US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 329 PM EDT Thu Jul 01 2021 Valid Sunday July 04 2021 - Thursday July 08 2021 Hazards: - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Mon-Thu, Jul 5-Jul 8. - Heavy rain across portions of the Southeast and the Mid-Atlantic, Tue-Thu, Jul 6-Jul 8. - Flooding possible across portions of the Great Lakes, the Ohio Valley, the Middle Mississippi Valley, and the Southern Plains. - Flooding occurring or imminent across portions of the Central/Southern Plains and the Middle Mississippi Valley. - Flooding likely across portions of the Central Plains and the Middle Mississippi Valley. - Excessive heat across portions of the Northern Plains, Sun, Jul 4. - Excessive heat across portions of the Pacific Northwest and the Northern Great Basin, Sun, Jul 4. - Much above normal temperatures across portions of California, the Pacific Northwest, the Northern Great Basin, and the Northern Rockies, Sun-Tue, Jul 4-Jul 6. - Much above normal temperatures across portions of the Upper Mississippi Valley, the Great Lakes, the Northern Plains, and the Northern Rockies, Sun, Jul 4. Detailed Summary: During the medium range period (Sunday, July 4th - Thursday, July 8th) the upper-level pattern is forecast to return to a more zonal, progressive flow with the demise of the highly anomalous ridging that has plagued the western United States. In spite of the anticipated regime change, daily high temperatures throughout the Northwest will likely sit around 15 degrees above average until Tuesday, with some areas consistently reaching the upper 90s or low 100s. Similar temperature anomalies are also expected to impact the Northern Tier from the Rockies to the Upper Great Lakes on Sunday. Lucky for these regions, a cold front is forecast to drop south from Canada and move over the north-central US Sunday evening, allowing temperatures to quickly drop down closer to normal by Monday. Due to the ongoing exposure to oppressively high daytime temperatures in parts of the Columbia Basin, an excessive heat area has been maintained for portions of eastern Washington, northern Oregon, and western Idaho for Sunday. Dangerous heat is also forecast to affect parts of the Dakotas on Sunday, where highs are anticipated to approach or reach triple digits. In both of these areas residents are urged to take proper precautions to safeguard their health and prevent the onset of heat-related illness. These precautions include: avoiding long periods of time outdoors in the sun, staying hydrated, remaining in a cool or air conditioned location, and canceling outdoor activities during the heat of the day. In stark juxtaposition to conditions out West, portions of the South are anticipated to experience cooler and wetter weather throughout the course of the medium range. Starting Monday, a cut-off upper low meandering from Texas to northern Mexico is forecast to work in tandem with a low pressure wave over the Sierra Madre to drive very moist air from the western Gulf of Mexico onshore. As this moist air interacts with shortwave energy at the surface, showers and thunderstorms with the potential to produce heavy rainfall rates and high accumulation totals will likely develop over western Louisiana and southern Texas. Taking into account the highly saturated soils and much above normal streamflow in these areas from recent anomalously high amounts of rain, the risk of widespread flash flooding will be a significant concern. Elsewhere, a long frontal boundary is forecast to drape over the north-central part of the country throughout much of the medium range period, extending from the Pacific Northwest to the Great Lakes. Though precipitation along the boundary is expected to remain relatively light, models suggest that heavy rain could develop in the Middle Mississippi Valley on Wednesday. At present, the models disagree as to where the heaviest rain will fall and how much, but the timing is consistent. Given the long lead time and the potential for the forecast to change over the course of the week no hazard area has been drawn, however, this region will be watched in the coming days for further development. Shifting focus to the tropics, Tropical Storm Elsa is making its way westward toward the Windward and southern Leeward Islands. Presently, the official track forecast from the National Hurricane Center has Elsa approaching Florida on Tuesday morning at tropical storm intensity. Current guidance is torn as to whether Elsa will move along the western or eastern coast of the state, translating into uncertainty as to where the heaviest rainfall will occur. Regardless of which model solution is right, the entirety of the Florida peninsula falls within the cone of uncertainty, making it susceptible to Elsa's heavy rain and tropical storm force winds Tuesday and Wednesday. After passing over Florida, the guidance points towards Elsa traveling through Georgia and up the East Coast to the Mid-Atlantic on Thursday before moving out to sea. As such, these areas may also be subject to heavy rain and high winds. Given the potential for the official storm track to change with time due to the high degree of disagreement among the models, the area outlined on today's graphic serves as a broad warning area for tropical cyclone related hazards. As the track forecast is fine-tuned with updated guidance over the next couple of days, the hazard area will also be revised and narrowed. No hazards have been posted for Alaska, however, it is worth mentioning that multiple frontal systems are forecast to pass over the state throughout the period that may produce localized heavy rainfall. While individual models suggest that accumulations in some areas could approach or even slightly exceed hazardous thresholds, there is no general consensus as to when, where, and how much rain will fall. Due to the high degree of uncertainty present in the guidance no area was highlighted on today's graphic. Also worthy of note are Monday's forecast highs over the eastern Interior, which have the potential reach the low 80s in some areas. Though relatively high, these temperatures are not expected to cause any issues. Zavadoff