460
FXUS02 KWBC 230747
PMDEPD
EXTENDED FORECAST DISCUSSION...AMENDED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
346 AM EDT WED AUG 23 2023
VALID 12Z SAT AUG 26 2023 - 12Z WED AUG 30 2023
***IMPROVING CONDITIONS FOR THE MIDWEST BUT THE HEAT AND HUMIDITY
CONTINUES INTO THE WEEKEND FOR THE GULF COAST STATES***
..SYNOPTIC OVERVIEW
WELCOMED CHANGES ARE COMING FOR THE NORTH-CENTRAL U.S. BY THE
WEEKEND AS THE MAJOR LATE SUMMER HEATWAVE ABATES AND THE UPPER
RIDGE IS SUPPRESSED TO THE SOUTH. THE AREAL COVERAGE OF EXCESSIVE
AND RECORD-BREAKING HEAT WILL SHRINK WITH IT, BECOMING MORE
LIMITED TO THE GULF COAST STATES BY THE WEEKEND WHERE ADDITIONAL
DAILY RECORD HIGHS ARE LIKELY. THE DEEP TROUGH DEVELOPING NEAR
THE GREAT LAKES AND THEN ACROSS THE NORTHEAST SHOULD BRING COOLER
TEMPERATURES, WITH SHOWERS AND STORMS LIKELY AHEAD OF THE COLD
FRONT. COOLER TEMPERATURES ALONG WITH SHOWERS AND STORMS WITH
POTENTIAL FOR SOME FLASH FLOODING ARE EXPECTED ACROSS PORTIONS OF
THE ROCKIES AND WESTERN HIGH PLAINS WITH MONSOONAL MOISTURE IN
PLACE INTO THE WEEKEND.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE IS IN EXCELLENT AGREEMENT ACROSS THE
CONTINENTAL U.S. THROUGH SUNDAY WITH ABOVE AVERAGE FORECAST
CONFIDENCE ON THE SYNOPTIC SCALE, AND THIS ALSO INCLUDES LESS
MODEL SPREAD WITH THE EVOLVING CLOSED UPPER LOW OFF THE PACIFIC
NORTHWEST COAST. THEREFORE A MULTI-DETERMINISTIC MODEL BLEND
SUFFICES AS A STARTING POINT IN THE FORECAST PROCESS FOR
FRONTS/PRESSURES FOR THE WEEKEND. LOOKING AHEAD TO THE FIRST HALF
OF NEXT WEEK, THE MODEL GUIDANCE IS STILL IN OVERALL DECENT
AGREEMENT, ALTHOUGH THE CMC IS FASTER WITH BRINGING THE UPPER LOW
INLAND ACROSS THE NORTHERN ROCKIES AND INDICATES A STRONGER
SHORTWAVE OFF THE SOUTHEAST COAST ON WEDNESDAY. THE GREATEST
DIFFERENCES ARE OVER SOUTH-CENTRAL CANADA, WHERE THE GFS IS
STRONGER WITH A TROUGH JUST NORTH OF THE GREAT LAKES. ENSEMBLE
MEANS ACCOUNTED FOR ABOUT 30-40% OF THE MODEL BLEND BY NEXT
WEDNESDAY, WHILST STILL KEEPING SIZABLE PORTIONS OF THE
CMC/GFS/ECMWF SOLUTIONS.
..WEATHER/HAZARDS HIGHLIGHTS
SHOWERS AND THUNDERSTORMS ARE EXPECTED TO BE PREVALENT ACROSS MUCH
OF COLORADO AND EXTENDING INTO PORTIONS OF THE CENTRAL PLAINS THIS
WEEKEND AS A COUPLE OF CONVECTIVE COMPLEXES ARE LIKELY TO DEVELOP,
ALTHOUGH THE HEAVIEST RAINFALL WILL LIKELY HAPPEN BEFORE SATURDAY.
A MARGINAL RISK AREA IS IN EFFECT FOR BOTH WEEKEND DAYS FROM
CENTRAL COLORADO TO ADJACENT PORTIONS OF NEBRASKA AND KANSAS, WITH
THE POTENTIAL FOR FUTURE UPGRADES TO SLIGHT RISKS ONCE MODELS
CONVERGE ON PLACEMENT OF QPF. ACROSS THE EASTERN U.S., THE COLD
FRONT WILL INTERCEPT A MOIST AND UNSTABLE AIRMASS ACROSS THE
CAROLINAS WITH SCATTERED TO NUMEROUS SHOWERS AND STORMS EXPECTED
TO DEVELOP, AND A MARGINAL RISK AREA IS IN EFFECT FOR THIS REGION
AS WELL. UNSETTLED WEATHER CONDITIONS ARE LIKELY TO CONTINUE
ACROSS PORTIONS OF THE SOUTHEAST U.S. GOING INTO EARLY NEXT WEEK,
WITH CONVECTION INCREASING ACROSS MUCH OF FLORIDA. MAINLY DRY
CONDITIONS CAN BE EXPECTED ACROSS MOST OF THE MIDWEST AND THE
TENNESSEE RIVER VALLEY.
THERE IS SOME GOOD NEWS TO REPORT ABOUT THE CENTRAL U.S. HEATWAVE
GOING INTO THE WEEKEND. A PATTERN CHANGE WILL LEAD TO THE BIG
UPPER RIDGE DECAYING SOME AS THE NORTHERN STREAM FLOW ACROSS THE
GREAT LAKES AND NEW ENGLAND WEAKENS IT. THIS WILL RESULT IN A
COLD FRONT SLOWLY SETTLING SOUTHWARD ACROSS THE DEEP SOUTH AND
THEN THE GULF COAST REGION BY EARLY NEXT WEEK. ALTHOUGH THE
HEATWAVE WILL HAVE CONCLUDED ACROSS THE MIDWEST, IT WILL STILL BE
QUITE HOT AND UNCOMFORTABLE FROM TEXAS TO SOUTH CAROLINA THIS
WEEKEND, WITH WIDESPREAD 100-105 DEGREE HIGHS EXPECTED ON SATURDAY
SOUTH OF THE INTERSTATE 40 CORRIDOR, AND THEN THE TRIPLE DIGITS
BECOME MORE CONFINED TO THE INTERSTATE 20 CORRIDOR AND POINTS
SOUTH ON SUNDAY. THIS WILL LIKELY ESTABLISH ADDITIONAL DAILY
RECORD HIGHS AND PROBABLY SECURE THE HOTTEST AUGUST ON RECORD FOR
MANY GULF COAST AND DEEP SOUTH CITIES. THE HEAT ABATES ACROSS THE
GULF COAST GOING INTO TUESDAY AND WEDNESDAY WITH MAINLY 90S FOR
HIGHS EXPECTED FOR THESE SAME AREAS. UNFORTUNATELY HEAT BUILDS
AGAIN ACROSS THE LOWER ELEVATIONS OF THE DESERT SOUTHWEST WITH
SOME 110S LIKELY BY THE WEEKEND. ELSEWHERE, TEMPERATURES WILL BE
PLEASANT ACROSS MUCH OF THE NORTHEASTERN QUADRANT OF THE NATION
WITH HIGHS MAINLY IN THE 70S AND 80S AND COMFORTABLE HUMIDITY
LEVELS.
HAMRICK
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, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
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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