Extended Forecast Discussion NWS Weather Prediction Center College Park MD 219 AM EDT Mon Jul 29 2024 Valid 12Z Thu Aug 01 2024 - 12Z Mon Aug 05 2024 ...Hazardous heat to shift from the south-central Plains early period to 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. A shortwave through the northern tier will eventually establish troughing in the East, allowing for the ridge to shift more into the West. This sets up what could be a rather stagnant upper pattern into early next week supporting increasing heat across the West, and unsettled weather over the East. ...Guidance/Predictability Assessment... The latest models and ensembles continue to show good agreement on the large scale pattern evolution, but plenty of uncertainty in the details. The main system of uncertainty is still with the shortwave through the Midwest on Thursday, leading to mean troughing over the East by the weekend. Compared to a day ago, models seem to be converging on a little slower solution, but the GFS is still notably faster than the consensus, though still with support from some of the AI/ML models. Models are still quite uncertain with the pattern in the northeastern Pacific, which could affect the Northwest as well. Still seeing support for possible tropical development in the Atlantic, which the latest outlook from the National Hurricane Center is highlighting. The operational ECMWF and its ensembles show a more eastern track, bringing a low northward off the coast of FL/the Southeast next weekend. The CMC is significantly stronger and shows a more southerly track south of FL into the Gulf. A look at ensemble low plots from the ECENS and GEFS illustrate the uncertainty on the track or even its existence as a defined tropical system, but this feature will need to be watched. The WPC forecast used a blend of deterministic guidance early in the period, with more ensemble mean support late period (with continued weighting towards the ECMWF). Overall, this maintained good continuity with the previous WPC forecast. ...Weather/Hazards Highlights... A wet pattern is likely from the Midwest to the Eastern Seaboard next week with ample moisture and instability in place as well as mean troughing aloft and surface frontal systems all supporting scattered thunderstorms. Thus 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. Some potential for mesoscale systems with heavy rainfall to move through the region, but way too much uncertainty for any sort of slights on the EROs still. Much of the north- central U.S. to the eastern third of the country should remain generally unsettled through next weekend and into early next week as the now established upper trough is slow to budge out of the region. Elsewhere, monsoonal convection over the Southwest continues to support marginal risks on the Days 4 and 5 EROs. Chances for convection may expand northeastward into later week depending on the shape of the southern Rockies/Plains ridge and upper level energy rotating around its western periphery. As such the Day 5/Thursday Marginal expands a bit northward into southern Colorado, and rain chances increase into the central High Plains by Friday. 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 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. 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. 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