105  
FXUS02 KWBC 172020  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
420 PM EDT WED AUG 17 2022  
 
VALID 12Z SAT AUG 20 2022 - 12Z WED AUG 24 2022  
 
...SIGNIFICANT MONSOONAL EXCESSIVE RAINFALL THREAT FOR THE  
SOUTHWEST AND SOUTH-CENTRAL GREAT BASIN/ROCKIES INTO THE WEEKEND  
MAY RELAX EARLY NEXT WEEK AS HAZARD FOCUS SHIFTS TO THE SOUTHERN  
PLAINS THEN LOWER MISSISSIPPI/TENNESSEE VALLEYS...  
...EXCESSIVE HEAT THREAT TO PERSIST FOR INTERIOR PORTIONS OF  
CALIFORNIA/NORTHWEST U.S. INTO THE WEEKEND...  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
CONFIDENCE IS ABOVE AVERAGE FOR A MULTI-DAY HEAVY RAIN EVENT THAT  
SPREADS FROM THE SOUTHWEST INTO THE SOUTHERN PLAINS THAT WILL  
RESULT IN SCATTERED TO WIDESPREAD AREAS WITH THREATS FOR FLASH  
FLOODING GIVEN NEAR SOIL SATURATION CONDITIONS IN THE SHORT-TERM  
PERIOD, HEAVY RAIN OVER REPEATED LOCATIONS PRIOR TO, AND INTO THE  
BEGINNING OF THE EXTENDED PERIODS ACROSS THE SOUTHWEST, BEFORE  
SHIFTING EASTWARD. A MAJORITY OF THE GUIDANCE SHOW 7 DAY AREAL  
AVERAGES OF 3 TO 7 INCHES; WITH ISOLATED MAXES POSSIBLY CLIMBING  
INTO THE UPPER SINGLES/LOWER DOUBLE DIGITS OVER THE COURSE OF THE  
WEEK. OVERALL, THE LATEST MODELS CONTINUE TO HANDLE THE MID-LARGER  
SCALE FEATURES WELL. THE GFS/UKMET ARE TRENDING ON THE  
FASTER/EASTERN EDGE OF THE CLUSTER WHICH WOULD SUPPORT QPF  
INCREASES A LITTLE FURTHER SOUTH/EAST THAN THE PREVIOUS FORECAST.  
THE ECWMF/CMC ARE STILL WITHIN THE CLUSTER BUT ARE FAVORING A  
SLIGHTLY SLOWER/WESTERN POSITION WITHIN THE CLUSTER. THE SMALL  
NUISANCES WILL LIKELY AFFECT THE EXACT LOCATIONS OF THE MAXIMUM  
QPF OVER THE SOUTHWEST AND AS IT TRANSLATES EASTWARD INTO THE  
SOUTHERN HIGH PLAINS, BOTH CAMPS HAVE AN AXIS WITH AMOUNTS OF 2 TO  
5+ INCHES. THE  
THE PREFERRED WPC BLEND USED A COMPOSITE OF  
GFS/ECMWF/UKMET/CANADIAN INITIALLY WITH SLIGHTLY MORE EMPHASIS ON  
THE GFS AND GEFS/ECMWF ENSEMBLES ALONG WITH THE NATIONAL BLEND OF  
MODELS.  
   
..PATTERN OVERVIEW AND WEATHER/HAZARDS HIGHLIGHTS
 
 
STRONG, DIURNALLY DRIVEN THUNDERSTORMS WILL CONTINUE TO OVERSPREAD  
THE SOUTHWEST, THE GREAT BASIN AND SOUTHERN ROCKIES THANKS TO  
MULTIPLE MID/UPPER-LEVEL IMPULSES AND OVER-ABUNDANT, POOLED  
MONSOONAL MOISTURE AND INFLUX OF PACIFIC MOISTURE INTO THE REGION.  
LOCAL DOWNPOURS ARE EXPECTED AND AT TIMES, OVER VERY SENSITIVE  
AREAS SUCH AS URBAN AREAS AND SLOT CANYONS, THAT WILL LIKELY  
RESULT IN RAPIDLY CHANGING AND VERY DANGEROUS SITUATIONS AS WATER  
RUSHES OFF. WPC HAS HOISTED AN EXPERIMENTAL DAY 4 MODERATE RISK  
(LEVEL 3/4) FOR PORTIONS OF SOUTHEAST ARIZONA AND SOUTHWEST NEW  
MEXICO AND EXPANDED THE SLIGHT RISK ACROSS CENTRAL AND EASTERN NEW  
MEXICO. SOME LOCATIONS ACROSS SOUTHERN ARIZONA AND NEW MEXICO  
COULD SURPASS 25-YEAR ARI. THE MONSOONAL PATTERN MAY RELAX EARLY  
NEXT WEEK. MEANWHILE, NHC ALSO INDICATES THAT ANOTHER TROPICAL  
WAVE MAY REACH NORTHEAST MEXICO AND SOUTHERN TEXAS OVER THE  
WEEKEND THAT COULD FOCUS LOCAL MOISTURE AND RAINFALL POTENTIAL.  
 
THE HEAVY RAIN AND FLOODING THREAT WILL SHIFT TO THE SOUTHERN  
PLAINS, LOWER MISSISSIPPI RIVER AND INTO THE WESTERN REACH OF THE  
TENNESSEE VALLEY FOR THE UPCOMING WEEK. THE THREAT SEEMS  
FORMIDABLE AS MOISTURE AND INSTABILITY POOL WITH RETURN FLOW INTO  
SLOW MOVING/WAVY FRONTS IN FAVORABLE UPPER FLOW AS UPPER TROUGH  
ENERGIES EJECT OUT FROM THE WEST. MODELS ARE SUGGESTING A STRONG  
SIGNAL FOR REPEAT/TRAINING OF CELLS AND HAVE SHIFTED THE QPF AXIS  
A LITTLE SOUTH FROM THE PREVIOUS RUN. WPC HAS AN EXPERIMENTAL DAY  
5 SLIGHT RISK FOR EXCESSIVE RAINFALL SPANNING FROM EASTERN NEW  
MEXICO TO ARKANSAS.  
 
SHOWERS AND THUNDERSTORMS ARE EXPECTED TO PERSIST INTO THE WEEKEND  
ALONG A SLOW-MOVING, WAVY FRONTAL BOUNDARY OVER THE SOUTH AND  
SOUTHEAST. THERE MAY BE LOCAL AREAS THAT HAVE HEAVY DOWNPOURS  
THANKS FOR VERY MOIST AIR POOLED OVER THE REGION. ORGANIZED RAINS  
WILL ALSO SLOWLY LIFT TO THE MID-ATLANTIC OVER THE WEEKEND WITH  
THE WAVY FRONT SLATED TO LIFT SLOWLY NORTHWARD. FARTHER NORTH,  
CONVECTION WILL GRADUALLY SPREAD ACROSS THE MIDWEST THIS  
WEEKEND/EARLY NEXT WEEK AS DIGGING SHORTWAVE ENERGY FORMS A CLOSED  
LOW. SLOW CELL MOTIONS AND INSTABILITY NEAR THE CLOSED FEATURE  
OFFER POTENTIAL FOR LOCAL DOWNPOURS WITH RUNOFF ISSUES.  
 
THE HEATWAVE OVER THE PACIFIC NORTHWEST WILL DRAG ON THROUGH THE  
WEEKEND, WITH DAILY HIGHS RANGING FROM THE MID 90S TO 100S AND  
OVERNIGHT LOWS IN THE 50S AND 60S. A VAST AREA OF FROM  
WASHINGTON/WESTERN AND SOUTHERN IDAHO TO CENTRAL/SOUTH-CENTRAL  
CALIFORNIA ALREADY HAVE HEAT ADVISORIES AND EXCESSIVE HEAT  
WARNINGS IN EFFECT THROUGH FRIDAY. THESE TEMPERATURES ARE LIKELY  
TO PRODUCE SOME RECORD VALUES, MOSTLY FOR OVERNIGHT TEMPERATURES.  
TEMPERATURES SHOULD BEGIN TO RELAX SOMEWHAT THROUGH THE WEEKEND  
AND INTO EARLY NEXT WEEK AS THE RIDGE WEAKENS. IN CONTRAST, BELOW  
NORMAL HIGHS ARE FORECAST ACROSS PARTS OF EAST-CENTRAL U.S. IN THE  
WAKE OF A WAVY FRONT. GIVEN THE CLOUD COVER AND RAINFALL OVER THE  
DESERT SOUTHWEST AND ACROSS THE SOUTHERN PORTIONS OF THE GREAT  
BASIN AND ROCKIES, DAILY TEMPERATURE READINGS NEAR OR BELOW NORMAL  
ARE EXPECTED.  
 
CAMPBELL  
 
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/LOWER MISSISSIPPI VALLEY,  
AND THE TENNESSEE/OHIO VALLEY, SUN-TUE, AUG 21-AUG 23.  
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN ROCKIES/PLAINS, AND  
THE SOUTHWEST, SAT, AUG 20.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHERN  
PLAINS.  
- FLOODING LIKELY ACROSS PORTIONS OF THE SOUTHERN PLAINS.  
- EXCESSIVE HEAT ACROSS PORTIONS OF THE PACIFIC NORTHWEST, THE  
NORTHERN ROCKIES, AND THE NORTHERN  
GREAT BASIN, SAT, AUG 20.  
- HEAVY RAIN ACROSS PORTIONS OF MAINLAND ALASKA, SAT-MON, AUG  
20-AUG 22.  
 
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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