US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
451 PM EDT Mon Jul 26 2021
 
Valid Thursday July 29 2021 - Monday August 02 2021
 
Hazards:
- Heavy rain across portions of the Front Range, as well as from the northern Plains to the 
mid-Mississippi Valley, Fri-Sun, Jul 30-Aug 1.
- Heavy rain across portions of the southern Appalachians, Sun, Aug 1.
- Excessive heat across portions of the central/southern Plains to the lower and mid-Mississippi 
Valley, as well as the interior Pacific Northwest, Thu-Sun, Jul 29-Aug 1.
- Excessive heat across portions of the central Plains to the mid-Mississippi Valley, Thu, Jul 29.
- Excessive heat across portions of the Carolinas, Fri, Jul 30.
- Heavy rain across the southern portions of Lisburne and Seward Peninsulas in mainland Alaska, 
Thu-Mon, Jul 29-Aug 2.
- Heavy rain across portions of southwestern Alaska, Sat-Mon, Jul 31-Aug 2.
- Heavy rain across portions of southwestern Alaska, Fri-Mon, Jul 30-Aug 2.
 
Detailed Summary:

The medium range forecast period (Thursday, July 29 - Monday, August 2) will begin with slightly 
cooler air entering the northern Plains, bringing some relief to the widespread triple-digit heat 
across the region earlier in the week.  Farther to the south however, the combination of afternoon 
heat and humidity will allow for very sultry conditions to persist across the lower to 
mid-Mississippi Valley and into portions of the central to southern Plains through the upcoming 
weekend.  Similar conditions are also expected across the eastern portion of the Carolinas on 
Friday before cooler air arrives by the weekend.  Meanwhile, a low pressure wave riding along the 
cold front could bring some heavy rainfall across the southern Appalachians on Sunday.  The frontal 
boundary is forecast to extend farther to the west across the Tennessee Valley and into the central 
Plains where an axis of heavy rain associated with organized thunderstorms could impact areas from 
southern South Dakota southeastward into Missouri Friday and into the weekend.  By next Monday, 
parts of the Southeast could see some localized to scattered heavy rain and thunderstorms ahead of 
a reinforcing shot of cool air from the north. However, uncertainty in the predicted pattern 
precludes specification of a heavy rain area at this time.

Across the West, the monsoonal rainfall appears to remain active through the medium range, with a 
tendency to spread farther north into the northern Rockies and northern Great Basin through the 
weekend.  Widespread terrain-enhanced rainfall with isolated local runoff issues can be expected 
from Arizona northward through the Great Basin and central to northern Rockies through early next 
week.  An area where models have emphasized the greatest potential for heavy rain is near/along the 
Front Range of Colorado where the combination of a subtle upper-level disturbance interacting with 
a lee trough/low could trigger heavy rain Friday and into the weekend.  Other areas that are 
susceptible to heavy rain are northeastern Utah, northwestern Wyoming, and eastern Idaho by next 
Monday, even though they have not been highlighted on the map at this time.

In Alaska, an extended period of wet and unsettled weather is in the offing through the medium 
range as a large low pressure system remains anchored over the northern portion of the Bering Sea.  
Surges of moisture are expected to overspread western Alaska as persistent deep-layer southerly 
flow interacts with a stalled stationary boundary across the North Slope.  Episodes of moderate to 
heavy rainfall are expected along the south-facing terrain of Lisburne and Seward Peninsulas where 
the heaviest rainfall could even approach climatological extremes.  Other areas in southwestern 
Alaska should also see heavy rain moving in later this week into the weekend.

Kong