US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
447 PM EDT Thu Sep 30 2021
 
Valid Sunday October 03 2021 - Thursday October 07 2021
 
Hazards:
- Heavy rain across portions of the Tennessee Valley, the Ohio Valley, and the Great Lakes, Sun, 
Oct 3.
- Heavy rain across portions of the Northeast, Mon, Oct 4.
- Heavy rain across portions of the Southern Appalachians and Piedmont, Tue-Wed, Oct 5-Oct 6.
- Flooding occurring or imminent across portions of the Great Lakes.
- High winds across portions of mainland Alaska and the Aleutians, Mon-Tue, Oct 4-Oct 5.
- Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Wed-Thu, Oct 
6-Oct 7.
 
Detailed Summary:

The main concern during the medium-range forecast period (Sunday, Oct 3rd  Thursday, Oct 7th) will 
be the threat for instances of heavy rain with a slow moving storm system across the eastern half 
of the country. At the beginning of the period, a low pressure center will be located over the 
Great Lakes with a stationary front draped eastward across the interior Northeast and New England 
and a trailing cold front extending southwestward through the Mississippi Valley into Texas. A 
shortwave rotating around the base of an upper-level low will help encourage the development of 
showers and storms ahead of the cold front from the Tennessee Valley northward to the Great Lakes 
on Sunday (Oct 3rd). Both the deterministic and ensemble model guidance show broad general 
agreement on widespread heavy rain totals. Showers and storms will likely continue on Monday (Oct 
4th) as the cold front moves further into the Southeast, but there is not as much agreement amongst 
the guidance on heavier rain totals at this time.  Heavy rain is also likely with showers and 
storms developing along the stationary front across portions of southern New York and northern New 
Jersey into southern New England on Monday, aided by the shortwave continuing northeast across the 
region. These areas have also seen several instances of significant rainfall recently, exacerbating 
flooding concerns with any additional heavy rainfall. 

Later in the period, the upper-level low is expected to become cut-off from the mean flow and stall 
over the Southeast. The cold front will move across the southern Appalachians on Tuesday (Oct 5th) 
and approach the Atlantic Coast by Wednesday (Oct 6th). Showers and storms are likely across the 
southern Appalachians and Piedmont on Tuesday and Wednesday, initially along the cold front and 
continuing with support from upper-level forcing on the east side of the cut-off low. Significant 
rainfall totals look possible, with storm development aided by broad low-level easterly flow and 
orographic forcing along the higher terrain of the southern Appalachians. Additional heavy rainfall 
is possible on Thursday (Oct 7th) to the east of the cut-off low, but there is not enough agreement 
among the models on the location/coverage of heavy rain for an additional outlook area at this 
time. 

For Alaska, a strong low pressure system crossing the Bering Sea, the remnants of Typhon Mindulle, 
is expected to bring high winds to the Aleutians and western coast of the mainland on Monday and 
Tuesday.  Increasing moisture ahead of this system, as well as a second system following 
immediately in its wake and moving into the Gulf of Alaska, is forecast to lead to both heavy snow 
in the mountains as well as heavy rain for lower elevations and coastal areas from the western 
Alaskan Range southeast to the Kenai Peninsula and into the Panhandle. A broad heavy precipitation 
area has been introduced for Wednesday and Thursday to cover this threat. 

Putnam