804
FXUS02 KWBC 210654
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 AM EDT MON AUG 21 2023
VALID 12Z THU AUG 24 2023 - 12Z MON AUG 28 2023
***MAJOR HEAT WAVE FOR THE CENTRAL U.S. AND EXTENDING TO THE GULF
COAST REGION WITH NUMEROUS RECORD HIGHS LIKELY***
..SYNOPTIC OVERVIEW
THE MONSTER UPPER RIDGE THAT WILL BE ANCHORED IN PLACE ACROSS THE
MIDWEST STATES THROUGH MID-WEEK WILL START DECAYING SOME GOING
INTO THE END OF THE WORK WEEK, AND THEN GETS DISPLACED TOWARDS THE
SOUTH AND THEN SOUTHWEST AS A STRONG TROUGH AMPLIFIES ACROSS THE
GREAT LAKES AND THEN THE NORTHEAST. THE RECORD BREAKING HEAT AND
ACCOMPANYING HUMIDITY WILL LIKELY CONTINUE TO MAKE WEATHER
HEADLINES FOR MUCH OF TEXAS AND INTERIOR PORTIONS OF THE GULF
COAST REGION GOING INTO THE WEEKEND AS THE HEATWAVE HERE WILL HAVE
MORE STAYING POWER. EXCEPT FOR A HOT DAY FRIDAY, MUCH OF THE
MID-ATLANTIC, NORTHEAST, AND GREAT LAKES REGION SHOULD AVOID THIS
HEATWAVE AS AN UPPER LEVEL TROUGH GOVERNS THE OVERALL WEATHER
PATTERN WITH A COLD FRONT ARRIVING IN TIME FOR THE WEEKEND.
SHOWERS AND STORMS WILL LIKELY CONTINUE FOR MUCH OF THE ROCKIES
AND PORTIONS OF THE INTERMOUNTAIN WEST WITH MONSOONAL MOISTURE IN
PLACE.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE IS IN EXCELLENT AGREEMENT ACROSS THE
CONTINENTAL U.S. THROUGH THE END OF THE WEEK WITH ABOVE AVERAGE
FORECAST CONFIDENCE ON THE SYNOPTIC SCALE, AND THIS ALSO INCLUDES
LESS MODEL SPREAD WITH THE SHORTWAVE TROUGH CROSSING SOUTHERN
CANADA THAT WILL AMPLIFY INTO A LARGER SCALE TROUGH ACROSS THE
NORTHEAST U.S. BY THE WEEKEND. THEREFORE A MULTI-DETERMINISTIC
MODEL BLEND SUFFICES AS A STARTING POINT IN THE FORECAST PROCESS
FOR FRONTS/PRESSURES THROUGH EARLY SATURDAY, ALTHOUGH THE GFS
CONTINUES TO PORTRAY EXTREMELY HOT TEMPERATURES ACROSS THE MIDWEST
ON THURSDAY THAT ARE UNLIKELY TO VERIFY SO THE ECMWF/NBM/ECENS
SERVED AS A BETTER PROXY FOR TEMPERATURES. LOOKING AHEAD TO THE
WEEKEND, THE MODEL GUIDANCE IS STILL IN VERY GOOD AGREEMENT, WITH
THE GREATEST DIFFERENCES NOTED ACROSS THE EASTERN PACIFIC
REGARDING CLOSED UPPER LOW EVOLUTION, AND TIMING OF THE NEXT
TROUGH DROPPING SOUTH FROM THE HUDSON BAY REGION. ENSEMBLE MEANS
ACCOUNTED FOR ABOUT 40% OF THE MODEL BLEND BY NEXT MONDAY, 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 REGION 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 NEXT WEEKEND. THERE SHOULD BE AT LEAST SCATTERED
TO OCCASIONAL WIDESPREAD COVERAGE OF CONVECTION ACROSS THE
SOUTHERN TO CENTRAL ROCKIES, AND THIS WARRANTS A MARGINAL RISK
AREA FOR BOTH THURSDAY AND FRIDAY FOR THIS REGION. AN AREA OF
ENHANCED QPF IS NOTED IN THE LATEST GUIDANCE ACROSS CENTRAL UTAH
ON THURSDAY, SO A SLIGHT RISK IS PLANNED HERE, AND A SLIGHT RISK
FOR FRIDAY IS ALSO PLANNED FOR PORTIONS OF EASTERN WYOMING AND
COLORADO WHERE MODELS ARE LIKELY PICKING UP ON A POTENTIAL MCS
DEVELOPING. ACROSS THE EASTERN U.S., A COUPLE OF CONVECTIVE
COMPLEXES EMBEDDED WITHIN NORTHWEST FLOW ALOFT AROUND THE RIDGE
MAY AFFECT PORTIONS OF THE GREAT LAKES AND EXTENDING ACROSS
NORTHERN PORTIONS OF THE MID-ATLANTIC FOR THURSDAY, SO A MARGINAL
RISK IS PLANNED FOR THIS POTENTIAL. THIS WILL THEN POTENTIALLY
AFFECT NEW ENGLAND GOING INTO FRIDAY WITH LOCALLY HEAVY RAINFALL
AHEAD OF THE APPROACHING COLD FRONT.
A MAJOR LATE SUMMER HEATWAVE WILL CONTINUE TO MAKE ALL KINDS OF
WEATHER HEADLINES ACROSS THE MIDWEST STATES THROUGH THURSDAY WITH
THE MASSIVE UPPER RIDGE IN PLACE AND SUPPRESSING CLOUD
DEVELOPMENT, FOLLOWED BY MUCH WELCOMED RELIEF AS A STRONG COLD
FRONT HERALDS THE ARRIVAL OF MORE SEASONAL TEMPERATURES.
WIDESPREAD 100+ DEGREE HIGH TEMPERATURES ARE EXPECTED FROM
NEBRASKA AND IOWA AND POINTS SOUTHWARD, WITH OPPRESSIVE DEWPOINTS
ABOVE 75 DEGREES IN MANY CASES. THESE READINGS ACROSS THE MIDWEST
EQUATE TO 15-20 DEGREES ABOVE AVERAGE, WITH THE CORE OF THE
ANOMALIES FROM IOWA TO NORTHERN INDIANA ON THURSDAY. MEANWHILE,
THE INTENSE HEAT IS EXPECTED TO PERSIST UNABATED ACROSS TEXAS AND
THE CENTRAL GULF COAST REGION THROUGH ABOUT SATURDAY BEFORE A
GRADUAL MODERATING TREND COMMENCES. 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 15 DEGREES BELOW AVERAGE OWING TO
GREATER CLOUD COVER AND SHOWERS THROUGH THE END OF THE WEEK.
TEMPERATURES SLOWLY MODERATE GOING INTO THE WEEKEND ACROSS THIS
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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