312
FXUS02 KWBC 072134
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
534 PM EDT MON AUG 07 2023
VALID 12Z THU AUG 10 2023 - 12Z MON AUG 14 2023
..HEAT WAVE TO PERSIST OVER THE SOUTH INTO THE SOUTHWEST
...EXCESSIVE RAIN/FLASH FLOOD THREAT OVER THE TENNESSEE
VALLEY/SOUTHERN APPALACHIANS THURSDAY...
..OVERVIEW
AS OF THURSDAY EXPECT AN ELONGATING UPPER RIDGE AXIS TO EXTEND
FROM THE RIO GRANDE VALLEY EASTWARD THROUGH THE FLORIDA PENINSULA.
BY THE WEEKEND AND EARLY NEXT WEEK A BUILDING UPPER-LEVEL HIGH
SHOULD BECOME STRONGER/MORE DOMINANT FARTHER WESTWARD, FOCUSING
OVER TEXAS AND THE SOUTHERN ROCKIES. THIS RIDGE WILL MAINTAIN THE
ONGOING SOUTHERN TIER HEAT WAVE WITH DAILY RECORD HIGH
TEMPERATURES POSSIBLE EVERY DAY OF THE FORECAST PERIOD, WITH THE
MOST ANOMALOUS TEMPERATURES LIKELY TO BE OVER TEXAS LATE THIS
WEEK. FARTHER NORTH, LOW AMPLITUDE FLOW ALOFT WILL INITIALLY HINT
AT A MEAN TROUGH AXIS OVER THE EAST-CENTRAL U.S. THE MEAN TROUGH
SHOULD GAIN BETTER DEFINITION BY SUNDAY-MONDAY AS A BUILDING
NORTHEAST PACIFIC UPPER RIDGE MAY EXTEND ITS INFLUENCE INTO THE
PACIFIC NORTHWEST AND FAR SOUTHWESTERN CANADA. THE UPPER RIDGE
MAY START TO BRING VERY WARM TO HOT TEMPERATURES TO THE PACIFIC
NORTHWEST BY THE START OF NEXT WEEK. SHORTWAVES WITHIN THE
CYCLONIC DOWNSTREAM FLOW WILL PRODUCE A SERIES OF CENTRAL-EASTERN
U.S. WAVES/FRONTAL SYSTEMS THAT ARE LIKELY TO PRODUCE EPISODES OF
LOCALLY HEAVY RAINFALL, BUT WITH SOME UNCERTAIN SPECIFICS DUE TO
THE LOWER PREDICTABILITY OF IMPORTANT DETAILS. THE NATIONAL
HURRICANE CENTER IS ISSUING ADVISORIES FOR TROPICAL STORM EUGENE
IN THE PACIFIC, WITH DISSIPATION OF THE SURFACE REFLECTION
EXPECTED BEFORE EARLY THURSDAY. HOWEVER THE SYSTEM'S REMAINING
UPPER LEVEL ENERGY AND POSSIBLY SOME MOISTURE COULD GET
INCORPORATED INTO AN UPPER TROUGH/LOW FORECAST TO EVOLVE NEAR THE
CALIFORNIA COAST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
FORECAST GUIDANCE INDICATES THE MEDIUM-RANGE PERIOD WILL BEGIN
DURING A BRIEF WEAKENING PHASE IN THE STAGNANT UPPER-LEVEL HIGH
THAT HAS BEEN IN PLACE ACROSS AT LEAST PORTIONS OF THE SOUTHERN
TIER OF THE COUNTRY FOR THE LAST FEW WEEKS. ENERGETIC UPPER-LEVEL
FLOW WITH EMBEDDED SHORTWAVES WILL BE IN PLACE ACROSS THE NORTHERN
2/3RDS OF THE EASTERN HALF OF THE U.S., WITH A BIT MORE
UPPER-LEVEL RIDGING SHIFTING NORTHWESTWARD KEEPING STRONGER FLOW
ALOFT OVER NORTHERN PORTIONS OF THE WEST. THE UPPER-LEVEL HIGH
BEGINS TO BUILD BACK IN, ANCHORED OVER THE SOUTH-CENTRAL U.S.,
INTO THE MIDDLE OF THE PERIOD, POTENTIALLY EXPANDING AND COMBINING
WITH AN UPPER-LEVEL HIGH OVER THE WESTERN ATLANTIC. THE PATTERN
ALSO LOOKS TO AMPLIFY A BIT AS WELL, WITH MEAN LONG-WAVE TROUGHING
OVER THE PLAINS/MIDWEST/NORTHEAST AS UPPER-LEVEL RIDGING BUILDS IN
EVEN MORE SO OVER THE WEST.
THE GUIDANCE REMAINS IN GOOD AGREEMENT ON THE LARGE-SCALE PATTERN
THROUGH THE MIDDLE OF THE PERIOD, WITH THE TYPICAL INCREASE IN
UNCERTAINTY ON SMALLER-SCALE SHORTWAVE FEATURES, BEFORE A MORE
SIGNIFICANT DIFFERENCE EMERGES UPSTREAM OVER THE NORTHEASTERN
PACIFIC IN THE MID- TO LATE PERIOD. THE 00Z ECMWF AND CMC SHOW A
MUCH MORE EXPANSIVE RIDGE OVER THE WEST, ANCHORED OVER THE
NORTHEASTERN PACIFIC, WITH AN UPPER-LEVEL HIGH DEVELOPING OVER THE
NORTHEASTERN PACIFIC. IN CONTRAST, THE MORE RECENT 00Z AND 06Z
RUNS OF THE GFS HAVE SHOWN A DEEP UPPER-LEVEL LOW OVER THE GULF OF
ALASKA TRANSITIONING INTO AN OPEN WAVE MOVING SOUTHEAST INTO
SOUTHWEST CANADA AND THE PACIFIC NORTHWEST. ANOTHER FEATURE OF
NOTE HAS BEEN THE EVOLUTION OF AN UPPER-LEVEL LOW ALONG THE COAST
OF CALIFORNIA RELATED TO THE REMNANTS OF TROPICAL STORM EUGENE
OVER THE EASTERN PACIFIC. RECENT RUNS OF THE GFS THROUGH 00Z HAVE
BEEN TRENDING TOWARDS A MORE EXPANSIVE WEAKNESS IN THE FLOW,
COMBINING WITH THE WAVE TO THE NORTH, AS OPPOSED TO A CUTOFF
UPPER-LOW EMBEDDED SOUTH OF THE RIDGE IN THE ECMWF, AND TO A
LESSER EXTENT THE CMC. THE 06Z GFS TRENDED SLIGHTLY BACK TOWARDS
THE 00Z ECMWF SOLUTION WITH RESPECT TO THESE FEATURES AS WELL AS
THE OVERALL PATTERN ACROSS THE WEST AND NORTHEASTERN PACIFIC,
THOUGH STILL SHOWS SIGNIFICANT DIFFERENCES. ALSO, THE 00Z CMC
DIFFERS FROM THE 00Z ECMWF AND 06Z GFS BY DEVELOPING A MORE POTENT
UPPER-LEVEL WAVE DROPPING SOUTH FROM NORTHWEST CANADA INTO THE
NORTH-CENTRAL U.S. TOWARDS THE END OF THE FORECAST PERIOD COMPARED
TO THE MEAN LONG-WAVE TROUGHING FURTHER EAST OVER THE NORTHERN
TIER IN THE OTHER GUIDANCE. THE 00Z ECENS MEAN FAVORS THE
UPPER-LEVEL HIGH OVER THE NORTHEASTERN PACIFIC AND MEAN LONG-WAVE
TROUGHING TO THE EAST, WITH A SIMILAR BUT SLIGHTLY LESS AMPLIFIED
SOLUTION IN THE 00Z GEFS MEAN.
THE UPDATED WPC FORECAST USES A GENERAL MODEL BLEND OF THE 00Z
DETERMINISTIC GUIDANCE (06Z FOR THE GFS) WITH A BIT MORE EMPHASIS
ON THE ECMWF GIVEN THE OVERALL TREND THROUGH THE FORECAST PERIOD.
THE 00Z ECMWF SOLUTION IS INCREASINGLY FAVORED IN THE MID- TO LATE
FORECAST PERIOD AS BOTH THE 00Z ECENS AND GEFS MEANS SUPPORT A
SIMILAR PATTERN EVOLUTION. CONTRIBUTIONS FROM THESE ENSEMBLE MEANS
ARE INCREASED AS SMALLER-SCALE DIFFERENCES GROW OVERALL IN THE
DETERMINISTIC GUIDANCE WITH INCREASING FORECAST LEAD TIME,
INCLUDING THE ADDITIONAL NOTED DIFFERENCES IN THE EVOLUTION OVER
THE NORTHERN TIER OF THE COUNTRY BETWEEN THE CMC AND ECMWF/GFS.
THIS BLEND REMAINS CONSISTENT TO THE PRIOR WPC FORECAST WHICH
FAVORED THE ECMWF/ECENS SOLUTIONS AND THUS RESULTS IN A SIMILAR
FORECAST WITH RESPECT TO BROAD UPPER-LEVEL RIDGING OVER THE
NORTHEASTERN PACIFIC/WESTERN CANADA AND U.S.
..WEATHER/HAZARDS HIGHLIGHTS
THE POTENTIALLY HEAVY CONVECTIVE EVENT EXPECTED OVER PARTS OF THE
MISSISSIPPI/TENNESSEE VALLEY REGION ON WEDNESDAY (NOW IN THE SHORT
RANGE TIME FRAME) SHOULD EXTEND EASTWARD TOWARD THE SOUTHERN
APPALACHIANS AND VICINITY BY THURSDAY, FAVORING MAINTENANCE OF THE
SLIGHT RISK AREA DEPICTED IN THAT REGION FOR THE NEW DAY 4
EXCESSIVE RAINFALL OUTLOOK. SIMILAR TO YESTERDAY, GUIDANCE OFFERS
SOME CONFLICTING IDEAS FOR SURROUNDING DETAILS FROM THE
MISSISSIPPI AND OHIO RIVERS THROUGH THE CENTRAL APPALACHIANS
WITHIN AN OVERALL SIGNAL FOR SOME LOCALLY HEAVY RAINFALL, WITH A
MARGINAL RISK MAINTAINED FOR THE REGION. DURING DAYS 4-5
THURSDAY-FRIDAY, THE OUTLOOKS SHOW A MARGINAL RISK AREA FROM THE
NORTHERN PLAINS INTO THE CENTRAL GREAT LAKES WITH THE SYSTEM
APPROACHING/CROSSING THE REGION. SOME LOCALLY INTENSE RAINFALL
MAY OCCUR BUT ANTECEDENT GROUND CONDITIONS ARE ON THE DRIER SIDE
AND MODERATE PROGRESSION MAY TEMPER TOTALS SOMEWHAT OVERALL. FOR
DAY 5 FROM THE EAST-CENTRAL PLAINS INTO THE SOUTHEAST, THERE ARE
SOME DIFFUSE GUIDANCE SIGNALS FOR LOCALLY HEAVY RAINFALL WITHIN AN
ENVIRONMENT OF MODERATELY ABOVE NORMAL PRECIPITABLE WATER VALUES
AND DECENT INSTABILITY. IN ADDITION ONE OR MORE WAVES/FRONTS MAY
PROVIDE SOME SYNOPTIC FOCUS FOR CONVECTION. THIS SCENARIO APPEARS
TO SUPPORT A MARGINAL RISK AREA AT THIS TIME, WITH BETTER
DEFINITION PERHAPS ARISING IN A FEW RUNS.
FROM THE WEEKEND INTO EARLY NEXT WEEK, EXPECT SOME SHOWERS AND
THUNDERSTORMS TO CONTINUE INTO THE EAST WITH PROGRESSION OF THE
GREAT LAKES SYSTEM AND TRAILING FRONT, WITH ANOTHER ROUND OF SOME
LIGHTER, SCATTERED SHOWERS POSSIBLE ACROSS THE NORTHERN TIER WITH
ANOTHER SYSTEM SUNDAY-MONDAY. EXPECT FLORIDA TO SEE AN INCREASE
OF RAINFALL THIS WEEKEND AS AN AREA OF ENHANCED MOISTURE MOVES IN
FROM THE EAST. THE FOUR CORNERS/SOUTHEAST/CALIFORNIA SHOULD SEE
DIURNALLY FAVORED EPISODES OF CONVECTION, THOUGH MODEL/ENSEMBLE
DIFFERENCES IN THE DISTRIBUTION/MAGNITUDE OF MOISTURE ANOMALIES
(INCLUDING WHAT MAY HAPPEN WITH ANY UPPER LEVEL MOISTURE FROM
EUGENE) KEEP CONFIDENCE LOWER THAN DESIRED FOR SPECIFICS. ONE OR
MORE FRONTS SETTLING INTO THE CENTRAL/SOUTH-CENTRAL PLAINS LOOK
PROVIDE A FOCUS FOR HEAVIER SHOWERS AND THUNDERSTORMS OVER THAT
REGION THIS WEEKEND, WITH SOME OF THE MOISTURE OVER THE WEST
POSSIBLY DRIFTING EAST TO CONTRIBUTE.
THE ONGOING HEAT WAVE OVER THE SOUTHERN TIER SHOULD CONTINUE
THROUGH THE WEEKEND AND EARLY NEXT WEEK, WITH GREATEST EMPHASIS
OVER THE SOUTHERN HIGH PLAINS WHERE HIGHS COULD REACH 10-15F ABOVE
NORMAL ESPECIALLY LATE THIS WEEK. TEMPERATURES MAY REACH OR
EXCEED DAILY RECORD HIGHS FROM THE CENTRAL/WESTERN GULF COAST INTO
THE SOUTHERN ROCKIES THURSDAY-FRIDAY, WITH THE COVERAGE OF
POSSIBLE RECORD HIGHS TENDING TO DECREASE GRADUALLY THEREAFTER.
HIGH HUMIDITY SHOULD LEAD TO MAXIMUM HEAT INDICES AT LEAST IN THE
110-115F RANGE ALONG AND NEAR THE WESTERN HALF OF THE GULF COAST.
THE DESERT SOUTHWEST SHOULD SEE A BRIEF LULL IN THE 110F+ HIGHS
THROUGH LATE WEEK BUT TEMPERATURES MAY REACH INTO THE LOWER HALF
OF THE 110S ONCE AGAIN BY SUNDAY-MONDAY AS THE UPPER RIDGE
STRENGTHENS OVER THE WEST. THE FLORIDA PENINSULA COULD ALSO SEE A
FEW RECORD HIGHS. 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. VERY
WARM TO HOT TEMPERATURES MAY EXTEND BEYOND THE MEDIUM RANGE
FORECAST PERIOD. IN CONTRAST, THE FORECAST PATTERN WILL TEND TO
FAVOR NEAR TO MODERATELY BELOW NORMAL HIGH TEMPERATURES FROM THE
NORTHERN ROCKIES INTO THE MIDWEST/OHIO VALLEY. THE UPPER
TROUGH/LOW DEVELOPING NEAR CALIFORNIA SHOULD KEEP HIGHS OVER MOST
OF THE STATE NEAR OR SLIGHTLY BELOW NORMAL AT LEAST THROUGH LATE
WEEK.
PUTNAM/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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN/CENTRAL APPALACHIANS,
AND THE OHIO/TENNESSEE VALLEY,
THU, AUG 10.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN PLAINS.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE MIDDLE
MISSISSIPPI VALLEY.
- FLOODING LIKELY ACROSS PORTIONS OF THE NORTHERN PLAINS.
- HAZARDOUS HEAT ACROSS PORTIONS OF CALIFORNIA AND THE PACIFIC
NORTHWEST, SUN, AUG 13.
- HAZARDOUS HEAT ACROSS PORTIONS OF CALIFORNIA AND THE PACIFIC
NORTHWEST, FRI-SUN, AUG 11-AUG 13.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,
THE SOUTHERN ROCKIES, CALIFORNIA,
THE SOUTHEAST, THE SOUTHERN PLAINS, AND THE SOUTHWEST, THU-MON,
AUG 10-AUG 14.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE CENTRAL PLAINS AND THE
SOUTHERN PLAINS, THU-FRI, AUG 10-AUG
11.
- HEAVY RAIN ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND
ALASKA, SAT, AUG 12.
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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