US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
344 PM EDT Mon Sep 13 2021
 
Valid Thursday September 16 2021 - Monday September 20 2021
 
Hazards:
- Heavy rain across portions of the Pacific Northwest and the Northern Great Basin, Fri-Sat, Sep 
17-Sep 18.
- Heavy rain across portions of the Northern Rockies and the Northern Great Basin, Sat-Sun, Sep 
18-Sep 19.
- Heavy rain across portions of the Southeast and the Lower Mississippi Valley, Thu, Sep 16.
- Flooding possible across portions of the Lower Mississippi Valley and the Southern Plains.
- High winds across portions of the Central Plains, the Central Great Basin, the Northern Plains, 
the Northern Rockies, the Central Rockies, California, the Northern Great Basin, and the Pacific 
Northwest, Sat-Sun, Sep 18-Sep 19.
- Heavy precipitation across portions of mainland Alaska, Thu, Sep 16.
- Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Mon, Sep 20.
 
Detailed Summary:

The medium range forecast period (Thursday, Sept. 16 to Monday, Sept. 20) will include an active 
and cool weather pattern across the Pacific Northwest, while summer-like warmth continues to hang 
on throughout the rest of the country. For the Southeast and central Gulf Coast, impacts associated 
with Nicholas are expected to linger into the latter part of this week as well. Whether as a 
tropical depression or remnants, heavy rain corresponding to Nicholas will potentially affect parts 
of the region from southern Louisiana to the western Florida Panhandle and southwest Alabama on 
Thursday. Uncertainty remains high regarding how far east and north the bulk of the heavy rain 
extends, with the potential for several inches of rain along slow-moving tropical downpours. As of 
the latest National Hurricane Center forecast track for Nicholas, the highlighted heavy rain area 
was placed to the south of the forecast low pressure center on Thursday, where the greatest 
moisture content and localized convergence axes should form. Heavy rain chances are expected to 
diminish and become even more localized by Friday. 

For the rest of the Lower 48, upper-level troughing is forecast to set up across the Northwest 
through early next week, while persistent ridging extends from the south-central U.S. to the East 
Coast. This will result in widespread above average temperatures from the Southern High Plains 
across the Midwest and into the Northeast. The highest temperature anomalies (10 to 20 degrees 
above average for this time of year) are forecast across the Central Plains and Midwest between 
Saturday and Monday. This equates to high temperatures into the upper 80s and low 90s. No 
highlighted areas were added to communicate the anomalously warm temperatures since they are likely 
to fall below heat advisory criteria and are not expected to threaten many daily records. Farther 
west, cooler and active weather is set to bring chances for heavy rain throughout the Pacific 
Northwest and Northern Rockies beginning on Friday. A cold front and associated upper-level trough 
will help produce around 1 to 3 inches of rain across parts of western Washington and Oregon, with 
higher amounts possible along the Cascade and Olympic mountains. Widespread showers and moderate 
rain may also reach into parts of northern Idaho and northwest Montana this weekend. Ahead of the 
cold front, gusty winds are possible throughout the Great Basin and into parts of the 
northern/central Rockies. Given the severe drought conditions in the area, an increase in fire 
weather danger is also possible. Finally, much cooler and below average temperatures are forecast 
to usher into the Northwest behind the aforementioned cold front. Highs are only expected to reach 
the 60s, with even colder temperatures in the higher elevations. Nighttime temperatures could drop 
into the 40s throughout the northern Great Basin and Northern Rockies, with snow possible in the 
tallest mountain ranges. A highlighted much below average temperature area was considered, but any 
frost concerns are expected to be very localized during this time frame.

For Alaska, a potent low pressure system in the Gulf of Alaska on Thursday will help aid in 
producing heavy coastal rain and mountain snow across the Kenai Peninsula and Prince William Sound, 
with the potential for liquid precipitation amounts to exceed 2 inches. By Monday, the next 
rainmaker may enter the Alaska Panhandle and produce several inches of rain. Current forecast 
guidance differs on timing, but most have similar impacts sometime early next week with an extended 
round of moisture advection and heavy rain. Otherwise, below average temperatures and snow showers 
are expected across northern and Interior Alaska, with temperature anomalies around 10 to 15 
degrees below average in spots and lows dipping well below freezing. 

Snell