717
FXUS02 KWBC 101927
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
327 PM EDT THU AUG 10 2023
VALID 12Z SUN AUG 13 2023 - 12Z THU AUG 17 2023
...SEVERE WEATHER AND FLASH FLOODING LIKELY ACROSS PARTS OF THE
CENTRAL TO EASTERN U.S. EARLY THIS WEEK...
...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. MEANWHILE, 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 CONVECTION WITH HEAVY RAINFALL. TOWARD
WEDNESDAY-THURSDAY UNCERTAINTY INCREASES REGARDING
STRENGTH/LOCATION OF THE NORTHERN PACIFIC/PACIFIC NORTHWEST RIDGE
AND SPECIFICS OF DOWNSTREAM TROUGHING, AFFECTING THE TEMPERATURE
FORECASTS AT THAT TIME.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE FIRST AREA OF CONCERN WITH MODEL DIAGNOSTICS IS WITH THE
VIGOROUS SHORTWAVE/EMBEDDED UPPER LOW AND ITS UNSEASONABLY STRONG
SURFACE LOW REFLECTION TRACKING THROUGH THE MIDWEST TO NORTHEAST.
TIMING DIFFERENCES REMAIN WITH THIS FEATURE, WITH GFS RUNS
INCLUDING THE NEWER 12Z RUN FARTHER EAST/FASTER THAN OTHER
GUIDANCE WHILE MANY GEFS ENSEMBLE MEMBERS AND THE MEAN DO THE
SAME. SINCE THIS CAN BE A FAIRLY TYPICAL MODEL BIAS OF THE GFS
SUITE, PREFERRED THE NON-NCEP GUIDANCE FOR THE MOST PART, FAVORING
ESPECIALLY THE ECMWF AND UKMET AS THE CMC WAS PERHAPS TOO SLOW.
THE INCOMING 12Z CYCLE OTHER THAN THE GFS DID CONVERGE EVEN BETTER
ON A PLACEMENT WITH THE EC AND UK SLOWING DOWN A BIT WITH THE CMC
SPEEDING UP A BIT. THESE DIFFERENCES DO HAVE SIGNIFICANT
IMPLICATIONS ON THE TIMING AND PLACEMENT OF QPF.
A MULTI-MODEL BLEND WORKED WELL FOR CONTINUED RIDGING ACROSS THE
SOUTH-CENTRAL TO SOUTHEAST U.S. AS WELL AS A WEAK UPPER LOW
OFFSHORE NEAR CALIFORNIA. ADDITIONALLY, AGREEMENT IS INCREASING
FOR RIDGING TO POKE INTO THE PACIFIC NORTHWEST THROUGH AROUND
TUESDAY, LEADING TO RISING TEMPERATURES THERE. MODELS ARE STILL
VARIABLE THOUGH WITH HOW LONG THIS RIDGY PATTERN STICKS AROUND,
WITH THE 00/06Z MODELS MORE AGGRESSIVE WITH IT MAINTAINING IT AND
PUSHING NORTHERN CANADA ENERGY EAST OF THAT COMPARED TO THE 12Z
GUIDANCE. WITH THIS UNCERTAINTY, TRANSITIONED TO USING AND
INCREASING THE AMOUNT OF GEFS AND EC ENSEMBLE MEANS TO JUST OVER
HALF OF THE BLEND BY THE END OF THE PERIOD, AFTER THE
DETERMINISTIC MODEL START FAVORING THE ECMWF.
..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 AND SEVERE WEATHER 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 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. THE SLIGHT
RISK IS QUITE BROAD GIVEN MODEL DISAGREEMENTS IN THE EXACT TIMING
AND TRACK OF THE FRONTS AND THE POSSIBILITY OF MULTIPLE AXES OF
ENHANCED RAINFALL. A MARGINAL RISK EXTENDS NORTHWARD INTO THE
UPPER MIDWEST CLOSER TO THE LOW TRACK ON SUNDAY/DAY 4, WITH GOOD
FORCING IN PLACE. MODEL GUIDANCE SHOWS THAT INSTABILITY COULD GET
TUCKED INTO THE LOW AS IT MOVES EAST INTO THE UPPER GREAT LAKES
REGION DAY 5/MONDAY, AND THUS MAINTAINED A SLIGHT RISK IN THE ERO
BY THEN FOR HIGHER RAIN RATE POTENTIAL. AREAS NEAR THE EASTERN
OHIO VALLEY AND CENTRAL APPALACHIANS COULD ALSO SEE HEAVY RAINFALL
TOTALS THAT COULD OVERLAP WITH LOWER FLASH FLOOD GUIDANCE VALUES
TO CAUSE SOME FLOODING ISSUES, SO THE SLIGHT RISK WAS MAINTAINED
THERE AND EXPANDED A BIT WESTWARD. MEANWHILE RAIN AMOUNTS TRENDED
DOWN IN THIS FORECAST CYCLE FARTHER EAST IN THE NORTHEAST ON
MONDAY. AS USUAL, OUTLOOKS COULD CHANGE PENDING FUTURE FORECASTS.
THE GOOD SUPPORT ALOFT COULD ALSO CONTRIBUTE TO SEVERE WEATHER
OVER EASTERN PARTS OF THE CENTRAL PLAINS INTO THE MID-MISSISSIPPI
VALLEY AND OHIO VALLEY SUNDAY-MONDAY.
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. BUT FLOW AHEAD OF THE AFOREMENTIONED
COLD FRONT COULD SUPPORT SOME ORGANIZED RAINFALL OVER FLORIDA BY
MIDWEEK. DIURNALLY FAVORED CONVECTION WILL LIKELY CONTINUE ACROSS
THE FOUR CORNERS STATES AND POSSIBLY FOCUS GENERALLY IN THE
SOUTHERN ROCKIES THROUGH MUCH OF NEXT WEEK. MARGINAL RISKS ARE IN
PLACE IN THE EROS SUNDAY AND MONDAY, WITH A POSSIBLE PEAK IN
COVERAGE/MAGNITUDES ON MONDAY. 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. THE 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 EARLY TO MID-NEXT WEEK, WITH HIGHS REACHING 10F TO
LOCALLY 20F ABOVE NORMAL OVER SOME LOCATIONS FROM SUNDAY ONWARD.
WIDESPREAD RECORD WARM LOWS WILL BE A PROMINENT ASPECT OF THIS
HEAT WAVE BUT SOME RECORD HIGHS ARE POSSIBLE AS WELL. AREAS FROM
THE NORTHERN ROCKIES THROUGH MOST OF THE EAST WILL SEE VARIABLE
TEMPERATURES DUE TO SYSTEM/FRONTAL PROGRESSION. OF PARTICULAR
NOTE, COOL AIR BEHIND THE EARLY WEEK MIDWEST-NORTHEAST SYSTEM MAY
BRING A DAY OR SO OF HIGHS 5-15F OR SO BELOW NORMAL FROM THE
NORTHERN ROCKIES/PLAINS INTO MIDWEST.
TATE/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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