382
FXUS02 KWBC 171900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SAT AUG 17 2024
VALID 12Z TUE AUG 20 2024 - 12Z SAT AUG 24 2024
...HAZARDOUS HEAT TO PERSIST FROM THE SOUTHERN PLAINS TO THE
WEST-CENTRAL GULF COAST NEXT WEEK...
..OVERVIEW
AN AMPLIFIED AND BLOCKY UPPER PATTERN IS FORECAST TO PREVAIL ACROSS
NORTH AMERICA THROUGH NEXT WEEK. THIS WILL BE HIGHLIGHTED BY A
BUILDING UPPER HIGH CENTERED OVER THE SOUTHERN HIGH PLAINS THAT
WILL PROMOTE HAZARDOUS HEAT FROM THE SOUTHERN PLAINS TO THE CENTRAL
GULF COAST. UPSTREAM, AMPLIFIED UPPER TROUGHING IS FORECAST TO
MEANDER NEAR/OFF THE WEST COAST. DOWNSTREAM, AN AMPLIFIED MEAN
UPPER TROUGH WILL SLOWLY LIFT AND EXIT THE EASTERN U.S.
..GUIDANCE/PREDICTABILITY ASSESSMENT
FORECAST SPREAD AND UNCERTAINTY IN GUIDANCE CONTINUES TO HOLD AT
BELOW NORMAL THRESHOLDS THROUGH MEDIUM RANGE TIME SCALES FOR NEXT
WEEK OVER MUCH OF OUR FINE NATION. MODELS HAVE GENERALLY TRENDED
TOWARD A LESS-AMPLIFIED AND MORE PROGRESSIVE SOLUTION REGARDING THE
DEEP UPPER LOW NEAR/OFF THE WEST COAST/PACIFIC NORTHWEST,
ESPECIALLY WITH THE ECMWF. THE ENSEMBLE MEANS SHOW RATHER GOOD
AGREEMENT THAT THE MEAN TROUGH AXIS WILL SLOWLY COME ONSHORE INTO
THE WEST COAST BY NEXT WEEKEND. THE MORE PROGRESSIVE SOLUTION HAS
RESULTED IN A FASTER SOUTHWARD PUSH OF A COOL AIR MASS DOWN WESTERN
CANADA LATER NEXT WEEK, WHILE A SOUTHERN-STREAM OCCLUSION IS
FORECAST TO DEVELOP IN ALBERTA, CANADA BY NEXT SATURDAY. THE MORE
PROGRESSIVE PATTERN ALSO INTRODUCED SOME TIMING AND LOCATION
DIFFERENCES FOR A WARM FRONTAL WAVE AND QPF TO DEVELOP OVER THE
NORTHERN PLAINS LATE NEXT WEEK.
AGREEMENT AMONG MODELS REMAINS VERY GOOD REGARDING THE TIMING
OF THE LOW PRESSURE SYSTEM EXITING THE NORTHEAST EARLY NEXT WEEK,
FOLLOWED BY A LARGE DOME OF COOL HIGH PRESSURE SYSTEM BUILDING INTO
THE REGION AND THEN FARTHER SOUTH INTO THE SOUTHEAST AND THE DEEP
SOUTH. MODELS GENERALLY AGREE THAT A LARGE POOL OF TROPICAL
MOISTURE WILL BE CONFINED IN THE GULF OF MEXICO AND FLORIDA TO THE
SOUTH OF A STATIONARY FRONT, ALTHOUGH THERE APPEARS SOME TENDENCY
FOR THE MODELS TO PLACE THE HEAVY RAIN CLOSER TO OR NEAR THE GULF
COAST IN THE MORNING MODEL CYCLE.FOR LATE NEXT WEEK INTO THE
WEEKEND.
THEREFORE, A GENERAL MODEL AND ENSEMBLE MEAN COMPOSITE BLEND
APPEARS TO PROVIDE A SOLID DETERMINISTIC FORECAST BASE AND RANGES
OF SOLUTIONS WITH THE POTENTIAL WEATHER HAZARDS, ALBEIT WITH
TYPICALLY LESS PREDICTABLE SMALLER SCALE WARM SEASON FEATURES AND
LOCAL WEATHER FOCUS TO BETTER ADDRESS AT CLOSER TIME SCALES.
..WEATHER/HAZARDS HIGHLIGHTS
AN EAST-CENTRAL TO EASTERN U.S. UPPER TROUGH OFFERS SOME LINGERING
UNSETTLED CONDITIONS, BUT RAINFALL DURING MUCH OF THE EARLIER
PERIOD IS EXPECTED TO TAPER OFF BY MIDWEEK AS SURFACE HIGH PRESSURE
BUILDS IN BEHIND THE COLD FRONT(S) IN THE WAKE OF ERNESTO LIFTING
WELL OFF INTO THE NORTH ATLANTIC. HOWEVER, TRAILING FRONTS SLATED
TO STALL FARTHER SOUTH ACROSS FLORIDA AND VICINITY WILL MAINTAIN
PERIODIC THUNDERSTORM CHANCES THERE. FLOODING ISSUES ARE A
POSSIBILITY IF HEAVY RAIN FALLS IN URBAN AREAS. THIS FRONT MOVES
SLOWLY AS IT BENDS BACK TO THE WEST ATOP THE CENTRAL GULF COAST AND
BACK NORTH INTO THE PLAINS. SCATTERED STORMS ARE POSSIBLE NEAR THE
FRONT AS IMPULSES "RIDE THE RIDGE" ALOFT, BUT WITH GENERALLY LOW
CONFIDENCE IN THE PREDICTED PLACEMENT.
MEANWHILE, MONSOONAL CONVECTION WILL AFFECT THE SOUTHWEST/FOUR
CORNERS STATES NEXT WEEK WITH MOIST SOUTHERLY FLOW WEST OF THE
UPPER RIDGE AXIS. THE WPC EXCESSIVE RAINFALL OUTLOOKS HAVE
MARGINAL RISKS MAINTAINED ACROSS THE INTERIOR SOUTHWEST INTO THE
FOUR CORNERS FOR NEXT WEDNESDAY, BUT THE MARGINAL RISK FOR TUESDAY
HAD BEEN TRIMMED TO INCLUDE ONLY PORTIONS OF ARIZONA, UTAH,
SOUTHEAST CALIFORNIA INTO SOUTHERN NEVADA. STORMS WITH EMBEDDED
HEAVY RAIN COULD CAUSE ISOLATED FLOODING, PARTICULARLY IN
VULNERABLE AREAS.
MEANWHILE, UPPER TROUGH AMPLIFICATION PROXIMITY ALONG/OFF THE WEST
COAST PORTENDS A COOLER AND WETTER PATTERN FOR THE NORTHWEST. SOME
RAINS ARE ALSO FORECAST TO BROADLY FOCUS DOWNSTREAM ACROSS THE U.S.
NORTHERN TIER AS THE WEEK PROGRESSES. SOME CONVECTION MAY BREAK OUT
ALONG/AHEAD OF RELATIVELY SLOW MOVING FRONTAL SYSTEMS ACROSS THE
NORTH-CENTRAL U.S. AS NEXT WEEK PROGRESSES, BUT FOCUS IS UNCERTAIN.
UPPER RIDGING OVER THE SOUTH-CENTRAL U.S. WILL MAINTAIN ABOVE
NORMAL TEMPERATURES BY 5-15 DEGREES FROM THE HIGH PLAINS EAST INTO
THE WEST-CENTRAL GULF COAST. HIGHS WELL INTO THE 100S IN MUCH OF
TEXAS 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
WAVE.
KONG/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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