US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
319 PM EDT Fri Aug 06 2021
 
Valid Monday August 09 2021 - Friday August 13 2021
 
Hazards:
- Flooding occurring or imminent across portions of the Southeast.
- Excessive heat across portions of California, the Pacific Northwest, and the Northern Great 
Basin, Wed-Fri, Aug 11-Aug 13.
- Excessive heat across portions of the Plains and the Middle/Upper Mississippi Valley, Mon, Aug 9.
- Excessive heat across portions of the Lower Mississippi Valley and the Southern Plains, Mon-Fri, 
Aug 9-Aug 13.
- Excessive heat across portions of the Mid-Atlantic and the Northeast, Tue-Fri, Aug 10-Aug 13.
- Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Mon-Fri, Aug 9-Aug 13.
 
Detailed Summary:

The pattern during the medium range forecast period (Monday, August 9 - Friday, August 13) will be 
characterized by upper-level ridging coming into the West Coast for the latter part of the week, 
upper ridging over the Eastern Seaboard as well, and periods of troughing across the north-central 
U.S. in between. Before a cold front pushes across the central U.S. ahead of an upper trough, 
Monday will be a warm day across the Central Plains and Middle Mississippi Valley, with 
temperatures around 10-15 degrees above average and heat indices potentially rising above 105F. The 
combination of typical summer heat and oppressive humidity should also lead to the potential for 
excessive heat centered in the Lower Mississippi Valley throughout next week, as any frontal 
systems that could ease the heat and humidity will be confined to the northern half of the CONUS. 
The heat is expected to stretch toward the Gulf Coast, but conditions there should be around normal 
for August. 

In addition, temperatures in the 90s and dewpoints in the 70s could combine to create uncomfortably 
to dangerously hot conditions across the southern Mid-Atlantic region underneath the upper-level 
ridging. This could be particularly dangerous in the major metropolitan areas that can trap heat. 
Warm low temperatures in the mid-70s from the Central/Southern Plains to the Middle/Lower 
Mississippi Valley and Southeast/Mid-Atlantic will mean there is little relief from the heat 
overnight. Temperatures are likely to be 5 to 10 degrees above normal stretching into the Northeast 
as well, but with heat indices staying below 100F. Then as upper ridging pushes toward the 
Northwest around midweek, temperatures will increase for Washington and Oregon. Temperature 
anomalies of 10-20 degrees above normal are forecast, with highs in the 90s likely and even in the 
100s for interior portions of the region, and breaking daily record highs already appears possible.

Frontal systems and moisture inflow will lead to scattered showers and thunderstorms for the 
central and eastern parts of the country through the week. At this point, however, the timing of 
the fronts and the midlevel shortwave troughs pushing them forward remain unclear given model 
guidance disagreements. Thus it is hard to determine any particular regions that could receive 
enhanced rainfall totals at this time, but locally heavy rainfall could be possible in some areas, 
potentially somewhere in the north-central U.S. to Ohio Valley. Monsoonal moisture is also expected 
to come into the Southwest next week, but rainfall amounts do not look to be especially anomalous, 
at least not for widespread areas. 

For Alaska, persistent upper-level troughing is forecast to be in place across the state during the 
period, which will lead to cooler than average temperatures, especially in terms of highs. But the 
main hazard for Alaska will be multiple rounds of rainfall occurring from the Southcentral region 
into the Panhandle as approaching low pressure systems and fronts bring much above normal moisture 
anomalies into the area through the week. Daily rainfall totals over 2 inches are likely with 
significantly higher amounts possible throughout the entire period. Not every area may receive 
heavy rain every day, but given uncertainty with timing of each wave and that there are multiple 
rounds expected, opted to broadbrush one heavy rain hazard area for the region at this point.

Tate