Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Wed Jun 28 2023 Valid 00Z Thu Jun 29 2023 - 00Z Sat Jul 01 2023 ...Record heat expected from the Central to Southern Plains into the Lower Mississippi Valley, Lower Ohio Valley,Lower Tennessee Valley and Central Gulf coast... ...Smoke from Canadian wildfires to continue to produce poor air quality from the Northern Plains into the Great Lakes, Mid West Ohio Valley and Mid-Atlantic... ...Heat also forecast to build through the interior valleys of California... ...Severe Thunderstorms possible from the Central Plains into the Mid Mississippi Valley and Lower Ohio Valley... ...Elevated to critical Fire Weather conditions to persist from the Four Corners region into the Southwest... An expanding mid to upper level ridge across the Southern Plains into the Lower Mississippi Valley will continue to drive the record heat wave affecting the southern portion of the nation. The record high temperatures that have been mostly over Texas and far southeast New Mexico over the past week will now be expanding into portions of the Central Plains, Lower Mississippi Valley and central Gulf coastal region over the next few days. Numerous record high maximum temperatures in the lower 100s and record high minimum temperatures in the upper 70s to lower 80s are possible over the next few days across these areas. This will continue to produce life threatening heat wave conditions across a large portion of the nation from southeast New Mexico, through much of the Southern Plains, eastern Kansas, into the Lower Mississippi Valley, Lower Ohio Valley, Lower Tennessee Valley and the central Gulf coastal region. Across these regions, excessive heat warnings and heat advisories are in effect and will likely remain in effect through the remainder of this week. The combination of the record high temperatures, along with high surface dew points will produce life threatening heat indices values in the 100 to 120 degree range across these areas. The highest heat indices over the next several days expected to affect cities from Dallas to Houston, New Orleans, Jackson, Little Rock, Memphis and Nashville, where heat indices values off 110 to 120 are expected. While the southern U.S. grapples with excessive heat over the next few days, poor air quality expected to continue as smoke from the persistent Canadian wildfires continues to be drawn southward into the Lower 48. Air quality advisories and alerts currently stretch from the Upper Mississippi Valley, through the Mid-West, Great Lakes, Ohio Valley and into the Mid-Atlantic. With no end in site to the Canadian wildfires and west to northwesterly winds expected to persist from south central Canada into the north central to northeast U.S., poor air quality conditions are likely to continue. Farther west, heat will also be building over the interior valley of California late this week as a mid to upper level ridge strengthens over California and the Great Basin. Excessive heat watches are in effect for much of the Sacramento and San Joaquin Valleys where high temperatures in the lower 100s are forecast from late week into this weekend. On the northern edge of the hot temperatures across the Southern to Central Plains, a stationary frontal boundary is expected to lie west to east across the Central Plains into the Mid Mississippi Valley and Lower Ohio Valley regions. This front will act a focus for potentially severe thunderstorms from Wednesday night through Friday. In addition to the severe weather threat, heavy rains from these storms also pose a risk for isolated flash floods. There is not expected to be any significant changes to the current weather pattern from the Four Corners region into the Southwest and portions of the Southern High Plains. Across these areas, dry conditions, lower relative humidities and gusty surface winds will continue to support a large region of elevated to critical fire weather conditions through late week. Oravec Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php