US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 335 PM EDT Tue May 14 2019 Valid Friday May 17 2019 - Tuesday May 21 2019 Hazards: - Heavy precipitation across portions of the Central Great Basin, California, and the Southwest, Fri, May 17 and Sun-Tue, May 19-May 21. - Heavy precipitation across portions of the Central Rockies, the Central Great Basin, the Northern Rockies, the Northern Great Basin, and the Northern Plains, Fri-Sat, May 17-May 18and Sun-Tue, May 19-May 21. - Heavy rain across portions of California and the Pacific Northwest, Fri-Sat, May 17-May 18and Sun-Mon, May 19-May 20. - Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Northern Plains, the Great Lakes, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Southern Plains, Fri-Sun, May 17-May 19. - Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Northern Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Southern Plains, Mon-Tue, May 20-May 21. - Severe weather across portions of the Central Plains, the Middle Mississippi Valley, the Southern Plains, the Upper Mississippi Valley, and the Northern Plains, Fri, May 17. - Severe weather across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, the Southern Plains, and the Upper Mississippi Valley, Sat, May 18. - Severe weather across portions of the Central Plains and the Southern Plains, Mon, May 20. - Severe weather across portions of the Central Plains, the Lower Mississippi Valley, the Northern Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Southern Plains, Tue, May 21. - Severe weather across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, the Great Lakes, the Ohio Valley, and the Tennessee Valley, Sun, May 19. - Flooding possible across portions of the Northern Rockies. - Flooding occurring or imminent across portions of the Central Plains, the Lower Mississippi Valley, the Northern Plains, the Great Lakes, the Middle Mississippi Valley, the Upper Mississippi Valley, the Southeast, the Southern Plains, and the Ohio Valley. - Flooding likely across portions of the Northern Rockies and the Northern Great Basin. - Much below normal temperatures across portions of California, the Central Great Basin, the Pacific Northwest, and the Northern Great Basin, Mon-Tue, May 20-May 21. Detailed Summary: Several weather hazards appear likely in the medium range period (May 17-May 21) across the central and western United States. Starting with the West, upper-level troughing will allow for multiple rounds of rain and mountain snow from southwest Oregon into the Sierra Nevada. The first system will be exiting the region by Friday. Snow accumulations upwards of 1-2 feet will be possible across the Sierra Nevada of central and northern California. Meanwhile 1-2 inches of rain will be possible across much of northern California and into southwest Oregon. Rain will likely stretch across southern California, but current forecast amounts don't warrant a highlighted area at the moment. The second system is currently projected to enter the West Coast by late Saturday and bring similar amounts of rain and snow, with rain extending into the Pacific Northwest as well. Total snowfall accumulations from both systems across the Sierra Nevada could approach 3-4 feet by Tuesday. Two rounds of heavy precipitation also look likely across portions of the Northern Rockies and Northern Great Basin during this time frame, with light rain or snow falling in between events. The first wave of low pressure will track across the Northern Rockies and into the Northern High Plains by Saturday. This will result in upslope flow and mostly heavy rain across western Montana and northern Idaho, with the higher elevations receiving snow. The second low pressure system will follow a similar path and impact the region by Monday, but will have relatively colder air to work with. Therefore, snow levels could drop where the heaviest precipitation occurs. Total liquid precipitation amounts are forecast to approach 2-3 inches across northern Idaho, far northern Wyoming, and much of Montana. High temperatures across much of the Western U.S. will run 10 to 20 degrees below average due to cloud cover and precipitation. Minimum temperatures will run around 10 degrees below normal across northern Nevada and into northern California, therefore an area highlighting much below normal temperatures was added to this area. The first system mentioned in the sections above will bring impacts to the Central U.S. by Friday. The Storm Prediction Center has highlighted areas at risk for severe thunderstorms each day, Friday through Tuesday. The risk areas start in the Central Plains on Friday and shift eastward Saturday and Sunday, before returning to the Central Plains Monday and Tuesday. Heavy rain will also be possible with the strong storms. The highest confidence areas for heavy rain (greater than 1 inch in 24 hours) in the medium range comes in two sections. The first area stretches across the eastern Great Plains into the Middle and Upper Mississippi Valley between Friday and Sunday. The other area at risk for heavy rain is associated with the second wave of low pressure entering the Plains by Monday. Thunderstorms are forecast to break out across northern Texas and southern Oklahoma on Monday, with heavy rain stretching into the Northern Plains by Tuesday. Much of these areas will still be recovering from earlier rainfall from the weekend, so flooding will be a concern. Alaska and the Eastern U.S. appear quiet with respect to hazardous weather between Fri. May 17 and Tues. May 21. The southern mid-Atlantic could see high temperatures around 10 degrees above normal between Saturday and Tuesday, while the Southeast is forecast to have high temperatures in the low 90s. However, these high temperatures are not considered hazardous at the moment. Snell