455
FXUS02 KWBC 011757
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
156 PM EDT SAT JUL 01 2023
VALID 12Z TUE JUL 04 2023 - 12Z SAT JUL 08 2023
...MAJOR HEATWAVE FROM TEXAS THROUGH THE MID-LOWER MISSISSIPPI
VALLEY TO THE SOUTHEAST TO EASE NEXT WEEK...
..OVERVIEW
THE LATEST MODELS AND ENSEMBLE MEANS MAINTAIN GOOD CONTINUITY AND
REASONABLE AGREEMENT FOR THE EXPECTED PATTERN FROM
TUESDAY/INDEPENDENCE DAY THROUGH NEXT SATURDAY. A WEAK UPPER
TROUGH WITH POSSIBLE EMBEDDED LOW WILL LIFT THROUGH THE NORTHEAST
U.S. AND EASTERN CANADA INTO MIDWEEK, PUSHING ALONG AN ASSOCIATED
WAVY FRONTAL SYSTEM THAT MAY PRODUCE SOME LINGERING RAINFALL EARLY
IN THE PERIOD. FARTHER WEST WILL BE THE PRIMARY FOCUS OF THE
FORECAST, A WAVY COLD FRONT THAT WILL PUSH SLOWLY BUT STEADILY
SOUTH AND EAST FROM THE NORTH-CENTRAL PLAINS INTO THE
SOUTHERN/EASTERN STATES AS AN UPPER TROUGH EXTENDING FROM CANADA
INTO THE LOWER 48 PROGRESSES EASTWARD. THIS FRONT WILL LIKELY BE
RESPONSIBLE FOR MULTIPLE DAYS OF SHOWERS AND THUNDERSTORMS FROM
THE CENTRAL INTO EASTERN U.S. MEANWHILE EASTERN PACIFIC RIDGING
SHOULD SUPPORT UPPER TROUGH DEVELOPMENT NEAR THE WEST COAST DURING
THE LATTER HALF OF NEXT WEEK, WHICH IN TURN MAY HELP TO STRENGTHEN
INTERIOR WEST/ROCKIES RIDGING A BIT.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
LATEST 00Z/06Z GUIDANCE FROM THIS MORNING CONTINUES TO SUPPORT A
GENERAL DETERMINISTIC MODEL BLEND THROUGH DAY 5, WITH ADDITION OF
THE GEFS/ECENS MEANS BY DAYS 6-7 GIVEN THE TYPICAL INCREASE IN
SPREAD OF THE DETAILS. ON THE LARGE SCALE THOUGH, MODELS DO SHOW
GOOD AGREEMENT ON THE OVERALL PATTERN THROUGH THE ENTIRE PERIOD.
THE 00Z UKMET IS A LITTLE DIFFERENT WITH THE TROUGHING THROUGH THE
NORTHEAST, BUT THE REST OF THE GUIDANCE DOES SHOW GOOD CONSENSUS
ON THAT FEATURE. ELSEWHERE, THE 06Z (AND TO A LESSER EXTENT THE
NEW 12Z) GFS IS SHARPER WITH THE SHORTWAVE UPSTREAM MOVING THROUGH
THE NORTHERN U.S. RESULTING IN A LITTLE STRONGER AND FARTHER SOUTH
SURFACE LOW PRESSURE NEAR THE GREAT LAKES LATE WEEK. OUT WEST, THE
LATEST CYCLE OF MODELS SHOWS THE SAME DIFFERENCES AS NOTED IN THE
PREVIOUS FORECAST -- THE GFS TENDING TO SPLIT ENERGY NEAR THE
NORTHWEST COAST. THIS PRESENTS SOME ISSUES FARTHER NORTH INTO
WESTERN CANADA AND NEAR ALASKA AS WELL, SO TRENDED AWAY FROM THE
GFS FOR THE LATTER HALF OF THE PERIOD. ONLY MINOR ADJUSTMENTS WERE
NEEDED FROM THE OVERNIGHT WPC MEDIUM RANGE PACKAGE.
..WEATHER/HAZARDS HIGHLIGHTS
THE WAVY COLD FRONT PROGRESSING FROM THE NORTHERN PLAINS AND UPPER
MIDWEST INTO THE EASTERN/SOUTHERN U.S. OVER THE COURSE OF NEXT
WEEK WILL LIKELY PRODUCE MULTIPLE EPISODES OF SHOWERS AND
THUNDERSTORMS, WITH SOME LOCALLY HEAVY. THE DAYS 4-5 EXCESSIVE
RAINFALL OUTLOOKS COVERING THE TUESDAY THROUGH WEDNESDAY NIGHT
TIME FRAME WILL DEPICT A FAIRLY BROAD MARGINAL RISK AREA FROM
PARTS OF THE MISSISSIPPI VALLEY INTO THE HIGH PLAINS, FOLLOWING
THE SOUTHEASTWARD PROGRESSION OF CONVECTION ALONG THE COLD FRONT.
LOW LEVEL UPSLOPE FLOW OVER THE HIGH PLAINS BEHIND THE FRONT COULD
ALSO ENHANCE RAINFALL, OVER AN AREA WHICH MAY BE RELATIVELY MORE
SENSITIVE GIVEN ABOVE NORMAL RAINFALL THE PAST COUPLE OF WEEKS.
CURRENTLY THOUGH, THERE IS NOT ENOUGH AGREEMENT FOR COMBINED
LOCATION/AMOUNTS OF HEAVIEST QPF TO FAVOR ANY EMBEDDED SLIGHT RISK
AREAS BUT ONE OR MORE COULD ARISE AT SOME POINT DEPENDING ON
SHORTER-TERM GUIDANCE CLUSTERING AND/OR OVERLAP WITH WET GROUND
CONDITIONS. BEYOND MIDWEEK EXPECT THE AREA OF SHOWERS/STORMS TO
CONTINUE MOVING SOUTHWARD AND EASTWARD, EVENTUALLY REACHING INTO
THE SOUTH AND EAST COAST REGIONS. PERSISTENCE OF THE TRAILING END
OF THE FRONT OVER THE CENTRAL HIGH PLAINS THROUGH THE REST OF THE
WEEK MAY HELP TO PROMOTE DEVELOPMENT OF ADDITIONAL CONVECTIVE
SYSTEMS OVER THE CENTRAL PLAINS.
ELSEWHERE, THE WEAKER WAVY FRONT CROSSING THE EAST EARLY-MID WEEK
SHOULD ALSO PRODUCE SOME AREAS OF LOCALLY HEAVY RAINFALL GIVEN
SUFFICIENT MOISTURE AND INSTABILITY. CURRENTLY THE BEST SIGNAL
FOR SOME OF THIS ACTIVITY TO LINGER INTO THE DAY 4 TIME FRAME
(TUESDAY-TUESDAY NIGHT) IS OVER NORTHERN NEW ENGLAND WHERE A
MARGINAL RISK AREA IS PLANNED IN LIGHT OF RECENT AND FORECAST
RAINFALL LEADING INTO THAT OUTLOOK. FARTHER SOUTH, THE LATEST DAY
4 OUTLOOK REFLECTS LATEST GUIDANCE SUGGESTION OF AN EASTWARD
EXPANSION OF THE MARGINAL RISK ALONG A WEAKENING FRONT FROM THE
MISSISSIPPI/TENNESSEE VALLEY TO THE NORTH CAROLINA COAST WITH SOME
POTENTIAL LASTING INTO WEDNESDAY AS WELL (STILL TOO UNCERTAIN FOR
EVEN A MARGINAL RISK THOUGH). AREAS CLOSER TO THE GULF COAST WILL
LIKELY SEE TYPICAL DIURNALLY ENHANCED SHOWERS/THUNDERSTORMS OF
VARYING INTENSITY EACH DAY.
EXCESSIVE HEAT ACROSS THE SOUTHERN TIER SHOULD BECOME LESS
WIDESPREAD NEXT WEEK AS UPPER RIDGING RETURNS CLOSER TO
CLIMATOLOGICAL STRENGTH AND LATITUDE. WITH TIME, THE BEST
POTENTIAL FOR MAXIMUM HEAT INDEX VALUES TO REACH 105-110F OR SO
SHOULD BECOME MORE CONFINED TO THE FAR SOUTHEAST/FLORIDA AND
SOUTHERN TEXAS. OVER THE WEST, THE GREATEST ANOMALIES WILL BE OVER
THE PACIFIC NORTHWEST WITH HIGHS UP TO 15-20F ABOVE NORMAL INTO
MIDWEEK FOLLOWED BY GRADUAL MODERATION AS UPPER TROUGHING SETS UP
ALONG THE WEST COAST. SOME DAILY RECORD LOW HIGHS MAY BE POSSIBLE
TUESDAY-WEDNESDAY. PERSISTENT UPPER RIDGING WILL KEEP HOT
CONDITIONS OVER THE SOUTHERN ROCKIES/HIGH PLAINS, WITH SOME
LOCATIONS SEEING HIGHS 5-10F ABOVE NORMAL ON ONE OR MORE DAYS. IN
CONTRAST, TO THE NORTH OF THE PLAINS COLD FRONT EXPECT
UNSEASONABLY COOL HIGHS OF 10-20F OR SO BELOW NORMAL TO DROP INTO
THE NORTHERN AND CENTRAL HIGH PLAINS TUESDAY-THURSDAY, WITH
GRADUAL MODERATION HEADING INTO THE WEEKEND. THE LEADING WARM
SECTOR WILL BRING ABOVE NORMAL TEMPERATURES FROM THE MIDWEST INTO
NORTHEAST DURING TUESDAY-THURSDAY, FOLLOWED BY A RETURN TO NEAR OR
SLIGHTLY BELOW NORMAL READINGS AFTER FRONTAL PASSAGE.
SANTORELLI/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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