US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
325 PM EDT Tue Aug 03 2021
 
Valid Friday August 06 2021 - Tuesday August 10 2021
 
Hazards:
- Heavy rain across portions of the Southwest, Sat-Mon, Aug 7-Aug 9.
- Excessive heat across portions of the Central Plains, the Lower Mississippi Valley, the Tennessee 
Valley, the Middle Mississippi Valley, the Southeast, the Southern Plains, and the Ohio Valley, 
Sun-Tue, Aug 8-Aug 10.
- Heavy rain across portions of mainland Alaska, Fri, Aug 6.
 
Detailed Summary:

The medium range forecast period extends from Friday, August 6th to Tuesday, August 10th and 
includes chances for heavy rain and excessive heat across the Lower 48. Regarding the potential for 
thunderstorms and associated downpours, a dissipating stationary boundary should lead to one final 
day of widespread shower activity on Friday across the Carolinas and Southeast. Little to impacts 
are expected. Meanwhile, multiple upper-level shortwaves are forecast to zip across the northern 
tier and spark thunderstorms throughout the Upper Midwest for much of the time frame. Current 
guidance depicts areas between northern Iowa the U.P. of Michigan as having the greatest chances of 
experiencing intense rainfall rates, but the combination of high uncertainty and the expectation of 
localized impacts resulted in no highlighted area on today's graphic. The Southwest Monsoon is 
forecast to relax quite a bit through early next week compared to the robust activity found 
throughout July, but a nose of anomalous atmospheric moisture will lead to continued chances for 
thunderstorms across far south-central and southeastern Arizona between Friday and Monday. Daily 
rainfall amounts could exceed 0.50" in certain locations, possibly leading to instances of flash 
flooding where terrain is most susceptible. 

A gradually building upper-level ridge over the Southeast and south-central-U.S. may lead to 
widespread and impactful heat beginning on Sunday between the central/southern Plains and the Lower 
Mississippi Valley. High temperatures throughout these regions are expected to reach into the 
upper-90s, with heat indices between 100-110 degrees. The excessive heat area depicted on the 
hazards graphic combined locations that could see maximum heat indices near or above 105 degrees, 
as well as minimum temperatures greater than 75 degrees. Oppressive heat is also likely along the 
central and western Gulf Coast, but temperatures will likely remain close to average for this time 
of year. Above average temperatures are also forecast to spread across the Midwest, Ohio Valley, 
Lower Great Lakes, and Mid-Atlantic to end the weekend and start the second week of August. High 
temperatures will reach into the 90s, with the potential for dangerous heat to build throughout the 
Mid-Atlantic on Tuesday. Once confidence increases, an excessive heat area may need to be added for 
the Mid-Atlantic as heat indices could reach into triple digits. 

Across Alaska, high atmospheric moisture content located across the central and eastern interior 
along with an approaching cold front entering from the arctic may fuel scattered showers and the 
potential for heavy rain on Friday. By Sunday, a strong low pressure system located over the Bering 
Sea and associated moisture plume to the southeast will have the potential to produce heavy rain 
from south-central sections of the state to the Panhandle through early next week. However, 
forecast confidence remains very low regarding both strength and timing of the aforementioned 
system. High winds are also possible, but current forecasts fall just below hazardous threshold. 

Snell