The stagnant upper-level ridge over the south-central U.S. and resultant multi-week heatwave will not only continue but begin to expand in reach over the next couple of days as the ridge builds northeastward.
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Highs from southeastern Arizona through southern New Mexico and into Texas will remain in the 100s Tuesday, with upper 90s to 100s spreading northward into the Central Plains and Middle/Lower Missouri Valley as well as east into the Lower Mississippi Valley Wednesday.
Some daily record-tying/breaking highs are once again possible for portions of Texas and the Lower Mississippi Valley.
Daily record-tying/breaking warm lows are also possible, with the abnormally warm temperatures overnight providing little to no relief from the heat, compounding the impacts of the heat wave.
The main driver of heat-related impacts differs across the region, with higher air temperatures in the deserts and High Plains/western Plains, and lower air temperatures but higher humidity and resultant heat indices to the east, both contributing to a significant risk of heat-related illnesses.
Temperatures in Florida will also remain quite hot Tuesday and Wednesday, with highs in the mid-90s close to tying/breaking a few daily records.
In addition to the heat, some robust thunderstorms are expected to develop along the Central High Plains Tuesday, later organizing and spreading southeastward, with the Storm Prediction Center outlining portions of northern Oklahoma and southern Kansas in a Slight Risk of severe weather (level 2/5) for the chance of damaging winds and large hail.
Widespread clusters of showers and thunderstorms will continue overnight Monday into the early morning hours Tuesday along the East Coast as a low pressure/frontal system pushes eastward through the region, with the risk of heavy rainfall/flash flooding and severe weather.
Western portions of the Mid-Atlantic and Carolinas will likely clear a little quicker Tuesday following the passage of the front than further north into the Northeast, where the system will take longer to pass through.
Some locally heavy rain will remain possible the next couple of days, with the potential for some isolated to scattered instances of flash flooding not out of the question, especially for areas that may have received a lot of rainfall on Monday.
Highs will remain well below average in the Great Lakes region, Upper Ohio Valley, and New England Tuesday and Wednesday, with upper 60s to low 70s forecast.
Highs will be a bit warmer further south and east into the Mid-Atlantic and Carolinas, with 80s expected.
A few scattered thunderstorms will be possible the next couple of days in the Southeast along the front passing through.
Highs will be in the upper 80s to low 90s.
Rain chances will continue from the Great Basin into the Northern Rockies/High Plains Tuesday ahead of a very slowly moving upper-level trough over the West Coast.
Showers and storms are also expected to spread eastward into the Northern Plains overnight Tuesday and the Upper Midwest Wednesday as energetic upper-level flow passes over the region.
Relatively high moisture along and east of the Rockies may lead to some locally heavy rainfall.
Further southwest, strong winds aloft associated with the upper-level trough will mix down and lead to some gusty winds, particularly for the eastern Great Basin and the central/southern Rockies.
The winds in combination with very low humidity and dry conditions have prompted a Critical Risk of Fire Weather from the Storm Prediction Center for the Four Corners region on Tuesday.
Temperatures will generally remain below average for much of the West under the influence of the upper-level trough.
Forecast highs will range from the mid-70s to low 80s for most of the Great Basin and northern Rockies.
The immediate West Coast will be in the 60s, with mid-80s to low 90s for the central California valleys and upper 90s to low 100s for much of the desert southwest outside of southeastern Arizona.
Highs will be above average for the Pacific Northwest, with upper 70s to low 80s for the I-5 urban corridor and mid- to upper 80s for the interior. ■