US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 400 PM EDT Thu May 16 2019 Valid Sunday May 19 2019 - Thursday May 23 2019 Hazards: - Heavy precipitation across portions of the Central Rockies, the Central Plains, the Northern Plains, and the Northern Rockies, Sun-Mon, May 19-May 20. - Heavy rain across portions of the Plains and Mississippi Valley, Mon-Tue, May 20-May 21. - Heavy rain across portions of the Northern Rockies, Wed-Thu, May 22-May 23. - Heavy rain across portions of the Central Rockies, Mon, May 20. - Heavy rain across portions of the Upper Great Lakes, Sun, May 19. - Severe weather across portions of the Central and Southern Plains, Mon, May 20. - Severe weather across portions of the Central and Southern Plains, Middle and Lower Mississippi Valley, Tue, May 21. - Severe weather across portions of the Great Lakes and the Ohio Valley, Sun, May 19. - Flooding possible across portions of the Central Plains, the Upper and Middle Mississippi Valley, the Northern Plains, and the Northern Great Basin. - Flooding occurring or imminent across portions of the Mississippi and Missouri River basins, the Southern Plains, and Northern Rockies. - Flooding likely across portions of the Northern Rockies. - Excessive heat across portions of the Southeast, Thu, May 23. - Much below normal temperatures across portions of California and Central Intermountain West, Sun-Thu, May 19-May 23. - Much below normal temperatures across portions of the Northern and Central Plains, and Upper Mississippi Valley, Sun-Tue, May 19-May 21. Detailed Summary: An amplified upper-level pattern consisting of a western trough and strengthening Southeast ridge will prevail during May 19-23, with a series of systems bringing periods of active weather across the western and central U.S. Expect chilly temperatures from the West through the northern Plains while very warm to hot conditions gradually expand across the Southeast. On Sunday May 19 the leading system that tracks through the Upper Mississippi Valley and Great Lakes will bring the threat of heavy rainfall centered over northern Wisconsin and UP of Michigan along with severe weather to locations farther south over the western Great Lakes toward the Lower Ohio Valley. The next system will spread a broad area of precipitation across the West from Sunday into early next week. Favored terrain from northern-central California east-northeast into the Rockies will likely see significant totals but at this time there is limited coverage for high-confidence areas exceeding hazard thresholds. Expect some snow at high elevations from the Sierra Nevada to the Rockies. As the storm tracks northeast across the central U.S. early-mid week, the Plains into parts of the Mississippi Valley will see a threat for heavy rainfall and/or severe weather. Refer to Storm Prediction Center products for more information on severe threats. Temperatures may be cold enough to allow for some snow over the north-central High Plains early next week. Another system will start to bring moisture into the West after Monday May 20. Initially the highest rainfall totals should be over extreme northwest California and southwest Oregon though remaining below hazard criteria. The pattern may favor an area of heavy rainfall over parts of northwest Montana by Wednesday-Thursday May 22-23. Within the broad area of much below normal temperatures from California and the Southwest/Great Basin through the northern Plains, clouds and precipitation will lead to the most extreme anomalies for cold daytime highs--generally at least 10-20F below normal. The northern High Plains region looks particularly chilly with some highs at least 20-25F below normal Sunday-Tuesday May 19-21. An upper ridge will build over the Gulf of Mexico and Southeast U.S. over the course of next week. This ridge will support above normal temperatures that should be the highest of the season thus far over the Southeast into parts of the Appalachians and Mid-Atlantic. For now the map focuses on areas over the Southeast where maximum heat index values may reach at least 95-100F by Thursday May 23. To the immediate north of this area high temperatures may be more anomalously warm and locally reach much above normal thresholds but with less extreme heat index values. Alaska will remain relatively quiet through midweek. A central Pacific storm may approach the eastern Aleutians late in the week but so far expect any effects to remain below hazard criteria through Thursday May 23. Rausch