US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
347 PM EDT Mon Jul 20 2020
 
Valid Thursday July 23 2020 - Monday July 27 2020
 
Hazards:
- Heavy rain across portions of the Southwest, the Central Great Basin, the Central/Southern 
Rockies, the Plains, the Upper Mississippi Valley, and the Great Lakes, Thu-Mon, Jul 23-Jul 27.
- Heavy rain across portions of the Southeast, the Mid-Atlantic, the Lower Mississippi Valley, and 
the Southern Plains, Thu-Fri, Jul 23-Jul 24.
- Flooding occurring or imminent across portions of the Upper Mississippi Valley and the Northern 
Plains.
- Flooding likely across portions of the Central Plains.
- Excessive heat across portions of the Central/Northern Plains and the Upper Mississippi Valley, 
Fri-Sat, Jul 24-Jul 25.
- Excessive heat across portions of the Southeast and the Mid-Atlantic, Thu, Jul 23.
- Excessive heat across portions of the Southeast and the Mid-Atlantic, Mon, Jul 27.
- Much above normal temperatures across portions of the Central/Northern Plains, the Upper 
Mississippi Valley, and the Great Lakes, Fri-Mon, Jul 24-Jul 27.
 
Detailed Summary:

The medium range period (Thursday, July 23 - Monday, July 27) will be characterized by upper-level 
high pressure centered over the Middle Mississippi Valley, creating a "ring of fire" summertime 
weather pattern, in which temperatures underneath the high are hot and thunderstorms form around 
the edges of the upper-level high's influence. High temperatures are forecast to be in the 90s most 
everywhere from the High Plains eastward to the Atlantic coast at least at some point from Friday 
to Monday, with the exceptions of New England and higher elevations of the Appalachians. The most 
abnormally high temperatures are expected for north-central parts of the country, slowly migrating 
eastward from the Plains into the Midwest and the Great Lakes region. Heat indices could be over 
100 degrees, even over 105, for the end of the week in parts of the Northern Plains and Upper 
Mississippi Valley, necessitating an Excessive Heat hazard area. Additionally, hot temperatures 
with high dewpoints will combine to create high heat indices for the Southeast and Mid-Atlantic on 
Thursday, as well as again next Tuesday as the warmth drifts eastward. 

To the west of the upper-level high, anomalously moist southerly flow from the Pacific and Gulf of 
Mexico will begin monsoon season in the Southwest and Four Corners region, ramping up late this 
week and continuing into early next week. Scattered to widespread thunderstorms could cause locally 
heavy rain. Temperatures a few degrees below normal are also forecast there. Then along the 
northern side of the high, an active jet stream could lead to multiple rounds of rain and 
thunderstorms across the Northern Plains to the Upper Midwest through the period. Farther south, a 
trough of low pressure with tropical moisture should move toward the western/central Gulf Coast 
late this week, which could cause heavy rainfall along the coast, but there is uncertainty with how 
far inland heavy rainfall will occur. Lastly, heavy rain could occur for the southeastern 
Mid-Atlantic region into South Carolina as moisture streams in south of a front.

In Alaska, no hazards are currently delineated. One item to watch is a low pressure system moving 
through the Gulf of Alaska early next week. Onshore flow with that system should increase rain 
chances over south-central and southeastern Alaska, but at this point, model guidance varies with 
the timing and depth of this low, which leads to uncertainty in how heavy the precipitation totals 
will be. A cool pattern is expected to persist through the period underneath lower than normal 
upper-level heights, with below normal temperatures, especially highs, for much of the state.

Tate