980
FXUS02 KWBC 021847
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 PM EDT SUN JUL 02 2023
VALID 12Z WED JUL 05 2023 - 12Z SUN JUL 09 2023
...MAJOR SOUTHERN TIER HEAT WAVE TO EASE THIS WEEK, BUT MAY START
TO REBUILD OVER THE SOUTHERN HIGH PLAINS AND VICINITY NEXT
WEEKEND...
..OVERVIEW
A WEAK SHORTWAVE WILL DEPART FROM THE NORTHEAST ON WEDNESDAY AND
TAKE ITS ASSOCIATED FRONTAL SYSTEM WITH IT, ASIDE FROM THE
TRAILING PART OF THE FRONT THAT WILL LINGER OVER THE SOUTHERN
MID-ATLANTIC. FARTHER WEST AN UPPER TROUGH EXTENDING FROM CANADA
INTO THE NORTHERN PLAINS AS OF WEDNESDAY WILL PROGRESS EASTWARD
WITH TIME, PUSHING A CENTRAL U.S. FRONT TOWARD THE EAST COAST AND
SOUTHERN STATES. PROGRESSION OF THIS FRONT WILL PRODUCE A BROAD
AREA OF SHOWERS/THUNDERSTORMS OVER THE CENTRAL-EASTERN STATES OVER
THE COURSE OF THE PERIOD. IN ADDITION, PERSISTENCE OF THE WESTERN
PART OF THE FRONT OVER THE PLAINS AND ITS EVENTUAL RETURN
NORTHEAST AS A WARM FRONT MAY HELP TO GENERATE MORE LOCALLY HEAVY
CONVECTION OVER THE CENTRAL PLAINS/MISSOURI VALLEY LATE THIS WEEK
INTO THE WEEKEND. MEANWHILE CONSENSUS MAINTAINS THE IDEA OF A
WEST COAST UPPER TROUGH (WITH POSSIBLE EMBEDDED LOW) SETTLING OVER
THE WEST COAST FROM THURSDAY ONWARD IN RESPONSE TO AN EASTERN
PACIFIC RIDGE. AN UPPER HIGH OVER THE SOUTHERN ROCKIES/HIGH
PLAINS THROUGH THE PERIOD COULD BEGIN TO STRENGTHEN SLIGHTLY NEXT
WEEKEND, WITH A SOMEWHAT BETTER DEFINED INTERIOR WEST/ROCKIES
RIDGE EXTENDING TO THE NORTH-NORTHWEST INTO CANADA LATE WEEK INTO
THE WEEKEND AS THE WEST COAST TROUGH BECOMES ESTABLISHED.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS REASONABLY WELL CLUSTERED THROUGH THE EARLY TO
MID-FORECAST PERIOD NEXT WEEK WITH DECENT RUN-TO-RUN CONTINUITY
ALSO EVIDENT IN THE ECMWF/GFS, INDICATIVE OF AN ABOVE AVERAGE
LEVEL OF PREDICTABILITY. A FRONTAL SYSTEM AND ASSOCIATED
UPPER-LEVEL WAVE WILL STALL/LINGER ALONG THE EAST COAST AS ANOTHER
SHORTWAVE UPSTREAM OVER SOUTH-CENTRAL CANADA DRIVES A COLD FRONT
SOUTHEASTWARD ACROSS THE PLAINS/MIDWEST. THIS STRONGER FRONT
SHOULD PASS THROUGH TO THE SOUTHERN TIER SUPPORTED BY ADDITIONAL
SUBTLE SHORTWAVE ENERGY IN THE MEAN FLOW, KEEPING PRECIPITATION
CHANCES UP ALONG THE BOUNDARY. WEAK UPPER-RIDGING IN THE SOUTHERN
STREAM SHOULD REMAIN IN PLACE OVER PORTIONS OF THE
SOUTH-CENTRAL/SOUTHWEST CONUS WITH A HINT THIS MAY BUILD NORTHWARD
TOWARDS THE END OF THE PERIOD. ONE NOTABLE AREA OF GUIDANCE
DISAGREEMENT AND MUCH LOWER PREDICTABILITY COMPARED TO THE REST OF
THE OVERALL PATTERN IS WITH THE DISTRIBUTION/EVOLUTION OF UPSTREAM
ENERGY OVER WESTERN CANADA AND THE NORTHEASTERN PACIFIC BEGINNING
TO IMPINGE ON THE PACIFIC NORTHWEST AT THE END OF THE FORECAST
PERIOD. MEAN RIDGING LOOKS TO DEVELOP IN THE NORTHERN STREAM OVER
WESTERN CANADA AS AN UPPER-LEVEL LOW CUTS OFF AND RETROGRADES WEST
A BIT, BUT THE DETAILS ARE STILL UNCLEAR AND THIS MAY HAVE AN
IMPACT ON ABOVE AVERAGE TEMPERATURES EXPECTED OVER THE PACIFIC
NORTHWEST THROUGH NEXT WEEKEND. THERE ARE ALSO SOMEWHAT SUBTLE BUT
LIKELY INFLUENTIAL DIFFERENCES WITH THE POTENTIAL FOR ANOTHER
NORTHERN STREAM SHORTWAVE TO DRIVE A FRONTAL SYSTEM SOUTHWARD INTO
THE NORTH-CENTRAL CONUS WHICH WAS ALSO NOTED IN THE PRIOR
FORECAST.
GIVEN THE RELATIVELY GOOD AGREEMENT IN THE EARLY TO MID-FORECAST
PERIOD A GENERAL MODEL BLEND OF THE 00Z ECMWF/CMC/UKMET AND 06Z
GFS IS USED FOR THIS UPDATE AND RETAINS CONTINUITY WITH THE PRIOR
FORECAST. A CONTRIBUTION FROM THE 00Z GEFS/ECENS MEANS IS
INTRODUCED MID PERIOD AS THE FORECAST TIME-LIMITED UKMET IS
REMOVED, AND INCREASED THROUGH THE END OF THE PERIOD AS MORE
SUBTLE DETAILS WITH REGARD TO SHORTWAVE ENERGY LOSE
PREDICTABILITY. A LARGER CONTRIBUTION FROM THE 00Z ECMWF IS
FAVORED OVER THE GFS TOWARDS THE END OF THE FORECAST PERIOD AS
WELL GIVEN BETTER RUN-TO-RUN CONTINUITY. OVERALL, THIS UPDATE LED
TO VERY MINIMAL CHANGES IN THE OVERALL WPC MEDIUM-RANGE PRODUCT
SUITE, ONCE AGAIN INDICATIVE OF ABOVE AVERAGE PREDICTABILITY AND
RUN-TO-RUN CONSISTENCY. HOWEVER, MESOSCALE DRIVEN SUMMERTIME
RAINFALL PATTERN LEADS TO LESS CONFIDENCE IN ASSOCIATED QPF
FORECAST DESPITE A GOOD HANDLE ON THE OVERALL SYNOPTIC PATTERN.
..WEATHER/HAZARDS HIGHLIGHTS
THE WAVY COLD FRONT PROGRESSING FROM THE UPPER MIDWEST/CENTRAL
PLAINS INTO THE EASTERN/SOUTHERN U.S. WILL LIKELY PRODUCE MULTIPLE
EPISODES OF SHOWERS AND THUNDERSTORMS, WITH SOME LOCALLY HEAVY.
THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS COVERING THE WEDNESDAY
THROUGH THURSDAY NIGHT TIME FRAME CONTINUE TO DEPICT A BROAD
MARGINAL RISK AREA FROM THE WESTERN GREAT LAKES THROUGH THE
MID/UPPER MISSISSIPPI VALLEY AND CENTRAL/SOUTH-CENTRAL PLAINS (DAY
4) AND OHIO VALLEY SOUTH-SOUTHWEST TO THE GULF COAST (DAY 5). AT
THIS TIME GUIDANCE SIGNALS ARE NOT YET COHERENT ENOUGH FOR ANY
SLIGHT RISK AREAS BUT ONE OR MORE COULD EVENTUALLY ARISE IF SHORT
RANGE MODELS BEGIN TO CLUSTER BETTER. FRONTAL WAVE SPECIFICS WILL
PLAY A ROLE IN HOW MUCH RAIN FALLS OVER THE UPPER MIDWEST AND
VICINITY AROUND MIDWEEK. BY THURSDAY-THURSDAY NIGHT, GUIDANCE IS
SIGNALING POTENTIAL FOR LOCALLY HEAVY CONVECTION TO DEVELOP OVER
THE CENTRAL PLAINS AS THE TRAILING PART OF THE FRONT STALLS TO THE
SOUTH AND WEST OF THE REGION. DIFFERENCES IN THE MODEL GUIDANCE
PRECLUDE ANYTHING MORE THAN A MARGINAL RISK FOR NOW, BUT SOME OF
THE GUIDANCE IS SIGNALING THE POTENTIAL FOR MORE WIDESPREAD AREAL
COVERAGE OF HEAVY RAIN TOTALS SUPPORTIVE OF A SLIGHT RISK.
MEANWHILE THE DAYS 4-5 OUTLOOKS HAVE A MARGINAL RISK AREA MAINLY
OVER THE CAROLINAS, WHERE ESPECIALLY ON DAY 4 LATEST SOLUTIONS
SHOW A DECENT COMBINATION OF INSTABILITY, ANOMALOUS MOISTURE, AND
CORRESPONDING LOCALLY HEAVY QPF, ALONG AND AHEAD OF A STALLING
SURFACE FRONT. THE FRONT MAY WEAKEN SOME BY DAY 5 BUT THE
MOISTURE AND INSTABILITY SHOULD PERSIST. BEYOND THURSDAY NIGHT,
EXPECT LOCALLY HEAVY RAINFALL TO CONTINUE EASTWARD TOWARD/THROUGH
THE EAST COAST INTO THE WEEKEND WHILE THE CENTRAL PLAINS INTO THE
MIDDLE/LOWER MISSOURI VALLEY WILL SEE ADDITIONAL HEAVY RAINFALL.
EXCESSIVE HEAT ACROSS THE SOUTHERN TIER SHOULD BECOME LESS
WIDESPREAD FOR A TIME THIS WEEK AS UPPER RIDGING RETURNS CLOSER TO
CLIMATOLOGICAL STRENGTH AND LATITUDE. THE BEST POTENTIAL FOR
MAXIMUM HEAT INDEX VALUES TO REACH 105-110F, LOCALLY UP TO 115F,
MID-LATE WEEK SHOULD BE MORE CONFINED TO THE FAR SOUTHEAST/FLORIDA
AND CENTRAL GULF COAST THROUGH SOUTHERN TEXAS. UPPER RIDGING OVER
THE SOUTHERN ROCKIES/HIGH PLAINS WILL KEEP TEMPERATURES 5-10
DEGREES ABOVE NORMAL, WITH THE POTENTIAL THIS MAY BUILD FURTHER
NORTHWARD NEXT WEEKEND. THE GREATEST ANOMALIES WILL BE OVER THE
PACIFIC NORTHWEST WITH HIGHS UP TO 15-20F ABOVE NORMAL WEDNESDAY
(WITH SOME DAILY RECORD HIGHS POSSIBLE) FOLLOWED BY GRADUAL
MODERATION AS UPPER TROUGHING LOOKS TO DIG IN FROM THE NORTH.
MEANWHILE, TO THE NORTH OF THE PLAINS COLD FRONT EXPECT
UNSEASONABLY COOL HIGHS 10-20F BELOW NORMAL OVER THE
NORTHERN-CENTRAL HIGH PLAINS ESPECIALLY ON WEDNESDAY, WITH GRADUAL
MODERATION LEADING TO SINGLE-DIGIT NEGATIVE ANOMALIES BY THE
WEEKEND. THE LEADING WARM SECTOR WILL BRING ABOVE NORMAL
TEMPERATURES FROM THE MIDWEST INTO NORTHEAST MID-LATE WEEK,
FOLLOWED BY NEAR OR SLIGHTLY BELOW NORMAL READINGS AFTER FRONTAL
PASSAGE.
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
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION, EXPERIMENTAL 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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