983  
FXUS02 KWBC 180712  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
311 AM EDT WED MAY 18 2022  
 
VALID 12Z SAT MAY 21 2022 - 12Z WED MAY 25 2022  
   
..RECORD HEAT IN PARTS OF THE EAST ON SATURDAY
 
 
...HEAVY RAINFALL AND SEVERE WEATHER THREAT TO FOCUS OVER THE  
EAST-CENTRAL U.S. THIS WEEKEND...  
 
   
..OVERVIEW
 
 
A RATHER AMPLIFIED PATTERN WILL BE IN PLACE BY THE START OF THE  
MEDIUM RANGE PERIOD WITH A DIGGING TROUGH OVER THE  
WEST/NORTH-CENTRAL U.S. AND STRONG RIDGING IN THE EAST. THIS  
YIELDS COOLER TEMPERATURES ACROSS THE ROCKIES AND CENTRAL U.S. AND  
RECORD HEAT IN THE EAST INTO THE WEEKEND. A STRONG COLD FRONT  
ACROSS THE MIDWEST AND EAST THIS WEEKEND WILL RESULT IN INCREASED  
CHANCES FOR HEAVY RAINFALL AND SEVERE WEATHER ALONG AND AHEAD OF  
IT. A NORTHWARD SURGE OF TROPICAL MOISTURE WILL ALSO INCREASE  
RAIN/THUNDERSTORM CHANCES ACROSS FLORIDA THIS WEEKEND AS WELL. BY  
SUNDAY INTO MONDAY, ANOTHER SHORTWAVE SHOULD ENTER THE WEST COAST  
WITH VERY UNCERTAIN DETAILS AS IT PUSHES EAST AND ALSO WITH  
ADDITIONAL ENERGY UPSTREAM AROUND NEXT WEDNESDAY.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
THE MODELS ARE SHOWING INCREASING AGREEMENT ON THE SHORTWAVE INTO  
THE UPPER MISSISSIPPI VALLEY ON SATURDAY AND AMPLIFIED TROUGHING  
TRACKING INTO THE EAST ON SUNDAY. A GENERAL MODEL BLEND SEEMS TO  
HANDLE THIS FINE. AS EARLY AS SUNDAY-MONDAY HOWEVER, DETAILS  
REGARDING FLOW OVER THE WEST BECOME HIGHLY UNCERTAIN. MODELS AGREE  
THE NEXT SHORTWAVE SHOULD CROSS THROUGH THE NORTHWEST ON SUNDAY,  
BUT THE ECMWF/ECENS MEAN CONTINUE TO BE QUITE A BIT WEAKER AND  
FASTER COMPARED THE GFS AND CMC WHICH FAVOR AMPLIFICATION OF THE  
SHORTWAVE OVER THE WEST AND THUS A MUCH SLOWER PROGRESSION (AND  
CONSEQUENTLY A BETTER TAPPING OF GULF MOISTURE AND PRECIP ACROSS  
THE CENTRAL U.S. EARLY NEXT WEEK). THIS ALL SEEMS TO STEM FROM  
DIFFERENCES IN HOW QUICKLY ENERGY FROM THE NORTH PACIFIC MOVES  
INTO WESTERN NORTH AMERICA. THE ECMWF IS MUCH FASTER TO BREAK DOWN  
THE EAST PACIFIC RIDGE WHICH ALLOWS THE ENERGY TO SLIDE INLAND,  
WHILE THE GFS TENDS TO MAINTAIN A MORE BLOCKY RIDGE ALLOWING FOR  
MORE AMPLIFICATION DOWNSTREAM ACROSS THE WEST. THE ENSEMBLE MEANS  
THEMSELVES SEEM TO AGREE WITH THEIR DETERMINISTIC COUNTERPARTS,  
WITH DETERMINISTIC MODELS ALSO SHOWING PLENTY OF RUN TO RUN  
DISCONTINUITIES. GIVEN THE UNCERTAINTY, THE WPC FORECAST FOR  
TONIGHT STAYED CLOSE TO CONTINUITY WHICH SEEMS TO SIDE SLIGHTLY  
MORE TOWARDS THE SLOWER/STRONGER GFS/CMC/GEFS MEAN. INTERESTINGLY,  
THE NEW 00Z ECMWF (AVAILABLE AFTER FORECAST GENERATION TIME) CAME  
IN MUCH MORE AMPLIFIED THAN PREVIOUS RUNS AND MORE CONSISTENT WITH  
THE GFS/CMC, WHICH INCREASES CONFIDENCE A BIT WITH THE LATE PERIOD  
FLOW PATTERN.  
 
   
..WEATHER/THREAT HIGHLIGHTS
 
 
THE RELENTLESS HEAT ACROSS THE SOUTHERN PLAINS/LOWER MISSISSIPPI  
VALLEY SHOULD FINALLY BREAK BY THIS WEEKEND THOUGH RECORD HEAT  
CONTINUES INTO SATURDAY ACROSS THE EAST. NUMEROUS DAILY RECORDS  
COULD BE MET OR EXCEEDED ON SATURDAY ACROSS THE APPALACHIANS,  
MID-ATLANTIC, AND NORTHEAST WITH A FEW LINGERING RECORDS ACROSS  
FAR SOUTHERN REGIONS IN TEXAS/LOUISIANA. A STRONG COLD FRONT WILL  
SPREAD RAIN AND THUNDERSTORMS THROUGH THE MISSISSIPPI VALLEY/OHIO  
VALLEY ON SATURDAY AND INTO THE EAST ON SUNDAY. HEAVY RAINFALL AS  
WELL AS SEVERE WEATHER IS POSSIBLE ALONG THIS BOUNDARY GIVEN ABOVE  
NORMAL MOISTURE AND INSTABILITY PRESENT. FLOODING AND FLASH  
FLOODING COULD BE AN ISSUE AS WELL, PARTICULARLY IN PLACES THAT  
MAY BE SENSITIVE TO ADDITIONAL RAINFALL GIVEN WET ANTECEDENT  
CONDITIONS. LEAD SOUTHERN STREAM IMPULSE ENERGY MAY ALSO FOCUS  
HEAVY RAINFALL AREAS ACROSS PARTS OF THE SOUTH AND GULF COAST AS  
TROPICAL MOISTURE SURGING NORTHWARD ALLOWS FOR HEAVY RAINFALL  
ACROSS THE FLORIDA PENINSULA THIS WEEKEND. TO THE WEST,  
UNSEASONABLY COOL TEMPERATURES WILL MOVE FROM THE ROCKIES INTO THE  
NORTH-CENTRAL U.S., LOWERING SNOW LEVELS ACROSS THE ROCKIES  
SATURDAY AND SUNDAY. THE NEXT SYSTEM DIGGING INTO THE  
SOUTH-CENTRAL U.S. INTO NEXT WEEK MAY RE-KINDLE  
CONVECTION/RAINFALL ACROSS THE CENTRAL U.S., ALBEIT WITH LESS  
CERTAINTY AT THESE LONGER TIME FRAMES AND HIGHLY DEPENDENT ON FLOW  
DETAILS. THE NORTHWEST SHOULD REMAIN FAIRLY DRY, THOUGH WITH SOME  
LIGHT PRECIPITATION ACCOMPANYING FRONTAL BOUNDARIES. THE SOUTHERN  
HALF OF THE WEST SHOULD SEE A SLIGHT WARMING TREND EXPAND FROM  
WEST TO EAST MONDAY THROUGH WEDNESDAY WHILE MEAN TROUGHING KEEPS  
TEMPEARTURES NEAR OR COOLER THAN NORMAL EAST OF THE ROCKIES.  
 
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, 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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