US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
427 PM EDT Mon Sep 27 2021
 
Valid Thursday September 30 2021 - Monday October 04 2021
 
Hazards:
- Heavy rain across portions of the Pacific Northwest and the Northern Great Basin, Thu, Sep 30.
- Heavy rain across portions of the Southern Rockies, the Central Plains, the Lower Mississippi 
Valley, and the Southern Plains, Thu-Sat, Sep 30-Oct 2.
- Flooding occurring or imminent across portions of the Great Lakes.
- Heavy precipitation across portions of mainland Alaska, Thu-Fri, Sep 30-Oct 1.
- Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Thu-Sat, Sep 
30-Oct 2.
- High winds across portions of the Alaska Panhandle, mainland Alaska, and the Aleutians, Thu, Sep 
30.
 
Detailed Summary:

As the month of September comes to a close and October begins, the weather pattern across the Lower 
48 features a pair of upper lows that will lead to cooler and/or seasonal temperatures for a couple 
regions while the rest observe abnormally warm temperatures. The upper lows at the start of the 
period are forecast to be positions in the Southwest and near the Northeast coast. The backside of 
the upper low near the Northeast will generally provide drier and seasonally cool temperatures 
heading into the weekend, but the upper low in the Southwest will be the primary weather maker for 
the period. A low-mid level ridge of high pressure over the Southeast, working in tandem with the 
Southwest upper low to tighten the pressure gradient over the South Central U.S., taps into Gulf of 
Mexico moisture that becomes directed into the Southern Plains and Southern Rockies. With the upper 
low forecast to slowly move east the first couple days of the medium range period, look for a 
prolonged stretch of heavy showers and thunderstorms to envelope much of the southern High Plains 
and into the New Mexico. Much of the region is enduring some form of drought and soil moisture is 
quite dry, but as the area becomes increasingly saturated, there could be a growing opportunity for 
localized flash flooding on Friday and into Saturday.

Temperature-wise, the vast majority of the Mississippi River Valley will experience mild daily 
minimum temperatures, but expansive cloud cover streaming over the Heartland should help to limit 
high temps from becoming much above normal. The upper low in the Southwest will be responsible for 
a cool temperature regime throughout the Four Corners region and the southern High Plains through 
the upcoming weekend, but minimum temps look to be closer to seasonal. In short, despite some 
anomalously cool min temps (max temps) in the Mississippi River Valley (Southwest) the period seems 
void of any much above or below normal temperature regimes.

In Alaska, it is a wet and snowy start to the medium range period from the central Gulf Coast on 
east into the Panhandle. The Panhandle will contend with a frontal system on Thursday that yields 
areas of rain and mountains snow before weakening as it tracks into western Canada. Meanwhile, a 
powerful and occluding storm system in the Bering Sea on Wednesday will give way to a new area of 
low pressure forming just south of the central Gulf Coast Thursday and into Friday. Copious amounts 
of lower elevation rainfall and heavy mountain snow are on tap Thursday from the southern half of 
the Kenai Peninsula to the Granite Pass. In addition, high winds are anticipated as wind gusts in 
excess of 50 knots are possible in parts of the Aleutians and the higher elevations of southeast 
Alaska. As the storm enters the Gulf on Friday, rich moisture become directed at the Panhandle with 
periods of rain and mountain snow expected to last into the upcoming weekend. Model spread in terms 
of intensity of the developing Gulf of Alaska low remains high, but should the storm trend more 
intense, the high wind threat may extend into the weekend. By early next week, focus shifts to 
Typhoon Mindulle which will undergo extra-tropical transitioning and race towards the Bering Sea by 
next Monday. This could mean strong winds and large swells for the Aleutians, but Mindulle's track 
and intensity as it reaches the Aleutians is not clear at this time.

Mullinax