US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
515 PM EDT Wed Oct 06 2021
 
Valid Saturday October 09 2021 - Wednesday October 13 2021
 
Hazards:
- Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, 
Sat-Mon, Oct 9-Oct 11.
- Heavy rain across portions of the Southeast, the Mid-Atlantic, the Upper Mississippi Valley, and 
the Northern Plains, Sat, Oct 9.
- Heavy rain across portions of the Southeast, the Southern Appalachians, the Mid-Atlantic, and the 
Central Appalachians, Fri-Sat, Oct 8-Oct 9.
- Heavy precipitation across portions of mainland Alaska, Fri, Oct 8.
- Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Fri-Sat, Oct 
8-Oct 9.
- High winds across portions of mainland Alaska and the Aleutians, Fri-Sat, Oct 8-Oct 9.
 
Detailed Summary:

The medium range forecast period (Saturday, October 9th - Wednesday, October 13th) features 
scattered heavy rain and mixed precipitation hazards this weekend amid a complex upper-level 
pattern, before a strong upper-trough digs into the Four Corners and ejects into the Central Plains 
early next week. The impending strong system is expected to produce numerous instances of hazardous 
weather over the Western and Central U.S., including appreciable high-elevation snow accumulations, 
severe weather, and heavy rain. Alaska remains in an active pattern as well, with wintry 
precipitation and gusty winds possible this weekend and more on the way next week. 

Beginning this Saturday, lingering heavy rain chances will persist across portions of the 
Appalachians, Coastal Carolinas, and Outer Banks as a weakening shortwave disturbance and frontal 
system lift east off the Mid-Atlantic coast. Antecedent rainfall over the Appalachians in the 
short-range period combined with possible upslope enhanced rain rates may facilitate a localized 
flood threat. To the east along the Carolina coastline, the offshore surface front and coastal 
trough may focus rainfall before the system slowly drifts off to sea by Tuesday. Over the Upper 
Midwest on Saturday, shortwave trough activity should propagate a strengthening frontal system and 
associated showers/thunderstorms across the Northern Tier. A plume of anomalous moisture ahead of 
the front will facilitate efficient rainfall production with this activity, before the system 
quickly exits to the east with the best rain chances. Wintry weather is also expected to make an 
appearance in the Cascades as moist Pacific air tied to an atmospheric river event ascends the 
terrain, although the mixed precipitation will remain tied to higher elevations. Meanwhile on 
Sunday, a shortwave disturbance within a split branch of the Polar Jet is forecast to swing from 
the Four Corners into the Central Plains and push a frontal system eastward. The approach of the 
storm from the west will usher in a moist and unstable airmass from the Gulf of Mexico to promote 
organized thunderstorms capable of producing heavy rain and severe weather over portions of the 
region (highlighted in the SPC Day 5 Outlook). The next batch of widespread hazardous weather 
arrives over the West late this weekend with the arrival of a strong upper trough digging south 
from the Pacific Northwest. The aforementioned mixed precipitation activity over the Cascades 
should renew through Monday before the activity shifts southeast toward the Great Basin. 
Anomalously cool temperatures with high temperatures 20-25 degrees below normal will overspread the 
western half of the U.S. behind a strong cold front which supports lowering snow levels throughout 
the region. Appreciable snow accumulations appear most likely by Monday in the North/Central 
Rockies along a forming deformation zone, as the system ejects east into the Plains. East of the 
Rockies, heavy rain and mixed precipitation is possible as the system taps into a feed of abundant 
Gulf moisture, although precipitation type will remain dependent on elevation and track of the 
closed low. Further south within the warm sector of the low, the overlap of unstable air and 
strengthening wind shear supports another threat of severe weather on Wednesday over the Southern 
Plains per the SPC Day 6 Outlook. Gusty winds are also possible across the Central U.S. as the 
system deepens, which will be monitored in subsequent Hazards updates.     

Over Alaska, the forecast remains on track for low pressure to produce high gusty winds across the 
Aleutians, Alaska Peninsula, and Kodiak Island through Saturday as the system makes its way toward 
the Gulf of Alaska, with lingering mixed precipitation along the terrain roughly from Yakutat to 
Ketchikan. Afterwards, the next round of active weather begins early next week as another frontal 
system arrives from the west. A fair amount of uncertainty remains regarding the strength and track 
of the system as it pivots through the Gulf of Alaska. However, reasonable ensemble agreement for 
higher totals along the southern Alaska coast to the Panhandle prompted the addition of a Heavy 
Precipitation area. Gusty winds remain possible with the system as well, but are more dependent on 
the strength and track of the low which remains nebulous for now. 

Asherman