US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
454 PM EDT Tue Oct 19 2021
 
Valid Friday October 22 2021 - Tuesday October 26 2021
 
Hazards:
- Heavy precipitation across portions of the central Great Basin into the northern Rockies, Utah, 
central to southern California, as well as the Cascades, Sun-Mon, Oct 24-Oct 25.
- Heavy precipitation across northern California, western Oregon and portions of Washington, 
Fri-Tue, Oct 22-Oct 26.
- Heavy rain across much of the Midwest into the Ohio Valley, Sun-Mon, Oct 24-Oct 25.
- Flooding possible across portions of the southeastern Georgia.
- Flooding occurring or imminent across portions of southern Texas.
- High winds across the western portion of the Aleutians, Fri, Oct 22 and Sun-Mon, Oct 24-Oct 25.
 
Detailed Summary:

The main hazard area in mainland U.S. will be over the West where a series of substantial Pacific 
cyclones and associated fronts are forecast to move onshore at frequent intervals.  The medium 
range period will likely begin with a frontal system moving onshore together with its heavy 
precipitation extending across much of the Pacific Northwest into Idaho and northern California on 
Friday (22nd).  Moisture from another Pacific front should then arrive on Saturday before a more 
energetic and moisture-laden system is forecast to push onshore by later on Sunday.  Heavy 
precipitation associated with this system is forecast to penetrate further south into southern 
California on Sunday, followed by the Great Basin and the northern Rockies on Monday.  As colder 
air moves in and snow levels lower, heavy wet snow is forecast to accumulate across the higher 
elevation of the interior northern two-thirds of the western U.S. on Monday.  The heaviest 
precipitation amounts are expected to occur along the Sierra Nevada where several inches of liquid 
equivalent is possible.  By Tuesday, the high-elevation snow is forecast to continue for much of 
the northern Rockies as yet another moisture-laden system is on the horizon for the West Coast, 
bringing no end to the threat of heavy rain for the lower elevations west of the Cascades.  
Portions of the lower elevations between the Olympic Peninsula and the Cascades including Seattle 
may escape the heavy rain due to rain-shadowing effects.

Over the mid-section of the country, moisture streaming northward from the western Gulf of Mexico 
will override an east-west oriented frontal boundary from Kansas to the Tennessee Valley by next 
Sunday.  A good chance of heavy rain appears to extend across much of the Midwest into the Ohio 
Valley on Sunday into early Monday.  Another area of enhanced rainfall could develop in the upper 
Midwest on Tuesday as the front lifts northward as a warm front, but confidence is rather low at 
this time.

For Alaska, a deep cyclone is forecast to track across the Bering Sea and the eastern Aleutians on 
Friday.  The tight pressure gradient on the backside of this system is forecast to bring very 
strong northwesterly winds across the western to central Aleutians on Friday.  Thereafter, recent 
model runs are now indicating the possibility of another deep cyclone to track across the western 
Aleutians around the Sunday-to-Monday time frame.  A high wind area is thus indicated for western 
Aleutians.  However, model uncertainty remains quite high with this fast-moving system and thus the 
hazard area(s) may be subject to change.

Kong