605
FXUS02 KWBC 291903
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
303 PM EDT MON JUL 29 2024
VALID 12Z THU AUG 01 2024 - 12Z MON AUG 05 2024
...HAZARDOUS HEAT FROM THE SOUTH-CENTRAL PLAINS EASTWARD GRADUALLY
BECOMING MORE SUPPRESSED WITH TIME WHILE BUILDING OVER THE
NORTHWEST LATER THIS WEEK...
..OVERVIEW
A STRONG UPPER RIDGE OVER THE CENTRAL U.S. INTO THE SOUTHEAST AS
THE PERIOD BEGINS THURSDAY WILL CONTINUE TO PROMOTE UNSEASONABLY
WARM TEMPERATURES OVER CENTRAL PARTS OF THE PLAINS AND INTO THE
SOUTHEAST. THEN GUIDANCE SHOWS UPPER RIDGING BUILDING OVER THE
WEST WHILE A MIDWEST SHORTWAVE DRIFTS INTO A DEVELOPING MEAN TROUGH
OVER THE EAST. TRAILING NORTHERN STREAM FLOW SHOULD MAINTAIN A MORE
SHALLOW EASTERN TROUGH BY EARLY NEXT WEEK. THIS SETS UP WHAT MAY
BECOME A STAGNANT UPPER PATTERN SUPPORTING INCREASING HEAT ACROSS
THE WEST AND UNSETTLED WEATHER OVER THE EAST. THE NATIONAL
HURRICANE CENTER IS ALSO MONITORING THE POTENTIAL FOR TROPICAL
DEVELOPMENT THAT COULD AT LEAST COME CLOSE TO AFFECTING LOCATIONS
NEAR THE SOUTHEASTERN COAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MOST GUIDANCE AGREES FAIRLY WELL FOR THE LARGE SCALE PATTERN BUT
STILL DISPLAYS IMPORTANT DIFFERENCES FOR SOME DETAILS. THE MOST
SIGNIFICANT ISSUES INVOLVE THE UPPER TROUGH CROSSING THE
NORTHEASTERN QUADRANT OF THE LOWER 48 (PLUS AMPLITUDE OF LINGERING
MEAN TROUGHING BY NEXT MONDAY) AND POTENTIAL TROPICAL DEVELOPMENT
THAT COULD TRACK NEAR THE SOUTHEASTERN COAST.
REGARDING THE INITIAL MIDWEST UPPER TROUGH, INCOMING 12Z GUIDANCE
GENERALLY MAINTAINS THE SPREAD FROM PRIOR RUNS WITH THE ECMWF
LEANING ON THE SLOWER SIDE AND THE GFS LEANING FASTER. THE 06Z/12Z
GFS RUNS HAVE ADJUSTED SOMEWHAT SLOWER TO EJECT THE FEATURE THAN
THE 00Z RUN THOUGH. MACHINE LEARNING (ML) MODELS SHOW SOME SPREAD
AS WELL BUT ON AVERAGE LEAN SOMEWHAT FASTER THAN AT LEAST THE
OPERATIONAL ECMWF. BY NEXT MONDAY THERE IS A SIGNIFICANT MAJORITY
OF DYNAMICAL AND ML MODELS RECOMMENDING MORE OF A LINGERING TROUGH
ACROSS THE GREAT LAKES/NORTHEAST VERSUS WHAT THE 06Z/12Z GFS RUNS
ADVERTISE. THE 00Z GFS ENDED UP CLOSER TO CONSENSUS BY NEXT MONDAY.
MOST GUIDANCE CONTINUES TO SUPPORT THE IDEA OF POSSIBLE TROPICAL
DEVELOPMENT IN THE ATLANTIC, AS HIGHLIGHTED IN THE NATIONAL
HURRICANE CENTER OUTLOOK. THE OPERATIONAL ECMWF AND ITS ENSEMBLES
MAINTAIN A MORE EASTERN TRACK, BRINGING A LOW NORTHWARD OFF THE
COAST OF FLORIDA/THE SOUTHEAST BY THE WEEKEND INTO EARLY NEXT WEEK.
THE NEW 12Z CMC HAS ADJUSTED EASTWARD FROM ITS 00Z RUN, GETTING
CLOSER TO THE ECMWF IDEA. ML MODELS (INCLUDING THE 18Z/00Z
GRAPHCAST GFS) GENERALLY SUPPORT SOME DEGREE OF DEVELOPMENT WITH A
TRACK CLOSER TO THE ECMWF CLUSTER. LATEST OPERATIONAL GFS RUNS HAVE
BEEN VERY ILL- DEFINED WITH ANY POSSIBLE SYSTEM, WITH THIS
SCENARIO VERY MUCH IN THE MINORITY AT THE MOMENT.
THE UPDATED FORECAST BASED ON 00Z/06Z SOLUTIONS STARTED WITH AN
OPERATIONAL MODEL COMPOSITE, WITH A LATER-PERIOD TREND TOWARD A
MODEL/ENSEMBLE MEAN MIX THAT TILTED A LITTLE MORE THAN AVERAGE
TOWARD THE ECMWF/ECENS MEAN GIVEN WPC-NHC PREFERENCES TOWARD THAT
CLUSTER OF SOLUTIONS FOR POSSIBLE TROPICAL DEVELOPMENT. MEANWHILE
THIS APPROACH PROVIDED A REASONABLE INTERMEDIATE SOLUTION FOR THE
MIDWEST THROUGH NORTHEAST TROUGH AND REFLECTED CONSENSUS FOR
LINGERING EASTERN TROUGHING BY NEXT MONDAY--WITH FAIRLY GOOD
CONTINUITY RELATIVE TO PREVIOUS FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
A WET PATTERN IS LIKELY FROM THE MIDWEST TO THE EASTERN SEABOARD
LATE THIS WEEK WITH AMPLE MOISTURE AND INSTABILITY IN PLACE WHILE A
SLOW MOVING UPPER TROUGH AND SURFACE/FRONTAL SYSTEMS ALL
SUPPORT AREAS OF SHOWERS AND THUNDERSTORMS. THE DAYS 4-5 EXCESSIVE
RAINFALL OUTLOOKS COVERING THURSDAY-FRIDAY NIGHT SHOW FAIRLY BROAD
MARGINAL RISKS ACROSS PARTS OF THE MIDWEST TO OHIO VALLEY AND THE
NORTHEAST/MID-ATLANTIC. LATEST GUIDANCE CONTINUES TO SHOW POTENTIAL
FOR EMBEDDED MESOSCALE SYSTEMS TO PRODUCE LOCALLY HEAVY RAINFALL
ACROSS PARTS OF THE ABOVE AREAS. HOWEVER THERE IS STILL A LOT OF
SPREAD FOR LOCATION OF HEAVIEST ACTIVITY, PLUS DEPENDENCE ON STILL-
UNCERTAIN SHORTER TERM RAINFALL AND RESULTING SOIL SENSITIVITY.
THEREFORE PREFERENCE REMAINS TO WAIT BEFORE INTRODUCING ANY SLIGHT
RISK AREAS. ALSO, AHEAD OF THE LATE WEEK SYSTEM, A DEPARTING
SHORTWAVE AND SUFFICIENT MOISTURE/INSTABILITY MAY PRODUCE LOCALLY
HEAVY RAINFALL OVER NORTHERN NEW ENGLAND WHERE THE DAY 4 OUTLOOK
DEPICTS A MARGINAL RISK AREA. MUCH OF THE NORTH-CENTRAL U.S. TO THE
EASTERN THIRD OF THE COUNTRY SHOULD REMAIN GENERALLY UNSETTLED
THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK WITH THE
AFOREMENTIONED UPPER TROUGH CONTINUING NORTHEASTWARD AND GENERAL
MEAN TROUGHING LIKELY TO PERSIST IN ITS WAKE. LOCATIONS NEAR THE
SOUTHEASTERN COAST SHOULD MONITOR LATEST FORECASTS REGARDING
POSSIBLE TROPICAL DEVELOPMENT DURING THE WEEKEND/EARLY NEXT WEEK
TIME FRAME.
ELSEWHERE, MONSOONAL CONVECTION OVER THE SOUTHWEST CONTINUES TO
SUPPORT MARGINAL RISK AREAS ON THE DAYS 4 AND 5 EROS. CHANCES FOR
CONVECTION MAY EXPAND NORTHEASTWARD LATE THIS WEEK DEPENDING ON THE
SHAPE OF THE SOUTHERN ROCKIES/PLAINS RIDGE AND UPPER LEVEL ENERGY
ROTATING AROUND ITS WESTERN PERIPHERY. THUS THE DAY 4/THURSDAY
MARGINAL RISK EXPANDS A BIT NORTHWARD INTO SOUTHERN COLORADO, AND
RAIN CHANCES INCREASE INTO THE CENTRAL HIGH PLAINS BY FRIDAY. FROM
THE WEEKEND INTO EARLY NEXT WEEK, FLOW BETWEEN THE UPPER RIDGE AND
A WEAK TROUGH SETTING UP OFF THE WEST COAST MAY SUPPORT A
NORTHWESTWARD/NORTHWARD EXPANSION OF SCATTERED CONVECTION.
THE HEAT WAVE OVER THE CENTRAL PLAINS EARLY THIS WEEK SHOULD
CONTINUE THROUGH THURSDAY, WITH DAYTIME HIGHS AROUND 10F ABOVE
NORMAL AND WIDESPREAD MAJOR TO LOCALLY EXTREME HEATRISK THREATS.
AN INCOMING FRONT WILL BRING RELIEF TO THE CENTRAL PLAINS BY
FRIDAY, BUT HEAT WILL CONTINUE ACROSS THE SOUTHEAST THROUGH FRIDAY
OR SATURDAY WITH WARM OVERNIGHT TEMPERATURES ONLY EXACERBATING HEAT
STRESS IN THAT REGION. MEANWHILE, MUCH OF THE WEST WILL TREND
WARMER, WITH LOWER ELEVATIONS SEEING 100F+ HIGH TEMPERATURES.
SCATTERED DAILY RECORD HIGHS ARE POSSIBLE AND APPEAR MOST LIKELY
OVER THE INTERIOR NORTHWEST ON FRIDAY-SATURDAY. SHORTER BURSTS OF
ABOVE NORMAL TEMPERATURES ARE ALSO LIKELY FOR THE MIDWEST TO OHIO
VALLEY TO THE MID- ATLANTIC/NORTHEAST LATE THIS WEEK, WITH PERHAPS
SOME MODERATION NEXT WEEKEND AFTER COLD FRONTS PASS THROUGH.
RAUSCH/SANTORELLI
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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