US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 323 PM EDT Fri May 01 2020 Valid Monday May 04 2020 - Friday May 08 2020 Hazards: - Heavy rain across portions of the Central/Southern Plains, the Middle/Lower Mississippi Valley, the Central/Southern Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southeast, and the Ohio Valley, Mon-Tue, May 4-May 5. - Severe weather across portions of the Central Plains, the Middle/Lower Mississippi Valley, and the Southern Plains, Mon, May 4. - Flooding possible across portions of the Middle/Upper Mississippi Valley, the Northeast, the Great Lakes, and the Ohio Valley. - Flooding occurring or imminent across portions of the Southeast, the Mississippi Valley, and the Northern Plains. - Flooding likely across portions of the Middle Mississippi Valley, the Great Lakes, and the Northern Rockies. - Much above normal temperatures across portions of California, the Northern/Central Great Basin, the Pacific Northwest, and the Southwest, Thu-Fri, May 7-May 8. - Much above normal temperatures across portions of the Central Great Basin, California, and the Southwest, Tue-Fri, May 5-May 8. - Much above normal temperatures across portions of the Southern Rockies, the Southern Plains, the Central Great Basin, and the Southwest, Mon-Fri, May 4-May 8. - Much above normal temperatures across portions of the Central/Southern Plains, the Central/Southern Rockies, the Central Great Basin, and the Southwest, Mon, May 4. - Heavy precipitation across portions of mainland Alaska, Mon, May 4 and Thu-Fri, May 7-May 8. Detailed Summary: The medium range period will begin on Monday 5/4 with quasi-zonal flow across much of the U.S., with embedded shortwaves. But an upper-level high over northern Mexico and then a ridge building across the West Coast as another upper high moves in from the Pacific should help keep heights above normal through the period over the southwestern quadrant of the nation. This will lead to much above normal temperatures continuing for the Southern Plains on Monday, and record highs are possible there with temperatures nearing or even exceeding 100 degrees in parts of Texas. The Southwest should be consistently hot, with temperatures increasing a few degrees around midweek on, which could cause excessive heat to be a threat. Above normal temperatures are forecast to stretch farther west and north for the latter half of the week as the ridge builds, even up to the Pacific Northwest by Friday. Early next week, an upper-level shortwave trough is forecast to move across the Northern Rockies to the Northern Plains by Tuesday, bringing chances for precipitation over those areas. Most precipitation should fall as rain, but higher elevation light snows in the Northern Rockies are expected as temperatures cool down with the trough. Farther east, model guidance has varied in terms of how much rain will fall and where, due to differences in their handling of the shortwave trough. There remains some potential for moderate to locally heavy rain in portions of the Northern Plains and the Upper Midwest early in the week. Windy conditions are also possible over the Rockies on Monday and the Plains Tuesday, but winds should remain below hazards criteria. Downstream of the trough, a better chance of heavy rainfall is forecast over portions of the Mississippi, Tennessee, and Ohio Valleys toward the Southern/Central Appalachians on Monday and Tuesday. Confidence in the latitudinal placement of the heaviest rain is not too high, but Gulf of Mexico moisture flowing into the vicinity of and overrunning a front is expected and could create a threat. Severe weather is also possible with this system. Over Alaska, a low pressure system in the Gulf of Alaska should spread precipitation to the coast on Monday, and model guidance is in good agreement that portions of the Kenai Peninsula, Kodiak Island, and portions of the Alaska Peninsula could see enhanced precipitation totals, so added a Heavy Precipitation hazard area there. Later in the week, another low pressure system approaches, and the pattern is again favorable for heavy precipitation with an influx of moisture along the Gulf coast. Model guidance is more varied with the placement of the higher totals this time, but the same favored areas could see another round of precipitation by Thursday and Friday. Additionally, ice jam and snowmelt flooding are possible over portions of the mainland, though specific locations where these issues could occur are hard to pinpoint in advance. Temperature anomalies are not expected to be significant, though warmer than average temperatures should be persistent over the southwestern mainland. Tate