Extended Forecast Discussion NWS Weather Prediction Center College Park MD 439 PM EDT Wed Jul 3 2024 Valid 12Z Sat Jul 06 2024 - 12Z Wed Jul 10 2024 ***Major heatwave expected for the lower elevations of California and the Desert Southwest into next week, and Beryl eventually headed for the western Gulf Coast*** ...Overview... An intense and prolonged heatwave is forecast to impact much of California and extending into the lower elevations of the Desert Southwest through the middle of next week. Meanwhile, the track and intensity of tropical cyclone Beryl will bear watching as it could be moving close to or over southern Texas by early next week. A low pressure system is forecast to cross the northern Great Lakes with a trailing front across the eastern U.S., with showers and storms firing south of the boundary across portions of the Southern Plains and extending east to the Ohio Valley and the Mid- Atlantic region. Hot and humid conditions will also continue for much of the southern states and extending to the East Coast. ...Guidance/Predictability Assessment... Model guidance continues to favor mean troughing to dip into the mid-section of the country while an anomalously strong upper ridge with heights possibly reaching 600dm remains anchored over the West Coast. The guidance suggests this ridge should drift slightly east over the southern Intermountain West by next Tuesday/Wednesday. The model consensus has continued to trend more amplified in this overall pattern with the ridge extending more to the north into western Canada. Meanwhile, periodic shortwave energy dipping toward the base of the mean trough will have implications on how far north tropical cyclone Beryl will track toward the western Gulf Coast region. The ECMWF, which has been the left-most track guidance for Beryl, has continued to shift Beryl's track more northwestward toward southern Texas to better agree with the GFS. Subtle mutual interaction between the mean trough and the circulation of Beryl together with the uncertain distance between the two systems continue to introduce a higher degree of forecast uncertainty over the vicinity of the western Gulf Coast region for early next week. A tropical wave behind Beryl could introduce additional forecast uncertainty in this region by the middle of next week as some models suggest this wave will develop over the western Gulf of Mexico behind Beryl. Latest model guidance also trends toward a faster eastward progression of upper troughing across the Great Lakes toward New England from early to midweek next week. The WPC medium-range forecasts were based on 40% from the 00Z ECMWF/EC mean, 40% from the 06Z GFS/GEFS, and 20% from the 00Z CMC/CMC mean, with a higher percentage from the ensemble means for Days 6 and 7. ...Weather/Hazards Highlights... On Saturday, there is enough of a model signal to maintain the Marginal Risk area for portions of the Mid-Atlantic, where some strong thunderstorms with heavy rain rates could develop quickly in the vicinity of the cold front with its forward motion slowing down. This is also extended to the north to include parts of New England where some heavy downpours will also be possible. Meanwhile, some of the outer rain bands of Beryl, forecast to re- intensify to a hurricane, could be approaching southern Texas by late Saturday and into early Sunday, when the heaviest rainfall will most likely be just off the coast. Going into the Day 5 period Sunday, the official NHC track of Beryl has it getting close to Brownsville, Texas, although there is still considerable uncertainty in where it could ultimately go. Given the forecast track, rain and embedded thunderstorms would be increasing in coverage across Deep South Texas through the day Sunday, with the potential for 3-6 inch totals by 12Z Monday south of Corpus Christi. Therefore, a Slight Risk area is maintained for the Day 5 ERO for this area, and a broader Marginal Risk area extending farther northward along the Texas coast to account for periods of heavy rainfall with the outer rain bands. Farther to the north across the Central Plains, a Marginal Risk area is also maintained with increasing model support for development of some MCS activity northeast of a surface low and and upper trough. An upgrade to a Slight Risk is given to portions of central Oklahoma where the heaviest rainfall appears more likely near the tail end of the possible MCS. A major heatwave will be ongoing for the inland lower elevations of California with widespread 105-115 degree readings likely. Readings could reach 120 degrees at the hottest locations in the Desert Southwest. Daily temperatures records may be tied or broken in many cases. The heat is forecast to expand across inland portions of Washington, Oregon, and much of the Intermountain West for the first half of next week, with 100+ degree highs likely for the lower valley locations. Elsewhere, widespread 90s for highs can be expected for much of the Southern U.S. and extending eastward to the East Coast, along with high humidity making it feel 5-10 degrees hotter in many cases. Kong/Hamrick 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