US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
411 PM EDT Mon Oct 18 2021
 
Valid Thursday October 21 2021 - Monday October 25 2021
 
Hazards:
- Heavy rain across portions of California, the Central Great Basin, and the Pacific Northwest, 
Thu-Fri, Oct 21-Oct 22.
- Heavy rain across portions of California and the Pacific Northwest, Sun-Mon, Oct 24-Oct 25.
- Heavy rain across portions of the Central Plains and the Middle Mississippi Valley, Sun, Oct 24.
- Heavy snow across portions of the Central Great Basin, California, and the Southwest, Sun-Mon, 
Oct 24-Oct 25.
- Flooding occurring or imminent across portions of the Southern Plains.
- Flooding likely across portions of the Southeast.
- High winds across portions of the Aleutians, Thu, Oct 21.
 
Detailed Summary:

Main hazard area will be over the West with a punctuated Atmospheric River event poised to bring a 
few rounds of rain and mountain snow to mostly northern California and into southern Oregon. First 
event will be later on Thursday into Friday as a front moves onshore. Parent low will be much 
farther north but influx of moisture off the Pacific (with ties back toward Hawaii) will promote 
modest to locally heavier rain along the coast and into higher elevations of the Klamath Mountains 
and Shasta Siskiyous. After that front moves past, the area will see a couple day break before a 
more energetic system moves into the West next Sunday-Monday. This system may have access to a bit 
more moisture and perhaps a slower progression through NorCal, which could support several inches 
of rain in lower elevations between coastal Oregon southward into northern sections of California. 
With a sustained southwest flow and colder temperatures, snowfall could be heavy for the Sierra but 
with fairly high snow levels to start until colder air moves in.

Next Sunday, moisture across the Plains will override an east-west stationary boundary from Kansas 
to the Tennessee Valley. Circulation around a weak area of high pressure will funnel this narrow 
axis of moisture toward Missouri, where the potential exists for some locally heavy rainfall. This 
should move off the northeast (into the Midwest) by next Monday where it could still produce at 
least modest rain, but confidence is lower in amounts and location.

For Alaska, an area of low pressure will move across the North Pacific and deepen as it crosses the 
western Aleutians late Wednesday into Thursday. On the backside of this low pressure, strong 
northwest winds are forecast over the western/central Aleutians as the low slows down into Bristol 
Bay, redeveloping its triple point well to the southeast.


Fracasso