540  
FXUS02 KWBC 311903  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
303 PM EDT FRI MAY 31 2024  
 
VALID 12Z MON JUN 03 2024 - 12Z FRI JUN 07 2024  
 
...EXCESSIVE HEAT LIKELY TO CONTINUE OVER SOUTHERN TEXAS, WHILE  
HEAT BUILDS IN THE WEST FOR THE LATTER HALF OF NEXT WEEK...  
 
   
..OVERVIEW
 
 
THE EARLY PART OF NEXT WEEK WILL FEATURE PROGRESSIVE SHORTWAVES  
AND FRONTAL SYSTEMS IN THE NORTHERN TWO-THIRDS OR SO OF THE LOWER  
48, LEADING TO PRECIPITATION CHANCES IN THE NORTHWEST ON MONDAY AND  
POSSIBLY MULTIPLE ROUNDS OF CONVECTION IN THE CENTRAL AND EASTERN  
U.S. THROUGH MIDWEEK. THE UPPER PATTERN LOOKS A LITTLE MORE BLOCKY  
FARTHER EAST, WITH A NARROW RIDGE OVER THE EASTERN GREAT  
LAKES/CANADA AND A NORTH ATLANTIC MEAN LOW NEAR THE CANADIAN  
MARITIMES. MEANWHILE VERY HOT AND HUMID CONDITIONS SHOULD CONTINUE  
ACROSS TEXAS (ESPECIALLY SOUTHERN AREAS) UNDER THE NORTHERN  
PERIPHERY OF AN UPPER RIDGE ANCHORED OVER MEXICO, TO THE SOUTH OF  
THE STORM TRACK. BY THE LATTER HALF OF THE WEEK, EXPECT A MORE  
AMPLIFIED AND PERSISTENT PATTERN TO DEVELOP, AS UPPER RIDGING  
EXPANDS FROM TEXAS INTO THE INTERIOR WEST (EXPANDING THE COVERAGE  
OF POTENTIALLY HAZARDOUS HEAT), WHILE AN UPPER TROUGH AXIS DEVELOPS  
DOWNSTREAM IN THE EAST.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE PRIMARY SYNOPTIC-SCALE QUESTIONS ARISE BY MID-LATE WEEK AS THE  
AMPLIFIED UPPER RIDGE-TROUGH PATTERN TAKES SHAPE. BY EARLY  
WEDNESDAY THE PAST COUPLE DAYS OF DYNAMICAL AND ECMWF-INITIALIZED  
MACHINE LEARNING (ML) MODELS HAVE BEEN INDICATING A BETTER RIDGE  
DEVELOPING OVER CALIFORNIA/NEVADA AND SOMEWHAT LOWER HEIGHTS OVER  
THE SOUTHERN PLAINS VERSUS WHAT GFS/GEFS RUNS HAVE BEEN  
ADVERTISING. HOWEVER THE 12Z UKMET/CMC HAVE NUDGED SOMEWHAT IN THE  
GFS DIRECTION. LATER IN THE WEEK, THE ML MODELS VARY IN THEIR  
DETAILS BUT ON AVERAGE SEEM TO FAVOR A COMPROMISE BETWEEN THE  
WESTERN RIDGE AXIS OF THE ECMWF/ECENS AND EASTERN AXIS OF THE  
GFS/GEFS. THE 06Z AND 12Z GFS RUNS HAVE BEEN STEADILY RAISING  
HEIGHTS OVER THE WEST COAST VERSUS THE 00Z RUN SO THIS COMPROMISE  
STILL LOOKS GOOD. DETAILS OF THIS RIDGE WILL ALSO AFFECT HOW MUCH  
MOISTURE COULD BEGIN TO LIFT INTO THE WEST FROM LOWER LATITUDES,  
WITH THE GFS MOST AGGRESSIVE IN THAT REGARD. FARTHER EAST, THE ML  
MODELS ULTIMATELY CLUSTER A BIT EAST/NORTHEAST OF THE 00Z ECMWF FOR  
THE UPPER LOW THAT MAY REACH ONTARIO OR VICINITY BY LATE IN THE  
WEEK. ONLY ONE OF FIVE ML MODELS SUPPORTED ANYTHING REMOTELY LIKE  
THE 00Z CMC THAT DROPPED ITS UPPER LOW INTO THE TENNESSEE VALLEY.  
THE NEW 12Z CMC ADJUSTED WELL NORTHWARD BY LATE WEEK BUT IS STILL A  
BIT ON THE SOUTHEAST SIDE RELATIVE TO MOST OTHER SOLUTIONS FOR THE  
UPPER LOW.  
 
WITH THE 00Z UKMET SHOWING FLATTER FLOW THAN CONSENSUS ACROSS THE  
NORTHERN TIER, THE UPDATED BLEND BASED ON 00Z/06Z GUIDANCE  
INCORPORATED THE 06Z GFS-GEFS/00Z ECMWF AND A LITTLE 00Z CMC FOR  
ABOUT THE FIRST HALF OF THE PERIOD (GEFS HELPING TO TONE DOWN SOME  
GFS TRACK ISSUES ACROSS SOUTHERN CANADA). THEN THE FORECAST  
TRANSITIONED TO SPLIT ECMWF/ECENS MEAN INPUT AND PHASE OUT THE CMC,  
ULTIMATELY YIELDING A COMPROMISE WITH A VERY SLIGHT TILT TO THE  
ECMWF/ECENS RELATIVE TO THE GFS/GEFS BY NEXT FRIDAY.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
AN UPPER-LEVEL WAVE AND ATMOSPHERIC RIVER COMING INTO THE  
NORTHWEST WILL BRING HEAVY RAINFALL CONTINUING INTO MONDAY. IN THE  
DAY 4 EXCESSIVE RAINFALL OUTLOOK, MARGINAL RISK AREAS REMAIN IN  
PLACE FOR FLOODING CONCERNS WITH THE HEAVY RAIN. SNOW LEVELS MAY BE  
LOWERING SOME BY MONDAY IN THE CASCADES AND NORTHERN ROCKIES AS  
THE SHORTWAVE MOVES OVERHEAD, BUT THERE IS STILL SOME CONCERN FOR  
RAIN AT ELEVATIONS THAT STILL HAVE A SNOWPACK, POSSIBLY INCREASING  
THE FLOODING THREAT. LATEST GUIDANCE SHOWS SOME PRECIPITATION  
CONTINUING INTO TUESDAY, BUT WITH A LESS PRONOUNCED MOISTURE FEED  
AND LESS SOUTHWARD EXTENT. THUS THERE ARE NO RISK AREAS OVER THE  
NORTHWEST IN THE DAY 5 ERO. EXPECT DRIER CONDITIONS MID-LATE WEEK  
AS UPPER RIDGING BUILDS.  
 
AN INITIAL LOW PRESSURE/FRONTAL SYSTEM IN THE CENTRAL U.S. AND THE  
NEXT ONE COMING IN FROM THE WEST, PLUS MORE DIFFUSE SHORTWAVES  
FARTHER SOUTH, WILL LEAD TO ROUNDS OF SHOWERS AND THUNDERSTORMS  
OVER A BROAD PORTION OF THE CENTRAL AND EASTERN U.S. THE FOCUS FOR  
POTENTIALLY HEAVIER RAIN IS RATHER UNCERTAIN FOR MONDAY AS  
INSTABILITY ABOUNDS IN WIDESPREAD AREAS, BUT THERE STILL SEEMS TO  
BE A GENERAL MODEL AND ENSEMBLE SIGNAL FOR MISSOURI/ARKANSAS AND  
SURROUNDING STATES TO MAINTAIN A MARGINAL RISK IN THE DAY 4 ERO. A  
VIGOROUS FRONTAL SYSTEM (ANCHORED BY SOUTHERN CANADA LOW PRESSURE)  
REACHING THE NORTHERN PLAINS BY AROUND LATE MONDAY NIGHT MAY ALSO  
PRODUCE LOCALLY HEAVY RAINFALL OVER NORTH DAKOTA, BUT FOR NOW THIS  
ACTIVITY APPEARS SUFFICIENTLY ISOLATED AND PROGRESSIVE TO PRECLUDE  
ANY RISK AREA IN THE ERO. BY DAY 5/TUESDAY, THE FOCUS FOR  
CONVECTION IS A LITTLE MORE CLEAR AS INSTABILITY POOLS AHEAD OF THE  
AFOREMENTIONED FRONT. A MARGINAL RISK IS STILL IN PLACE ACROSS  
NORTHERN AND CENTRAL PARTS OF THE MISSISSIPPI VALLEY TUESDAY. SOME  
LOCATIONS WITHIN THIS AREA WILL BE SENSITIVE DUE TO RAINFALL FROM  
PRIOR DAYS. CURRENT DETAIL/TIMING DIFFERENCES SUGGEST IT MAY TAKE  
UNTIL CLOSER TO THE EVENT TO DETERMINE WHETHER THERE MAY BE ANY  
MERIT TO AN EMBEDDED SLIGHT RISK AREA.  
 
CONTINUED PROGRESSION OF THE PLAINS COLD FRONT SHOULD SHIFT THE  
BEST SHOWER/THUNDERSTORM FOCUS INTO THE EASTERN THIRD OF THE  
COUNTRY BY MID-LATE WEEK. SOME AREAS OF MODERATE TO HEAVY RAINFALL  
WILL BE POSSIBLE BUT THERE IS STILL CONSIDERABLE UNCERTAINTY OVER  
TIMING AND LOCATION OF HIGHEST RAINFALL TOTALS. ADDITIONAL WEAK  
UPPER-LEVEL ENERGIES FROM THE SOUTHERN PLAINS TO THE SOUTHEAST  
WILL ALSO KEEP UP THE POTENTIAL FOR ADDITIONAL STORMS. A PERIOD OF  
LOW LEVEL UPSLOPE FLOW BEHIND THE FRONT REACHING THE SOUTHERN  
PLAINS BY WEDNESDAY COULD ALSO EVENTUALLY HELP TO DEVELOP SOME  
CONVECTION OVER PARTS OF THE SOUTHERN ROCKIES/PLAINS. ALSO OF NOTE  
FROM THE HAZARDS PERSPECTIVE EARLIER IN THE WEEK, THE NORTHERN  
ROCKIES MAY SEE HIGH WINDS ON TUESDAY BEHIND THE STRONG SOUTHERN  
CANADA/NORTHERN TIER U.S. SYSTEM.  
 
NEXT WEEK WILL REMAIN HOT ACROSS SOUTH TEXAS WESTWARD THROUGH THE  
RIO GRANDE VALLEY, WHERE THE COMBINATION OF HOT TEMPERATURES INTO  
THE 90S AND 100S AS WELL AS HUMIDITY WILL KEEP HEAT INDICES IN THE  
UPPER 100S, LOCALLY 110+. TEMPERATURES NEARING OR EXCEEDING 100F  
MAY STRETCH ACROSS THE SOUTHERN HIGH PLAINS EARLY IN THE WEEK BUT  
SHOULD MODERATE SOMEWHAT BY MIDWEEK BEHIND A FRONTAL PASSAGE. SOME  
ABOVE NORMAL TEMPERATURES ARE POSSIBLE ACROSS THE NORTHERN TIER AT  
TIMES. BUT THE NEXT BIG CONCERN WILL BE INCREASING HEAT ACROSS THE  
WEST AS UPPER RIDGING BUILDS IN. HIGHS BROADLY WILL BE RUNNING  
10-15 DEGREES ABOVE AVERAGE, WITH EVEN WARMER ANOMALIES OF 15-20+  
DEGREES FOR THE CENTRAL CALIFORNIA VALLEYS AND PORTIONS OF THE  
GREAT BASIN. TEMPERATURES SHOULD REACH OVER 100F ACROSS THE CENTRAL  
CALIFORNIA VALLEYS, AND REACHING OVER 110F IN THE DESERT  
SOUTHWEST. PER THE CLIMATE PREDICTION CENTER, THIS HOT PATTERN  
COULD CONTINUE AT LEAST INTO NEXT WEEKEND.  
 
RAUSCH/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 FORECAST (QPF), EXCESSIVE RAINFALL  
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT  
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:  
 
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  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW  
 

 
 
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