034
FXUS02 KWBC 211850
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
250 PM EDT WED AUG 21 2024
VALID 12Z SAT AUG 24 2024 - 12Z WED AUG 28 2024
..HAZARDOUS HEAT FOCUS OVER THE SOUTHERN PLAINS
..OVERVIEW
AN EXPANDING RIDGE WILL REMAIN IN PLACE OVER THE SOUTHERN PLAINS,
COOLING TROUGH OVER THE NORTHEAST/EAST WHILE THE PACIFIC NORTHWEST
TO NORTHERN-CENTRAL U.S. TRANSITIONS TO A WET PATTERN AS A PACIFIC
TROUGH/LOW EJECTS INLAND. THIS PATTERN OFFERS A HAZARDOUS HEAT
FOCUS OVER TEXAS, MOIST MONSOONAL FLOW LINGERING INTO THE WEEKEND
OVER THE FOUR CORNERS STATES, COOLED SURFACE HIGH PRESSURE ALONG
THE EASTERN SEABOARD AND TROPICAL MOISTURE LURKING NEAR THE GULF
COAST AND ESPECIALLY ACROSS SOUTH FLORIDA.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST RUNS OF GUIDANCE CONTINUE TO SHOW DIFFERENCES IN THE
TIMING AND DEPTH OF AN EASTERN PACIFIC TROUGH THAT MAKES ITS WAY
INLAND ACROSS THE NORTHWEST/WEST THIS WEEKEND. AS NOTED IN THE
PREVIOUS DISCUSSION, MULTIPLE RUNS OF THE GFS HAD LOCKED ON TO A
MORE PROGRESSIVE SOLUTION AND BECAUSE OF THAT THE PREFERRED MODEL
BLEND HAD BEEN THE ECWMF/EC ENSEMBLE MEAN/CMC. THE LATEST RUNS OF
CMC REMAINS SYNCED WITH THE ECWMF/EC ENSEMBLE THROUGH ABOUT HOUR
120 BEFORE SPEEDING UP MORE TOWARDS THE GFS PLACEMENT. ALTHOUGH THE
NAEFS MEAN CONSISTS OF THE CMC, IT ACTUALLY LOCKED IN WELL WITH THE
ECWMF AND THE EC ENSEMBLE BY FAVORING A SLOW PROGRESSION DUE TO
STRONG RIDGING.
WPC PREFERRED BLEND FOR TODAY COMPRISED OF ECMWF/CANADIAN AND
ECMWF ENSEMBLE MEAN EARLY ON BEFORE REDUCING WEIGHTING OF CMC AND
ULTIMATELY REPLACING IT WITH THE NAEFS.
..WEATHER/HAZARDS HIGHLIGHTS
WITH AN AMPLIFYING UPPER TROUGH APPROACHING THE WEST COAST AND
MOVING INLAND MUCH OF THE PACIFIC NORTHWEST WILL TREND COOLER AND
WETTER. RAINS AND SPOTTY HIGH ELEVATION MOUNTAIN SNOWS MAY WORK
INLAND ACROSS THE NORTH-CENTRAL INTERMOUNTAIN WEST/ROCKIES THIS
WEEKEND INTO EARLY NEXT WEEK DEPENDENT ON THE TRACK/TIMING OF THE
SUPPORTING UPPER TROUGH/LOW EJECTION. THERE'S POTENTIAL FOR
ENHANCED RAINFALL AMOUNTS ASSOCIATED WITH CONVECTION.
RAINS/CONVECTION MAY ALSO CONSOLIDATE DOWNSTREAM OVER THE NORTH-
CENTRAL U.S. EARLY NEXT WEEK GIVEN FOCUS FROM POSSIBLE MODERATE
CYCLOGENESIS/FRONTOGENESIS.
FOR THE SOUTHWEST, THE MONSOONAL CONVECTIVE PATTERN WILL LINGER
BUT GRADUALLY EASE OVER THE FOUR CORNERS REGION INTO SATURDAY WITH
MOIST SOUTHERLY FLOW WEST OF A SLOW TO DISLODGE UPPER RIDGE AXIS
CENTERED OVER THE SOUTHERN PLAINS. SOME MOISTURE MAY BE PULLED
NORTHWARD INTO THE NORTHERN INTERMOUNTAIN WEST/ROCKIES THIS WEEKEND
AHEAD OF PACIFIC UPPER TROUGH/LOW TRANSLATION OVER THAT REGION. WPC
CONTINUES TO CARRY A DAY 4 MARGINAL RISK FOR EXCESSIVE RAINFALL. LOCAL
STORMS WITH EMBEDDED HEAVY RAIN MAY CAUSE FLASH FLOODING,
PARTICULARLY IN VULNERABLE AREAS.
WITH THE UPPER RIDGING IN PLACE MUCH OF THE SOUTH-CENTRAL U.S.
WILL QUITE WARM. DAILY TEMPERATURES ARE PROGGED TO BE 5 TO 15
DEGREE ABOVE NORMAL FOR LATE AUGUST. HIGHS WELL INTO THE 100S IN
MUCH OF TEXAS IN PARTICULAR COULD SET DAILY RECORDS AND HIGH
DEWPOINTS SHOULD PRODUCE HEAT INDICES LIKELY ABOVE 110 DEGREES. LOW
TEMPERATURES IN THE UPPER 70S TO LOW 80S WILL EXACERBATE HEAT
STRESS AND COULD SET RECORDS FOR WARM MINIMUM TEMPERATURES.
EXPERIMENTAL HEATRISK CONTINUES TO INDICATE MAJOR TO EXTREME
IMPACTS FROM THIS HEAT. THIS WILL BE IN CONTRAST TO COOLING
CONDITIONS INTO THE WEST/NORTHWEST AND ALSO OVER THE CENTRAL TO
EASTERN U.S. UNDER THE INFLUENCE OF DAMMED SURFACE HIGH PRESSURE.
SOME RECORD COOL OVERNIGHT TEMPERATURE VALUES ARE POSSIBLE OVER THE
EAST IN THIS PATTERN INTO LATER WEEK, BUT EXPECT SUMMER HEAT TO
THEN STEADILY RETURN WITH SPREAD ACROSS THE CENTRAL-EASTERN U.S..
A TRAILING FRONT STALLING ACROSS FLORIDA WILL MAINTAIN PERIODIC
RAIN/THUNDERSTORM CHANCES THERE AND INTO SOUTHEAST U.S. COASTAL
AREAS LATER WEEK INTO NEXT WEEK. MOIST FLOW AND PATTERN LONGEVITY
MAY LEAD TO POSSIBLE FLOODING ISSUES, ESPECIALLY IF HEAVY RAIN
FALLS IN URBAN AREAS. WPC DAY4/ ERO HIGHLIGHTS A MARGINAL RISK
AREA FOR SOUTH FLORIDA GIVEN MOISTURE.
CAMPBELL/SCHICHTEL
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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