Extended Forecast Discussion NWS Weather Prediction Center College Park MD 227 AM EDT Sun Jul 28 2024 Valid 12Z Wed Jul 31 2024 - 12Z Sun Aug 04 2024 ...Hazardous heat to shift from the south-central Plains early period to the Northwest later next week... ...Overview... Guidance continues to show a pattern evolving from a southern Rockies/Plains upper ridge earlier in the week to an amplifying Western ridge later in the week. This would help set up a prolonged period of hot weather over many areas with the most anomalous heat expected over central parts of the Plains early to midweek. Warmer than normal temperatures are forecast to expand north toward the U.S./Canadian border later in the week, despite shortwave energy moving through the Midwest and eventually developing mean troughing over the eastern U.S. that will support a broad area of showers/thunderstorms drifting across the eastern half of the country. ...Guidance/Predictability Assessment... The latest models and ensembles continue to show good agreement on the large scale regarding the initial southern tier ridge shifting and building over the West. The main model uncertainties continue to lie north of the ridge, with the timing and strength of a shortwave through the northern tier into the Northeast. The ECMWF (and the UKMET) continue to be slower with this feature, even as early as Thursday, while the CMC and GFS are faster. The ensemble means are weaker and more in the middle, but there is good support from the ECMWF-based AI/ML models for the faster solutions boosting confidence to lean away from the operational ECMWF. Guidance and ensembles continue to hint at possible tropical development into/towards the Gulf, which the latest outlook from the National Hurricane Center is highlighting. The operational ECMWF and its ensembles show a more eastern track (owing to stronger ridging into the Gulf), bringing a low northward off the coast of FL next weekend. The CMC (with some support from the GEFS as well) shows a more southerly track south of FL into the Gulf. A lot of uncertainty still on the track or even its existence as a defined tropical system, but this feature will need to be watched. The WPC forecast leaned more heavily towards the GFS/CMC early in the period, increasing the weighting of the ensemble means Thursday onward to 60 percent of the total blend by day 7. Overall, this maintained good continuity with the previous WPC forecast through Saturday. ...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 for scattered thunderstorms. Thus the Days 4-5 Excessive Rainfall Outlooks covering Wednesday-Thursday night show fairly broad Marginal Risks across parts of the Midwest to the Northeast. Model guidance has been hinting at a likely mesoscale convective system with heavy rain rates moving on the cusp of the instability gradient in northwest mean flow that should affect parts of the Midwest Wednesday-Wednesday night. There is some placement spread with this, but antecedent wet conditions and the heavy rainfall potential seems to warrant a Day 5/Wednesday Slight Risk across the Midwest, though the area will likely be adjusted in future forecasts if/when models converge. Much of the north- central U.S. to the eastern third of the country should remain generally unsettled the rest of the week as a upper trough is slow to budge out of the region while it generally weakens. Elsewhere, monsoonal convection over the Southwest should stay confined to southern areas through midweek, and Marginal Risks remain reasonable for the Days 4-5 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. The forecast pattern evolution will support an expanding area of warmer than average temperatures across the Lower 48 into next weekend. The most significant high temperature anomalies should be over the Central Plains early on where some locations should see multiple days with highs 10-15F or so above normal and high temperatures near 105F. The experimental HeatRisk likewise reflects an expanding area of Major to even Extreme risks of heat- related impacts through next Wednesday. An incoming front will cause some easing/southward shift of the heat late next week in that region, with some heat building across parts of the Southeast as well. Much of the West will trend warmer after Wednesday, with lower elevations seeing 100F+ high temperatures. The Ohio Valley to East Coast and south to the Gulf should also trend warmer with time 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