Weather Across America

(NATIONAL) Increasing severe weather and excessive rainfall threats over the Central U.S. and sweltering heat continues across the South.

An energetic upper-level pattern will bring a couple rounds of storms to the central U.S. over the next few days. Moist return flow following a warm front moving northward through the Plains and ahead of a dryline over the High Plains will provide more than enough instability to trigger robust thunderstorm development over the Central Plains into Monday. Increasing upper-level winds will promote supercells with the threat of large hail and a few tornadoes. Storms are also expected to grow upscale into one or more organized convective systems, bringing a heightened threat for potentially widespread, significant damaging winds. 

As such, the Storm Prediction Center has issued a Moderate Risk of severe weather (level 4/5). Storm chances will shift northeastward into the Upper Midwest Sunday night and into the Great Lakes by Monday following an initial  upper-wave/accompanying surface frontal system. An amplifying long-wave trough over the West will help to enhance lee cyclogenesis over the High Plains bringing another chance of storms to the Central Plains/Missouri Valley by Monday evening. The Storm Prediction Center has included a Slight Risk (level 2/5) for the threat of some more damaging winds and large hail, and possibly a tornado. Some locally heavy downpours will also be possible, particularly from the Central Plains into the Upper Mississippi Valley Sunday and the Central Plains once again Monday, with an isolated chance of flash flooding.

There will be a renewed threat for heavy rainfall and thunderstorms over the Northern/Central Plains and Upper/Middle Mississippi Valley on Tuesday as a deepening low pressure system tracks across the region. The Storm Prediction Center issued an Enhanced Risk (level 3/5) of Severe Thunderstorms from eastern Kansas to Southwest Wisconsin. There's also a Slight Risk (at least 15%) of Excessive Rainfall for parts of southern and eastern Minnesota, much of Wisconsin and northern Illinois. There are also some isolated chances for severe weather and excessive rainfall into northern Texas and eastern Oklahoma.

The active upper-level pattern will also bring some precipitation chances to the Northern/Central Rockies and eastern Great Basin over the next couple of days. Rainfall should generally remain light to moderate, though some locally heavier storms will be possible especially over Wyoming on Monday. Some heavy snow is expected for much of the Absaroka and Bighorn mountains, where between 6-12 inches, with isolated higher amounts, of snow could fall on Tuesday. To the east, an area of low pressure lingering just off the Atlantic coast of the Southeast with a trailing frontal boundary moving through Florida will keep temperatures below average on Monday. Storm chances will decrease into the day Monday from north to south as the front pushes southward, expected to clear the coast by Tuesday morning.

Intense Summer-like heat will continue over portions of South Florida and from southern Texas into the southern High Plains the next couple of days. Highs in the 90s with high humidity values for areas closer to the coast will bring heat indices into the 105-110 degree range. While not as humid, temperatures will soar into the 100s farther inland into west Texas/the southern High Plains. Some record-tying/breaking temperatures are possible. While not as hot, conditions will still be well above average more broadly across the central/eastern U.S. Highs in 80s will be common, even into more northerly locations like the Great Lakes and the interior Northeast. 

One exception will be where onshore flow keeps things a bit cooler along the East Coast, with highs in the 60s and 70s expected from coastal New England south into the Mid-Atlantic and coastal Carolinas. Highs over the Pacific Northwest/northern Rockies will remain cool tonight behind a cold front, with highs in the 50s and 60s. These cooler temperatures will spread southward into the Great Basin Monday. Highs in the 80s and 90s are forecast south of the front over the Southwest.