US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
514 PM EDT Mon Aug 23 2021
 
Valid Thursday August 26 2021 - Monday August 30 2021
 
Hazards:
- Heavy rain across portions of the Southern Plains, Sun-Mon, Aug 29-Aug 30.
- Heavy rain across portions of the Upper/Middle Mississippi Valley, the Great Lakes, and the 
Northern Plains, Thu-Sat, Aug 26-Aug 28.
- Flooding possible across portions of the Mid-Atlantic and the Northeast.
- Flooding occurring or imminent across portions of the Northeast and the Great Lakes.
- Flooding likely across portions of the Mid-Atlantic.
- Excessive heat across portions of the Middle/Lower Mississippi Valley, the Ohio Valley, and the 
Tennessee Valley, Thu, Aug 26.
- High significant wave heights for coastal portions of mainland Alaska, Thu, Aug 26.

Detailed Summary:

On Thursday, a wave of low pressure over the Northern High Plains/Northern Rockies will move 
eastward over the Upper Midwest. On Saturday, the main low will move into Central Canada as the 
boundary moves into Upper Great Lakes to the Central Rockies. The front will tap into a plume of 
moisture from the Western Gulf of Mexico and stay connected through early Saturday. The front will 
produce showers and thunderstorms with heavy rain over parts of the Upper Mississippi Valley into 
the Upper Great Lakes on Thursday and Friday. On Saturday, the area of showers and thunderstorms 
with heavy rain will be much smaller.  Therefore, an area of heavy rain is depicted on the Hazard 
Chart over the same area on Thursday and Friday.  On Saturday, an area of heavy rain will be over 
parts of Wisconsin within the larger region of heavy rain.  The front will continue to move 
eastward into the Great Lakes to the Central Plains by Monday.

An upper-level ridge over the Middle Mississippi Valley will start to weaken on Thursday into 
Friday as upper-level energy associated with the previously mentioned front moves over the area.  
With temperatures in the 90s and the dew point in the low-60s to mid-70s, the heat index will be 
above 105 degrees. Because of that, an area of excessive heat is depicted on the Hazards Chart on 
Thursday over parts of the Middle/Lower Mississippi Valley and parts of the Western Ohio Valley.    

A tropical cyclone may move into Mexico just south of the Texas border on Monday.  The system will 
produce rain along parts of the coast of Texas. However, there is uncertainty on the track and 
where the associated rain will fall. Some models have the rain extending into Louisiana, while 
other models have much less coverage. However, there is an area of heavy rain depicted on the 
Hazards Chart over the far southern part of Texas on Sunday and Monday. The area of heavy rain may 
change as the event becomes closer in time.

Over Alaska, a front with a deep area of low pressure over the Far North will produce high waves 
over the coast from Wainwright to the mouth of the Noatak River on Thursday. Therefore, an area of 
high waves is depicted on the Hazards Chart for this region of Alaska.  The boundary will move 
across the Far North into Canada by Saturday as the trailing boundary rest across the Southcentral 
portion of the state on Saturday and Sunday.

Ziegenfelder