The general flow pattern features slowly retreating troughing in the West/Northwest and an upper trough in the Northeast which should be the mildest portions of the Lower 48 while a warm core ridge wanders and wavers in strength between the Southern/Central Plains and Southeast, keeping those locations hot.
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Widespread Heat Advisories are in effect from the Missouri Valley southeast to the Middle Mississippi Valley and Mid-South (in some places through Wednesday) as the combination of high temperatures and high humidity push heat indices closer to an uncomfortable 105-110 degrees.
A few record highs are forecast between the Southern Plains and Southern Appalachians.
Morning lows will remain in the mid-70s to near 80 providing little relief from the heat overnight - some record high minima are expected between the ArkLaTex and Mid-South as well as the Southern Appalachians.
A low pressure system will move across the Great Lakes to the Northeast Coast today with trailing frontal boundaries remaining across the Midwest, Central Plains, Northern High Plains, with more wavering seen across the Mid-Atlantic states, leading showers and thunderstorm development through mid week.
The excessive rainfall and severe weather threat over the next few days will be highest near the front between the Northern Continental Divide, Midwest, Ohio Valley, and with time portions of the Mid-Atlantic states and Carolinas as organized thunderstorms round the top of the Plains ridge and dive down the base of the Eastern Trough, feeding off the available high moisture and instability near a front.
Despite the nearby upper trough, the best chances of rain in the western portion of the Lower 48 lie across portions of the Pacific Northwest and Northern Continental Divide.
To the southeast of where the rain is expected, SPC has highlighted a Fire Weather threat for today for portions of the Great Basin as humidity remains low and windy conditions are expected to persist across the area. ■
A clipper system will move quickly across the northern Plains into the Midwest Friday and the Northeast by Saturday, bringing a wintry mix of rain and snow showers ahead of a sweeping cold front.