896  
FXUS02 KWBC 190706  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
306 AM EDT SUN MAY 19 2024  
 
VALID 12Z WED MAY 22 2024 - 12Z SUN MAY 26 2024  
 
   
..OVERVIEW
 
 
MULTIPLE PROGRESSIVE UPPER SHORTWAVES/POSSIBLE CLOSED LOWS AND  
SURFACE LOW PRESSURE/FRONTAL SYSTEMS WILL TRAVERSE THE WEST TO  
NORTHERN/CENTRAL PLAINS AND MIDWEST DURING THE MEDIUM RANGE PERIOD.  
BY WEDNESDAY, A POTENT SHORTWAVE AND DEEP SURFACE LOW WILL BE  
MOVING THROUGH THE UPPER MIDWEST WHILE ITS ATTENDANT COLD FRONT  
WILL PUSH ACROSS THE EAST AND PARTWAY INTO THE SOUTH BEYOND  
MIDWEEK, WITH RAIN AND STORMS ALONG AND AHEAD OF IT AND COOLER  
TEMPERATURES BEHIND. SOME RECURRING THREAT FOR HEAVY RAINFALL ALONG  
THE WESTERN SIDE OF THIS FRONT FROM PARTS OF TEXAS INTO THE LOWER  
MISSISSIPPI VALLEY AS THE BOUNDARY STALLS AND LIFTS BACK NORTH AS A  
WARM FRONT. FARTHER SOUTH, HEAT WILL CONTINUE TO BE HAZARDOUS FOR  
AT LEAST SOUTHERN TEXAS THOUGH. ANOTHER COUPLE ROUNDS OF ENERGY MAY  
PUSH THROUGH THE NORTHWEST AND EASTWARD LATE WEEK AND NEXT  
WEEKEND, BUT WITH MORE UNCERTAINTY.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODELS SHOW REASONABLE AGREEMENT WITH THE FIRST SHORTWAVE IN THE  
UPPER MIDWEST AT THE START OF THE PERIOD ON WEDNESDAY, ALTHOUGH THE  
PAST FEW RUNS OF THE GFS HAVE BEEN SLIGHTLY FASTER WITH THE SYSTEM  
AS IT MOVES INTO SOUTHEAST CANADA. STILL, A GENERAL MODEL BLEND  
SEEMS TO SERVE AS A GOOD STARTING POINT.  
 
THE NEXT UPPER LOW SHOULD ARRIVE INTO THE NORTHWEST BY WEDNESDAY  
AS WELL WITH PLENTY OF LINGERING UNCERTAINTY LATE WEEK AS IT MOVES  
INTO THE UPPER MIDWEST. MODELS CONTINUE TO STRUGGLE WITH ITS  
EVOLUTION AND POSSIBLE COMBINATION OF ENERGY WITH ANOTHER SHORTWAVE  
ACROSS CENTRAL CANADA AT THE SAME TIME. THE GFS AND ECMWF (AND NOW  
THE NEW 00Z CMC) SHOW CONSOLIDATION OF THIS ENERGY INTO ONE BIG  
LOW OVER SOUTH-CENTRAL CANADA NEXT SATURDAY. HOWEVER, THE ECMWF-  
INITIALIZED ML MODELS SHOW MORE SUPPORT FOR STREAM SEPARATION. SO  
LOTS OF QUESTIONS ON THE EVOLUTION AND THE ENSEMBLE MEANS ARE VERY  
WASHED OUT WITH THIS ENERGY.  
 
THE WPC FORECAST FOR TONIGHT USED A BLEND OF THE DETERMINISTIC  
SOLUTIONS THE FIRST HALF OF THE PERIOD AMIDST BETTER AGREEMENT. BY  
LATE WEEK AND ESPECIALLY NEXT WEEKEND, CONTINUED TO MAINTAIN MORE  
OF THE DETERMINISTIC SOLUTIONS THAN USUAL ALONG WITH THE ENSEMBLE  
MEANS TO HELP SMOOTH OUT THE DETAIL DIFFERENCES BUT STILL MAINTAIN  
SYSTEM DEFINITION. THIS LATE PERIOD BLEND ALSO SERVES WELL FOR YET  
ANOTHER UPPER LOW THAT DROPS INTO THE NORTHWEST NEXT SATURDAY.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE COLD FRONT ASSOCIATED WITH A DEEP SURFACE LOW IN PLACE ACROSS  
THE UPPER MIDWEST ON WEDNESDAY WILL BE THE MAIN FOCUS FOR SHOWERS  
AND THUNDERSTORMS FROM THE SOUTHERN PLAINS INTO THE OHIO VALLEY ON  
WEDNESDAY. THE DAY 4/WEDNESDAY ERO SHOWS A BROAD AND ELONGATED  
MARGINAL RISK STRETCHING FROM THE SOUTHERN PLAINS TO THE OHIO  
VALLEY. THERE IS AN EMBEDDED SLIGHT RISK FROM NORTHEAST TEXAS INTO  
THE LOWER OHIO VALLEY AS THE WESTERN PORTION OF THE BOUNDARY STALLS  
AND EVENTUALLY BEGINS TO LIFT NORTH AS A WARM FRONT. THIS WILL  
CONTINUE THE HEAVY RAINFALL THREAT INTO THURSDAY AS WELL ACROSS  
PARTS OF THE SOUTHERN PLAINS TO LOWER MISSISSIPPI VALLEY - A REGION  
THAT HAS BEEN VERY LATE AS OF LATE. GIVEN THE OVERLAP TOO WITH DAY  
4, A SLIGHT RISK WAS INTRODUCED FROM NORTHEAST TEXAS INTO  
SOUTHEAST OKLAHOMA AND CENTRAL ARKANSAS WITH A BROADER MARGINAL  
RISK SURROUNDING. APPROACH/ARRIVAL OF ANOTHER COUPLE OF SYSTEMS AS  
CURRENTLY ADVERTISED INTO THE NORTHWEST BY MIDWEEK AND NEXT WEEKEND  
WOULD PRODUCE SOMEWHAT MORE ORGANIZED PRECIPITATION THERE, AND  
POTENTIAL FOR HEAVY SNOW IN THE MOUNTAINS, WITH SNOW LEVELS  
DEPENDENT ON THE DEPTH OF THE UPPER LOW(S).  
 
EXPECT SOUTH TEXAS TO SEE MULTIPLE DAYS OF HAZARDOUS HEAT DURING  
THE PERIOD WITH HIGHS PERSISTENTLY RUNNING 10-15F ABOVE NORMAL WITH  
MAX HEAT INDEX VALUES POSSIBLY REACHING AT LEAST 110F. HIGHS NEAR  
100 DEGREES COULD STRETCH FARTHER NORTH ACROSS THE SOUTHERN HIGH  
PLAINS AT TIMES AS WELL. SOME DAILY RECORDS FOR HIGHS/WARM LOWS  
WILL BE POSSIBLE. ABOVE NORMAL HIGHS WILL ALSO TRACK EAST INTO THE  
NORTHEAST/MID-ATLANTIC WEDNESDAY-THURSDAY BUT SHOULD MODERATE  
THEREAFTER AS THE COLD FRONT PUSHES THROUGH THE REGION. THE  
FORECAST PATTERN WILL FAVOR BELOW AVERAGE HIGHS OVER THE NORTHWEST  
TO NORTHERN PLAINS FOR MOST OF NEXT WEEK.  
 
SANTORELLI  
 
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 FORECAST (QPF), EXCESSIVE RAINFALL  
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT  
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:  
 
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  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW  
 

 
 
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