781  
FXUS02 KWBC 121856  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
254 PM EDT THU MAY 12 2022  
 
VALID 12Z SUN MAY 15 2022 - 12Z THU MAY 19 2022  
 
...HEAT THREAT FOR THE DESERT SOUTHWEST EARLY NEXT WEEK WHILE  
PERSISTENT SOUTHERN PLAINS HEAT INTENSIFIES AND EXPANDS EASTWARD  
INTO THE SOUTHEAST...  
 
   
..OVERVIEW
 
 
A TROUGH-RIDGE-TROUGH PATTERN ALOFT ACROSS THE U.S. NORTHERN TIER  
IS FORECAST TO MAKE GRADUAL PROGRESS EASTWARD NEXT WEEK, SUCH THAT  
THE MEAN TROUGHS SHOULD REACH NEAR THE EAST AND WEST COASTS AROUND  
WEDNESDAY. RIDGING EARLY IN THE WEEK ACROSS THE SOUTHWESTERN TO  
SOUTH-CENTRAL U.S. FOLLOWED BY RISING HEIGHTS OVER THE SOUTHEAST  
SHOULD LEAD TO A BROAD AREA OF UNSEASONABLY HOT WEATHER ACROSS THE  
SOUTHERN U.S., WITH THE MOST PERSISTENT RECORD-BREAKING HEAT  
CENTERED IN TEXAS AND LOUISIANA. MEANWHILE SHOWERS AND  
THUNDERSTORMS OF VARYING INTENSITY ARE POSSIBLE ALONG FRONTS  
PUSHED BY THE MEAN TROUGH CROSSING THE EASTERN U.S. AND WITH  
STALLING FRONTS ACROSS THE PLAINS. THE WEST SHOULD SEE COOLING  
TEMPERATURES IN RESPONSE TO UPPER TROUGHING AS THE WEEK  
PROGRESSES, ALONG WITH LOWERING SNOW LEVELS BY MIDWEEK WITHIN  
ROUNDS OF PRECIPITATION.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
RECENT GUIDANCE CONTINUES TO BE AGREEABLE WITH THE MEAN PATTERN,  
BUT WITH LINGERING DIFFERENCES WITH 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 THAT MAY TAKE  
UNTIL THE SHORT RANGE TO RESOLVE. OVER THE PAST FEW DAYS, CMC RUNS  
HAVE BEEN GENERALLY SLOW AND DEEP WITH THE EASTERN TROUGH AROUND  
MON-TUE. THIS PERSISTED IN THE 00Z RUN BUT TO A LESSER EXTENT,  
WHILE THE NEWER 12Z RUN APPEARS EVEN CLOSER TO CONSENSUS  
FORTUNATELY. CMC RUNS HAVE ALSO BEEN MORE AMPLIFIED THAN MOST  
OTHER GUIDANCE WITH THE PACIFIC TO WESTERN U.S. TROUGHING LATER  
TUESDAY INTO WEDNESDAY-THURSDAY--THOUGH THIS FEATURE BEGINS  
SHOWING MORE SPREAD IN GENERAL BY MIDWEEK ONWARD AMONG  
DETERMINISTIC MODELS AND GEFS/EC/CMC ENSEMBLE MEMBERS AS NOT ONLY  
UNCERTAIN SHORTWAVES PIVOT, BUT AS STRONGER ENERGY STEMMING FROM  
AN INITIAL UPPER LOW SPINNING JUST WEST OF BRITISH COLUMBIA COULD  
START SPILLING SOUTHWARD. MODELS VARY WITH WHETHER ENERGY WILL  
CONSOLIDATE INTO ONE UPPER LOW/TROUGH FEATURE OR POSSIBLY TWO  
UPPER LOWS/TROUGHS, WITH THE LATTER SHOWN BY THE 00Z CMC AND 12Z  
GFS FOR EXAMPLE. FOR THE UPDATED WPC FORECAST, BEGAN WITH A BLEND  
OF THE 00Z/06Z DETERMINISTIC GUIDANCE LED BY THE ECMWF AND GFS  
RUNS, THEN PHASED OUT THE CMC (AND THE UKMET AS IT ENDS) IN FAVOR  
OF GRADUALLY INCREASING PROPORTIONS OF THE GEFS AND EC ENSEMBLE  
MEANS THAT WERE REASONABLY AGREEABLE TO DOWNPLAY THE MORE  
UNCERTAIN DETAILS.  
 
   
..WEATHER/THREAT HIGHLIGHTS
 
 
INITIAL RIDGING ACROSS THE SOUTHWEST AND SOUTHERN PLAINS AND THEN  
EVENTUALLY RISING HEIGHTS FARTHER EAST OVER THE DEEP SOUTH WILL  
LIKELY PROMOTE A BROAD AREA OF HEAT ACROSS MUCH OF THE SOUTHERN  
U.S. DURING THE PERIOD. THE GREATEST AND MOST LASTING ANOMALIES  
THROUGH THE PERIOD SHOULD BE OVER TEXAS (PERSISTING FROM THE SHORT  
RANGE TIME FRAME) WHERE SOME LOCATIONS COULD SEE HIGHS UP TO  
15-25F ABOVE NORMAL. THE SOUTHERN HALF OR SO OF THE WEST WILL TEND  
TO SEE HIGHS UP TO 10-15F ABOVE NORMAL FOR THE EARLY PART OF THE  
WEEK, FOLLOWED BY A SLIGHT 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  
INTO LOUISIANA, WITH NUMEROUS RECORDS LIKELY TO BE SET.  
 
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 AROUND MONDAY. THERE  
COULD BE SOME LOCALIZED FLOODING IMPACTS OVER NEW ENGLAND GIVEN A  
SUITABLE ENVIRONMENT FOR HIGH RAINFALL RATES, BUT DRY SOILS AND  
THE FRONT BEING PROGRESSIVE MAY TEMPER EFFECTS. 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 ACROSS THE NORTHERN HALF OF THE  
PLAINS AND MISSISSIPPI VALLEY INTO THE OHIO VALLEY AND CENTRAL  
APPALACHIANS. SOME RAINFALL MAY BE HEAVY, WITH SOME ADDED TIME  
REQUIRED TO REFINE THE DETAILS OF COVERAGE AND TIMING OF HIGHEST  
TOTALS.  
 
TATE/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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