Extended Forecast Discussion NWS Weather Prediction Center College Park MD 246 AM EDT Tue Jul 30 2024 Valid 12Z Fri Aug 02 2024 - 12Z Tue Aug 06 2024 ...Hazardous heat from the south-central Plains eastward becoming more suppressed with time while building over the Northwest later this week... ...Overview... A broad upper ridge stretched from the West to the Southeast as the period begins Friday will focus in the West by this weekend and beyond as the Southeast portion gets suppressed by troughing over the East later this week. This will promote some lingering heat across the south-central U.S. into the Southeast Friday, but building and lingering heat over the West. Northern stream flow will generally maintain shallow troughing over the East into next week as the Western ridge starts to build back into the Central U.S. late period. 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. Timing of a shortwave into the Great Lakes/Northeast on Friday has improved compared to recent days, but there is uncertainty regarding amplitude and timing of additional energy through the region this weekend into early next week. The ridge over the West should be sufficiently strong to prevent any major intrusions, but guidance struggles on possible energy sliding into the Northwest and over the top of the ridge on Sunday which could affect its overall strength/northward extent by early next week. Most guidance continues to support the idea of possible tropical development in the Atlantic, as highlighted in the National Hurricane Center outlook, but a lot of lingering uncertainty in the exact track. Guidance and ensembles seem to be trending towards a more easterly track, as the ECMWF has been showing the past day or two. Questions on its speed off the Southeast Coast though late period, with the CMC the quickest to race it northeastward away from the Mid-Atlantic. Latest operational GFS runs remain fairly ill- defined with any possible system, though maybe more so bringing the tropical wave more into the Gulf very late period. WPC forecast used a blend of the operational guidance for the first half of the period amidst sufficient model agreement. Increased the ensemble means to 50 percent of the blend by the end of the period to help mitigate differences. The operational model half leaned more heavily towards the ECMWF which shows the best support for WPC/NHC preferences on the potential tropical system. ...Weather/Hazards Highlights... A generally wet and unsettled pattern is likely from the Ohio Valley to the Eastern Seaboard into this weekend 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 Friday-Saturday night show fairly broad Marginal Risks across parts of the 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. Parts of the north- central U.S. to the eastern third of the country should remain generally unsettled into early next week with general mean troughing likely to persist. Locations near Florida and 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 with time depending on the shape of the southern Rockies/Plains ridge and upper level energy rotating around its western periphery. 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 wane by the start of the medium range period with an incoming front, but heat will continue across the Southeast through Friday or Saturday with warm overnight temperatures only exacerbating heat stress in that region. Meanwhile, hazardous heat threats will increase over much of the West, with lower elevations seeing 100F+ high temperatures, and 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. Heat may expand back into the northern-central Plains early next week. 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