Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM 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 next week, and Beryl eventually headed for the Western Gulf*** ...Overview... The main thing making weather headlines during this forecast period will the intense and prolonged heatwave encompassing much of California and extending into the lower elevations of the Desert Southwest. Hot and humid conditions will also continue for much of the southern states and extending to the East Coast. 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 near boundary across portions of the Southern Plains and extending east to the Ohio Valley and the Mid- Atlantic region. The track of Beryl is expected to enter the Bay of Campeche and the Western Gulf by Saturday with rainfall chances increasing for portions of southern Texas by the weekend. ...Guidance/Predictability Assessment... The 00Z model guidance suite indicates good overall synoptic scale agreement across the Continental U.S. going into the weekend, and better agreement on the massive upper ridge building over the West Coast, likely reaching 600dm. The guidance suggests this ridge should slowly move east over the southern Intermountain West by next Tuesday/Wednesday. Meanwhile, a general trough axis situated over the north-central U.S. should be anchored in place by another ridge axis over the western Atlantic Ocean, with a somewhat blocky pattern developing. A general deterministic model blend sufficed as a good starting point in the forecast process for the weekend, and then increased the ensemble means to about 40% by next Tuesday/Wednesday. The latest forecast from the National Hurricane Center has Hurricane Beryl reaching the Yucatan Peninsula around Friday morning, and then emerging over the Bay of Campeche by Saturday, followed by more of a northwestward turn. There remains a split in the guidance as the storm approaches the Mexico/Texas coast, with the GFS/GEFS mean to the north, and the ECMWF/UKMET farther south, and the CMC a middle ground solution. The trough over the Central U.S. will be a big factor in determining the eventual track. Beryl's track will continue to be closely monitored over the next several days, and the NHC has additional information pertaining to this. ...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. Some of the outer rain bands of Beryl could be approaching southern Texas by late Saturday and into early Sunday, but the intensity and location of Beryl will likely keep the heaviest rainfall 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 planned 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 planned where some MCS activity may develop in the general vicinity of a surface low and upper trough. 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. 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