Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 407 PM EDT Fri Jun 25 2021 Valid 00Z Sat Jun 26 2021 - 00Z Mon Jun 28 2021 ...Dangerous and record-breaking heat wave likely throughout the Pacific Northwest and Northern Great Basin this weekend... ...Multiple rounds of showers and potentially severe thunderstorms anticipated between the Central/Southern Plains and Great Lakes, generating a significant flash flooding concern that will abate as the weekend progresses... Today marks the beginning of what is expected to be a multi-day extreme heat event across the northwestern United States. An anomalously strong upper-level ridge has settled into its new home over British Columbia, Canada where it is forecast to strengthen over the next few days as it remains virtually motionless, held in place by an Omega blocking pattern. Egged on by the persistent ridging and with no precipitation or cold fronts in sight to keep temperatures in check, daily highs are anticipated to rise progressively throughout the weekend into record-breaking territory. High temperatures throughout much of Oregon and Washington will likely soar 20 to 30 degrees above normal into triple digits, holding steady well into next week. Numerous temperature records are slated to fall throughout the course of this event, with some monthly and even the all-time records for Washington, Oregon, and Idaho in the cross hairs. Excessive Heat Warnings have been issued for much of Washington, Oregon, and Idaho as well as northern California in preparation for the dangerously hot conditions to come. Excessive Heat Watches have also been put into effect for portions of central and southern California, western Nevada, and south-central Idaho. It is worth noting here that heat is the leading cause of weather-related fatalities over a 30-year average from 1991-2020. As such, residents are urged to take the proper precautions to deal with the upcoming extreme conditions by staying hydrated, avoiding long periods of time outdoors, and remaining in air-conditioned rooms. Furthermore, with overnight temperatures remaining in the 70s throughout the duration of the event and thus providing little relief from the heat, heat stress and heat related illness will also be major concerns. Looking east, active weather is set to be found across the central U.S. for much of the weekend. A quasi-stationary front is forecast to extend from the Great Lakes to the Central/Southern Plains throughout much of the short-range period and be the focus for multiple rounds of heavy rain and thunderstorms. Given the stalled frontal boundary, sufficient atmospheric moisture, and the slow-moving nature of thunderstorms in the area, flash flooding will be a major concern from southeast Kansas to west-central Indiana through Saturday morning. Thunderstorms have already led to significant flash flooding and over 10 inches of rain in far northeast Kansas and northwest Missouri. Moving in concert with the southward progression of the front, the greatest flash flooding threat will slowly push southward overnight into the Southern Plains. The Weather Prediction Center has issued a Moderate Risk for Excessive Rainfall through Sunday morning that covers parts of the Central/Southern Plains, Middle Mississippi Valley, and western Ohio Valley in anticipation of the heavy rainfall rates and high accumulation totals that are expected to occur over the next couple of days. Flash Flood Watches have been posted from the Southern Plains through the Great Lakes, while Flood Warnings have been issued for portions of the Middle Mississippi Valley. In addition to flash flooding, severe weather will be another hazard to look out for along the active frontal boundary through Sunday morning. A Slight Risk for severe thunderstorms has been issued by the Storm Prediction Center for an area encompassing the central/southern High Plains to Illinois and a smaller area covering portions of Michigan, Indiana, and Ohio. Isolated tornadoes, damaging winds gusts, and large hail are all a possibility as storms form and strengthen along the stalled frontal boundary this afternoon/evening. By Saturday, the severe weather threat is forecast to shift southward into the southern High Plains as the western edge of the front pushes south. Zavadoff/Snell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php