365
FXUS02 KWBC 201849
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
249 PM EDT TUE AUG 20 2024
VALID 12Z FRI AUG 23 2024 - 12Z TUE AUG 27 2024
..HAZARDOUS HEAT TO PERSIST FOR THE SOUTHERN PLAINS
..OVERVIEW
AN AMPLIFIED UPPER PATTERN WILL BE HIGHLIGHTED BY A CENTRAL CONUS
RIDGE CENTERED OVER THE SOUTHERN PLAINS, WITH TROUGHING OVER THE
NORTHEAST INTO THIS WEEKEND AND A LOW MOVING OVER THE NORTHWEST
THEN NORTH-CENTRAL U.S. WITH CYCLOGENESIS INTO NEXT WEEK. THIS
PATTERN OFFERS HAZARDOUS HEAT EMINATING FROM TEXAS, MOIST
MONSOONAL FLOW LINGERING OVER THE SOUTHWEST/FOUR CORNERS, COOLER
SURFACE HIGH PRESSURE ALONG THE EASTERN SEABOARD, AND TROPICAL
MOISTURE LURKING NEAR THE GULF COAST AND ACROSS FLORIDA.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE MAIN STORY WITH RESPECT TO THE GUIDANCE IS THAT THE 06Z GFS
DEVIATES QUITE A BIT FROM THE REST OF THE 00/06Z MODELS WITH THE
AMPLITUDE OF THE UPPER TROUGH WHILE IT MOVES THROUGH THE INTERIOR
WEST BEGINNING ON DAY 4. THE EURO CLUSTERED WELL WITH THE NON-GFS
GUIDANCE, INCLUDING THE ENSEMBLES AND MACHINE LEARNING (ML) MODELS.
THE DAYS 3 MASS FIELD BLEND CONSISTED OF THE 06Z GFS AND 00Z
ECMWF/CMC/UKMET. THE UKMET, WELL IN-LINE WITH MOST OF THE ML
MODELS, WAS MODESTLY FAVORED ON DAY 4. THE ENSEMBLES ARE INTRODUCED
TO THE BLEND ON DAY 5, WHILE THE OPERATIONAL GFS WAS SIGNIFICANTLY
REDUCED DUE TO ITS INCONSISTENT WEAKENING OF THE WESTERN U.S.
TROUGH COMPARED TO THE OTHER MODELS. DAYS 6 & 7 ARE MADE UP OF A
MAJORITY ENSEMBLE BLEND WITH SOME OPERATIONAL EURO ADDED IN TO HELP
CAPTURE A MID-LEVEL DISTURBANCE PROPAGATING ACROSS THE GULF COAST
AND ROTATING AROUND THE SOUTHERN PERIPHERY OF THE UPPER RIDGE,
WHICH IS CENTERED OVER THE MISSISSIPPI VALLEY.
..WEATHER/HAZARDS HIGHLIGHTS
UPPER TROUGH AMPLIFICATION PROXIMITY ALONG/OFF THE WEST COAST
PORTENDS A COOLER AND WETTER PATTERN FOR THE NORTHWEST LATER THIS
WEEK. 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 UNCERTAIN
TRACK/TIMING OF SUPPORTING, BUT LIKELY AMPLIFIED UPPER TROUGH/LOW
EJECTION. THERE'S POTENTIAL FOR ENHANCED RAINFALL AMOUNTS
ASSOCIATED WITH CONVECTION ALONG THE COASTAL RANGES OF SOUTHERN
OREGON/NORTHERN CALIFORNIA FRIDAY AFTERNOON/EVENING.
RAINS/CONVECTION MAY ALSO CONSOLIDATE DOWNSTREAM OVER THE NORTH-
CENTRAL U.S. EARLY NEXT WEEK GIVEN POSSIBLE MODERATE
CYCLOGENESIS/FRONTOGENESIS FOR FOCUS IN THIS SCENARIO.
MEANWHILE, A MONSOONAL CONVECTIVE PATTERN WILL LINGER BUT
GRADUALLY EASE OVER THE SOUTHWEST/FOUR CORNERS STATES FRIDAY 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 INTO
SATURDAY CONTINGENT AND IN ADVANCE OF POSSIBLE PACIFIC UPPER
TROUGH/LOW TRANSLATION TOWARD THAT REGION. THE WPC DAY 4/5
EXCESSIVE RAINFALL OUTLOOKS (EROS) FOR FRIDAY/SATURDAY SHOW
ELONGATED MARGINAL RISKS AREAS. LOCAL STORMS WITH EMBEDDED HEAVY
RAIN COULD CAUSE FLASH FLOODING, PARTICULARLY IN VULNERABLE AREAS.
UPPER RIDGING FOCUS OVER THE SOUTH-CENTRAL U.S. WILL SUPPORT 5-15
DEGREE ABOVE NORMAL TEMPERATURES. 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..
ELSEWHERE, 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. A WPC DAY5/SATURDAY ERO MARIGINAL RISK
AREA WAS INTRODUCED FOR SOUTH FLORIDA GIVEN A GROWING SIGNAL.
KEBEDE/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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