Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 345 AM EDT Thu Jul 04 2024 Valid 12Z Thu Jul 04 2024 - 12Z Sat Jul 06 2024 ...Extremely dangerous and record-breaking heatwave to impact much of the West through this weekend... ...One more day of oppressive heat and humidity across the Southern Plains and Lower Mississippi Valley today before steamy temperatures focus over the Mid-Atlantic and Southeast... ...Flash flooding and severe thunderstorms possible throughout parts of the Midwest, Ohio Valley, and Southern Plains this Independence Day... A significant and extremely dangerous heatwave is set to build throughout the West to end this week and into the extended holiday weekend, with several days of record-breaking heat forecast. An upper-level high situated just off the West Coast today is forecast to strengthen and reorient directly over the western U.S. by Friday. This pattern will support well above average temperatures over California and into southwest Oregon today before heat spreads further throughout the western U.S. this weekend. High temperatures are forecast to reach into the 105-115F range for interior California away from the immediate coastline, as well as across much of the Desert Southwest. Locally higher temperatures into the 120s are possible in the typical hot spots of the Desert Southwest. Searing afternoon temperatures will also spread into the Northwest and parts of the central Great Basin, with widespread highs rising into the 90s and low 100s. Dozens of daily record high temperatures are possible, expressing the rarity of this early-July heatwave. The duration of this heat is also concerning as scorching above average temperatures are forecast to linger into next week. Heat impacts can compound over time, therefore it is important to remain weather aware and follow the advice of local officials. This level of heat throughout parts of the Mojave Desert and Sacramento/San Joaquin valleys of California could pose a risk to anyone if proper heat safety is not followed. It is imperative to stay hydrated, out of direct sunlight, and in buildings with sufficient air-conditioning when possible. It is also equally as important to check on the safety of vulnerable friends, family, and neighbors. Oppressive heat and humidity will also be found throughout the southern Plains and lower Mississippi Valley today, while expanding eastward to the Mid-Atlantic and Southeast for the end of the week. High temperatures rising into the upper 90s and low 100s are expected, with heat indices soaring into the 110s across the lower Mississippi Valley. Warm overnight conditions in the upper 70s and low 80s will offer little relief, leading to a dangerous situation for those without access to adequate cooling. A cold front entering the southern Plains is anticipated to offer cooler and below average temperatures to Oklahoma, much of northern/western Texas, and the Mid-South by Friday. Above average temperatures are then anticipated to confine to the Southeast and Mid-Atlantic for the start of the weekend, with afternoon highs into the mid-to-upper 90s. If planning to spend an extended amount of time outdoors this Fourth of July, be sure to use caution and act quickly if you see signs of heat-related illnesses. An active and stormy weather pattern over the central U.S. is expected to create chances for severe thunderstorms and heavy rainfall, which could impact holiday gatherings through early this weekend. A developing area of low pressure over the northern Plains is forecast to progress into the upper Midwest by tonight and team up with a lingering frontal boundary stretching from the lower Great Lakes to the southern Plains to trigger some meteorological fireworks. Thunderstorm chances span from the southern Plains/Rockies to the middle/upper Mississippi Valley and also eastward to the Ohio Valley and Mid-Atlantic. However, the greatest threat for strong to severe thunderstorms will be near/along the frontal boundary through parts of the middle/upper Mississippi Valley and southern Plains. Damaging wind gusts and frequent lightning are the most likely weather hazard associated with these Fourth of July storms. Flash flooding will remain a concern throughout the upper Midwest as well due to yet another round of thunderstorms overlapping areas dealing with ongoing river flooding and saturated soils, with scattered flash flooding also possible between the Ohio Valley and southern Plains. On Friday, thunderstorms will continue to progress eastward with the frontal boundary into much of the eastern third of the country. Isolated strong to severe storms and flash flooding are possible. The greatest threat for damaging wind gusts associated with these storms will be across the upper Ohio Valley. Elsewhere, daily thunderstorm chances associated with daytime heating are possible along the Gulf Coast and Florida. Scattered showers and thunderstorms are also possible throughout the north-central U.S. this weekend as upper troughing remains over the region. Residents and visitors located within areas expecting severe weather and/or heavy rainfall are advised to remain weather aware, have multiple ways to receive warnings, and never drive across flooded roadways. Have a safe Independence Day! Snell Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php