US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
448 PM EDT Fri Oct 22 2021
 
Valid Monday October 25 2021 - Friday October 29 2021
 
Hazards:
- Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, 
Wed-Thu, Oct 27-Oct 28.
- Heavy precipitation across portions of California, the Pacific Northwest, and the Northern Great 
Basin, Mon-Tue, Oct 25-Oct 26.
- Heavy precipitation across portions of the Great Basin, the Northern/Central Rockies,  
California, and the Southwest, Mon, Oct 25.
- Heavy rain across portions of the Southeast, the Lower Mississippi Valley, the Southern 
Appalachians, the Ohio Valley, and the Tennessee Valley, Wed, Oct 27.
- Heavy rain across portions of the Great Lakes, the Mid-Atlantic, the Northeast, and the Central 
Appalachians, Tue-Fri, Oct 26-Oct 29.
- Severe weather across portions of the Central/Southern Plains, and the Middle/Lower Mississippi 
Valley, Tue, Oct 26.
- Severe weather across portions of the Southeast, the Lower Mississippi Valley, and the Tennessee 
Valley, Wed, Oct 27.
- 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 Monday, a plume of moisture will stream into Central/Southern California that will weaken by 
Monday evening. However, the moisture will produce heavy precipitation over the Sierra Nevada 
Mountains. Overnight Monday, another plume of moisture will stream into Northern California then 
weaken by Wednesday morning. The moisture will start producing rain and higher elevation snow over 
Northern California from Monday into Tuesday. Moreover, a weaker but more steady stream of moisture 
will stream into the Pacific Northwest. Therefore, heavy precipitation is depicted on the Hazards 
Chart from Northern California into the Pacific Northwest on Monday into Tuesday.  The moisture 
will stream into the Pacific Northwest on Wednesday into Thursday, with heavy precipitation falling 
over the Northwest. By Friday, the moisture flow becomes parallel to the coast so that the heavy 
precipitation will end.   Furthermore, a very deep 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 
ocean 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 posted on the Hazards Chart. 

The front moves inland, moving off the East and Gulf Coast by Friday.  Additionally, 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.  On Tuesday, as the front moves into the Central/Southern Plains, the 
atmosphere will become unstable and develop severe thunderstorms. Therefore, an area of Severe 
Weather is depicted on the Hazards Chart.  As the boundary moves into the Lower Mississippi Valley, 
the atmosphere will become unstable over the Central Gulf Coast into parts of the Southeast, 
producing another area of severe thunderstorms. Likewise, an area of Severe Weather is depicted on 
the Hazards Chart over the area. 

Meanwhile on Tuesday, one area of low pressure will move over the Northeast then off the coast, 
followed by a second area of low pressure moving over the Northeast by Friday.  The systems will 
produce heavy rain over parts of the Northeast into the northern Mid-Atlantic from Tuesday into 
Friday.  Moreover, as the associated front moves over the Southeast and the Ohio Valley, an area of 
heavy rain will develop over parts of the Ohio and Tennessee Valleys and parts of the Lower 
Mississippi Valley and the Southeast on Thursday.  

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.

Low pressure consolidating over the Gulf of Alaska will produce mountain snow for the Western 
Alaska Range plus Kenai Mtns. and including the Wrangell St. Elias National Park on Wednesday into 
Friday.

Ziegenfelder