142
FXUS02 KWBC 200656
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
255 AM EDT SUN AUG 20 2023
VALID 12Z WED AUG 23 2023 - 12Z SUN AUG 27 2023
***MAJOR HEAT WAVE FOR THE CENTRAL U.S. AND EXTENDING TO THE GULF
COAST REGION FOR MUCH OF NEXT WEEK WITH NUMEROUS RECORD HIGHS
LIKELY***
..SYNOPTIC OVERVIEW
THE HIGHLY IMPRESSIVE UPPER RIDGE THAT IS EXPECTED TO PEAK AT OR
SLIGHTLY ABOVE 600DM EARLY THIS WEEK IS FORECAST TO START DECAYING
SOME GOING INTO THE END OF THE WEEK AND THEN GETS DISPLACED
TOWARDS THE SOUTH AS SHORTWAVE ENERGY IMPINGES UPON IT FROM THE
NORTH, BUT THE HEAT AND HUMIDITY WILL LIKELY CONTINUE TO MAKE
WEATHER HEADLINES FOR MUCH OF THE SOUTH-CENTRAL STATES THROUGH
NEXT WEEKEND. ACROSS THE NORTHEAST U.S., AN UPPER LEVEL TROUGH IS
EXPECTED TO BE IN PLACE FOR MOST OF THE WEEK AND THIS WILL SHIELD
THE REGION FROM THE EXCESSIVE HEAT THAT IS EXPECTED ACROSS THE
CENTRAL U.S., AND COOLER TEMPERATURES ARE ALSO LIKELY FOR MUCH OF
THE INTERIOR WESTERN U.S., ALONG WITH SCATTERED TO NUMEROUS
SHOWERS AND STORMS WITH CONTINUED 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 FRIDAY, ALTHOUGH THE GFS CONTINUES TO
PORTRAY EXTREMELY HOT TEMPERATURES ACROSS THE CENTRAL U.S. 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 POTENTIAL
CLOSED LOW EVOLUTION. ENSEMBLE MEANS ACCOUNTED FOR ABOUT 35% OF
THE MODEL BLEND BY NEXT SUNDAY, 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
LIKELY CONTINUING INTO NEXT WEEKEND. THERE SHOULD BE AT LEAST
SCATTERED COVERAGE OF CONVECTION ACROSS THE SOUTHERN TO CENTRAL
ROCKIES, AND THIS WARRANTS A MARGINAL RISK AREA FOR BOTH WEDNESDAY
AND THURSDAY FOR THIS REGION. SCATTERED TO NUMEROUS SHOWERS AND
STORMS ARE ALSO EXPECTED ACROSS THE RIO GRANDE VALLEY ON WEDNESDAY
ASSOCIATED WITH THE REMNANTS OF THE TROPICAL WAVE MOVING INLAND
FROM THE WESTERN GULF, AND A MARGINAL RISK AREA IS ALSO PLANNED
HERE AS WELL. 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 BOTH WEDNESDAY AND
THURSDAY, SO A MARGINAL RISK IS PLANNED FOR THIS POTENTIAL. THIS
WILL THEN POTENTIALLY AFFECT THE NORTHEAST U.S. 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 ABOUT THURSDAY
WITH THE MASSIVE UPPER RIDGE IN PLACE AND SUPPRESSING CLOUD
DEVELOPMENT. WIDESPREAD 100+ DEGREE HIGH TEMPERATURES ARE
EXPECTED FROM SOUTHERN SOUTH DAKOTA/SOUTHERN MINNESOTA AND POINTS
SOUTHWARD, AND SOME OVERNIGHT LOWS MAY STAY ABOVE 80 DEGREES,
ESPECIALLY FOR LARGER URBAN AREAS. THESE READINGS ACROSS THE
MIDWEST ARE IN SOME CASES UP TO 20 DEGREES ABOVE LATE AUGUST
AVERAGES, WITH THE CORE OF THE ANOMALIES CENTERED MAINLY OVER IOWA
AND PORTIONS OF ADJACENT STATES ON WEDNESDAY/THURSDAY. THE GOOD
NEWS HERE IS A STRONG COLD FRONT WILL HERALD THE ARRIVAL OF A MUCH
MORE PLEASANT AIRMASS IN TIME FOR THE WEEKEND FOR ALL OF THE
MIDWEST AND OHIO VALLEY WITH AFTERNOON HIGHS RETURNING TO THE 70S
AND LOW 80S IN MOST AREAS. MEANWHILE, THE INTENSE HEAT IS
EXPECTED TO PERSIST UNABATED ACROSS TEXAS AND THE CENTRAL GULF
COAST REGION THROUGH THE END OF THE WEEK AND INTO THE WEEKEND WITH
HIGHS RUNNING 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 MONTHLY RECORD
HIGHS ARE EXPECTED.
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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