US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
428 PM EDT Tue Sep 21 2021
 
Valid Friday September 24 2021 - Tuesday September 28 2021
 
Hazards:
- Heavy rain across portions of northern New England, Fri-Sat, Sep 24-Sep 25.
- Flooding possible across portions of lower Michigan.
- Flooding occurring or imminent across portions of the Tennessee Valley.
- Heavy precipitation across portions of coastal and higher terrain of southern into the Alaska 
Panhandle, Fri, Sep 24.
- Heavy rain across southern portion of the Alaska Panhandle, Fri, Sep 24 and Mon-Tue, Sep 27-28.
 
Detailed Summary:

The medium range forecast period (Friday, Sept. 24 to Tuesday, Sept. 28) will likely begin with a 
heavy rain threat progressing into portions of northern New England ahead of an upper-level closed 
low lifting northward across the Great Lakes into Canada.  Models continue to show difficulties 
resolving the timing of the associated frontal boundary as well as the surge of pre-frontal 
Atlantic moisture under this amplified and blocky synoptic pattern while a reinforcing shortwave 
trough in its wake adds more complexity to the pattern.  The best estimate at present calls for the 
threat of heavy rain to slowly work its way across northern New England through this weekend.  The 
reinforcing shortwave will then push the heavy rainfall out into the Canadian Maritimes by next 
Monday.  Southern New England is more susceptible to flooding after an extremely wet summer due to 
the repeated passages of tropical systems.  Parts of northern New England is in a rainfall deficit 
however.  The Southwest will also have chances for showers and perhaps some locally heavier 
downpours as an upper-level low tracks across the region.  Widespread heavy rain is not anticipated.

Towards the latter portion of the medium-range period, models are indicating a surge of moisture 
reaching portions of the Pacific Northwest.  No heavy rain areas are highlighted at this time.  
However, it is possible that meaningful rainfall could reach the Olympic Peninsula and the northern 
Cascades on Monday.

No hazardous temperatures are currently forecast for mainland U.S. during the medium range period.  
A reinforcing cold front will likely bring another surge of autumn weather from the northern Plains 
eastward into much of the East Coast by early next week.  Patchy frost is possible across the upper 
Midwest to the Great Lakes and over parts of the Appalachians into the weekend.  Meanwhile, a 
warming trend in the western U.S. will bring above average temperatures into the Intermountain West 
on Saturday, spreading into much of the Great Plains by Sunday.  High temperatures from the 80s to 
the lower 90s are forecast to continue over the Plains into early next week.

In Alaska, models have significantly backed off on the intensity of a cyclone forecast to move 
across the Aleutians to the Gulf of Alaska this weekend.  The forecast track has also trended 
southward.  The ensemble mean track is more stable with time--generally bringing a low center from 
south of the Aleutians eastward into the Gulf of Alaska.  A heavy rain area is indicated across the 
southern portion of the Alaska Peninsula next Monday into Tuesday as the cyclone is projected to 
reach the area based on the ensemble mean track, as well as support from the latest GFS and ECMWF 
deterministic runs.  Meanwhile, heavy precipitation associated with an occluded cyclone in the 
short range period is expected to linger into Friday along the southern coastal sections of Alaska 
and into the Alaska Peninsula.

Kong