US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
430 PM EDT Wed Sep 22 2021
 
Valid Saturday September 25 2021 - Wednesday September 29 2021
 
Hazards:
- Heavy rain across portions of the Pacific Northwest, Sun-Tue, Sep 26-Sep 28.
- Heavy rain across portions of the western slopes of the Cascades, Mon-Tue, Sep 27-Sep 28.
- Heavy rain across the eastern portion of Maine, Sat-Sun, Sep 25-Sep 26.
- Much above normal temperatures for much of the northern and central Plains, Sun-Tue, Sep 26-Sep 
28.
- Flooding possible across the central Appalachians into the northern Mid-Atlantic, as well as 
portions of the lower Great Lakes and northern Florida.
- Flooding occurring or imminent across portions of central Tennessee.
- Heavy precipitation across the Alaska Panhandle, Wed, Sep 29.
 
Detailed Summary:

The medium range forecast period (Saturday, Sept. 25 to Wednesday, Sept. 29) will likely begin with 
a heavy rain threat for at least the eastern portion of Maine where a frontal boundary lingers.  
Models continue to show difficulties resolving the timing of the frontal boundary as well as the 
depth and amplitude of a reinforcing upper trough pushing through the Great Lakes toward New 
England this weekend.  This reinforcing upper trough may act to keep the threat of heavy rain 
across eastern Maine into early Monday when the trough could trigger the rapid formation of a new 
low pressure system just east of Maine.  The threat of heavy rain should end later on Monday as the 
system is forecast to move further away into the Canadian Maritimes, though scattered showers will 
likely linger.

Meanwhile, there are increasing model signals for additional moisture to reach portions of the 
Pacific Northwest this weekend.  The moisture influx appears to be most significant from Sunday 
into Monday, lingering into early Tuesday.  Thus, heavy rain areas are indicated for the Olympic 
Peninsula and into the western slopes of the Cascades through this period.

Over the southern Plains, there is emerging model support for tropical moisture from the western 
Gulf of Mexico to push northward into the region by early next week.  This is especially true with 
the ECMWF solutions where the upper trough in the southwestern U.S. is now forecast to move faster 
into the central/southern Plains.  However, uncertainty is currently too high as to how much 
moisture will be drawn northward to warrant a heavy rain area at this time.

Meanwhile, between the two areas of heavy rain in the Pacific Northwest and New England, a warm 
ridge of high pressure aloft will ensure at least a few days of much above normal temperatures over 
much of the northern and central Plains during the medium range period.  High temperatures well 
into the 80s to the lower 90s are forecast to continue daily down into Oklahoma.  These 
temperatures are 10 to 20 degrees above normal for this time of year.

In Alaska, an occluded cyclone should track toward British Columbia Sunday into Monday.  Since the 
forecast track for this cyclone continues to shift further to the south, the threat of heavy rain 
for the southern portion of the Alaska Peninsula has decreased.  By the middle of next week, there 
is good model agreement to support a heavy rain area for much of the Alaska Peninsula where a 
rather sizable and deep cyclone is currently forecast to approach from the Gulf of Alaska.

Kong