Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 PM EDT Wed Jul 31 2024 Valid 12Z Sat Aug 03 2024 - 12Z Wed Aug 07 2024 ...Hazardous heat likely this weekend for parts of the West and Southeast, working back into the South-central U.S. next week... ...Overview... Amplified upper ridging over the Western U.S. on Saturday will gradually get suppressed with time and expand eastward back into parts of the south-central U.S.. This will promote heat threats shifting from the West into the central Plains and Southeast. Northern stream flow and energy digging to the lee of the upper ridge will reinforce troughing over the Upper Midwest to the East that lasts through the middle of next week. The National Hurricane Center is also monitoring the potential for tropical development that could affect the Southeast from the weekend into next week. ...Guidance/Predictability Assessment... Latest guidance agrees fairly well for the large scale pattern, but still displays important differences in the details. There is uncertainty regarding amplitude and timing of energies to carve out a Midwest/eastern U.S. mean upper trough this weekend into next week, but a general model compromise serves as a good starting point. The ridge over the West should be sufficiently strong to prevent any major intrusions from upstream, 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. There remains quite a bit of uncertainty, but there is still better support for a more easterly track up through the Bahamas and off the Southeast U.S., and less so for something more westward into the Gulf. WPC forecast today trended closer to the easterly track consistent with continuity and NHC thoughts. The WPC medium range forecast suite was heavily weighted towards the ECENS mean. This was reasonable given good agreement in the rest of the guidance over the majority of the CONUS and the best support for WPC/NHC preferences on the potential tropical system. This solution discounted much more inundating model QPF solutions out from the Gulf and possible slowed potential system forward speed over time. However, a more westward track to the Gulf is plausible as overall supported by latest 12 UTC guidance trends. ...Weather/Hazards Highlights... It overall remains the case that a generally wet and unsettled pattern is likely from the upper 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 and Day 5 Excessive Rainfall Outlooks centered on Saturday and Sunday show broad Marginal Risks from the Ohio Valley/Appalachians and the Mid- Atlantic into the Northeast. Latest guidance continues to show potential locally heavy rainfall across parts of the above areas but 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. Day 4/Saturday and Day 5/Sunday Marginal Risk areas for Southeast Florida portend the uncertain rainfall threat given potential tropical system proximity. Elsewhere, monsoonal convection over the Southwest continues to support Marginal Risk areas on the Days 4 and 5 EROs. Chances for convection may expand northward with time depending on the shape of the southern Rockies/Plains ridge and upper level energy rotating around its periphery. Heat should remain a threat across parts of the West into next week, with lower elevations seeing near 100F high temperatures most days. Scattered record highs and record high min temps are possible on Saturday as well. Above normal temperatures from the northern Plains to the Northeast into Saturday should moderate and shift south as shortwave energy moves through these regions. As the upper ridge builds back eastward next week, hazardous heat will return to parts of the central/southern Plains to the Southeast. Santorelli/Schichtel 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