761
FXUS02 KWBC 220659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT TUE AUG 22 2023
VALID 12Z FRI AUG 25 2023 - 12Z TUE AUG 29 2023
***IMPROVING CONDITIONS FOR THE MIDWEST BUT THE HEAT AND HUMIDITY
CONTINUES INTO THE WEEKEND FOR THE GULF COAST STATES***
..SYNOPTIC OVERVIEW
FINALLY SOME WELCOMED CHANGES ARE COMING FOR THE NORTH-CENTRAL
U.S. BY FRIDAY AND INTO THE WEEKEND AS THE MAJOR LATE SUMMER
HEATWAVE ABATES AS THE HUGE 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
POSSIBLE. THE DEEP TROUGH DEVELOPING NEAR THE GREAT LAKES AND
THEN ACROSS THE NORTHEAST SHOULD PRODUCE A PLEASANT COOL DOWN, AND
WILL ALSO PUSH A COLD FRONT OR TWO ACROSS THE EASTERN HALF OF THE
U.S. WITH SHOWERS AND STORMS AHEAD OF THE BOUNDARIES. COOLER
TEMPERATURES AND WIDESPREAD RAIN AND STORMS WITH POTENTIAL FOR
FLASH FLOODING ARE EXPECTED ACROSS PORTIONS OF THE INTERMOUNTAIN
WEST AND ROCKIES WITH MONSOONAL MOISTURE IN PLACE LATE THIS WEEK
INTO THE WEEKEND.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE IS IN EXCELLENT AGREEMENT ACROSS THE
CONTINENTAL U.S. THROUGH SATURDAY WITH ABOVE AVERAGE FORECAST
CONFIDENCE ON THE SYNOPTIC SCALE, AND THIS ALSO INCLUDES LESS
MODEL SPREAD WITH THE EVOLVING CLOSED UPPER OFF THE PACIFIC
NORTHWEST COAST. THEREFORE A MULTI-DETERMINISTIC MODEL BLEND
SUFFICES AS A STARTING POINT IN THE FORECAST PROCESS FOR
FRONTS/PRESSURES THROUGH SATURDAY NIGHT. LOOKING AHEAD TO SUNDAY
AND EARLY NEXT WEEK, THE MODEL GUIDANCE IS STILL IN VERY GOOD
AGREEMENT, WITH THE GREATEST DIFFERENCES ACROSS THE MIDWEST AND
GREAT LAKES REGARDING THE TIMING AND PLACEMENT OF A SECOND TROUGH
DROPPING SOUTH FROM CANADA, WITH THE CMC INDICATING MORE OF AN
UPPER RIDGE EXTENDING ACROSS THE NORTHERN PLAINS AND THE GFS
INDICATING MORE OF A BROAD TROUGH AXIS. ENSEMBLE MEANS ACCOUNTED
FOR ABOUT 30-40% OF THE MODEL BLEND BY EARLY NEXT WEEK, WHILST
STILL KEEPING SIZABLE PORTIONS OF THE CMC/GFS/ECMWF SOLUTIONS.
..WEATHER/HAZARDS HIGHLIGHTS
THE REGION WITH THE GREATEST COVERAGE OF SHOWERS AND THUNDERSTORMS
IS EXPECTED TO BE ACROSS THE FOUR CORNERS STATES IN RESPONSE TO
MONSOONAL MOISTURE IN PLACE ON THE BACKSIDE OF THE UPPER RIDGE.
SOUTHERLY LOW-MID LEVEL FLOW WILL ENSURE A CONTINUED TRANSPORT OF
MOISTURE FROM WESTERN MEXICO THROUGH THE END OF THE WEEK AND
CONTINUING INTO THE WEEKEND, WITH A LARGE MARGINAL RISK IN THE ERO
FOR FRIDAY AND A SLIGHT RISK INTO PORTIONS OF COLORADO AND WYOMING
WHERE THERE ARE INCREASING CHANCES OF MCS DEVELOPMENT. ACROSS THE
EASTERN U.S. ON FRIDAY, THE FRONT AND ASSOCIATED RAIN SHOULD REACH
EASTERN NEW ENGLAND WHERE A MARGINAL RISK AREA IS PLANNED.
SCATTERED CONVECTION IS BECOMING MORE LIKELY FARTHER SOUTH ALONG
AND AHEAD OF THE COLD FRONT ON SATURDAY ACROSS PORTIONS OF THE
CAROLINAS AND INTO THE HAMPTON ROADS AREA IN VIRGINIA, AND THERE
IS ENOUGH MOISTURE AND INSTABILITY HERE TO MERIT A PLANNED
MARGINAL RISK AREA FOR THE NEW DAY 5 OUTLOOK.
A MAJOR LATE SUMMER HEAT WAVE WILL CONTINUE TO MAKE ALL KINDS OF
WEATHER HEADLINES ACROSS THE GULF COAST STATES THROUGH THE END OF
THE WEEK AND EVEN INTO THE WEEKEND WITH THE MASSIVE UPPER RIDGE IN
PLACE AND SUPPRESSING CLOUD DEVELOPMENT. MUCH WELCOMED RELIEF IS
ANTICIPATED FOR THE MIDWEST AND OHIO VALLEY AS A STRONG COLD FRONT
HERALDS THE ARRIVAL OF MORE SEASONAL TEMPERATURES. WIDESPREAD
100+ DEGREE HIGH TEMPERATURES ARE EXPECTED FROM TEXAS TO SOUTHERN
GEORGIA, WITH OPPRESSIVE DEWPOINTS ABOVE 75 DEGREES IN MANY CASES.
HIGHS ARE EXPECTED TO BE 10-15 DEGREES ABOVE AVERAGE, WITH MANY
LOCATIONS ACROSS THE DEEP SOUTH LIKELY HAVING THEIR WARMEST AUGUST
ON RECORD. NUMEROUS DAILY RECORDS AND PERHAPS SOME ALL-TIME
RECORD HIGHS ARE EXPECTED, PARTICULARLY ACROSS PORTIONS OF
MISSISSIPPI AND LOUISIANA. THE OPPOSITE HOLDS TRUE ACROSS MUCH OF
THE INTERIOR WESTERN U.S. WITH TEMPERATURES RUNNING 5 TO 10
DEGREES BELOW AVERAGE OWING TO GREATER CLOUD COVER AND SHOWERS
THROUGH THE END OF THE WEEK. TEMPERATURES SLOWLY MODERATE GOING
INTO THE WEEKEND ACROSS THAT REGION AND RETURN CLOSER TO LATE
AUGUST AVERAGES. MUCH OF THE NORTHEAST U.S. SHOULD ALSO AVOID THE
BRUTAL HEAT WITH MULTIPLE SHORTWAVE PASSAGES REINFORCING A
COMFORTABLE AIRMASS ACROSS THE REGION.
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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