795  
FXUS02 KWBC 120701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT THU MAY 12 2022  
 
VALID 12Z SUN MAY 15 2022 - 12Z THU MAY 19 2022  
 
...HEAT THREAT FOR CALIFORNIA AND THE SOUTHWEST FROM THE WEEKEND  
INTO NEXT WEEK WHILE PERSISTENT SOUTHERN PLAINS HEAT INTENSIFIES  
AND EXPANDS EASTWARD...  
 
   
..OVERVIEW
 
 
THE LATEST MODELS AND ENSEMBLE MEANS CONTINUE TO SUGGEST THAT A  
TROUGH-RIDGE-TROUGH PATTERN ALOFT WILL MAKE GRADUAL EASTWARD  
PROGRESS WITH TIME, SUCH THAT THE MEAN TROUGHS SHOULD REACH NEAR  
THE EAST AND WEST COASTS AROUND WEDNESDAY. TROUGHING MAY BEGIN TO  
AMPLIFY SOMEWHAT OVER THE WEST THEREAFTER WHILE THE DOWNSTREAM  
RIDGE BROADENS AS IT CROSSES THE PLAINS/MISSISSIPPI VALLEY.  
INITIAL WESTERN U.S. AND SOUTHERN PLAINS RIDGING FOLLOWED BY  
RISING HEIGHTS OVER THE SOUTHEAST WILL LEAD TO A BROAD AREA OF  
UNSEASONABLY HOT WEATHER ACROSS THE SOUTHERN U.S. THIS HEAT WILL  
BE MOST PERSISTENT OVER THE SOUTHERN PLAINS AND VICINITY WHILE IT  
SHOULD PEAK OVER WESTERN AREAS DURING SUNDAY-TUESDAY AND EXTEND  
FARTHER EAST FROM THE PLAINS/LOWER MISSISSIPPI VALLEY BY AROUND  
TUESDAY-THURSDAY. HIGH TEMPERATURES WILL LIKELY CHALLENGE DAILY  
RECORDS FOR MULTIPLE DAYS AT SOME LOCATIONS. A SERIES  
SHORTWAVES/FRONTS EJECTING FROM THE TROUGH EVENTUALLY ARRIVING  
INTO THE WEST WILL PRODUCE COOL CONDITIONS WITH PERIODS OF RAIN  
AND PERHAPS HIGH ELEVATION SNOW OVER THE NORTHWEST. MEANWHILE  
FRONTS PUSHED ALONG BY THE MEAN TROUGH CROSSING THE EASTERN HALF  
OF THE COUNTRY AND STALLING BACK OVER THE PLAINS WILL HELP TO  
FOCUS AREAS OF SHOWERS AND THUNDERSTORMS OF VARYING INTENSITY  
THROUGH THE PERIOD.  
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
FOR THE MOST PART, THE LATEST GUIDANCE AGREED FAIRLY WELL FOR THE  
MEAN PATTERN BUT WITH PERSISTENT DIFFERENCES FOR  
LOW-PREDICTABILITY SHORTWAVE DETAILS WITHIN THE EASTERN U.S.  
TROUGH AS WELL AS FOR SHORTWAVES MOVING THROUGH AND EJECTING FROM  
THE PACIFIC TROUGH EVENTUALLY PUSHING INTO THE WEST. DAY-TO-DAY  
FRONTAL POSITION AND THUS SPECIFICS OF CONVECTIVE FOCUS WILL BE  
SENSITIVE TO THESE UNCERTAIN MEDIUM TO SMALLER SCALE ASPECTS OF  
THE FORECAST. FROM THE LARGE SCALE PERSPECTIVE, THE LATEST CMC  
RUNS HAVE OFFERED THE GREATEST DISCREPANCIES VERSUS REMAINING  
GUIDANCE AS THEY ARE MORE AMPLIFIED WITH THE EASTERN TROUGH AND  
STRAY TO THE PROGRESSIVE EXTREME WITH WESTERN-CENTRAL U.S. ENERGY  
TUESDAY-THURSDAY. THE NEW 00Z RUN IS NOT AS EXTREME AS ITS PRIOR  
RUN IN THE EAST BUT STILL QUESTIONABLE. MEANWHILE THE 18Z GFS WAS  
A BIT ON THE FLATTER SIDE WITH THE EASTERN TROUGH, WHILE IN THE  
LATTER HALF OF THE PERIOD THE 18Z GFS WAS DEEPER WITH ENERGY  
COMING INTO THE NORTHWEST AROUND TUESDAY BUT THE 12Z RUN ULTIMATE  
STRAYED TO THE DEEP SIDE WITH TRAILING AMPLIFICATION BY NEXT  
THURSDAY. NOT SURPRISING GIVEN SOME OF THE OPERATIONAL MODEL  
DIFFERENCES THAT DEVELOP WITH THE EASTERN PACIFIC/WESTERN U.S.  
TROUGH, GEFS/ECENS/CMCENS MEMBER SPREAD BECOMES NOTICEABLY MORE  
PRONOUNCED BY WEDNESDAY-THURSDAY. GUIDANCE COMPARISONS ULTIMATELY  
LED TO EMPHASIZING THE 12Z ECMWF/UKMET AND 12Z/18Z GFS FOR THE  
UPDATED FORECAST DURING THE FIRST HALF OF THE PERIOD AND THEN  
RAPIDLY INCREASED 18Z GEFS/12Z ECMWF MEAN INPUT (REACHING A TOTAL  
OF 60 PERCENT BY DAY 7 THURSDAY) TO EMPHASIZE THE MORE AGREEABLE  
LARGE SCALE PATTERN WHILE DOWNPLAYING THE UNCERTAIN DETAILS.  
   
..WEATHER/THREAT HIGHLIGHTS
 
 
INITIAL SOUTHERN PLAINS/WESTERN RIDGING AND THEN EVENTUALLY RISING  
HEIGHTS FARTHER EAST OVER THE SOUTH WILL LIKELY PROMOTE BROAD AREA  
OF HEAT ACROSS MUCH OF THE SOUTHERN U.S. DURING THE PERIOD. THE  
GREATEST ANOMALIES THROUGH THE PERIOD SHOULD BE OVER THE SOUTHERN  
PLAINS (PERSISTING FROM THE SHORT RANGE TIME FRAME) WHERE SOME  
LOCATIONS COULD SEE HIGHS UP TO 15-20F ABOVE NORMAL. THE SOUTHERN  
HALF OR SO OF THE WEST WILL TEND TO SEE HIGHS UP TO 10-15F ABOVE  
NORMAL FROM SUNDAY INTO AT LEAST THE FIRST PART OF NEXT WEEK  
FOLLOWED BY A COOLING TREND THAT REACHES CALIFORNIA INITIALLY AND  
EXTENDS FARTHER EASTWARD BY NEXT THURSDAY AS PACIFIC UPPER  
TROUGHING ARRIVES. MEANWHILE BY TUESDAY OR WEDNESDAY THROUGH  
THURSDAY THE COVERAGE OF HIGHS 10-15F ABOVE NORMAL SHOULD EXTEND  
EASTWARD THROUGH THE LOWER MISSISSIPPI VALLEY AND INTO THE  
SOUTHEAST. POTENTIAL FOR DAILY RECORD HIGHS WILL BE MOST  
PERSISTENT THROUGH THE PERIOD OVER PARTS OF THE SOUTHERN PLAINS.  
NUMEROUS RECORD HIGHS WILL BE POSSIBLE EACH DAY OVER AREAS WITH  
PLUS 10F AND GREATER HIGH TEMPERATURE ANOMALIES.  
 
IN CONTRAST, THE SERIES OF SURFACE WAVES/FRONTS AHEAD OF THE  
APPROACHING/ARRIVING EASTERN PACIFIC UPPER TROUGH WILL KEEP THE  
PACIFIC NORTHWEST ON THE COOL SIDE WITH FREQUENT EPISODES OF  
PRECIPITATION. THE TROUGH SHOULD REACH FAR ENOUGH EASTWARD TO  
BRING HIGHS DOWN TO 10-15F BELOW NORMAL OVER THE  
NORTHWEST/NORTHERN ROCKIES BY NEXT WEDNESDAY-THURSDAY. SNOW LEVELS  
SHOULD BE QUITE HIGH INTO EARLY NEXT WEEK AND THEN BEGIN TO  
DECLINE AS THE UPPER TROUGH ARRIVES. IT WILL LIKELY TAKE INTO THE  
SHORT RANGE TIME FRAME TO RESOLVE TIMING/INTENSITY ASPECTS OF EACH  
PRECIPITATION EPISODE DUE TO THE MEDIUM TO SMALLER SCALE OF THE  
SUPPORTING SHORTWAVES.  
 
AREAS TO THE EAST OF THE ROCKIES SHOULD GENERALLY SEE TWO RAINFALL  
REGIMES DURING THE PERIOD. FROM SUNDAY INTO MONDAY THE BEST FOCUS  
FOR SHOWERS AND THUNDERSTORMS WILL BE ALONG A COLD FRONT PUSHING  
THROUGH THE EAST. THERE MAY BE ONE AREA OF EMPHASIS OVER AND NEAR  
THE SOUTH-CENTRAL MISSISSIPPI VALLEY ON SUNDAY WHILE ADDITIONAL  
AREAS OF LOCALLY MODERATE TO HEAVY RAINFALL MAY OCCUR FROM THE  
GREAT LAKES/OHIO VALLEY INTO NEW ENGLAND. FRONTAL PROGRESSION MAY  
TEMPER AMOUNTS OVER THESE LATTER AREAS EVEN IF SOME OF THE  
RAINFALL IS FAIRLY INTENSE WHILE MUCH OF NEW ENGLAND HAS DRY SOIL  
CONDITIONS TO MITIGATE EFFECTS OF ANY LOCALLY HEAVY RAINFALL. THEN  
FROM LATER MONDAY THROUGH THURSDAY, THE STALLING OF THE LEADING  
FRONT AND ANOTHER ONE BEHIND IT OVER THE PLAINS ALONG WITH  
SHORTWAVES ALOFT WILL PROVIDE FOCUS FOR MULTIPLE AREAS OF SHOWERS  
AND THUNDERSTORMS/CONVECTIVE COMPLEXES FROM THE NORTHERN-CENTRAL  
PLAINS INTO THE CENTRAL APPALACHIANS OR VICINITY. SOME RAINFALL  
MAY BE HEAVY, WITH SOME ADDED TIME REQUIRED TO REFINE THE DETAILS  
OF COVERAGE AND TIMING OF HIGHEST TOTALS.  
 
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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