US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 318 PM EDT Fri Aug 21 2020 Valid Monday August 24 2020 - Friday August 28 2020 Hazards: - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Mon-Tue, Aug 24-Aug 25. - Heavy rain across portions of the Southeast and the Lower Mississippi Valley, Mon-Wed, Aug 24-Aug 26. - Heavy rain across portions of the Lower Mississippi Valley, the Southeast, the Tennessee Valley, the Ohio Valley, the Southern/Central Appalachians, and the Mid-Atlantic, Wed-Fri, Aug 26-Aug 28. - Heavy rain across portions of the Southeast, Mon, Aug 24. - Excessive heat across portions of California, Mon, Aug 24. - Excessive heat across portions of the Central Great Basin, California, and the Southwest, Mon-Fri, Aug 24-Aug 28. - Excessive heat across portions of the Southern Plains, Thu-Fri, Aug 27-28. - Much above normal temperatures across portions of the Central Great Basin, the Northern/Central Rockies, the Northern/Central Plains, the Upper/Middle Mississippi Valley, the Great Lakes, and the Ohio Valley, Mon-Wed, Aug 24-Aug 26. Detailed Summary: Over the medium range period (Monday, August 24 - Friday, August 28), tropical weather is a threat from what are, as of Friday afternoon, Tropical Depression Fourteen and Tropical Storm Laura. The current National Hurricane Center track takes Tropical Depression Fourteen toward the western Gulf Coast on Tuesday, and Tropical Storm Laura south and west of the Florida peninsula and into the Gulf of Mexico Monday through Wednesday, but this is subject to change and forecasts should continue to be monitored. No high winds hazards were placed on the hazards graphic for now due to uncertainty in strength and placement of the tropical cyclones making landfall. Despite the exact track of the storms, heavy rainfall is likely with the influx of tropical moisture into much of the Gulf Coast and then the Southeast by midweek. After that, it appears tropical moisture and low pressure will spread northward into the Tennessee and Ohio Valleys and Appalachians around Thursday and Friday. There is some potential for heavy rain farther north as the moisture could combine with a front meandering across the Northeast, while some model guidance spreads rain eastward into the Mid-Atlantic, but uncertainty remains high with precipitation amounts in those areas. Persistent upper-level high pressure over the Four Corners region will lead to continued above normal temperatures by 5-15 degrees for much of the western half of the U.S. Thus, excessive heat remains a threat in the Desert Southwest. The San Joaquin Valley could see temperatures over 100 degrees on Monday, and may warm back up later in the period as well. Much above normal temperatures are also likely to spread eastward into the Northern/Central Plains and Midwest by Tuesday/Wednesday under the influence of the ridge. Then, high heat indices are likely in southern Texas late next week, with high dewpoints combined with hot temperatures. Over Alaska, a low in the Gulf of Alaska is forecast to spread moisture into south-central and southeastern Alaska and then into the Panhandle for the first half of the workweek. Generally modest rainfall totals are expected, but locally heavy rainfall totals are possible, and cooler than average high temperatures are likely there. Then, a developing low in the Bering Sea could cause some rain and gusty winds to the Aleutians, Alaska Peninsula, and the southwestern mainland by Thursday and Friday. Model uncertainty with the evolution of this low remains high, however, leaving rainfall amounts uncertain as well, so no hazard areas were delineated at this point. Tate