US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 356 PM EDT Mon May 13 2019 Valid Thursday May 16 2019 - Monday May 20 2019 Hazards: - Heavy precipitation across portions of the Central Great Basin, California, and the Southwest, Thu-Fri, May 16-May 17and Sun-Mon, May 19-May 20. - Heavy precipitation across portions of the Northern Plains, the Northern Rockies, and the Northern Great Basin, Thu-Sat, May 16-May 18and Mon, May 20. - Heavy rain across portions of California and the Pacific Northwest, Thu-Fri, May 16-May 17and Sun-Mon, May 19-May 20. - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Sat-Mon, May 18-May 20. - Heavy rain across portions of the Central Plains, the Upper Mississippi Valley, and the Northern Plains, Sat-Sun, May 18-May 19. - Severe weather across portions of the Central Plains, the Southern Plains, and the Northern Plains, Fri, May 17. - Severe weather across portions of the Central Plains and the Southern Plains, Sat, May 18. - Flooding possible across portions of the Southeast, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley. - 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 Southern Plains, and the Ohio Valley. - Flooding likely across portions of the Northern Plains, the Northern Rockies, and the Northern Great Basin. - Much above normal temperatures across portions of the Central Plains and the Middle Mississippi Valley, Thu-Fri, May 16-May 17. Detailed Summary: Multiple weather hazards appear likely in the medium range period (May 16-May 20) 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 enter Thursday and exit by Friday. Snow accumulations upwards of 1-2 feet will be possible across the Sierra Nevada of central California. Meanwhile 1-2 inches of rain will be possible across much of northern California and into southwest Oregon. Rain will also be possible across southern California, but the amounts don't warrant a highlighted area at the moment. The second system is currently forecast to enter the West Coast by Sunday and bring similar amounts of rain and snow, with rain extending into the Pacific Northwest this round. Two rounds of heavy precipitation also look likely across portions of the Northern Rockies and Northern Great Basin during this time frame. 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 highest mountain peaks 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. High temperatures across the Western U.S. will run 10 to 20 degrees below average due to cloud cover and precipitation, but minimum temperatures remain just slightly below average. Thus, decided to opt out of highlighting a much below average 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 an area at risk for severe thunderstorms from west Texas to southern South Dakota on Friday. This severe area shifts eastward on Saturday and can be found across much of the Southern Plains from southern Kansas to central Texas. Heavy rain will also be possible with the strong storms. The highest confidence areas for heavy rain (greater than 1 inch in 24 hours) comes in two sections. The first area can be found across the Southern Plains, Middle and Lower Mississippi valleys between Saturday and Monday. As the upper-level energy makes its way across the Plains, heavy rain will be possible as thunderstorms combine and move eastward. The other area at risk for heavy rain is north of the main low pressure system across the Northern Plains on Saturday and Sunday, where 1-2 inches of rain will be possible. A heavy rain area was considered across northern Illinois and Iowa for Friday as a few models show heavy rain along a stationary front, but confidence was too low. By the tail end of the forecast period another round of heavy rain is possible across the central Plains, but confidence and the idea that most of the rain will fall after Monday led to the area being left out. High temperatures are forecast be quite warm across the Central Plains on Thursday and Friday. High temperature anomalies will run 15 to 20 degrees above average, with heat indices in the low-to-mid 90s. Since this is one of the first "hot" days across these areas this year, the highlighted section was added. Alaska and the Eastern U.S. appear quiet with respect to hazardous weather between Thurs. May 16 and Mon. May 20. Snell