185
FXUS02 KWBC 100700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT THU AUG 10 2023
VALID 12Z SUN AUG 13 2023 - 12Z THU AUG 17 2023
...HEAT WAVE TO PREVAIL ACROSS THE SOUTH INTO THE SOUTHWEST INTO
LATE NEXT WEEK...
..HAZARDOUS HEAT POSSIBLE OVER THE PACIFIC NORTHWEST NEXT WEEK
..OVERVIEW
EXPECT THE SOUTHERN TIER HEAT WAVE, WITH DAILY RECORD HIGH
TEMPERATURE RECORDS MOST PERSISTENT OVER TEXAS AND PARTS OF THE
CENTRAL GULF COAST, TO CONTINUE THROUGH AT LEAST NEXT WEEK AND
GRADUALLY EXPAND INTO THE SOUTHWEST AS A STRONG UPPER RIDGE
INITIALLY CENTERED OVER TEXAS AND THE LOWER MISSISSIPPI VALLEY
PUSHES SLOWLY WESTWARD AND POSSIBLY EXPANDS NORTHWESTWARD. THIS
RIDGE SHOULD DISPLACE AN UPPER LOW FORECAST TO BE NEAR THE
CALIFORNIA COAST DURING THE WEEKEND AND EARLY NEXT WEEK. A
SEPARATE NORTHEAST PACIFIC UPPER RIDGE MAY EXTEND INTO THE PACIFIC
NORTHWEST AT TIMES AND CONNECT WITH RIDGING TO THE SOUTHEAST,
BRINGING WHAT MAY BE AN EXTENDED PERIOD OF HOT TEMPERATURES TO
PARTS OF THE NORTHWEST. GUIDANCE SHOWS BROAD CYCLONIC MEAN FLOW
PERSISTING OVER THE NORTHERN HALF OR SO OF THE LOWER 48 EAST OF
THE ROCKIES, BUT WITH A TRANSITION FROM A SERIES OF INDIVIDUAL
SOUTHERN CANADA/NORTHERN U.S. SHORTWAVES TOWARD A LARGER SCALE
MEAN TROUGH OVER AND SOUTH FROM CANADA BY MID-LATE WEEK.
INDIVIDUAL SYSTEMS, IN PARTICULAR THE ONE FORECAST TO TRACK FROM
THE MIDWEST INTO THE NORTHEAST EARLY NEXT WEEK, MAY GENERATE
EPISODES OF STRONG AND HEAVY CONVECTION. TOWARD
WEDNESDAY-THURSDAY UNCERTAINTY INCREASES REGARDING
STRENGTH/LOCATION OF THE NORTHERN PACIFIC/PACIFIC NORTHWEST RIDGE
AND SPECIFICS OF DOWNSTREAM TROUGHING.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
WITHIN THE LEADING SUCCESSION OF UPPER SHORTWAVES AND ASSOCIATED
SURFACE LOWS/FRONTAL SYSTEMS, TRENDS SEEN IN THE 18Z AND NEW 00Z
GFS RUNS TOWARD THE ESTABLISHED ECMWF MAJORITY CLUSTER HAVE LED TO
IMPROVED AGREEMENT VERSUS PRIOR DAYS FOR THE SYSTEM TRACKING OVER
SOUTHEASTERN CANADA/NEW ENGLAND ON SUNDAY AND THEN THE
UNSEASONABLY STRONG SYSTEM EXPECTED TO EVOLVE FROM THE MIDWEST
THROUGH THE NORTHEAST, SUPPORTED BY A VIGOROUS SHORTWAVE/EMBEDDED
UPPER LOW. AMONG THE 00Z RUNS, THE NEW CMC IS THE EXTREME IN
SHOWING SLOWER TIMING THAN OTHER GUIDANCE. INTO EARLY DAY 5
TUESDAY THERE IS DECENT AGREEMENT/CONTINUITY FOR A COLD FRONT TO
REACH THE NORTHERN TIER AT THAT TIME, AS THE CHARACTER OF MEAN
TROUGHING BEGINS TO CHANGE. AFTER EARLY TUESDAY THERE IS
INCREASING DIVERGENCE AMONG CONSECUTIVE OPERATIONAL MODEL RUNS AND
INDIVIDUAL ENSEMBLE MEMBERS FOR THE POSITION AND STRENGTH OF
NORTHEASTERN PACIFIC/PACIFIC NORTHWEST UPPER RIDGING ALONG WITH
DETAILS OF CORRESPONDING DOWNSTREAM TROUGHING. FOR EXAMPLE, THE
18Z/00Z GFS RUNS DRIFT THE PACIFIC RIDGE AND DOWNSTREAM TROUGH
AXIS WELL EASTWARD OF THE 12Z RUN, WHILE THE 12Z ECMWF ALSO
SHIFTED WELL EASTWARD OF ITS PRIOR 00Z VERSION. THUS FAR THE
ENSEMBLE MEANS HAVE BEEN FAIRLY STABLE IN KEEPING THE UPPER RIDGE
MORE OFFSHORE WITH FLATTER FLOW REACHING THE NORTHERN PACIFIC
NORTHWEST AND SOUTHWESTERN CANADA. AFTER AN OPERATIONAL MODEL
BLEND TO REFLECT THE MOST AGREEABLE THEMES IN GUIDANCE DURING THE
FIRST HALF OF THE PERIOD, THE UPDATED FORECAST RAPIDLY TRANSITIONS
TOWARD 40-70 PERCENT 18Z GEFS/12Z ECMWF MEAN INPUT (WITH THE 18Z
GFS/12Z ECMWF-CMC MAKING UP THE REST) TO PROVIDE REASONABLE
FORECAST CONTINUITY WHILE INCORPORATING A MODEST NUDGE OF THE
OPERATIONAL RUNS IN CASE THEIR RECENT TRENDS PERSIST.
..WEATHER/HAZARDS HIGHLIGHTS
THE MOST PROMINENT FOCUS FOR ACTIVE WEATHER DURING THE
SUNDAY-MONDAY NIGHT PERIOD REFLECTED IN THE DAYS 4-5 EXCESSIVE
RAINFALL OUTLOOKS WILL EXTEND FROM THE EASTERN PLAINS THROUGH
PARTS OF THE MID-ATLANTIC AND NORTHEAST, AS AN AMPLIFYING UPPER
TROUGH (LIKELY WITH EMBEDDED LOW) AND SURFACE LOW THAT WOULD BE
UNSEASONABLY STRONG FOR AUGUST SHOULD PRODUCE AREAS OF STRONG AND
HEAVY CONVECTION. THE DAY 4 OUTLOOK DEPICTS A SLIGHT RISK AREA
FROM THE EAST-CENTRAL PLAINS INTO THE MID MISSISSIPPI/LOWER OHIO
VALLEY, WHERE THERE IS REASONABLE AGREEMENT THAT INSTABILITY AND
ANOMALOUS MOISTURE SHOULD INTERACT WITH A WARM FRONT LIFTING
NORTHEASTWARD AHEAD OF THE PRIMARY SURFACE SYSTEM ASSOCIATED WITH
THE STRONG UPPER TROUGH. WITHIN THE BROADER MARGINAL RISK AREA
FARTHER NORTH, THERE ARE ALSO SOME SIGNALS FOR ENHANCED RAINFALL
NEAR THE SURFACE/UPPER LOW BUT INSTABILITY IS LESS PRONOUNCED AND
THERE IS A FAIR AMOUNT OF GUIDANCE SCATTER. MEANWHILE NO CHANGE
HAS BEEN MADE WITHIN THE MARGINAL RISK EXTENDING FROM THE CENTRAL
PLAINS INTO THE SOUTHERN ROCKIES. FOR DAY 5, GUIDANCE DISPLAYS
TYPICALLY GREATER SPREAD FOR QPF DETAILS. ONE AREA OF RELATIVELY
BETTER HEAVY RAINFALL POTENTIAL EXISTS OVER PARTS CENTRAL/NORTHERN
MICHIGAN/FAR NORTHEAST WISCONSIN NEAR THE SURFACE/UPPER LOW
CENTER, WITH GUIDANCE SUGGESTING POTENTIAL FOR HIGHER LOCALIZED
TOTALS THAN IN THE DAY 4 TIME FRAME. THE OTHER AREA OF RELATIVELY
GREATER CONFIDENCE IS THE CENTRAL APPALACHIANS WHERE THERE IS THE
BEST OVERLAP OF MEANINGFUL RAINFALL IN THE GUIDANCE AND LOWER
FLASH FLOOD GUIDANCE VALUES. THEREFORE PLAN TO INTRODUCE SLIGHT
RISK AREAS OVER THOSE TWO REGIONS. OTHER LOCATIONS WITHIN THE
ENCOMPASSING MARGINAL RISK MAY BE UPGRADED AT SOME POINT (OR
CURRENT SLIGHT RISK AREAS ADJUSTED) PENDING BETTER GUIDANCE
CONSENSUS. LATEST GUIDANCE IS SUGGESTING THAT SOUTHERN ROCKIES
CONVECTION MAY BE HEAVIER DURING THE DAY 5 PERIOD VERSUS DAY 4,
BUT THIS IS A FAIRLY NEW TREND. THEREFORE PREFERRED TO START WITH
A MARGINAL RISK ON DAY 5 AND AWAIT SOME STABILIZATION IN THE
GUIDANCE.
THE COLD FRONT ANCHORED BY THE MIDWEST THROUGH NORTHEAST SYSTEM
SHOULD REACH THE SOUTH BY TUESDAY-WEDNESDAY, BRINGING SOME SHOWERS
AND THUNDERSTORMS WITH IT. SOME ENHANCED MOISTURE MAY LEAD TO
LOCALLY MODERATE TO HEAVY SHOWERS/STORMS OVER FLORIDA EARLY IN THE
PERIOD, BUT FOR NOW THEY DO NOT APPEAR TO BE WIDESPREAD ENOUGH TO
MERIT A RISK AREA IN THE ERO. FLOW AHEAD OF THE AFOREMENTIONED
COLD FRONT COULD SUPPORT SOME ORGANIZED RAINFALL OVER FLORIDA BY
MIDWEEK. DIURNALLY FAVORED CONVECTION WILL LIKELY CONTINUE INTO
LATE WEEK OVER THE FOUR CORNERS STATES AND POSSIBLY SOME OTHER
LOCATIONS OVER THE WEST. A COLD FRONT DROPPING INTO THE NORTHERN
PLAINS ON TUESDAY MAY SUPPORT SHOWERS AND THUNDERSTORMS THROUGH
THURSDAY AS IT PUSHES SOUTH AND EAST.
FORECAST TEMPERATURES ACROSS MOST OF THE SOUTHERN TIER SHOW LITTLE
CHANGE, WITH THE OPPRESSIVE HEAT LIKELY CONTINUING THROUGH AT
LEAST NEXT THURSDAY. GREATEST EMPHASIS WILL BE OVER THE SOUTHERN
PLAINS THROUGH CENTRAL GULF COAST REGION WHERE HIGHS WILL LIKELY
BE 5-10F OR SO ABOVE NORMAL NEARLY EVERY DAY. SOME LOCATIONS IN
FLORIDA SHOULD SEE HIGHS SEVERAL DEGREES ABOVE NORMAL AS WELL,
WITH A SLIGHT DECREASE POSSIBLE BY NEXT WEDNESDAY-THURSDAY.
WESTWARD EXPANSION OF THE UPPER RIDGE AS CURRENTLY FORECAST WOULD
RAISE TEMPERATURES IN THE SOUTHWEST UP TO 5-10F ABOVE NORMAL BY
NEXT TUESDAY-THURSDAY (LEADING TO SOME HIGHS EXCEEDING 110F).
DAILY RECORD HIGHS WILL BE MOST LIKELY OVER THE SOUTHERN PLAINS,
CENTRAL GULF COAST, AND FLORIDA. HIGH HUMIDITY SHOULD LEAD TO
MAXIMUM HEAT INDICES AT LEAST IN THE 110-115F RANGE ALONG AND NEAR
THE WESTERN-CENTRAL GULF COAST, OVER THE LOWER MISSISSIPPI VALLEY,
AND PERHAPS WITH SLIGHTLY LESS COVERAGE FARTHER EAST. RECORD WARM
LOWS WILL BE POSSIBLE ACROSS A BROAD PORTION OF THE SOUTHERN TIER
EACH NIGHT. MEANWHILE STRENGTHENING UPPER RIDGING SHOULD BRING
HIGHER TEMPERATURES TO THE PACIFIC NORTHWEST DURING THE WEEKEND
AND EARLY NEXT WEEK, WITH HIGHS REACHING 10F OR MORE ABOVE NORMAL
OVER SOME LOCATIONS FROM SUNDAY ONWARD. VERY WARM TO HOT
TEMPERATURES MAY EXTEND BEYOND THE MEDIUM RANGE FORECAST PERIOD.
RECORD WARM LOWS SHOULD BE THE MOST PROMINENT ASPECT OF THIS HEAT
WAVE BUT A FEW ISOLATED RECORD HIGHS MAY BE POSSIBLE BY
WEDNESDAY-THURSDAY. AREAS FROM THE NORTHERN ROCKIES THROUGH MOST
OF THE EAST WILL SEE VARIABLE TEMPERATURES TO SYSTEM/FRONTAL
PROGRESSION. OF PARTICULAR NOTE, COOL AIR BEHIND THE EARLY WEEK
MIDWEST-NORTHEAST SYSTEM MAY BRING A DAY OR SO OF HIGHS 5-10F OR
SO BELOW NORMAL FROM THE NORTHERN ROCKIES/PLAINS INTO MIDWEST.
RAUSCH
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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