US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
424 PM EDT Fri Jul 31 2020
 
Valid Monday August 03 2020 - Friday August 07 2020
 
Hazards:
- Heavy rain across portions of the Southeast, the Mid-Atlantic, the Northeast, and the Central 
Appalachians, Mon-Tue, Aug 3-Aug 4.
- Heavy rain across portions of the Mid-Atlantic and the Northeast, Tue-Wed, Aug 4-Aug 5.
- Flooding possible across portions of the Northern Plains.
- Flooding occurring or imminent across portions of the Middle Mississippi Valley and the Northern 
Plains.
- High winds across portions of the Southeast, the Mid-Atlantic, and the Northeast, Mon-Tue, Aug 
3-Aug 4.
- High winds across portions of the Northeast, Tue-Wed, Aug 4-Aug 5.
- High significant wave heights for coastal portions of the Southeast and the Mid-Atlantic, Mon, 
Aug 3.
- High significant wave heights for coastal portions of the Mid-Atlantic and the Northeast, Tue, 
Aug 4.
- Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Aug 3-Aug 4.
 
Detailed Summary:

Isaias impacting much of the East Coast (starting in Florida this weekend) is the headliner for 
potential weather hazards the first week of August. First off, the eventual track and intensity of 
the storm, even as the weekend begins, remains unclear. It will track over the very warm waters 
surrounding the Bahamas, but also experience lingering mid-upper level wind shear that is 
attempting to keep the storm disorganized internally. That said, the Bermuda ridge and the upper 
level trough over the east-central U.S. dictates the steering flow, ultimately forcing Isaias to 
track northeast along the Eastern Seaboard the first half of the week. Heavy rain and 
thunderstorms, some of which could produce torrential rainfall rates, is anticipated from the 
Southeast to the Mid-Atlantic with localized flash flooding and even river flooding possible  
Monday into Tuesday. The axis of heavy rainfall is reliant upon storm track: closer to or just off 
the coast means more rain along the coast (less inland) while a more inland track brings heavy 
rainfall deeper into the Southeast and Mid-Atlantic mainland. One common threat for these regions 
coastlines are battering waves and the potential for tropical storm force winds. As a result, 
beaches and inlets could contend with some coastal flooding and beach erosion. By Tuesday, Isaias 
is forecast to make its way up the Northeast coast with the aforementioned hazards (heavy rain, 
high waves, strong winds) accompanying the system. Similar to the southern regions, whether the 
storm tracks along the coast or slightly farther inland determines where the most rainfall takes 
shape. The heavy rain threat in the Northeast is aided by the region's placement under the 
right-entrance region of a jet streak located over the St. Lawrence River Valley, supporting the 
potential for a predecessor rainfall event (PRE) over the Northeast. The storm could still be 
making its way off the coast of New England on Wednesday but more tranquil conditions will return 
the second half of the week.

Meanwhile, an upper-level ridge will remain a commanding feature over the western U.S. much of the 
week. Temperatures should range between 5 to 10 degrees above normal across much of the interior 
western U.S. before an upper trough ushers cooler air into the Pacific Northwest and the northern 
Rockies by early next week. High temperatures are expected to top 115 degrees for the hottest 
locations in Desert Southwest on Monday before moderating very gradually toward the middle of next 
week. The hottest high temp anomalies may be centered over eastern New Mexico and West Texas. Over 
the northern Plains and Midwest, much cooler than normal temperatures will remain in place behind 
the slow-moving upper trough entrenched across the east-central U.S..

Over Alaska, the pattern appears to get more active as a pair of significant occluded cyclones are 
forecast to impact the southern periphery of the state. This appears to be more of a prolonged rain 
event than heavy rain falling in a short time-frame. A heavy rain area is indicated on the map from 
the southern coastal sections of Alaska down along the Panhandle from the first half of the week. 
The second occluded cyclone late week is currently expected to bring additional heavy rainfall to 
the Panhandle during that span, but there is still some uncertainty in the track and timing of this 
storm system that could make for wetter conditions along the south-central coast of the state.

Mullinax