685  
FXUS02 KWBC 060701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT FRI MAY 06 2022  
 
VALID 12Z MON MAY 09 2022 - 12Z FRI MAY 13 2022  
 
...BLOCKY PATTERN NEXT WEEK TO SUPPORT RECORD HEAT OVER THE  
SOUTHERN PLAINS/LOWER MISSISSIPPI VALLEY INTO THE MIDWEST ALONG  
WITH EPISODES OF NORTH-CENTRAL U.S. CONVECTION AND NORTHERN GREAT  
BASIN/ROCKIES SNOW...  
   
..OVERVIEW
 
 
THE FIRST PART OF THE WEEK WILL FEATURE A PATTERN CLOSE TO AN  
OMEGA-STYLE BLOCK, WITH AN AMPLIFIED WESTERN MEAN TROUGH, A STRONG  
RIDGE EXTENDING FROM MEXICO INTO SOUTHEASTERN CANADA, AND AN UPPER  
LOW JUST OFF THE EAST COAST. WITH TIME THE CENTRAL/SOUTHERN PART  
OF THE RIDGE SHOULD WEAKEN WHILE THE NORTHERN PART MAY ULTIMATELY  
CONNECT WITH A RETROGRADING ATLANTIC RIDGE THAT SHOULD PUSH THE  
UPPER LOW TOWARD THE SOUTHEAST COAST. WITHIN THE WESTERN TROUGH,  
A LEADING SHORTWAVE WILL EJECT FROM THE NORTHERN HIGH PLAINS AND  
THEN UPSTREAM ENERGY SHOULD SHARPEN INTO MIDWEEK BEFORE EJECTING  
NORTHEASTWARD (POSSIBLY LEADING TO STRONG LOW PRESSURE). ANOTHER  
SYSTEM MAY REACH THE NORTHWEST LATE IN THE WEEK. THIS PATTERN  
WILL LEAD TO VERY WARM TO HOT WEATHER OVER THE  
CENTRAL/EAST-CENTRAL U.S., CHILLY AND UNSETTLED WEATHER OVER THE  
WEST, AND PERIODS OF RAIN/THUNDERSTORMS BETWEEN THESE TWO REGIMES.  
THE RETROGRADING UPPER LOW MAY ALSO BRING SOME MOISTURE INTO THE  
EAST LATE IN THE WEEK.  
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
THE UPDATED FORECAST STARTED WITH A COMPOSITE OF 12Z/18Z  
OPERATIONAL MODELS FOR ABOUT THE FIRST HALF OF THE PERIOD AND THEN  
TRANSITIONED TO INCREASING WEIGHT OF 18Z GEFS/12Z ECMWF MEANS,  
REACHING 60 PERCENT TOTAL BY DAY 7 WITH REMAINING INPUT FROM THE  
12Z ECMWF AND SOMEWHAT LESS OF THE 18Z GFS. THE MOST SIGNIFICANT  
FORECAST UNCERTAINTY DURING THE PERIOD WILL INVOLVE DETAILS OF THE  
WESTERN U.S. MEAN TROUGH ALOFT, SPECIFICALLY HOW ENERGY THAT  
SHARPENS INTO MIDWEEK EJECTS OUT OF THE WEST IN RESPONSE TO AN  
UPSTREAM NORTHEASTERN PACIFIC SYSTEM THAT MAY CONTAIN A FAIRLY  
DEEP CLOSED LOW. THE 12Z CMC STRAYED MOST FROM CONSENSUS IN THAT  
IT HELD ITS NORTHEASTERN PACIFIC UPPER LOW FARTHER SOUTHWEST,  
LEADING TO FLATTER FLOW COMING INTO THE WEST AND IN TURN A  
FLATTER/FASTER SHORTWAVE EJECTING FROM THE WEST MID-LATE WEEK.  
THE NEW 00Z CMC HAS ADJUSTED CLOSER TO REMAINING GUIDANCE BUT  
STILL APPEARS TO HAVE ADDITIONAL TRENDING TO DO. REMAINING  
GUIDANCE FROM RECENT DAYS ALONG WITH LATEST ENSEMBLE MEMBERS  
SUGGEST A FAIR DEGREE OF UNCERTAINTY WITH SPECIFICS OF EACH  
FEATURE. 18Z/00Z GFS RUNS LEAN TO THE AMPLIFIED/SOUTHERN SIDE OF  
THE SPREAD FOR UPPER LOW REACHING THE WEST BY NEXT FRIDAY AND  
COULD BE A TAD FAST WITH THE EJECTING SHORTWAVE AHEAD OF IT, WHILE  
EITHER THE 12Z ECMWF OR 18Z/00Z GFS HANDLING OF THE INCOMING  
FEATURE COULD SUPPORT SLIGHTLY FASTER EJECTION THAN THE 12Z ECMWF.  
THE LATE-PERIOD MODEL/MEAN PREFERENCE PROVIDES A REASONABLE  
INTERMEDIATE SOLUTION FOR THE EJECTING SYSTEM AND TRENDED TO THE  
CONSERVATIVE SIDE IN DEPICTING THE INCOMING ENERGY BY DAY 7  
FRIDAY. HOWEVER THE NEW 00Z ECMWF HAS TRENDED SOMEWHAT SLOWER  
WITH EACH FEATURE, WIDENING THE SPREAD SOMEWHAT AND HIGHLIGHTING  
THE UNCERTAINTY WITH THIS OVERALL EVOLUTION. THE LATE-PERIOD  
MODEL/MEAN PREFERENCE PROVIDES A REASONABLE INTERMEDIATE SOLUTION  
FOR THE EJECTING SYSTEM AND TRENDED TO THE CONSERVATIVE SIDE IN  
DEPICTING THE INCOMING ENERGY BY DAY 7 FRIDAY. MEANWHILE AN  
AVERAGE OF LATEST GFS/ECMWF RUNS AND THEIR MEANS OFFERS THE MOST  
STABLE SOLUTION FOR THE UPPER LOW NEAR THE EAST COAST. OTHER  
MODELS DIFFER AT TIMES DUE TO DIFFERENCES IN HANDLING EMBEDDED  
IMPULSES.  
   
..WEATHER/THREAT HIGHLIGHTS
 
 
STRONG UPPER RIDGING WILL LEAD TO PERSISTENT MUCH ABOVE NORMAL  
TEMPERATURES OVER THE CENTRAL-SOUTHERN PLAINS AND MOST OF THE  
MISSISSIPPI VALLEY THROUGH THE WEEK, WITH SOME OF THIS WARMTH  
GRADUALLY EXPANDING THROUGH THE GREAT LAKES AND NORTHEAST AS WELL.  
EXPECT A BROAD AREA OF HIGHS/MORNING LOWS 10-20F ABOVE NORMAL  
WITH SOME LOCALIZED AREAS REACHING HIGHER THAN THAT. NUMEROUS  
DAILY RECORDS ARE LIKELY THROUGH THE WEEK OVER THE SOUTHERN PLAINS  
AND LOWER MISSISSIPPI VALLEY, AND MAY ALSO EXTEND INTO THE CENTRAL  
PLAINS/MIDWEST AROUND TUESDAY/WEDNESDAY. HIGHEST HEAT INDEX  
VALUES WILL BE OVER SOUTHERN TEXAS EARLY IN THE WEEK BUT THE  
COMBINATION OF HEAT AND HUMIDITY MAY STILL PRODUCE MAXIMUM HEAT  
INDEX VALUES OVER 100F AT SOME SOUTHERN LOCATIONS INTO LATE WEEK.  
 
IN CONTRAST, THE WEST WILL SEE UNSEASONABLY COOL AND UNSETTLED  
CONDITIONS NEXT WEEK. COLDEST ANOMALIES SHOULD BE EARLY IN THE  
WEEK WHEN HIGHS WILL LIKELY BE 10-20F OR SO BELOW NORMAL. BEST  
POTENTIAL FOR SOME DAILY RECORDS FOR COLD HIGHS WILL BE ON MONDAY.  
TEMPERATURES MAY APPROACH NORMAL OVER SOUTHERN AREAS BY NEXT  
FRIDAY BUT LOCATIONS FARTHER NORTH SHOULD REMAIN AT LEAST  
MODERATELY BELOW NORMAL. PERIODS OF RAIN AND HIGHER ELEVATION  
SNOW WILL TEND TO BE LIGHT TO MODERATE, BUT THERE COULD BE A  
PERIOD OF ENHANCED ACTIVITY ALONG AND INLAND FROM THE WEST COAST  
LATE IN THE WEEK DEPENDING ON DETAILS OF AN ARRIVING NORTHEASTERN  
PACIFIC SYSTEM.  
 
BETWEEN THESE TWO REGIMES, THE CENTRAL U.S. WILL SEE PERIODS OF  
RAIN AND THUNDERSTORMS AS EJECTING WESTERN SHORTWAVES PRODUCE  
MULTIPLE LOWS, ALONG WITH A ROCKIES TO UPPER MIDWEST FRONT THAT  
ULTIMATELY STALLS AND THEN LIFTS NORTHWARD AHEAD OF ANOTHER SYSTEM  
THAT BRINGS A COLD FRONT INTO THE PLAINS LATE IN THE WEEK.  
DECELERATION OF THE LEADING FRONT AND THEN THE LATE WEEK SYSTEM  
MAY PRODUCE AREAS OF SIGNIFICANT RAINFALL THAT WOULD BE A RUNOFF  
THREAT OVER NORTHERN TIER AREAS THAT ALREADY HAVE VERY WET SOIL.  
THE STORM PREDICTION CENTER HIGHLIGHTS A CONCERN FOR SEVERE  
WEATHER OVER PARTS OF THE NORTHEASTERN PLAINS/UPPER MIDWEST EARLY  
IN THE WEEK, WHILE THE LATE-WEEK SYSTEM COULD MERIT WATCHING FOR  
STRONG CONVECTION AS WELL.  
 
MOST RAINFALL WITH THE SYSTEM OFF THE EAST COAST SHOULD JUST  
OFFSHORE EARLY IN THE WEEK, BUT IS LIKELY TO EXPAND BACK TO THE  
WEST LATE IN THE WEEK AS THE VERTICALLY STACKED LOW RETROGRADES  
BACK TOWARD THE SOUTHEAST COAST.  
 
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  
 
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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