784
FXUS02 KWBC 010659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM 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
THE CURRENT DISTRIBUTION OF GUIDANCE CONTINUES TO SUPPORT A
FORECAST APPROACH OF USING A COMPOSITE OF OPERATIONAL MODELS FOR
ABOUT THE FIRST HALF OF THE PERIOD (12Z/18Z RUNS IN THE CASE OF
THIS LATEST UPDATE) AND THEN ADDING IN SOME GEFS/ECMWF MEANS BY
DAYS 6-7 FRIDAY-SATURDAY GIVEN THE TYPICALLY INCREASING SPREAD OF
SOME MODEL DETAILS. MAJORITY CLUSTERING HAS BEEN FAIRLY
CONSISTENT OVER THE PAST DAY FOR THE WEAK TROUGH CROSSING THE
NORTHEAST (WITH EMBEDDED LOW MOST LIKELY TRACKING JUST WEST/NORTH
OF MAINE) EVEN THOUGH THERE ARE FINER-SCALE DETAILS THAT TEMPER
PREDICTABILITY. THE NEW 00Z UKMET DOES NOT COMPARE WELL TO OTHER
GUIDANCE THOUGH. CONSENSUS ALSO LOOKS GOOD FOR THE UPSTREAM
TROUGH CROSSING CANADA AND THE NORTHERN HALF OR SO OF THE LOWER
48, REACHING EAST-CENTRAL NORTH AMERICA BY NEXT SATURDAY. THE
AFOREMENTIONED APPROACH LED TO ONLY MINOR ADJUSTMENTS FROM
CONTINUITY FOR THE UPPER TROUGH AND LEADING WAVY FRONT. TOWARD
THE END OF NEXT WEEK THE GFS HAS BEEN DIFFERING FROM THE MAJORITY
FOR FLOW DETAILS OVER/NEAR THE NORTHWEST, AS ITS RECENT RUNS HAVE
BEEN TENDING TO PUSH PACIFIC RIDGING MORE INTO WESTERN CANADA AND
SPLITTING THE ENERGY THAT SHOULD FORM THE WEST COAST UPPER TROUGH.
THIS LEADS TO THE GFS SCENARIO HAVING A FARTHER WEST/SOUTHWEST
UPPER LOW OFF THE WEST COAST WHILE MORE TROUGH ENERGY PROGRESSES
FARTHER EASTWARD ACROSS THE NORTHERN TIER STATES AND SOUTHERN
CANADA (ESPECIALLY THE 12Z/30 AND NEW 00Z RUNS). THE 00Z GEFS
MEAN IS MUCH CLOSER TO THE MAJORITY FOR THE WEST COAST TROUGH.
..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. PORTIONS OF THE NORTHERN-CENTRAL PLAINS
MAY BE RELATIVELY MORE SENSITIVE TO ADDITIONAL RAINFALL GIVEN
ABOVE-AVERAGE RAINFALL OBSERVED OVER THE PAST COUPLE WEEKS.
CURRENTLY 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 DAY 4
OUTLOOK WILL REFLECT LATEST GUIDANCE SUGGESTION OF A WESTWARD
SHIFT OF THE MARGINAL RISK AREA OVER THE MISSISSIPPI/TENNESSEE
VALLEY REGION FOR CONVECTION THAT COULD DEVELOP ALONG A WEAK
FRONT. THERE ARE SOME INDICATIONS THAT MOISTURE AND CONVECTIVE
POTENTIAL COULD INCREASE ALONG THIS FRONT FARTHER EAST OVER THE
CAROLINAS AND VICINITY BY DAY 5 (WEDNESDAY-WEDNESDAY NIGHT). THE
SIGNAL DOES NOT APPEAR TO BE QUITE COHERENT ENOUGH FOR A RISK AREA
YET BUT IS WORTH MONITORING. 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 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.
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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