776
FXUS02 KWBC 222044
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
443 PM 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 EARLY NEXT WEEK FOR THE GULF COAST STATES...
..SYNOPTIC OVERVIEW
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 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 BRING COOLER TEMPERATURES, WITH SHOWERS AND STORMS LIKELY
AHEAD OF THE COLD FRONT. 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 LATEST MODEL GUIDANCE REMAINS IN GOOD ENOUGH AGREEMENT FOR A
GENERAL DETERMINISTIC MODEL BLEND DAYS 3-5. AFTER THIS, THERE ARE
SOME DIFFERENCES IN TIMING OF THE COLD FRONT OFF THE EAST COAST
AND DETAILS WITH BROAD TROUGHING ACROSS THE EASTERN U.S..
EVENTUALLY, TROPICAL STORM FRANKLIN SHOULD GET WRAPPED UP INTO
THIS TROUGHING EARLY NEXT WEEK, THOUGH SHOULD REMAIN FAR ENOUGH
AWAY FROM THE NORTHEAST COAST LIMITING ANY SENSIBLE WEATHER
IMPACTS BESIDES HIGH SURF. OUT WEST, A DEEP UPPER LOW SHOULD
MEANDER OFF THE NORTHWEST COAST THROUGH AT LEAST MONDAY. THERE IS
DISAGREEMENT IN THE GUIDANCE ON WHEN THE LOW MAY START TO SHIFT
INLAND, RELATED TO STRENGTH OF A BLOCKY UPPER RIDGE OVER WESTERN
CANADA. THE WPC BLEND FOR THE LATE PERIOD TRENDED TOWARDS A 50/50
BLEND OF THE ENSEMBLE MEAN GUIDANCE AND DETERMINISTIC GUIDANCE TO
HELP MITIGATE THESE DIFFERENCES.
..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 HIGHLIGHTED.
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 MARGINAL RISK
AREA FOR THE 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. MUCH WELCOMED RELIEF IS ANTICIPATED FOR THE MIDWEST AND
OHIO VALLEY THOUGH 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 LEADING TO
HEAT INDICES WELL INTO THE 100S. 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 MORE COMFORTABLE AIRMASS ACROSS
THE REGION.
SANTORELLI/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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL ROCKIES AND THE
CENTRAL PLAINS, FRI, AUG 25.
- HAZARDOUS HEAT ACROSS PORTIONS OF CALIFORNIA AND THE SOUTHWEST,
SUN-TUE, AUG 27-AUG 29.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE CENTRAL/SOUTHERN PLAINS,
THE TENNESSEE VALLEY, THE GREAT
LAKES, THE MIDDLE/LOWER MISSISSIPPI VALLEY, AND THE OHIO VALLEY,
FRI, AUG 25.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE SOUTHEAST, THE LOWER
MISSISSIPPI VALLEY, THE SOUTHERN
PLAINS, AND THE TENNESSEE VALLEY, FRI-TUE, AUG 25-AUG 29.
- HEAVY RAIN ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND
ALASKA, SAT-SUN, AUG 26-AUG 27.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page