562  
FXUS02 KWBC 070654  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
253 AM EDT SUN AUG 07 2022  
 
VALID 12Z WED AUG 10 2022 - 12Z SUN AUG 14 2022  
 
...POTENTIALLY HEAVY RAINFALL AND FLASH FLOODING ARE POSSIBLE IN  
THE OHIO/TENNESSEE VALLEYS WEDNESDAY WHILE MONSOONAL MOISTURE  
CONTINUES IN THE WEST...  
 
   
..OVERVIEW
 
 
THE OVERALL WEATHER PATTERN ACROSS THE CONTIGUOUS U.S. THROUGH THE  
LATTER HALF OF THIS WEEK IS FORECAST TO AMPLIFY INTO A  
TROUGH-RIDGE-TROUGH PATTERN, AS SHORTWAVES COMBINE TO DEEPEN A  
TROUGH IN THE EAST, AN UPPER LOW OFF THE WEST COAST LIFTS  
NORTHEASTWARD TOWARD THE PACIFIC NORTHWEST, AND AN UPPER HIGH  
NUDGES EASTWARD FROM THE CENTRAL ROCKIES INTO THE CENTRAL/SOUTHERN  
PLAINS. MOISTURE LIFTED AHEAD OF THE EASTERN TROUGH AND ASSOCIATED  
COLD FRONT WILL LIKELY LEAD TO AREAS OF HEAVY RAIN AND  
THUNDERSTORMS MAINLY ACROSS THE OHIO AND TENNESSEE VALLEYS INTO  
THE MID-ATLANTIC AND NORTHEAST WEDNESDAY, WITH SCATTERED  
CONVECTION POSSIBLE FARTHER SOUTH AS WELL. MEANWHILE, PERSISTENT  
MONSOONAL MOISTURE LOOKS TO CONTINUE ACROSS PORTIONS OF THE WEST,  
LEADING TO ADDITIONAL RAINFALL WITH A GRADUAL NORTHWARD EXPANSION  
OF THE RAIN TOWARD THE NORTHERN ROCKIES AS THE WEEK PROGRESSES.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
RECENT MODEL GUIDANCE REMAINS QUITE AGREEABLE WITH THE UPPER  
HIGH/RIDGE PERSISTING AND MEANDERING A BIT ACROSS THE CENTRAL U.S.  
THROUGH THE WEEK INTO NEXT WEEKEND, AND ALSO AGREES UPON THE  
TROUGH DEEPENING ACROSS THE EAST LATE WEEK, WITH DETAIL  
DIFFERENCES WELL WITHIN NORMAL SPREAD FOR A MEDIUM RANGE FORECAST.  
THE BIGGEST MODEL DIFFERENCES CONTINUE TO BE RELATED TO THE UPPER  
LOW CENTERED JUST OFF THE WEST COAST, WHERE MODELS HAVE BEEN  
WAFFLING CONSIDERABLY WITH TRACK AND TIMING. IN TERMS OF THE  
12/18Z MODEL CYCLE THAT COULD BE UTILIZED FOR THE WPC FORECAST,  
THE ECMWF AND UKMET INDICATED A FASTER SOLUTION, TAKING THE  
LOW/TROUGH INLAND ACROSS THE PACIFIC NORTHWEST THURSDAY WHILE GFS  
RUNS SHOWED THE LOW SPINNING OFFSHORE AND EVENTUALLY MOVING INLAND  
BY THE WEEKEND. THE CMC APPEARED TO BE A MIDDLE GROUND SOLUTION IN  
BETWEEN THE TWO, THOUGH WITH LOW CONFIDENCE AS ENSEMBLE MEMBERS  
FROM THE EC/GEFS/CMCE SHOWED CONSIDERABLE SPREAD, SMOOTHING OUT  
THE ENSEMBLE MEANS. HOWEVER, NEWER 00Z GUIDANCE IS ALMOST  
UNIFORMLY PREFERRING A SLOW SOLUTION WITH THE UPPER LOW  
QUASI-STATIONARY CENTERED OFFSHORE THROUGH LATE WEEK, LIKE THE  
OLDER GFS RUNS AND ALSO LIKE AN EC RUN FROM A DAY OR SO AGO.  
HOPEFULLY THIS AGREEMENT PERSISTS THROUGH FUTURE MODEL CYCLES BUT  
GIVEN THE PAST BACK AND FORTH IN THE GUIDANCE, CONFIDENCE IS STILL  
SOMEWHAT LOW.  
 
THE WPC FORECAST WAS BASED ON A MULTI-MODEL BLEND EARLY ON, BUT  
WITH INCREASING WEIGHTS OF THE ENSEMBLE MEANS PERHAPS EARLIER THAN  
NORMAL IN THE MEDIUM RANGE PERIOD GIVEN THE DIFFERENCES ESPECIALLY  
WITH THE WESTERN LOW/TROUGH. IN GENERAL, CONTINUITY WITH THE  
PREVIOUS FORECAST WAS FAIRLY GOOD, BUT WITH SOME CHANGES TO  
FRONTAL TIMING DIFFERENCES IN THE NORTHWESTERN/NORTH-CENTRAL U.S.,  
WHICH WILL LIKELY HAVE TO BE EDITED IN FUTURE FORECASTS AS WELL.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
AS THE MEDIUM RANGE PERIOD BEGINS WEDNESDAY, AN AXIS OF LOCALLY  
HEAVY RAIN AND THUNDERSTORMS AHEAD OF A COLD FRONT IS EXPECTED TO  
CONTINUE PUSHING SOUTHEASTWARD ACROSS THE OHIO VALLEY TO NORTHEAST  
INTO THE TENNESSEE VALLEY AND MID-ATLANTIC REGION. THE RELATIVELY  
SLOW MOVEMENT OF THE FRONT COULD LEAD TO TRAINING STORMS THAT  
COULD CAUSE FLASH FLOODING. FLOODING CONCERNS ARE PARTICULARLY  
ENHANCED ACROSS PORTIONS OF KENTUCKY/TENNESSEE/WEST VIRGINIA, AS  
THEY HAVE RECEIVED ABUNDANT RAINFALL RECENTLY AND ARE SENSITIVE TO  
ADDITIONAL RAIN AMOUNTS, SO A SLIGHT RISK REMAINS IN THE  
EXPERIMENTAL DAY 4 ERO. THE NORTHEAST/NEW ENGLAND ALSO MAY RECEIVE  
HEAVY RAIN THAT COULD CAUSE FLASH FLOODING GIVEN A SHARPENING  
TROUGH ALOFT PROVIDING UPPER LEVEL SUPPORT AND ABOVE AVERAGE  
MOISTURE, BUT MODEL SPREAD IN THE EXACT PLACEMENT OF THE HEAVIEST  
RAINFALL PRECLUDED ADDING A SLIGHT RISK THERE AT THIS  
TIME--SPECIFICALLY WITH RECENT GFS RUNS SHOWING RAINFALL OFFSHORE  
INSTEAD. THE FRONT CONTINUING TO PUSH SOUTHEASTWARD INTO THE  
LATTER HALF OF THE WEEK SHOULD CLEAR RAINFALL OUT OF THE  
NORTHEASTERN QUADRANT OF THE COUNTRY, BUT SCATTERED CONVECTIVE  
ACTIVITY IS FORECAST TO CONTINUE IN THE SOUTHEAST. MEANWHILE,  
MONSOONAL MOISTURE (THAT COULD BE ENHANCED DUE TO T.D. NINE-E)  
CONTINUES TO IMPACT THE SOUTHWEST WITH RAINFALL, WITH A TREND  
TOWARD INCREASING CHANCES FOR RAIN FARTHER NORTH AS THE MOISTURE  
PLUME EXPANDS INTO THE INTERMOUNTAIN WEST/GREAT BASIN AND EASTWARD  
INTO THE NORTHERN/CENTRAL ROCKIES, WITH SOME LOCALLY HEAVY TOTALS  
POSSIBLE.  
 
VERY WARM TO HOT TEMPERATURES AROUND 10-15F ABOVE AVERAGE, THOUGH  
NOT QUITE TO RECORD-BREAKING LEVELS, ARE FORECAST ACROSS THE  
NORTHERN/CENTRAL PLAINS THROUGH THE LATTER PART OF THE WEEK, WITH  
A SLIGHT EASTWARD TREND AS THE UPPER HIGH MOVES THAT DIRECTION.  
FARTHER EAST, SLIGHTLY BELOW NORMAL HIGHS ARE POSSIBLE IN THE OHIO  
AND TENNESSEE VALLEYS BEHIND THE COLD FRONT, WHILE TEMPERATURES  
ALONG THE EASTERN SEABOARD WILL FLIP FROM SLIGHTLY ABOVE TO  
SLIGHTLY BELOW AVERAGE. GIVEN THE RAINFALL AND CLOUDINESS OVER THE  
SOUTHWEST AND GREAT BASIN, HIGHS ARE LIKELY TO BE SEVERAL DEGREES  
BELOW NORMAL THERE THROUGH NEXT WEEKEND.  
 
TATE  
 
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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