US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 250 PM EDT Thu May 13 2021 Valid Sunday May 16 2021 - Thursday May 20 2021 Hazards: - Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Central Appalachians, the Middle Mississippi Valley, the Southern Appalachians, the Southern Plains, and the Ohio Valley, Sun-Mon, May 16-May 17. - Heavy rain across portions of the Central Plains and the Southern Plains, Tue-Thu, May 18-May 20. - Heavy rain across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Sun-Thu, May 16-May 20. - Flooding possible across portions of the Northern Great Basin. - Flooding occurring or imminent across portions of the Lower Mississippi Valley and the Southern Plains. Detailed Summary: The main weather hazards during the medium-range forecast period (Sunday, May 16th through Thursday, May 20th) will be associated with the threat of heavy rain across central and south-central sections of the country. At the surface, high pressure is set to remain locked in place throughout the eastern U.S. into the middle of next week. Meanwhile, a warm front situated from the Central Plains to Ohio Valley should meander over the region for much of the forecast period. This frontal boundary will be the focus of showers and thunderstorms that eventually grow upscale into multiple mesoscale convective complexes between Kansas and West Virginia. Thus, the threat of heavy rain from these thunderstorms extends from the Central Plains to the Ohio Valley between Sunday and Monday. A few severe thunderstorms are not out of the question as well, but the overall magnitude of the severe threat still appears low at this time. By Monday, a weakening upper-level low ejecting out of the Southwest is also expected to spark thunderstorms across the Southern Plains and Lower Mississippi Valley. At the same time, a larger scale upper-level trough is expected to develop over the Northwest and funnel continued Pacific energy over the Southern Plains, leading to multiple days of active weather. Moisture return from the western Gulf of Mexico should be sufficient and aid in scattered to widespread instances of heavy rain through at least Thursday across the region. Confidence is highest on Tuesday and Wednesday regarding 1+ inches of rain in 24 hours across southern Oklahoma, as well as north-central and eastern portions of Texas. Additionally, an isolated severe threat is a possibility across much of the Southern Plains during this time period as a more typical May dryline pattern should be found in Texas and Oklahoma. Thunderstorms with heavy rainfall rates could also impact southeast Texas and the Lower Mississippi Valley on Sunday as a shortwave crosses the far northwestern Gulf of Mexico. Additional rain is then expected to enter by Tuesday and Wednesday as convection moves eastward from central Texas. Elsewhere, heavy rain may make a return southern Florida by Thursday, but confidence was too low to add a highlighted area on the hazards chart today. Temperatures across CONUS will start below average throughout the Southeast on Sunday before warming to near normal by the beginning of next week. Meanwhile, high temperatures will reach upwards of 10 to 20 degrees above average from the Northwest to the Northern Plains through Tuesday/Wednesday until a cold front slowly sweeps through the Intermountain West. Little to no precipitation is expected across the West outside of the Cascade and Olympic Mountains. For Alaska, much of the area should remain relatively quiet through the greater part of next week. A potent storm system may impact the Aleutians on Tuesday and Wednesday, but wind gusts at the moment appear to remain below hazardous threshold. There is also a signal for heavy precipitation to enter coastal sections of the Gulf of Alaska on Thursday, but confidence is fairly low at the moment. Snell