893
FXUS02 KWBC 041841
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
241 PM EDT TUE JUN 4 2024
VALID 12Z FRI JUN 07 2024 - 12Z TUE JUN 11 2024
...MAJOR HEATRISK EXPECTED FOR MANY AREAS IN THE WEST LATE WEEK
WITH RECORD HIGH TEMPERATURES...
..OVERVIEW
BROADLY, A WESTERN UPPER RIDGE AND EASTERN UPPER TROUGH PATTERN
WILL SET UP LATE THIS WEEK, THOUGH WEAK TROUGHING MAY APPROACH THE
WEST COAST EARLY NEXT WEEK. THE RIDGE WILL PRODUCE POTENTIALLY
HAZARDOUS HEAT ACROSS MUCH OF THE WEST THROUGH THE END OF THE WEEK.
THE FORECAST PATTERN SHOULD SUPPORT INCREASING COVERAGE AND
INTENSITY OF SHOWERS/STORMS OVER THE CENTRAL OR SOUTH-CENTRAL
ROCKIES AND PLAINS AS SYSTEMS RIDE THE RIDGE THROUGH MUCH OF THE
FORECAST PERIOD. MEANWHILE, PERIODS OF LIGHT TO MODEST RAIN ARE
LIKELY IN THE NORTHEASTERN U.S. UNDERNEATH THE SLOW-MOVING
TROUGH/LOW.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WHILE MODEL GUIDANCE IS GENERALLY AGREEABLE IN SHOWING THE WESTERN
RIDGE/EASTERN TROUGH PATTERN IN SOME FASHION, DIFFERENCES IN THE
DETAILS WILL IMPACT SENSIBLE WEATHER ACROSS THE LOWER 48. THE
GREATEST AREA OF UNCERTAINTY REMAINS IN THE EVENTUAL EVOLUTION OF
THE EASTERN TROUGH, INCLUDING A DEEP GREAT LAKES UPPER LOW AND
ADDITIONAL ENERGY DROPPING IN FROM CENTRAL CANADA. SOME OF THE
LATEST 00Z GUIDANCE (AVAILABLE AFTER FORECAST GENERATION TIME) HAS
TRENDED STRONGER WITH THE SECONDARY ENERGY ACTING TO PUSH THE GREAT
LAKES LOW EAST FASTER THAN PREVIOUS RUNS. AT LEAST THROUGH THE
00Z/06Z GUIDANCE (WHICH IS WHAT TODAY'S WPC FORECAST WAS BASED ON),
THERE WAS SOME AGREEMENT BETWEEN THE GFS AND ECMWF AND ENSEMBLE
MEANS IN THE EAST, BUT THE NEW 12Z GFS IS SIGNIFICANT STRONGER WITH
SECONDARY ENERGY FORMING ANOTHER DEEP CLOSED LOW INTO THE UPPER
MIDWEST/GREAT LAKES EARLY NEXT WEEK AND ACTUALLY INDICATING WEAK
RIDGING BUILDING BACK IN OVER THE EAST. RUN TO RUN CONTINUITY IN
THE RELOADING OF THE EASTERN TROUGH THROUGH THE PERIOD IS NOT GREAT
AND SO UNCERTAINTY IN HOW THE FORECAST ACROSS THE EAST WILL EVOLVE
IS VERY LOW. OUT WEST THERE IS ALSO A LOT OF UNCERTAINTY IN
SMALLER SCALE SHORTWAVES PERIODICALLY INTERRUPTING THE WESTERN U.S.
RIDGE AND A LARGER TROUGH MOVING TOWARDS THE WEST COAST LATE
WEEKEND/EARLY NEXT WEEK. THE STRENGTH OF THE RIDGE WILL HELP
DETERMINE HOW MUCH OF THAT ENERGY IS ABLE TO PENETRATE INTO THE
WEST.
THE WPC FORECAST WAS ABLE TO USE A GENERAL BLEND OF THE LATEST
DETERMINISTIC GUIDANCE FOR THE EARLY PERIOD (FRIDAY-SATURDAY)
AMIDST GOOD MODEL AGREEMENT. BUT BY SUNDAY AND ESPECIALLY BEYOND,
GREATER ISSUES AND UNCERTAINTIES ARISE AS INDICATED ABOVE AND SO
INCREASED PERCENTAGES OF THE ENSEMBLE MEANS WERE USED TO HELP
TEMPER THE DETAILS SOMEWHAT. OVERALL, THIS MAINTAINED GOOD LARGE
SCALE AGREEMENT WITH PREVIOUS SHIFT WPC CONTINUITY, BUT SOME
CHANGES IN FRONTAL STRUCTURE/PLACEMENT WERE NEEDED.
..WEATHER/HAZARDS HIGHLIGHTS
SOME RETURN FLOW OF MOISTURE (INCLUDING PACIFIC MOISTURE ADVECTING
AROUND THE UPPER RIDGE) IS LIKELY ACROSS THE SOUTHERN/CENTRAL
ROCKIES AND PLAINS, WITH ONE OR MORE SURFACE BOUNDARIES HELPING TO
FOCUS MULTIPLE ROUNDS OF SHOWERS AND THUNDERSTORMS. PLACEMENT OF
THIS CONVECTION REMAINS UNCERTAIN, BUT THERE IS POTENTIAL FOR
HEAVIER AMOUNTS. GIVEN SOME BETTER CONSENSUS IN THE LATEST
GUIDANCE, WAS ABLE TO TIGHTEN UP THE CURRENT DAY 4/FRIDAY MARGINAL
RISK ON THE ERO TO ONLY INCLUDE MUCH OF CENTRAL/EASTERN NEBRASKA
INTO SOUTHWEST MISSOURI WHERE MODELS SHOW THE BEST POTENTIAL FOR
EXCESSIVE QPF AMOUNTS. BY DAY 5/SATURDAY, MOISTURE TRANSPORT IS
FORECAST TO INCREASE EVEN MORE AND THE INSTABILITY AND OVERALL
SETUP WILL LIKELY CAUSE HEAVY RAIN RATES. RECENT MODEL GUIDANCE IS
NOTABLY AGREEABLE AT LEAST FOR NOW IN A HEAVY RAINFALL AXIS OF 3-5
INCHES NEAR THE OKLAHOMA/KANSAS/MISSOURI/ARKANSAS INTERSECTION.
GIVEN THESE FACTORS, CONTINUED A SLIGHT RISK FOR THAT AREA ON
SATURDAY WITHIN A BROADER MARGINAL COVERING SOUTH- CENTRAL PARTS OF
THE PLAINS AND MISSISSIPPI VALLEY. THOUGH THE EXACT PLACEMENT MAY
HAVE TO SHIFT AROUND IN FUTURE CYCLES, THE INGREDIENTS WILL
CERTAINLY BE SUFFICIENT FOR FLASH FLOODING CONCERNS. ADDITIONAL
ROUNDS OF RAIN ARE LIKELY IN THE PLAINS AND SOUTH-CENTRAL PARTS OF
THE MISSISSIPPI VALLEY EARLY NEXT WEEK. RAIN CHANCES SHOULD ALSO
GRADUALLY INCREASE ACROSS THE SOUTHERN AND CENTRAL ROCKIES LATE
WEEK THROUGH THE WEEKEND AND REMAIN INTO EARLY NEXT WEEK. THE
THREAT FOR HEAVY RAINFALL TO CAUSE FLASH FLOODING THERE SEEMS SUB-
MARGINAL AT THIS POINT GIVEN RECENT DRIER THAN AVERAGE CONDITIONS.
SCATTERED LIGHT RAINFALL IS POSSIBLE LATE IN THE WEEK OVER PARTS OF
THE INTERIOR WEST/NORTHERN ROCKIES, LIKELY INCREASING IN COVERAGE
AND AMOUNTS EARLY NEXT WEEK AS UPPER TROUGHING APPROACHES.
ROUNDS OF RAIN AND POSSIBLE THUNDERSTORMS ARE EXPECTED ACROSS THE
LOWER GREAT LAKES TO THE NORTHEAST UNDERNEATH THE UPPER TROUGH. THE
HEAVIEST RAIN AMOUNTS DURING THE MEDIUM RANGE PERIOD ARE FORECAST
ON FRIDAY, BUT SINCE THE INITIAL FRONT WILL BE COMING THROUGH AND
AMOUNTS LOOK TO DECREASE COMPARED TO THE SHORT RANGE PERIOD, DO NOT
HAVE ANY MARGINAL RISK IN THE ERO FOR DAY 4/FRIDAY. HOWEVER, THERE
IS A NON-ZERO RISK OF FLOODING CONCERNS ESPECIALLY IF HEAVY RAIN
FALLS IN SIMILAR AREAS AS THE PREVIOUS DAYS.
THE WESTERN RIDGE WILL PROMOTE NOTABLY/RECORD HOT TEMPERATURES
ACROSS THE WEST ESPECIALLY FOR THE LATTER PART OF THIS WEEK. HIGHS
BROADLY WILL RUN 10-20 DEGREES ABOVE AVERAGE AND LOCALLY 20+
DEGREES ABOVE AVERAGE IN THE GREAT BASIN. HIGH TEMPERATURES ABOVE
110F ARE FORECAST FOR THE DESERT SOUTHWEST (INCLUDING LAS VEGAS),
WITH 90S AND 100S STRETCHING INTO THE CENTRAL CALIFORNIA VALLEYS TO
THE GREAT BASIN TO MUCH OF TEXAS. DAILY RECORD HIGH MINIMUM AND
MAXIMUM TEMPERATURES ARE POSSIBLE. THROUGH FRIDAY, THE EXPERIMENTAL
HEATRISK PRODUCT SHOWS A LARGE AREA OF MAJOR (LEVEL 3 OF 4) AND
SOME EXTREME (LEVEL 4 OF 4) RISK. THE HIGHER TEMPERATURE ANOMALIES
LOOK TO SHIFT INTO THE NORTHWEST FOR THE WEEKEND WITH SOME MINOR
MODERATION OF THE TEMPERATURES AND HEATRISK IN THE SOUTHWEST AS THE
WEAKENING UPPER LOW APPROACHES FROM NORTHWESTERN MEXICO.
MEANWHILE, MOST AREAS EAST OF THE ROCKIES SHOULD TREND TO SLIGHTLY
BELOW NORMAL BEHIND THE COLD FRONT. EXCEPTIONS TO THIS TREND WILL
BE TEXAS (ESPECIALLY SOUTHERN AREAS), AND FLORIDA WHERE HIGHS
SEVERAL DEGREES ABOVE NORMAL MAY LEAD TO SOME DAILY RECORDS.
SANTORELLI/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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