745
FXUS02 KWBC 090659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT WED AUG 09 2023
VALID 12Z SAT AUG 12 2023 - 12Z WED AUG 16 2023
...HEAT WAVE TO PERSIST OVER THE SOUTH INTO THE SOUTHWEST THROUGH
AT LEAST THE MIDDLE OF NEXT WEEK...
..HAZARDOUS HEAT POSSIBLE OVER THE PACIFIC NORTHWEST NEXT WEEK
..OVERVIEW
NOT MUCH HAS CHANGED IN THE GUIDANCE ACROSS THE SOUTHERN TIER,
WITH STRONG SOUTHERN PLAINS THROUGH FLORIDA UPPER RIDGING LIKELY
TO BUILD GRADUALLY WESTWARD TOWARD THE SOUTHWEST U.S., EVENTUALLY
DISPLACING AN UPPER LOW FORECAST TO HOVER NEAR THE CALIFORNIA
COAST THROUGH THE WEEKEND. THERE IS STILL POTENTIAL FOR THE
NORTHWESTERN PART OF THIS RIDGE TO CONNECT WITH A SEPARATE RIDGE
BUILDING OVER THE NORTHEASTERN PACIFIC. THE EXPANDING RIDGE WILL
MAINTAIN THE 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 INTO THE
CENTRAL GULF COAST REGION, WHILE SUPPORTING A HOTTER TREND OVER
THE SOUTHWEST BY NEXT WEEK. THE PACIFIC NORTHWEST SHOULD SEE VERY
WARM TO HOT TEMPERATURES BY NEXT WEEK AS WELL. AWAY FROM THE
BROAD AREA OF UPPER RIDGING, BROAD CYCLONIC FLOW WILL PREVAIL OVER
THE NORTHERN HALF OR SO OF THE LOWER 48 EAST OF THE ROCKIES. A
SUCCESSION OF EMBEDDED SHORTWAVES SHOULD SUPPORT SURFACE
WAVES/FRONTAL SYSTEMS THAT MAY BE CAPABLE OF PRODUCING EPISODES OF
LOCALLY STRONG/HEAVY CONVECTION. THESE FEATURES HAVE VARYING
DEGREES OF PREDICTABILITY, WITH GREATER CONFIDENCE IN THE GENERAL
PATTERN OF PROGRESSIVE SURFACE WAVES/FRONTS THAN SOME OF THE FINER
BUT IMPORTANT DETAILS.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
OVERALL THE MODELS AND ENSEMBLE MEANS HAVE BEEN AGREEING ON THE
GENERAL THEME OF SHORTWAVES WITHIN THE PROGRESSIVE NORTHERN TIER
FLOW SUPPORTING A SERIES OF SURFACE LOWS/FRONTAL SYSTEMS, BUT WITH
SOME TYPICAL DISCREPANCIES GIVEN THE SCALE OF THE SHORTWAVES.
ALREADY BY THE START OF THE PERIOD EARLY SATURDAY, RECENT GFS RUNS
HAVE BEEN DIFFERING SOMEWHAT FROM MOST OTHER GUIDANCE FOR DETAILS
OF FLOW COMING INTO WESTERN CANADA, WITH INCREASINGLY NOTICEABLE
EFFECTS DOWNSTREAM WITH TIME. THE GFS IS A BIT ON THE SLOWER SIDE
WITH THE LEADING SYSTEM TRACKING EAST/NORTHEAST FROM THE GREAT
LAKES DURING THE WEEKEND, BUT DIFFERENCES ARE MORE SIGNIFICANT
WITH THE TRAILING SHORTWAVE/SURFACE SYSTEM. THE GFS IS IN THE
MINORITY SHOWING A SOMEWHAT FASTER/BROADER SHORTWAVE AS OF SUNDAY,
AND WHILE ITS SHORTWAVE SHARPENS LIKE CONSENSUS BY MONDAY THE END
RESULT IS TO LOSE THE WELL-DEFINED GREAT LAKES SURFACE SYSTEM SEEN
IN THE LATEST ECMWF/CMC/UKMET RUNS AND THE ECENS/CMCENS MEANS.
LATEST GEFS MEANS TILT IN THE GFS DIRECTION IN SLIGHTLY MORE
SUBDUED FORM. FROM MONDAY ONWARD, THIS MEANS A DIFFERENCE BETWEEN
THE ECMWF CLUSTER SHOWING YET ANOTHER RATHER STRONG SYSTEM
TRACKING INTO NEW ENGLAND OR SOUTHEASTERN CANADA VERSUS THE
18Z/00Z GFS DEPICTING A WEAKER COASTAL WAVE. THE 12Z GFS DID HAVE
SOME ASPECTS CLOSER TO THE ECMWF CLUSTER THOUGH.
ANOTHER POINT OF CONTENTION ARISES BY TUESDAY-WEDNESDAY WHEN
AMPLIFICATION OF INCOMING PACIFIC FLOW AND POSSIBLY CENTRAL CANADA
FLOW TO THE NORTH REACHES INTO THE NORTHERN TIER STATES. THE 18Z
GFS IN PARTICULAR LOOKED SOMEWHAT UNDERDONE WITH ITS TROUGH
AMPLITUDE, KEEPING THE ASSOCIATED SURFACE FRONT FARTHER NORTH.
AGAIN THE 12Z GFS WAS SOMEWHAT CLOSER TO THE AVERAGE OF OTHER
MODELS/MEANS, THOUGH IT MAY HAVE BEEN A BIT SLOW WITH ITS OVERALL
TROUGH AXIS. ALSO OF NOTE OVER THE WEST, THE 00Z GFS IS STRONGER
THAN OTHER GUIDANCE WITH SHORTWAVE ENERGY THAT LIFTS INTO THE
GREAT BASIN/INTERMOUNTAIN WEST BY EARLY NEXT WEEK.
BASED ON GUIDANCE COMPARISONS FROM THE 12Z/18Z CYCLE, THE UPDATED
FORECAST FOR THE FIRST HALF OF THE PERIOD STARTED WITH INPUT FROM
THE 12Z ECMWF/UKMET/CMC WITH A SMALL CONTRIBUTION FROM THE 18Z
GEFS MEAN IN PLACE OF THE SEEMINGLY LESS DESIRABLE 18Z GFS. THEN
THE BLEND TRANSITIONED TOWARD SOMEWHAT MORE EMPHASIS ON THE 12Z
ECENS/CMCENS AND 18Z GEFS MEANS RELATIVE TO THE ECMWF/CMC RUNS
GIVEN TYPICALLY INCREASING DETAIL UNCERTAINTIES. THIS APPROACH
YIELDED FAIRLY GOOD OVERALL CONTINUITY WHILE BEGINNING TO TREND
PARTIALLY TOWARD THE STRONGER GREAT LAKES-NEW ENGLAND SYSTEM
AROUND THE START OF NEXT WEEK.
..WEATHER/HAZARDS HIGHLIGHTS
DURING THE SATURDAY-SUNDAY NIGHT PERIOD COVERED BY THE DAYS 4-5
EXCESSIVE RAINFALL OUTLOOKS, BOTH DAYS SHOULD SEE SOME POTENTIAL
FOR LOCALLY HEAVY CONVECTION OVER PARTS OF THE SOUTHERN
ROCKIES/SOUTH-CENTRAL HIGH PLAINS WITH SOME SHORTWAVE
ENERGY/MOISTURE LIFTING NORTHWARD BETWEEN THE UPPER LOW OVER THE
CALIFORNIA COAST AND RIDGE TO THE EAST, WHILE A COUPLE FRONTS MAY
DROP INTO THE CENTRAL HIGH PLAINS TO PROVIDE ADDED FOCUS. A
MARGINAL RISK AREA ACCOUNTS FOR THIS POTENTIAL. AREAS FROM THE
SOUTHEAST INTO PARTS OF THE MISSISSIPPI/TENNESSEE VALLEY AND
NORTHEASTWARD INTO THE AND NEAR THE EASTERN GREAT LAKES ARE ALSO
IN A MARGINAL RISK AREA FOR DAY 4, WITH A COUPLE FRONTAL SYSTEMS
INTERACTING WITH ABOVE NORMAL MOISTURE AND INSTABILITY. ONE OR
MORE EMBEDDED SLIGHT RISK AREAS COULD EVENTUALLY ARISE IF SHORTER
TERM GUIDANCE EVENTUALLY STARTS TO REFINE WHERE MORE PRONOUNCED
FOCUS MAY EXIST. THERE IS ALSO A DIFFUSE SIGNAL FOR LOCALLY HEAVY
CONVECTION OVER PARTS OF THE NORTH-CENTRAL PLAINS/MIDWEST ON DAY 4
BUT CLUSTERING DOES NOT APPEAR SUFFICIENT TO WARRANT A RISK AREA
AT THIS TIME. ON DAY 5, LEANING TOWARD THE MAJORITY ECMWF CLUSTER
FOR UPPER LEVEL AND SURFACE EVOLUTION OVER THE MIDWEST WOULD
SUPPORT A FAIRLY BROAD AREA OF LOCALLY HEAVY CONVECTIVE POTENTIAL
THAT COULD LINK BACK TO THE SOUTH-CENTRAL HIGH PLAINS. THUS PLAN
TO DEPICT A MARGINAL RISK AREA OVER THE MIDWEST AND CONNECTING
WITH THE AFOREMENTIONED SOUTHERN ROCKIES/HIGH PLAINS AREA.
FLORIDA MAY SEE SOME INCREASED RAINFALL DURING DAYS 4-5 AS
MOISTURE ANOMALIES INCREASE BUT COMPARED TO A COUPLE DAYS AGO THE
GUIDANCE HAS BECOME MORE DIVERSE REGARDING THE TIMING AND
MAGNITUDE OF MOISTURE ANOMALIES, SO WILL NOT DEPICT A RISK AREA
THERE AT THIS TIME.
MOISTURE AND SHORTWAVE ENERGY SHOULD PRODUCE SOME DIURNALLY
ENHANCED SHOWERS AND THUNDERSTORMS OVER OTHER PORTIONS OF THE WEST
DURING THE PERIOD, WITH CONFIDENCE TEMPERED BY GUIDANCE
DIFFERENCES IN SPECIFICS OF LOCATION/STRENGTH OF THE UPPER LEVEL
ENERGY AND MOISTURE DETAILS. MEANWHILE THE SYSTEM WHICH THE
GUIDANCE MAJORITY DEPICTS OVER THE GREAT LAKES BY MONDAY COULD
PRODUCE ANOTHER EPISODE OF CONVECTION THAT COULD BE STRONG/HEAVY
OVER SOME AREAS OF THE EASTERN U.S. CONTINUE TO MONITOR FORECASTS
AS GUIDANCE EVENTUALLY COMES INTO BETTER AGREEMENT ON SYSTEM
DETAILS. YET ANOTHER COLD SHOULD DROP INTO THE NORTHERN PLAINS BY
TUESDAY-WEDNESDAY, WITH SOME ASSOCIATED RAINFALL POSSIBLE.
THE HEAT ACROSS THE SOUTHERN TIER WILL LIKELY CONTINUE THROUGH AT
LEAST THE MIDDLE OF NEXT WEEK WITH THE GREATEST EMPHASIS 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, WHILE WESTWARD EXPANSION OF THE UPPER RIDGE AS CURRENTLY
FORECAST WOULD ALSO RAISE TEMPERATURES IN THE SOUTHWEST UP TO
5-10F ABOVE NORMAL BY NEXT MONDAY-WEDNESDAY (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 WILL BE POSSIBLE
BY EARLY-MID WEEK BUT FORECAST HIGHS ARE NOT YET REACHING DAILY
RECORD VALUES. AREAS FROM THE NORTHERN ROCKIES THROUGH
NORTHERN-CENTRAL PARTS OF THE EAST WILL SEE VARIABLE TEMPERATURES
UP TO 5-10F ON EITHER SIDE OF NORMAL, CORRESPONDING TO
SYSTEM/FRONTAL PROGRESSION. THE UPPER TROUGH/LOW NEAR CALIFORNIA
SHOULD KEEP HIGHS OVER THE SOUTHWEST SLIGHTLY BELOW NORMAL INTO
THE WEEKEND, FOLLOWED BY A WARMER TREND AS THE FEATURE DRIFTS
WESTWARD.
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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