US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 533 PM EDT Thu Oct 21 2021 Valid Sunday October 24 2021 - Thursday October 28 2021 Hazards: - Heavy precipitation across portions of California, the Pacific Northwest, and the Northern Great Basin, Mon-Thu, Oct 25-Oct 28. - Heavy precipitation across portions of California, the Great Basin, the Pacific Northwest, and the Southwest, Sun-Mon, Oct 24-Oct 25. - Heavy precipitation across portions of the Northern/Central Rockies, and the Great Basin, Mon-Tue, Oct 25-Oct 26. - Heavy rain across portions of the Central Plains, the Upper/Middle Mississippi Valley, the Great Lakes, and the Ohio Valley, Sun, Oct 24. - Heavy rain across portions of the Middle/Lower Mississippi Valley, the Tennessee Valley, the Southern Appalachians, the Southeast, and the Ohio Valley, Wed, Oct 27. - Severe weather across portions of the Central/Southern Plains, and the Lower/Middle Mississippi Valley, Sun, Oct 24. - Flooding occurring or imminent across portions of the Southern Plains. - High significant wave heights for coastal portions of California and the Pacific Northwest, Mon, Oct 25. Detailed Summary: On Sunday, an intense area of low pressure will be over the Eastern Pacific off the coast from the Northwest that moves inland into West-Central Canada by Tuesday. The front moves inland, too advancing to the Great Lakes to parts of the Central Gulf Coast. The waves associated with the deep low will impact the coast of Oregon to just north of the San Francisco Bay Area on Monday with waves 20 feet or greater; the wind will be strong along the coast, too. Therefore, a significant waves hazard is on the Hazards Chart. Moreover, moisture from the Pacific streams into California on Sunday. The moisture will aid in producing rain and higher elevation snow into parts of California on Sunday into Monday. Therefore, an area of heavy precipitation is depicted on the hazards chart over this region from Sunday into Monday. On Tuesday, another moisture area will stream into Northern California, moving into parts of the Pacific Northwest on Thursday. Likewise, the moisture will produce an area of heavy precipitation over parts of the Pacific Northwest from Monday into Thursday. Furthermore, as the boundary crosses the Northern Intermountain Region into parts of the Northern Rockies, an area of heavy precipitation will develop over parts of the region, with snow at higher elevations and rain in the valleys on Monday and Tuesday. Meanwhile, a front over the Central/Southern Plains and the Middle/Lower Mississippi Valley will destabilize the atmosphere over the region producing conditions favorable for severe thunderstorms. Therefore an area of Severe Weather is depicted on the Hazards Chart on Sunday. Related to the front, an area of heavy rain will develop over parts of the Middle Mississippi Valley into the Ohio Valley on Sunday. On Wednesday, moisture from the Gulf of Mexico will stream northward over the plains into the Mississippi Valley ahead of a front transiting the area. The front will aid in producing an area of heavy rain over parts of the Middle/Lower Mississippi Valley and the Ohio/Tennessee Valleys. As the front moves eastward, there could be another area of heavy rain over the Northeast or from the Lower Great Lakes into the Mid-Atlantic and the Southeast. However, the spread in the models makes it very uncertain at this time whether or not to put an area. The WPC will keep investigating this area and will apply the appropriate hazard if needed. Over Alaska, no hazards are depicted on the Hazards Chat at this time. Nevertheless, WPC will monitor the situation to see if it changes over the next few days. On Sunday, an area of low pressure will move south of the Aleutians across the North Pacific. The low will have a tight pressure gradient but will not meet the criteria for high wind over the region. In general troughing will be over the state during this period. Although there will be much deeper low pressure over the Gulf of Alaska into the Eastern Pacific, the bulk of the weather will be elsewhere, with some snow showers over parts of the state through Thursday. Ziegenfelder