436  
FXUS02 KWBC 201847  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
247 PM EDT FRI MAY 20 2022  
 
VALID 12Z MON MAY 23 2022 - 12Z FRI MAY 27 2022  
 
...HEAVY RAINFALL/RUNOFF AND STRONG THUNDERSTORM THREAT FROM THE  
SOUTHERN PLAINS AND LOWER MISSISSIPPI/TENNESSEE VALLEYS TO THE  
OHIO VALLEY AND GREAT LAKES EARLY-MID NEXT WEEK...  
 
   
..WEATHER PATTERN OVERVIEW
 
 
A LEAD FRONT IS FORECAST TO PUSH ACROSS THE SOUTH AND EAST INTO  
MONDAY TO END THE PROTRACTED HEAT WAVE OVER THE SOUTH AND ALSO  
USHER IN A COOLER AND MORE COMFORTABLE AIRMASS OVER MUCH OF THE  
EASTERN U.S. AFTER A SWELTERING WEEKEND. MEANWHILE, A RATHER  
ACTIVE WEATHER PATTERN IS EXPECTED TO DEVELOP ACROSS THE  
CONTINENTAL U.S. GOING INTO NEXT WEEK, AS MULTIPLE WAVES OF LOW  
PRESSURE DEVELOP ALONG A RESURGENT FRONTAL BOUNDARY FROM THE  
PLAINS TO THE GREAT LAKES. THIS WILL BE IN RESPONSE TO A BUILDING  
UPPER LEVEL TROUGH OVER THE HIGH PLAINS AND THIS MAIN SYSTEM WILL  
SLOWLY MOVE EASTWARD THROUGH NEXT WEEK. THIS OFFERS A WIDESPREAD  
THREAT FOR HEAVY RAINFALL/CONVECTION AND LOCAL RUNOFF ISSUES AS  
MOISTURE AND INSTABILITY FOCUS AHEAD/OVER THE WELL ORGANIZED AND  
WAVY SYSTEM. THE EXPERIMENTAL WPC DAY 4/5 EXCESSIVE RAINFALL  
OUTLOOK HAS A "SLIGHT" RISK FROM THE SOUTHERN PLAINS TO THE LOWER  
MISSISSIPPI VALLEY, WITH ACTIVITY SPREADING UP THROUGH THE MIDWEST  
AND EVENTUALLY ACROSS THE EAST. MEANWHILE, A WARMING PATTERN OVER  
THE WEST BY EARLY-MID NEXT WEEK MAY BE PARTIALLY SUPPLANTED LATE  
WEEK AS PACIFIC UPPER TROUGHING WORKS A FRONT INLAND WITH MODEST  
PRECIPITATION ACROSS THE NORTHWEST IN AN OTHERWISE MAINLY DRY WEEK  
WEST OF THE ROCKIES.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
FORECAST SPREAD HAS DECREASED SIGNIFICANTLY WITH THE LATEST MODEL  
RUNS WHOSE MID-LARGER SCALE FLOW EVOLUTIONS ARE NOW MUCH BETTER  
CLUSTERED WITH THE ENSEMBLE MEANS DAYS 3-7. WHILE LOCAL CONVECTIVE  
RAINFALL FOCUS REMAINS MUCH LESS SETTLED THROUGH MEDIUM RANGE TIME  
SCALES, GUIDANCE OFFERS FAIRLY CONSISTENT AND UNIFORM REGIONAL  
AREAS OF THREAT. THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY  
DERIVED FROM A COMPOSITE BLEND OF THE 06 UTC GFS AND 00 UTC  
ECMWF/UKMET/CANADIAN AND THE 13 UTC NATIONAL BLEND OF MODELS (NBM)  
DAYS 3-5 (MONDAY-WEDNESDAY) BEFORE ENOUGH UNCERTAINTY IS  
INTRODUCED TO GRAVITATE MORE TOWARD THE 06 UTC GEFS MEAN AND 00  
UTC ECMWF ENSEMBLE MEAN ALONG WITH THE BEST MATCHED GFS/ECMWF AND  
NBM FOR BETTER LOCAL DETAIL CONSISTENT WITH PREDICTABILITY. THIS  
GENERAL PLAN MAINTAINS GOOD WPC PRODUCT CONTINUITY AND SEEMS IN  
LINE WITH LATEST OVERALL 12 UTC MODELS AND ENSEMBLES DESPITE LOCAL  
CONVECTIVE FOCUS DIFFERENCES ALONG WITH SOME LINGERING RUN TO RUN  
SYSTEM TIMING/AMPLITUDE DIFFERENCES.  
 
   
..SENSIBLE WEATHER/THREAT HIGHLIGHTS
 
 
TEMPERATURES BEHIND THE COLD FRONT EXITING THE EAST COAST NEXT  
WEEK SHOULD RETURN TO NEAR SEASONAL LEVELS AFTER A POTENTIALLY  
RECORD SETTING EARLY SEASON HEATWAVE. LOW PRESSURE FORMING ALONG  
THE TRAILING FRONT AS IT MEANDERS NEAR THE SOUTHEAST COAST MAY  
CONTINUE A MODERATE TO HEAVY RAINFALL THREAT INTO MONDAY AS WELL  
FOR THE SOUTHERN APPALACHIANS/MID-ATLANTIC AND SOUTHEAST.  
 
THE NEXT SYSTEM DEVELOPING OVER THE SOUTH-CENTRAL U.S. INTO  
EARLY-MID NEXT WEEK IS EXPECTED TO BECOME THE MAIN WEATHER  
HEADLINE OF THIS FORECAST PERIOD. THERE WILL LIKELY BE WIDESPREAD  
CONVECTION AND HEAVY RAINFALL FROM THE SOUTHERN PLAINS TO THE OHIO  
VALLEY WITH MOIST RETURN FLOW INTO ANOTHER SLOW MOVING AND WAVY  
FRONTAL SYSTEM. THERE IS THE POTENTIAL FOR FLASH FLOODING WITH THE  
SLOWER MOVING STORMS WITHIN A VERY MOIST AND UNSTABLE ATMOSPHERE.  
THE POTENTIAL EXISTS FOR ADDITIONAL HEAVY RAIN AS THE SYSTEM  
TRANSLATES EASTWARD INTO MID-LATER NEXT WEEK.  
 
THE WESTERN-CENTRAL U.S. TROUGH SHOULD KEEP TEMPERATURES BELOW  
NORMAL ACROSS ROCKIES AND PLAINS THROUGH AT LEAST TUESDAY. MUCH OF  
THE WESTERN U.S. SHOULD REMAIN MAINLY DRY THROUGH THE MIDDLE OF  
NEXT WEEK AS UPPER RIDGING BUILDS OVER THE REGION AND WARMER  
TEMPERATURES EXPAND ACROSS THE REGION, WITH THE EXCEPTION OF SOME  
SHOWERS ENTERING THE NORTHWEST INTO FRIDAY. THIS MAY LEAD TO AN  
EXCESSIVE HEAT EPISODE OVER INTERIOR CALIFORNIA AND THE DESERT  
SOUTHWEST NEXT WEEK, WITH LEAD TRANSIENT SYSTEM WARMING ACROSS THE  
INTERMOUNMTAIN WEST.  
 
SCHICHTEL/HAMRICK  
 
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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