209  
FXUS02 KWBC 011856  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
255 PM EDT THU SEP 01 2022  
 
VALID 12Z SUN SEP 04 2022 - 12Z THU SEP 08 2022  
 
...PROLONGED AND DANGEROUS HEAT WAVE FOR PORTIONS OF THE WESTERN  
U.S. THROUGH THE HOLIDAY WEEKEND AND BEYOND...  
 
...HEAVY RAIN THREAT FROM SOUTHERN PARTS OF TEXAS THROUGH THE  
SOUTHEAST AND SOUTHERN APPALACHIANS...  
 
   
..OVERVIEW
 
 
A PERSISTENT UPPER HIGH OVER THE GREAT BASIN AND THE ASSOCIATED  
RIDGE WILL BRING HOT, RECORD-BREAKING, AND POTENTIALLY DANGEROUS  
HEAT TO PORTIONS OF THE WESTERN U.S. INTO THE ROCKIES AND NORTHERN  
HIGH PLAINS. THE NORTHWEST IN PARTICULAR SHOULD SEE COOLING  
TEMPERATURES STARTING AROUND MIDWEEK NEXT WEEK AS AN UPPER TROUGH  
EDGES CLOSER WITH A COLD FRONT AHEAD OF IT. FARTHER EAST, ANOTHER  
FOCUS FOR SIGNIFICANT WEATHER WILL BE FOUND ACROSS SOUTHERN  
PORTIONS OF TEXAS AND EASTWARD AS A STALLING FRONTAL BOUNDARY, A  
WEAK UPPER LEVEL DISTURBANCE, AND PLENTIFUL GULF MOISTURE COULD  
BRING MULTIPLE DAYS OF MODERATE TO HEAVY RAINFALL AND POTENTIAL  
FLASH FLOODING. ADDITIONALLY, A COLD FRONT SLOWLY PRESSING  
SOUTHEASTWARD COULD PRODUCE RAIN AND THUNDERSTORMS ACROSS THE  
EASTERN THIRD OF THE NATION EARLY NEXT WEEK, WITH A PARTICULAR  
RAINFALL FOCUS LIKELY OVER THE SOUTHERN APPALACHIANS.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
MODEL AGREEMENT AS THE PERIOD BEGINS SUNDAY IS FAIRLY GOOD, WITH  
THE STRONG UPPER RIDGE IN THE WEST SUPPRESSED BY A SHORTWAVE IN  
THE NORTHERN HIGH PLAINS, AND BROADER TROUGHING CENTERED IN THE  
EAST-CENTRAL CONUS. MODELS DIFFER SOMEWHAT REGARDING HOW STRONG  
THE SHORTWAVE IS THROUGH MONDAY-TUESDAY, WITH GFS RUNS STAYING ON  
THE STRONGER SIDE, BUT A MULTI-MODEL DETERMINISTIC BLEND FROM THE  
AVAILABLE 00Z/06Z MODELS WAS A REASONABLE COMPROMISE THROUGH DAYS  
3-4 OF THE FORECAST FOR THAT SHORTWAVE AND THE LARGER SCALE  
SYNOPTIC PATTERN. BY DAY 5/TUESDAY, MOST GUIDANCE SHOWS THE MAIN  
TROUGH AXIS SHIFTING INTO THE EASTERN U.S., BUT THE MAIN EXCEPTION  
WAS THE 00Z ECMWF. IT INDICATES AN UPPER LOW MAINLY STATIONARY  
CENTERED OVER ILLINOIS EVEN THROUGH DAY 7/THURSDAY. THIS WAS ON  
THE SLOWER SIDE OF THE GUIDANCE, INCLUDING THE ENSEMBLE MEANS AND  
MOST INDIVIDUAL ENSEMBLE MEMBERS, SO PREFERRED A SOMEWHAT MORE  
PROGRESSIVE SOLUTION. THE CURRENTLY INCOMING 12Z ECMWF IS MORE  
PROGRESSIVE FROM THE 00Z RUN AS WELL. THEN MODELS VARY SOMEWHAT  
WITH THE TIMING AND DEPTH OF TROUGHING COMING INTO THE PACIFIC  
NORTHWEST, AND WITH POTENTIAL FOR AN EASTERN PACIFIC TROPICAL  
SYSTEM TO DEVELOP AND COME NEAR BAJA CALIFORNIA, AND POSSIBLY  
EVENTUALLY DISRUPTING THE FLOW OVER THE U.S. AS WELL. THE LATTER  
PART OF THE MEDIUM RANGE PERIOD PHASED IN THE GEFS AND EC ENSEMBLE  
MEANS TO ABOUT 60 PERCENT BY DAY 7 WHILE LESSENING THE PROPORTION  
OF THE DETERMINISTIC GUIDANCE, ESPECIALLY THE 00Z EC, IN THE  
FORECAST BLEND.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
AN EARLY SEPTEMBER HEAT WAVE ACROSS THE WESTERN U.S. IS EXPECTED  
TO PRODUCE DAILY HIGH TEMPERATURE ANOMALIES OF 10-20F EACH DAY  
FROM CALIFORNIA NORTHEASTWARD INTO THE GREAT BASIN, NORTHERN  
ROCKIES, AND NORTHERN HIGH PLAINS. TEMPERATURES WILL BE WELL INTO  
THE 100S WITH SOME 110S POSSIBLE FOR CALIFORNIA'S CENTRAL VALLEY  
AND INTO THE DESERT SOUTHWEST, WHILE FARTHER NORTH 90+ DEGREE  
TEMPERATURES WILL BE WIDESPREAD, NEARING OR EXCEEDING 100F AT SOME  
LOCATIONS. WIDESPREAD DAILY HIGH TEMPERATURE RECORDS ARE POSSIBLE,  
WITH SOME LOCATIONS POSSIBLY REACHING MONTHLY RECORDS. LOW  
TEMPERATURES ARE ALSO FORECAST TO BE 10-20 DEGREES ABOVE NORMAL  
AND NEAR RECORD WARM, ADDING TO THE HEAT STRESS, SO THE HEAT WAVE  
COULD BECOME INCREASINGLY DANGEROUS FOR VULNERABLE POPULATIONS  
THROUGH THE HOLIDAY WEEKEND AND INTO NEXT WEEK. WIDESPREAD HIGH TO  
VERY HIGH HEAT RISK LEVELS ARE EXPECTED ALONG AND NEAR THE CENTRAL  
VALLEY AND DESERT REGIONS OF CALIFORNIA THROUGH THE FIRST HALF OF  
NEXT WEEK. TEMPERATURES MAY MODERATE SOME BY NEXT THURSDAY, AT  
LEAST IN THE NORTHWEST AFTER A COLD FRONT MOVES THROUGH.  
 
A RESIDUAL FRONTAL BOUNDARY DRAPED ALONG THE GULF COAST  
INTERACTING WITH FAVORABLE GULF MOISTURE TRANSPORT AND A WEAK  
UPPER LEVEL DISTURBANCE WILL HELP FOCUS WIDESPREAD SHOWERS AND  
THUNDERSTORMS THROUGH THE WEEKEND INTO EARLY NEXT WEEK. FOR  
SUNDAY, THE FOCUS FOR THE HEAVIEST RAIN POTENTIAL REMAINS ACROSS  
PORTIONS OF SOUTHERN TO SOUTHEAST TEXAS WHERE THE COMBINATION OF  
INTENSE RAIN RATES AND PROLONGED WIDESPREAD MODERATE TO HEAVY RAIN  
COULD TOTAL A FEW INCHES PER THE LATEST FORECAST GUIDANCE. MANY  
AREAS ARE ALREADY RUNNING ABOVE NORMAL PRECIPITATION DEPARTURES  
RECENTLY, WHICH COULD CONTRIBUTE TO ADDITIONAL FLASH FLOODING. A  
SLIGHT RISK IN THE EXPERIMENTAL DAY 4 (12Z SUN - 12Z MON)  
EXCESSIVE RAINFALL OUTLOOK REMAINS IN EFFECT FOR THESE AREAS. BY  
SUNDAY, THE BOUNDARY BECOMES MORE DIFFUSE AND THE SIGNAL FOR HEAVY  
RAIN IS NOT AS STRONG, BUT IS STILL SOMETHING TO MONITOR OVER THE  
COMING DAYS ACROSS SOUTHERN TEXAS, WITH FLOODING ISSUES POSSIBLE  
PARTICULARLY IN AREAS THAT RECEIVE MULTIPLE ROUNDS OF HEAVY  
RAINFALL. GUIDANCE ALSO POINTS TO FAVORABLE MOISTURE TRANSPORT AND  
LIFT ACROSS THE SOUTHEASTERN U.S., AND THE SOUTHERN APPALACHIANS  
IN PARTICULAR COULD BE AN AREA OF FOCUS FOR HEAVY RAIN GIVEN A  
FRONT NEARBY AND FORCING ALOFT. THE SOUTHEASTERN QUADRANT OF THE  
COUNTRY IS LIKELY TO REMAIN COOLER THAN NORMAL AT LEAST IN TERMS  
OF HIGHS DUE TO THE CLOUDS AND RAIN CHANCES. RAIN AND STORMS ARE  
ALSO POSSIBLE FARTHER NORTH FOR THE OHIO VALLEY, MID-ATLANTIC, AND  
NORTHEAST NEAR THE FRONT FOR THE EARLY PART OF NEXT WEEK.  
 
TATE  
 
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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