US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 427 PM EDT Mon Jul 05 2021 Valid Thursday July 08 2021 - Monday July 12 2021 Hazards: - Heavy rain across portions of the Southeast and the Mid-Atlantic, Thu, Jul 8. - Heavy rain across portions of the Northeast, Thu-Fri, Jul 8-Jul 9. - Heavy rain across portions of the Southern Plains, Thu-Fri, Jul 8-Jul 9. - Heavy rain across portions of the Northern Plains, the Upper/Middle Mississippi Valley, the Great Lakes, and the Ohio Valley, Fri-Sun, Jul 9-Jul 11. - Severe weather across portions of the Northern/Central Plains and the Upper/Middle Mississippi Valley, Fri, Jul 9. - Flooding possible across portions of the Southeast and the Southern Plains. - Flooding occurring or imminent across portions of the Middle Mississippi Valley and the Southern Plains. - Excessive heat across portions of the Central Great Basin, California, and the Southwest, Fri-Mon, Jul 9-Jul 12. - Much above normal temperatures across portions of the Pacific Northwest, California, and the Northern Great Basin, Fri-Mon, Jul 9-Jul 12. - Much above normal temperatures across portions of the Central Great Basin, California, and the Southwest, Sat-Mon, Jul 10-Jul 12. - Much above normal temperatures across portions of the Northern/Central Great Basin and the Northern Rockies, Sat-Sun, Jul 10-Jul 11. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Sat-Mon, Jul 10-Jul 12. Detailed Summary: During the medium-range period (Thursday, July 8th - Monday, July 12th), a busy and diverse upper-level flow pattern will aid in the development of a multitude of hazards over the CONUS in addition to those caused by the landfall of Tropical Storm Elsa. Starting out in the west, an area of high pressure aloft is forecast to slowly meander from northern Arizona to central California throughout the period. With no relieving rainfall or cold front passage in sight temperatures are expected to rise 10 to 15 degrees above normal in the Pacific Northwest on Friday before the anomalous warmth spreads to the south and east over the weekend. As temperatures are pushed into the high 90s and low 100s, a handful of daily records from the Pacific Northwest to the Southwest stand to be broken or tied. With daily highs forecast to consistently reach triple digits up to and including the 110s over portions of California and Nevada with reduced overnight relief due to above average lows, excessive daytime heat and illness due to heat stress will be a significant concern. Residents of these areas are urged to take proper precautions to safeguard their health including: 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 the conditions out West, areas east of the Rockies are anticipated to experience cooler and wetter weather throughout the course of the medium range. Pushed along by a shortwave trough aloft, an occluded low pressure system at the surface is expected to dive down from the Canadian Rockies into the Northern Plains on Friday before moving into the Upper Midwest over the weekend, strengthening along its path. As this system propagates to the south and east, showers and thunderstorms are expected to develop along and ahead of the warm front within a very moist and unstable airmass. According to the Storm Prediction Center, some of the storms that form on Friday from the eastern Dakotas to western Iowa may become severe and pose a threat for damaging wind gusts. Widespread rainfall accumulations of 1 to 2+ inches in 24 hours will be possible along the system's path as well as high rain rates associated with convective precipitation. Directly to the south in the Southern Plains, an upper-level low meandering from central 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 and instability at the surface, showers and thunderstorms with the potential to produce heavy rainfall rates and high accumulation totals will likely develop over southern Texas Thursday and Friday. Current guidance suggests that later in the period heavy rainfall may redevelop around Big Bend, however, given the long lead time and the amount of uncertainty among the models no hazard area has been drawn at this time. Shifting focus to the tropics, Tropical Storm Elsa is making its way northwest through Cuba. Though presently at Tropical Storm strength, the National Hurricane Center expects Elsa to let go of some of its intensity and downgrade to Tropical Depression Elsa as it passes through, Georgia, the Carolinas and Chesapeake region on Thursday. Along the storm track quick/intense rain rates over sensitive urban areas will be possible in addition to rainfall totals of 2 to 3+ inches in 24 hours, making local and urban flash flooding a significant concern. Moderate winds of 38mph or less are expected to accompany the heavy rain. As Elsa moves offshore it is forecast to re-intensify into a Tropical Storm and pass by portions of the East Coast on Friday. Despite not making a second landfall, Elsa will likely remain close enough to land to make a last stand by bringing some heavy rain to coastal New England. Meanwhile, a stationary boundary draped across the Northeast is expected to interact with a shortwave aloft and unstable, moist air at the surface to produce heavy showers and thunderstorms throughout the region on Thursday and Friday. For Alaska, an occluded low pressure system is anticipated to track through the Gulf of Alaska over the weekend and into early next week. Anomalously moist air pulled into the low pressure center is expected to interact with shortwave energy ahead of the system to produce heavy rainfall over the southern Mainland from Saturday to Monday. Widespread rainfall accumulations of 2+ inches in 24 hours will be possible from the northern Panhandle to Kodiak Island and the Upper Alaska Peninsula. Additionally, for the first half of the period virtually the entire state is forecast to experience daily highs 10 to 20 degrees below normal, while daily lows will likely hover close to or slightly below normal. Despite the anomalously low temperatures, no hazard area was included on today's graphic due to the fact that the temperatures themselves are not expected to cause any issues. Zavadoff