
FASTER OVER THE PAST COUPLE DAYS SO A MULTI-MODEL COMPROMISE SEEMS  
REASONABLE. ONE LAST ITEM OF NOTE IS THAT BY DAY 7 FRIDAY THE NEW  
00Z GFS DEVELOPS MUCH MORE UPPER TROUGHING OFFSHORE THE PACIFIC  
NORTHWEST THAN OTHER GUIDANCE INCLUDING THE GEFS MEAN.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE WIDESPREAD HEAVY TO EXTREME RAINFALL ACROSS THE SOUTHWEST AND  
SOUTH-CENTRAL GREAT BASIN/ROCKIES DURING THE SHORT RANGE PERIOD  
THROUGH THE WEEKEND SHOULD TREND LIGHTER FOR NEXT WEEK. LINGERING  
MOISTURE AND INSTABILITY OVER THE REGION COULD STILL ALLOW FOR  
SOME LOCALLY ENHANCED RAINFALL BUT OVERALL THE THREAT FOR  
EXCESSIVE RAINFALL WILL DECREASE. MEANWHILE THE FOCUS FOR  
SUBSTANTIAL HEAVY RAIN WILL SHIFT TO THE SOUTHERN PLAINS INTO THE  
LOWER MISSISSIPPI VALLEY FOR SEVERAL DAYS AS MOISTURE AND  
INSTABILITY PLUS MULTIPLE SHORTWAVE FEATURES ALOFT INTERACT WITH A  
WAVY STATIONARY SURFACE FRONT. HEAVIEST RAINFALL SHOULD ALIGN OVER  
TEXAS AND SOUTHERN OKLAHOMA, WITH MEANINGFUL TOTALS EXTENDING  
EASTWARD TO SOME DEGREE. WPC EXPERIMENTAL DAYS 4-5 OUTLOOKS  
HIGHLIGHT A SLIGHT RISK FOR EXCESSIVE RAINFALL OVER THIS AREA FROM  
MONDAY INTO EARLY WEDNESDAY. SOME ADJUSTMENTS IN THE RAINFALL  
FORECAST ARE LIKELY OVER COMING DAYS, GIVEN THE RELATIVELY LOW  
PREDICTABILITY OF IMPORTANT SMALL-SCALE FEATURES ALOFT AS WELL AS  
DEPENDENCE ON MESOSCALE CONVECTIVE ASPECTS THAT MAY NOT BECOME  
APPARENT UNTIL CLOSE TO THE EVENT.  
 
ELSEWHERE, RAINFALL MAY GRADUALLY EXPAND BETWEEN THE NORTHERN  
ROCKIES AND THE UPPER GREAT LAKES AS A FRONT SETTLES OVER THIS  
AREA. THE COMBINATION OF THE UPPER TROUGH/LOW CROSSING THE  
NORTHWEST AND POTENTIAL FOR LOW LEVEL UPSLOPE FLOW COULD ENHANCE  
RAINFALL OVER AND NEAR THE NORTHERN HIGH PLAINS. MEANWHILE ONE OR  
MORE WAVY FRONTS OVER THE EAST WILL HELP TO FOCUS EPISODES OF  
SHOWERS AND THUNDERSTORMS, SOME OF WHICH MAY BE LOCALLY HEAVY AND  
LEAD TO RUNOFF ISSUES. COVERAGE SHOULD BE GREATEST DURING THE  
FIRST HALF OF THE WEEK AS A DEFINED SHORTWAVE LIFTS FROM THE GREAT  
LAKES/OHIO VALLEY THROUGH THE NORTHEAST. DIURNAL CONVECTION  
SHOULD PERSIST OVER THE SOUTH THROUGH THE END OF THE WEEK.  
 
CLOUDS AND RAINFALL WILL LIKELY KEEP SOUTHERN TIER HIGH  
TEMPERATURES BELOW NORMAL THROUGH THE PERIOD, WITH SOME LOCATIONS  
SEEING ONE OR MORE DAYS WITH HIGHS 10-15F BELOW NORMAL ESPECIALLY  
DURING THE FIRST HALF OF THE WEEK. MODERATELY BELOW NORMAL HIGHS  
SHOULD SETTLE INTO NORTHERN PARTS OF THE PLAINS LATER IN THE WEEK  
AFTER THE REGION SEES ABOVE NORMAL READINGS ON MONDAY.  
TEMPERATURES OVER THE NORTHWEST SHOULD TREND WARMER MID-LATE WEEK  
AFTER THE UPPER TROUGH PASSES THROUGH, WITH HIGHS REACHING UP TO  
10-15F OR SO ABOVE NORMAL. A BROADER PORTION OF THE WEST WILL SEE  
ABOVE NORMAL LOWS THROUGH THE WEEK.  
 
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 LOWER MISSISSIPPI VALLEY AND  
THE SOUTHERN PLAINS, MON-THU, AUG  
22-AUG 25.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHERN  
PLAINS.  
- EXCESSIVE HEAT ACROSS PORTIONS OF CALIFORNIA, THE PACIFIC  
NORTHWEST, AND THE NORTHERN GREAT  
BASIN, THU-FRI, AUG 25-AUG 26.  
 
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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