Weather across America

(NATIONAL) Heavy rain is likely to continue the flash flood risk over the southern Mid-Atlantic, central/southern Appalachians, and into parts of the Ohio/Tennessee Valley, severe thunderstorms will be possible across the Upper Midwest, and excessive heat persists over the Pacific Northwest before spreading into the northern Plains. 

A lingering frontal boundary draped across the Mid-Atlantic and Ohio Valley is finally forecast to begin lifting northward Sunday night and produce continuing concerns for flash flooding. Parts of southeastern Kentucky are most at risk to flash flooding as soils remain overly saturated from previous drenching rainfall from the past week. Additional storms containing intense rainfall rates are likely to create instances of flash flooding if they pass over this region, prompting a Moderate Risk (level 3/4) of Excessive Rainfall to remain in effect over southeast Kentucky through Sunday night. 

Elsewhere, a Slight Risk (level 2/4) of Excessive Rainfall extends along the same boundary from the southern Mid-Atlantic to the lower Mississippi Valley. Here, scattered chances for flash flooding exist. Flooding can be particularly dangerous and hard to see at night, residents are advised to plan ahead before traveling and never drive through a flooded roadway. By Monday, the overall heavy rain threat is expected to diminish as thunderstorm activity becomes more scattered and less organized. However, there remains a concern for additional flash flood chances over susceptible terrain along the central/southern Appalachians and into eastern Kentucky/Tennessee.

The other area contending with heavy rainfall chances is over the Southwest and associated with the summer monsoon. Anomalous moisture in place throughout the Southwest and into the central Great Basin will aid thunderstorm development and the potential for numerous downpours. In order to highlight the flash flooding concern, a Slight Risk of Excessive Rainfall is in effect through Sunday night from southern Nevada and Utah to south-central Arizona and western New Mexico, including parts of southeast California. Areas near recent burn scars, slot canyons, urban corridors, and other vulnerable terrain are most at risk for flooding impacts. The current plume of monsoonal moisture is expected to gradually lift northward on Monday into the Great Basin and eventually spread into the northern Rockies by Tuesday, where isolated flash flooding is possible.

Hazardous weather in the form of severe thunderstorms is also possible heading into the beginning of August for some parts of the Nation. An advancing cold front located over the Midwest and central Plains Sunday evening may spark a few strong thunderstorms capable of containing damaging wind gusts, isolated tornadoes, and large hail. Thus, the Storm Prediction Center has issued a Slight Risk (level 2/5) of severe weather over portions of eastern Minnesota and northwestern Wisconsin.

Additionally, a few tornadoes and damaging wind gusts cannot be ruled out across North Carolina and southern Virginia Sunday night as thunderstorms form along a warm front. By Monday, as the aforementioned cold front over the Midwest advances eastward, severe thunderstorms are possible over the Ohio Valley and into parts of the Mid-Mississippi Valley. Damaging wind gusts are expected to be the primary hazard associated with these storms. 

Fast-forwarding to Tuesday, a separate system entering the northern Plains will potentially produce another round of severe thunderstorms in/around Minnesota. Record-breaking summer heat will remain a major weather story across the Pacific Northwest on Monday, but relief is on the way as the well above normal temperatures shift eastward into the northern Plains by Tuesday. The anomalous upper-level ridge currently located over this Northwest is forecast to be suppressed by strong upper-level energy entering western Canada. This will allow for temperatures over Washington and Oregon to return to near normal by Tuesday. However, highs are still anticipated to reach into the upper 90s and low 100s across the Columbia Basin on Monday, which may threaten daily high temperature records. 

For the northern Plains, highs 10 to 20 degrees above average are expected over Montana, the western Dakotas, and western Nebraska on Monday, which equates to highs right around 100 degrees. By Tuesday, excessive heat consolidates over South Dakota and surrounding states, where highs are forecast to reach into the triple digits.