Weather across America

(NATIONAL) Heavy rain with the risk of localized flash flooding and severe weather stretching from the Northeast to the Ohio/Tennessee Valley, less intense heat across the South but excessively hot over California and the Desert Southwest, and much above normal temperatures for portions of the northern Plains and upper Midwest ahead of rain/storm chances. 

A low pressure wave developing along a frontal boundary across the central portion of the country will set the weather pattern into faster motion through the eastern half of the country.  

This will push the active thunderstorms farther to the east across the Ohio Valley toward the central Appalachians Sunday, and into the Mid-Atlantic by Sunday night. Meanwhile, scattered showers and embedded thunderstorms are expected to become more numerous and widespread over New England Sunday as a warm front lifts across the region.  

The best chance of seeing severe weather together with heavy rain Sunday appears to be over the Ohio Valley/Tennessee where large hail and damaging winds are possible. The upper-level trough associated with the developing low pressure wave is gradually eroding the upper ridge responsible for the prolonged heat wave that has been gripping the South.  

With the eroding ridge, afternoon heat is expected to become less intense across the region for the rest of the weekend and heading toward the 4th of July holiday. By Monday, much of the Ohio Valley will have a chance to dry out behind a cold front as the main low pressure center is forecast to move into the Northeast.  

The associated showers and thunderstorms will likely linger into the 4th of July holiday when the low begins exiting into the Canadian Maritimes.  

Meanwhile, excessive heat will remain in place across California into the Desert Southwest with perhaps slight improvement arriving on Independence Day.  

Forecast highs will range from 110-115 for the deserts, 105-110 degrees for the central California valleys, and upper 90s to low 100s for other lower-elevations of California outside of the immediate coast for Sunday and Monday. A few record-tying/breaking highs will be possible.  Also notable is a continued stretch of forecast near-record and record-tying/breaking highs for Florida in the mid- to upper 90s which looks to continue beyond the current forecast period. 

Across the northern Plains, a brief heat wave is forecast to spread from west to east across the region ahead of a cold front. The cold front will usher in much cooler air from Canada into the northern portion of the country as we head toward the 4th of July holiday.  

Together with the cool down will be rain and embedded thunderstorms that are forecast to expand westward into the northern High Plains and the foothills of the northern Rockies by early on Independence Day behind the cold front. The thunderstorms will also expand eastward across the northern Plains toward the upper Midwest as a low pressure wave attempts to form along the front.